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Upper Board Camp Creek (BCC) in western Arkansas drains the Wolf Pen Gap (WPG) Trail Complex, a designated Off-Highway Vehicle (OHV) area in use since the 1990s. The mixed bedrock-alluvial channel is quite active, with extensive bars and eroding banks present within the higher-order, main-valley channels. This study was conducted to determine the relative magnitudes of sediment storage and production within the channel, and whether geomorphic changes are synchronous with establishment and increasing OHV use levels on the trail system. Fourteen geomorphically active reaches within the main-valley channels, representing the range of conditions of BCC within the WPG complex, were examined in detail. All sites had significant alluvial storage in the form of point, lateral, or mid-channel bars dominated by cobble and gravel. Sediment storage volumes ranged from 140 to nearly 10,000 m3 per kilometer of channel, with a mean of about 3400. Eleven of 14 reaches also had actively eroding banks. Ten reaches (71%) exhibited net sediment storage. Two are possible net sources, and two may be in approximate steady state (storage ≈ erosion). The imbalance between local bank erosion sources and in-channel storage, and the evidence of activity and mobility of most of the bars indicates a connected system, with coarse sediment mobile during banktop flow events, and no evidence of sediment starvation. Finer (<8 mm) sediment from the trail system does not seem to be accumulating in the stream, suggesting that most is either sequestered before reaching BCC Creek, transported downstream, or deposited on floodplains during overbank flow. Many of the channel bars predate the trail complex, and most are active. This suggests that these features constitute mainly transient storage and are an inherent feature of the channel. At only two reaches could geomorphic changes be confidently attributed to the trail system. Like many streams, BCC has an active channel, independent of the WPG trail system. These results highlight the difficulty of attributing fluvial change to specific causes or forcings in active fluvial systems. • Examined 14 active reaches of stream in off-highway vehicle (OHV) trail complex. • Net coarse sediment storage at 10 sites; 2 net sources; 2 approximately steady state. • Coarse sediment connectivity observed. • Only two sites showed changes clearly attributable to OHV use. • Results show difficulties of change attribution in inherently active fluvial systems. [ABSTRACT FROM AUTHOR]

The Roer is a small river which drains the Rhenish shield and confluences with the Meuse River. Up to now the geological, climatological, biostratigraphical, and pedological setting of the Roer Valley were not sufficiently integrated to disentangle the effects of external forcing factors on the Roer River. In this study we perform a detailed and integrated reconstruction of the fluvial morphology and palaeogeography of the Roer River in order to determine responses to combined climatic, tectonic and anthropogenic forcing factors. The Roer River has formed five terrace levels since the Weichselian Late Pleniglacial. Fluvial planform of the Roer River was predominantly climate-controlled during the Lateglacial and Early Holocene. Reach-to-reach variations in river terrace formation and fluvial planform change occur due to variations in tectonic setting, subsurface geology, base-level fluctuations and the confluence with tributary systems. Differential subsidence by active faulting in the Roer Valley Graben during the early Lateglacial caused a preferential usage of the down-tilt channels of the, up to then, double channel belt systems in the Roer Valley. This preferred channel avulsion towards a fault zone, leaving an underfit system on the up-tilted side, and the clustering of Holocene Roer channels along that fault zone, meet the criteria for a lateral response of the Roer River to a tectonic forcing. Anthropogenic influences in the form of deforestation and land-use changes during the Late Holocene are responsible for the formation of a final terrace level and overbank sediments. Unlabelled Image • River terraces of the Roer River were formed by combined external forcing factors. • The avulsion of the Roer River during the early Lateglacial was tectonically forced. • Reach-specific terrace formation and preservation is present in the Roer Valley. • Late Holocene terrace formation in the Roer Valley was anthropogenically forced. [ABSTRACT FROM AUTHOR]

Landslide damming of valleys may have a significant effect on the evolution of fluvial landscapes. The southeastern Tibetan Plateau is highly prone to landslide damming due to its deeply incised valleys and young, active geology. Here we present a sedimentological investigation of a landslide-dammed lake in the upper reach of Lulang River on the eastern Himalayan syntaxis. Detailed interpretation of lacustrine varve, lakeshore, and subaqueous delta sediment shows that Lulang landslide-dammed lake (LLDL) had a surface elevation of 3360 m a.s.l., an area of 3.3 × 106 m2, and a volume of 6.5 × 107 m3. Radiocarbon dating of six organic clay lacustrine samples demonstrate that LLDL formed before 24.2 ka cal. BP and persisted for at least 8.8 ka. Sediment infill reached full capacity soon after 15.4 ka cal. BP and fluvial conditions then prevailed. Sedimentary evidence and morphological analysis of cross sections along the LLDL outlet channel revealed a larger, earlier lake with a total volume of 4.3 × 109 m3 and water surface elevation at 3570 m a.s.l. that failed catastrophically; the resulting outburst flood drained 98.5% of the impounded lake. The remnant lake maintained a relatively stable water level of 3360 m a.s.l. for its lifetime of at least 8.8 ka. Long profile and steepness index analysis indicate that the location of the catastrophic dam failure and subsequent long-term blockage is associated with a knickpoint. The origin of the knickpoint may have been polygenetic, however, the landslide damming seems to have increased its distinctiveness and persistence. The relatively wide valley and low channel slope characteristic of reaches upstream of LLDL is likely to have resulted from glacial activity, rather than backwater aggradation which had only a local influence. • Lulang landslide dammed lake persisted from 24.2 ka cal. BP. to 15.4 ka cal. BP. • Sedimentary evidences show that It drained catastrophically in the very beginning. • The remnant lake maintained stable without significant fluctuations of lake level. • The sediments infilling reached its full capacity eventually. • The breach channel of landslide dam corresponds to a knickpoint of river profile. [ABSTRACT FROM AUTHOR]

Climatic oscillations occurring during the Pleniglacial and Lateglacial periods are generally associated with several changes in fluvial morphology and processes. This study investigated two reaches of the Cher River basin (Noyers-sur-Cher and Thénioux) regarding morphological adjustments during the Lateglacial period and the early Holocene. Transitions from the Pleniglacial to the Lateglacial and from the Lateglacial to the early Holocene (ca. 14,700–11,500 cal. BP) are considered as interesting study cases because it consists of rapid and abrupt climate oscillations generally clearly recorded in current floodplains. The sites studied are located in the Cher River floodplain, which is one of the main tributaries of the Loire River. Several investigations have been conducted in the main valley, but few of them specifically focused on geomorphological evolutions of medium-sized catchments such as tributaries of the Loire River. Therefore, we examined this specific period through investigations recently conducted in the middle valley of the Cher River. This study aimed to (1) provide a geomorphological approach to fluvial adjustments during the Lateglacial from cases located in lowland areas of a medium-sized basin and (2) analyse the spatio-temporal variability of fluvial responses. Assessment of geomorphological trajectories of the two reaches studied highlights that fluvial metamorphosis occurring during the Lateglacial and early Holocene seems to be characterised by lateral readjustments and a low signal of morphological instability (shallow incision and aggradation processes, slow and progressive change in channel morphology). This observation is enhanced by the comparison with known geomorphological evolution patterns of adjacent basins. The intrinsic components of the Cher basin such as slope and valley width were considered as explanatory factors for the lack of morphogenetic processes. In addition, the geographical location of the reaches studied may also have led to a moderated expression of climate forcing. Indeed, the elevation as well as the north– south and east–west gradients may contribute to the low level of geomorphological adjustments in response to these climatic oscillations. This gradient could also have support this the fluvial response because of the weakly developed loess cover, which may have limited the fine sediment supply and the aggradation of the valley bottom. [ABSTRACT FROM AUTHOR]

Geomorphological and sedimentary records near the confluences of the Tana River and major tributaries draining the eastern slopes of Mt. Kenya and the Nyambeni Range, indicate impacts of Late Quaternary volcanic activity in their fluvial records. The main reconstructed event was triggered by a 366.9 ka basalt flow (40Ar/39Ar dated) which flowed along Kazita River from the Nyambeni Range blocking both Kazita River and Tana River near Kibuka Grand Falls, causing a temporary lake. Consequently, Tana River and Kazita River started to build volcanoclastic Gilbert type deltas. The preserved pro-delta sediments rich in trachytic pumice fragments display a mineralogical and age match with known Ithanguni trachytic tuffs, indicating delta build up right after a contemporary Ithanguni eruption. This trachytic eruption caused the deposition of lahars and fluvial volcaniclastic sediments in all river records draining the Eastern side of Mt. Kenya. The multiple lahars seem to be triggered by eruptions under glacial conditions (basalt age indicates MIS 10). The lava dammed lake was only short lived (estimated to have lasted only a few years to decades) and breached before a complete lake infill could occur. The current Kibuka Grand Falls can be viewed as the delayed incisional response of this lava dam breach, indicating that after >366.9 ka, Tana River is still responding and adjusting to this short-lived disruptive phase. The current Kazita River has re-incised adjacent to a MIS 4 basalt flow down into the crystalline Basement System rocks. The MIS 10 pre-volcanic sedimentary record indicates that more sediments were in the fluvial system during glacial conditions than during the interglacial conditions. An implication of our reconstruction is that the Late Quaternary fluvial record of Tana River is of only limited use to reconstruct uplift rates because reconstructed Quaternary incision rates are reflecting both volcanic disruptions as climate change trends of aridification and decreasing glaciation extents. Unlabelled Image • Excellent examples of fluvial volcanic interactions in a tropical continental rift setting. • New insights into the geochronological fluvial – volcanic framework of Tana river and Mt. Kenya. • In a dominant incising system with limited fluvial preservation, volcanic activity and glaciations are driving large fluvial aggradation phases. • Quaternary climate change of aridification is inferred by decreasing sediment supply and decreasing fluvial aggradation. [ABSTRACT FROM AUTHOR]

Abstract Megaclast-dominated fluvial systems have been largely ignored by researchers. Yet megaclasts exert an important control on channel geomorphology, flow behaviour and sediment transport, and such systems are probably far more common than this neglect would suggest. Despite the explicit identification of megaclasts as the products of cataclysmic flow, observation of modern fluvial systems confirms that megaclasts can be entrained by flows that lie within the normal flow regime. The pattern of fining along the megaclast-dominated Sabeto River of western Viti Levu, Fiji reveals a strong negative exponential relationship between particle size and distance downstream, and a rate of downstream fining comparable with that of other gravel-bed rivers. The downstream fining pattern is straightforward and step-like discontinuities in the fining gradient are absent. This is suggestive of a sedimentary system only minimally disrupted by the supply of sediment from tributaries or the reworking of material from sources such as hillslopes and alluvial terraces. There is evidence, however, of anomalously coarse sub-populations at two sites. These coarser components must pre-date the other deposits at the sites. We speculate that they represent the products of earlier and higher-magnitude events. The bed sediments may thus be composite features, made up of individual components each transported by a specific event of particular magnitude. Our work confirms the relationship between the rate of downstream fining and particle size. This may arise because the distance over which individual particles are transported is likely to be size dependent. It is also possible that abrasion may be more effective in the case of larger particles than smaller ones, with the result that the coarser fraction of the river's bed sediment fines downstream more rapidly than the finer fraction. There is a long-standing debate about the relative roles of abrasion and sorting in downstream fining. Our data reveal little evidence for a downstream increase in the roundness of the river's gravels, implying that abrasion is likely to play a minor role in the fining process in this system. Highlights • Megaclast-dominated rivers occur widely, but have been largely ignored by researchers. • Megaclasts may be entrained by normal flows and not solely by catastrophic events. • Megaclast downstream-fining rates are comparable with those of other gravel-bed rivers. • There is a close relationship between bed-sediment size and rate of downstream fining. • Bed-sediment assemblages consist of discrete components, each transported by individual events. [ABSTRACT FROM AUTHOR]

Abstract Massive bed degradation (20 m in 7 years) has been observed in the Shi‑ting River, Sichuan Province, China, since the 2008 Wenchuan Ms. 8.0 earthquake. The reason for the massive bed degradation has not been well understood. A hypothesis has been proposed that relates bed degradation to the augmentation of sand supply after the earthquake. The effect of sand on gravel mobility (magic sand effect) has long been observed in laboratory experiments. In this paper, we study whether the augmentation of sand supply and its magic sand effect can lead to the observed massive degradation at decadal scales. A one-dimensional river morphodynamic model is implemented to study the problem in general at field scale and in context of the gravel-bed Shi‑ting River. Sediment transport is calculated with the Wilcock and Crowe (2003) relation, in which the magic sand effect is explicitly embedded in terms of a function relating reference Shields number to the surface sand fraction. We find that the augmentation of gravel supply leads to bed aggradation, whereas the augmentation of sand supply can indeed lead to bed degradation and surface fining. The magnitude and timescale of bed degradation are not sensitive to the sand supply rate but are sensitive to the flood intermittency factor , i.e., the fraction of time the river is in flood. However, an unrealistic flood intermittency factor (≥0.3) would be required in order to match the observed timescale of bed degradation, thus indicating that the magic sand effect might not be the governing reason for massive bed degradation in the Shi‑ting River, and by implication in gravel-bed rivers in general. Our simulation results also indicate that despite the fact that magic sand effects are not explicitly included in most sediment transport relations, they are at least partly built in via the hiding function that is contained in most sediment transport relations for gravel-sand mixtures. While here we use the Shi‑ting River as an example, our results have applicability to gravel-bed rivers subjected to augmentation in sand supply in general. Highlights • Augmentation of gravel supply leads to bed aggradation • Augmentation of sand supply leads to enhanced gravel transport and bed degradation • Magic sand effects alone cannot induce the observed river incision at decadal scale • Magic sand effects can be partly incorporated with a dimensionless hiding function [ABSTRACT FROM AUTHOR]

Abstract In this study we explore the controls over suspended sediment yield in 11 stations situated along six major rivers of Western – Northern Greece (Arachthos, Achelooos, Evinos, Aoos, Kalamas and Aliakmon). Values of area specific sediment yield for these stations come from reanalysis of existing records, by adaptation of the broken rating curve concept, and range from 140 to 2300 t km−2 y−1. We investigate the correlations among suspended sediment yield values and many geomorphic - topographic, morphometric, textural, tectonic, geological-lithological and climatic (precipitation-runoff) characteristics of the corresponding basins, along with land cover variables and RUSLE factors (LS, R, K and C RUSLE), from maps of the European Soil Data Center. We find the principal controls to be slope and lithology followed by precipitation, runoff and landslide frequency. Factors such as ground cover (percentage of barren land within the basin) and alluviation of the river, have also some relevance. With the use of stepwise multiple regression analysis we build a model that employs three variables: slope (in percent), precipitation (mean annual, in mm) and lithology (as percentage of the easily erodible geological formations within the catchment), where the contribution of lithology is an additive term to the slope-precipitation power relationship. The proposed model achieves good statistics (NSE = 0.84). From the other models tested with our data set BQART performs well while RUSLE2015 of the ESDC performs poorly. [ABSTRACT FROM AUTHOR]

Abstract Landslide damming is an important disturbance factor in the river evolution of mountain belts and may control river morphology at variable timescales. This temporal aspect is mostly discussed in terms of the spatial relationships between the dams and river longitudinal profiles within any given region. Largely lacking are detailed studies of the geomorphic response for individual dams. Here we present field evidence and 24 optically stimulated luminescence (OSL) ages that show the history of a landslide dam in an upstream reach of Yangtze River at the southeastern margin of the Tibetan Plateau and its influence on river evolution. The distribution of lacustrine ages suggests that there was only one long-term damming event, induced by landslide blocking the river. The dammed lake formed at 12.1 ka, and disappeared at 7.5 ka. The estimated dam height was 120 m, lake area was 96 km2, and lake volume was 7.5 km3. In addition, the grain size and distribution of lacustrine deposits indicate the dam failed cataclysmically when the lake finally drained. Today, the river long profile upstream of the dam site remains lower and the channel is wider in contrast to the downstream reach. Consequently, the former dam still influences channel morphology. Our study shows that the interaction of landslide dams with the rivers in the southeastern Tibetan Plateau may impeded valley incision and headward erosion in those cases where damming continued over periods of several thousand years. Graphical abstract Unlabelled Image Highlights • The 24 ages show the Baimakou dammed lake continued from 12.1 ka to7.5 ka. • It was not likely to be induced by earthquake from the lacustrine characteristics. • The grain size and distribution of deposits indicated the dam failed cataclysmically. • The dams continued few thousand years may impede valley and headward erosion. [ABSTRACT FROM AUTHOR]

Abstract The northward motion of the Pamir mountains relative to Eurasia results in uplift and shortening of the Pamir and Tian Shan orogens. The Vakhsh River catchment (Tajikistan) is situated along a thrust system in the collision zone between the Northern Pamir and the Western Tian Shan. In this study, spatial variations in catchment-wide denudation rates are reported from the Vakhsh River catchment with in situ-produced cosmogenic 10Be and 26Al of 22 samples from active river channels. Samples distributed along 140 km of the main Vakhsh River yield denudation rates between 1.28 ± 0.16 to 1.94 ± 0.26 mm/yr. In detail, samples from rivers draining the Northern Pamir indicate denudation rates of ~1.7 mm/yr, and a river draining the Alai Valley indicates denudation rates of 1.14 ± 0.14 mm/yr. In contrast, rivers draining the Western Tian Shan show increasing denudation rates from 0.18 ± 0.02 mm/yr in the west to 2.70 ± 0.36 mm/yr in the east, coincident with a small increase in the fluvial normalized steepness index (k sn). Measured 26Al/10Be ratios range from 5.2 to 7.6, indicating a low influence of sediment storage and reworking of partially shielded material. In addition, locations resampled one year later confirm previously calculated denudation rates along the main trunk. Analysis of in situ-produced cosmogenic 10Be from depth profiles collected from a sequence of terraces preserved along the main trunk of the Vakhsh River indicate terrace incision starting at ~3 kyr as well as paleo-denudation rates ranging between 1.75 ± 0.54 to 2.01 ± 0.39 mm/yr (2 s.d. errors). All these results suggest consistent high denudation rates in the Northern Pamir block, and a spatial (along strike) gradient in Western Tian Shan denudation rates. The most likely explanation for the spatial gradient in Western Tian Shan and Vakhsh River denudation rates is a regional gradient in tectonic rock uplift. Highlights • Cosmogenic nuclide concentrations constrain regional variations in denudation. • Modern river samples document lateral denudation gradients along active faults. • Denudation rate patterns are poorly correlated with precipitation. • River terrace formation and incision occurred in the late Holocene. [ABSTRACT FROM AUTHOR]

Abstract Quantifying flow resistance and sediment transport rates in steep streams is important for flood and debris flow prediction, habitat restoration, and predicting how mountainous landscapes evolve. However, most studies have focused on low gradient rivers and the application of this work is uncertain for steep mountain streams where surface flows are shallow and rough, subsurface flows are not negligible, and there is form-drag from bed- and channel-forms that differs from those in low gradient rivers. To evaluate flow resistance relations and sediment transport rates for steep channel beds, experiments were conducted using a range of water discharges and sediment transport rates in a 12 m long recirculating flume with bed slopes of 10%, 20%, and 30%, and a bed of nearly uniform natural gravel. Flow resistance for planar beds and beds that developed bedforms match empirical models that account for bedload-dependent roughness. Some bedforms were atypical for natural rivers at these bed slopes, such as stepped alternate bars and upstream migrating alternate bars. Total flow resistance increased with decreasing particle submergence and energetic sediment transport and drag on bedforms. Using linear stress partitioning to calculate bed stresses due to grain resistance alone, sediment flux relations developed for lower gradient rivers perform well overall, but they overestimate fluxes at 20% and 30% gradients. Based on previous theory, mass failure of the bed, which did not occur, was predicted for the highest Shields stresses investigated at 20% and 30% bed slopes; instead a concentrated layer, four to ten particle diameters deep, of highly concentrated granular sheetflow was observed. Highlights • Flow resistance increased with shallow flow, bedforms, and high sediment transport intensity. • Downstream and upstream migrating alternate bars developed on bed slopes up to 20%. • Transition to upper plane bed coincided with development of concentrated sheetflow. [ABSTRACT FROM AUTHOR]

Abstract Floods on sediment-rich semiarid rivers often lead to significant geomorphic change, but luminescence dating of sediments deposited by past flood events has hitherto been unable to meaningfully inform on past flood dynamics. This is important because luminescence dating has commonly been applied to flood sediments, but the calculated sediment ages are in almost all cases older than the ages of known floods responsible for sediment deposition. Correctly interpreting these older ages in the context of flood dynamics is therefore a key problem. This study addresses this problem by discussing relationships between luminescence dating, sediments, and reach-scale geomorphology along the semiarid Sabie River, northeastern South Africa. Twelve luminescence ages were obtained from near-surface sediments (<10 cm depth) from five sites across a 60-km distance of the lowland part of the river. Luminescence ages of 26–163 years suggest that sediments are differentially mobilized by successive floods and that high suspended sediment concentrations in the water column were insufficient to effectively zero the luminescence signal of the quartz grains. Analysis of equivalent dose values and distributions from individual dated samples using abanico plots shows the relative degree of bleaching, thus informing of the mixed composition of the sample and its likely source. Different landforms (bars, fans, flood drapes) were developed during maximal and waning flow stages, followed by fallout from suspension across the flooded valley that formed a drape that thins toward the upper flood limit. Different grain size properties and luminescence signals are found in these different fluvial settings. These landform and sediment properties can help explain why differential bleaching took place during fluvial sediment transport, which gave rise to the scatter in equivalent doses found within the dated samples. A model is proposed that describes these corelationships and provides a hypothesis of these relationships to test in future studies. Highlights • Luminescence dating of near-surface sediments on the Sabie River, South Africa, was undertaken • Calculated luminescence ages are considerably older than the most recent floods • Analysis of equivalent dose values and distributions was done using abanico plots • A model is proposed to link degree of bleaching to sediment processes during floods • Channels and floodplains have different luminescence signatures [ABSTRACT FROM AUTHOR]

Debris flows with long reaches are one of the major natural hazards to human life and property on alluvial fans, as shown by the debris flow that occurred in the Dongyuege (DYG) Gully in August 18, 2010, and caused 96 deaths. The travel distance and the runout distance of the DYG large-scale tragic debris flow were 11 km and 9 km, respectively. In particular, the runout distance over the low gradient channel (channel slope < 5°) upstream of the depositional fan apex reached up to 3.3 km. The build-up and maintenance of excess pore pressure in the debris-flow mass might have played a crucial role in the persistence and long runout of the bouldery viscous debris flow. Experiments to measure pore pressure and pore water escape have been carried out by reconstituting the debris flow bodies with the DYG debris flow deposit. The slurrying of the debris is governed by solid volumetric concentration (SVC), and the difference between the lower SVC limit and the upper SVC limit can be defined as debris flow index ( I d ). Peak value ( K p ) and rate of dissipation ( R ) of relative excess pore pressure are dependent on SVC. Further, the SVC that gives the lowest rate of dissipation is regarded as the optimum SVC ( C v o ). The dissipation response of excess pore pressure can be characterized by the R value under C v o at a given moment (i.e., 0.5 h, 1 h or 2 h later after peak time). The results reveal that a relatively high level of excess pore pressure developed within the DYG debris-flow mass and had a strong persistence capability. Further research shows that the development, peak value and dissipation of excess pore pressure in a mixture of sediment and water are related to the maximum grain size (MGS), gradation and mineralogy of clay-size particles of the sediment. The layer-lattice silicates in clay particles can be the typical clay minerals, including kaolinite, montmorillonite and illite, and also the unrepresentative clay minerals such as muscovite and chlorite. Moreover, small woody debris can also contribute to the slurrying of sediments and maintenance of debris flows in well vegetated mountainous areas and the boulders suspended in debris flows can elevate excess pore pressure and extend debris-flow mobility. The parameters, including I d , K p , R and etc., are affected by the intrinsic properties of debris. They, therefore, can reflect the slurrying susceptibility of sediments, and can also be applied to the research on the occurrence mechanisms and risk assessment of other debris flows. [ABSTRACT FROM AUTHOR]

The Waiapu River catchment (drainage area of 1734-km 2 ) is one of the most prolific conveyors of sediment in the world, annually delivering roughly 35 Mt of fine material to the ocean from eroding gullies, hillslopes, and reworked sediment on valley floors. Tectonic and geologic influences, in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes, predisposes this region to high rates of erosion. The bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse-grained, poorly sorted sediment mixture. Rapid abrasion and breakdown leads to high rates of suspended sediment yield. A wave of bedload material, manifesting as elevated bed levels and significant widening of active alluvial fills, has been triggered by large inputs of hillslope material from a few key tributary catchments following Cyclone Bola in 1988. We review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years, appraising some of the legacy effects that may endure, as associated with reworking of the considerable alluvial stores within the Waiapu system. We use Structure-from-Motion (SfM) techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades. A record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment (1958–2017) indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley-bottom deposits. The channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river, giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network. The largest impacts occur in the upper steepland rivers, closest to the landslide-derived sediment supply. Transport rates here, as inferred from cross section change, are at a maximum during an aggradational phase following Cyclone Bola then taper off, despite the large sediment accumulations remaining in the system. As of 2017, the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre-Bola conditions. The compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape, as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment. [ABSTRACT FROM AUTHOR]

Understanding flow-sediment interactions is important for comprehending river functioning. Fine sediment accumulation processes, in particular, have key implications for ecosystem health. However, the amount of fines generated by intragravel flows and later accumulated in gravel streambeds may have been underestimated, as the hydraulic-related driving transport mechanisms in play are not clearly identified. Specifically, the relative contribution of fines from upper vs. lower sediment layers in gravel beds is not well understood. By recreating flooded and dewatered conditions in an experimental flume filled with natural sediment, we estimated such contributions by observing and collecting intragravel transported fines that were later accumulated into a void in the middle of the sediment matrix. Near-bed transport in the upper sediment layers (named Brinkman load ) during flooded conditions accounted for most (90%) of the accumulated fines. Intragravel transport in the lower sediment layers (named Interstitial load ) was the sole source of transport and accumulation during dewatered conditions with steeper hydraulic gradients. Interstitial load accounted for 10% of the total transport during flooded conditions. Although small, such estimations demonstrate that hydraulic-gradient transport in the lower sediment layers occurs in spite of the contradicting analytical assessments. We provide a case study to challenge the traditional approaches of assessing intragravel transport, and a useful framework to understand the origin and relative contribution of fine sediment accumulation in gravel beds. Such knowledge will be highly useful for the design of monitoring programs aiding river management, particularly in regulated rivers. [ABSTRACT FROM AUTHOR]

Fine sediment processes in gravel beds may have significant impacts to overall river ecosystem function. In addition to gravitational deposition, horizontal intragravel transport has been recognized to influence fine sediment accumulation. However, the specific hydraulic mechanisms and origin of fine sediment movement are not clearly identified. The purpose of this study was to investigate key hydraulic drivers and patterns of fine sediment accumulation. Using a conceptual framework to set the scene, we implemented an experimental setup in a gravel lateral bar subject to irregular flow fluctuations in the Kiewa River (Australia). We installed nine sets of sediment collector pairs and piezometers into the gravel. Each pair included one horizontally and one horizontally-vertically perforated collector. Mid-range, rather than peak flows, covering the site in water drove fine sediment deposited in the collectors. We estimated horizontal contribution to final deposition as 59%. Such contribution resulted from shear stresses > 3 N m − 2 promoting streamwise near-bed turbulence at the water-sediment interface during flooded conditions. Despite high subsurface hydraulic gradients, intragravel transport in the lower sediment layers via Darcy flow did not show any influence to fine sediment deposition. Our findings contribute to an improved understanding of fine sediment accumulation processes, key for overall river ecosystem functioning, particularly in regulated rivers. [ABSTRACT FROM AUTHOR]

Pool-riffle maintenance has been documented in numerous studies, but it has been almost impossible to characterize detailed natural pool-riffle formation mechanisms because of the lack of baseline data prior to pool establishment. In 2013, a study was conducted on the Blackledge River in Connecticut to document the formation of a new pool-riffle couplet on a section of river that had previously been studied from 1999 to 2001. In 2001, the study reach contained a scour hole with a residual depth of 0.08 ± 0.09 m downstream of a 1930s paired deflector with no identifiable riffle immediately downstream. At this time, a large, severely undercut, hemlock tree was noted along the left bank. Sometime between fall 2001 and 2004, the tree fell perpendicular to flow across the channel and formed a large wood (LW) jam and new pool-riffle couplet several meters downstream of the old scour hole. Pool spacing along the reach decreased from 4.47 bankfull widths (BFW) in 1999 to 3.83 BFW after the new pool-riffle couplet formed. The new pool has a residual depth, the water depth of the streambed depression below the elevation of the immediate downstream hydraulic control, of 1.36 ± 0.075 to 1.59 ± 0.075 m, which resulted from a combination of 1.32 ± 0.09 m or less of incision below the old scour hole (95.6% or less of the depth increase) and up to 0.18 ± 0.09 m of downstream deposition and associated backwater formation (13.2% or less of the depth increase). To assess dynamic stability of the pool-riffle couplet over several flood cycles, surficial fine-sediment and organic material along the reach were quantified. The 23-m-long pool stores 25.7% of the surficial fine grained sediments and 15.4% of organic material along a 214-m-long reach that includes one additional artificially created pool. An adjacent 50-m-long secondary channel impacted by the LW jam stores 65.3% of the surficial fine-grained sediments and 54.8% of organic material along the full reach. [ABSTRACT FROM AUTHOR]

Sediment budgets are an important tool for understanding how riverine ecosystems respond to perturbations. Changes in the quantity and grain size distribution of sediment within river systems affect the channel morphology and related habitat resources. It is therefore important for resource managers to know if a river reach is in a state of sediment accumulation, deficit or stasis. Many sediment-budget studies have estimated the sediment loads of ungaged tributaries using regional sediment-yield equations or other similar techniques. While these approaches may be valid in regions where rainfall and geology are uniform over large areas, use of sediment-yield equations may lead to poor estimations of loads in regions where rainfall events, contributing geology, and vegetation have large spatial and/or temporal variability. Previous estimates of the combined mean-annual sediment load of all ungaged tributaries to the Colorado River downstream from Glen Canyon Dam vary by over a factor of three; this range in estimated sediment loads has resulted in different researchers reaching opposite conclusions on the sign (accumulation or deficit) of the sediment budget for particular reaches of the Colorado River. To better evaluate the supply of fine sediment (sand, silt, and clay) from these tributaries to the Colorado River, eight gages were established on previously ungaged tributaries in Glen, Marble, and Grand canyons. Results from this sediment-monitoring network show that previous estimates of the annual sediment loads of these tributaries were too high and that the sediment budget for the Colorado River below Glen Canyon Dam is more negative than previously calculated by most researchers. As a result of locally intense rainfall events with footprints smaller than the receiving basin, floods from a single tributary in semi-arid regions can have large (≥ 10 ×) differences in sediment concentrations between equal magnitude flows. Because sediment loads do not necessarily correlate with drainage size, and may vary by two orders of magnitude on an annual basis, using techniques such as sediment-yield equations to estimate the sediment loads of ungaged tributaries may lead to large errors in sediment budgets. [ABSTRACT FROM AUTHOR]

Our understanding of the effectiveness of reintroduced large wood for restoration is largely based on studies from high energy river systems. By contrast, few studies of the effectiveness of reintroducing large wood have been undertaken on large, low energy, lowland river systems: river systems where large wood is a significant physical feature on the in-channel environment. This study investigated the effect of reintroduced large wood on the hydraulic landscape of the Barwon-Darling River, Australia, at low flows. To achieve this, the study compared three hydraulic landscapes of replicated reference (naturally wooded), control (unwooded,) and managed (wood reintroduced) treatments on three low flow periods. These time periods were prior to the reintroduction of large wood to managed reaches; several months after the reintroduction of large wood into the managed reaches; and then more than four years after wood reintroduction following several large flood events. Hydraulic landscapes of reaches were characterised using a range of spatial measures calculated from velocity measurements taken with a boat-mounted Acoustic Doppler Profiler. We hypothesised that reintroduced large wood would increase the diversity of the hydraulic landscape at low flows and that managed reaches would be more similar to the reference reaches. Our results suggest that the reintroduction of large wood did not significantly change the character of the hydraulic landscape at the reach scale after several months ( p = 0.16) or several years ( p = 0.29). Overall, the character of the hydraulic landscape in the managed reaches was more similar to the hydraulic landscape of the control reaches than the hydraulic landscape of the reference reaches, at low flows. Some variability in the hydraulic landscapes was detected over time, and this may reflect reworking of riverbed sediments and sensitivity to variation in discharge. The lack of a response in the low flow hydraulic landscape to the reintroduction of large wood is inferred because the character (the size and complexity of individual pieces) and positioning of large wood in managed reaches did not mimic that of reference reaches effectively despite the abundance of wood pieces being similar in the reference and managed reaches. The results of this study highlight the importance of understanding the natural character and distribution of large wood on hydraulic landscapes in large low energy lowland river systems, especially when reintroducing large wood for river management purposes. [ABSTRACT FROM AUTHOR]

Intermittently Closed/Open Lakes and Lagoons (ICOLLs) are a particularly dynamic form of estuary characterised by periodic entrance closure to the ocean. Closure occurs when a subaerial sand berm stabilises across the entrance channel during times of low fluvial discharge. ICOLLs are of global importance as they provide valuable ecological habitats for many species and are associated with a wide range of management issues due to their cycle of entrance closure and opening. ICOLLs are found to be more widespread globally than previously described with 1477 of these estuaries being identified in this study. This constitutes an estimated 3% of the world's estuaries and 15% of all estuaries along microtidal coastlines. ICOLLs are concentrated along microtidal to low mesotidal coastlines in the mid-latitudes and predominantly on coasts with temperate climates. This distribution is related to greater wave heights as driven by high intensity winds and a longer fetch distance. The highest proportion of ICOLLs are present in Australia (21% all global ICOLLs), South Africa (16%) and Mexico (16%). In Australia, a comparison with fluvial input found that it is less important than marine processes in determining ICOLL formation and that ICOLLs are associated with a relative tidal range of < 3.22. Additionally the majority of ICOLLS are small systems with catchments < 2000 km 2 and tidal prisms < 30 × 10 6 m 3 , forming at the mouths of rivers with generally low mean annual and specific discharges. [ABSTRACT FROM AUTHOR]

Gravel mining has been a widespread activity in ephemeral rivers worldwide whose long-lasting hydrogeomorphological impacts preclude effective implementation of water and environmental policies. This paper presents a GIS-based method for temporal assessment of morphosedimentary changes in relation to in-channel gravel mining in a typical ephemeral Mediterranean stream, namely the Rambla de la Viuda (eastern Spain). The aims of this work were to identify morphosedimentary changes and responses to human activities and floods, quantify river degradations and analyze factors favoring fluvial recovery for further applications in other rivers. Aerial photographs and LiDAR topography data were studied to analyze geomorphic evolution over the past 70 years along a 7.5-km reach of an ephemeral gravel stream that has been mined intensively since the 1970s. To evaluate changes in the riverbed, we mapped comparable units applying morphological, hydraulic, and stability (based on vegetation density and elevation) criteria to 13 sets of aerial photographs taken from 1946 to 2012. A detailed spatiotemporal analysis of comparable units revealed a 50% reduction in the active section and a 20% increase in stable areas, compared to the conditions observed prior to gravel mining. Instream mining was first observed in 1976 aerial photograph covering already up to 50% of the 1956 riverbed area. River degradation since then was quantified by means of a LiDAR DTM and RTK-GPS measurements, which revealed a 3.5-m incision that had started simultaneously with gravel mining. Climate and land use changes were present but the effects were completely masked by changes produced by instream gravel mining. Therefore, river incision/degradation was triggered by scarcity of sediment and lack of longitudinal sedimentary connection, creating an unbalanced river system that is still adjusting to the present hydrosedimentary conditions. [ABSTRACT FROM AUTHOR]

High resolution digital models, combined with GIS or other terrain modelling software, allow many new possibilities in geoscience. In this paper we develop, describe and test a novel method, the GLA method, to detect active tectonic uplift or subsidence along river courses. It is a modification of Hack's SL-index method in order to overcome the disadvantages of the latter. The core assumption of the GLA method is that over geological time river profiles quickly adjust to follow an exponential decrease in elevation along the river course. Any large deviation can be attributed to active tectonic movement, or to disturbances in erosion/sedimentation processes caused by an anthropogenic structure (e.g. artificial dam). During the testing phase, the locations of identified deviations were compared to the locations of faults, identified on a 1:100,000 geological map. Results show that higher magnitude deviations are found within a maximum radius of 200 m from the fault, and the majority of detected deviations within a maximum radius of 600 m from faults or thrusts. However, these results are not the best that could be obtained because the geological map that was used (and the only one available for the area) is not of the appropriate scale, and was therefore not precise enough. Comparison of deviation magnitudes against PSInSAR measurements of vertical displacements in the vicinity revealed that in spite of the very few suitable points available, a good correlation between both independent methods was obtained (R 2 = 0.68 for the E research area and R 2 = 0.69 for the W research area). The GLA method was applied to the three test sites where previous studies have shown active tectonic movements. It shows that deviations occur at the intersections between active faults and river courses, as well as also correctly detected active uplift, attributed to the increased sedimentation rate above an artificial hydropower dam, and an increased erosion rate below. The method gives promising results, and it is acknowledged that the GLA method needs to be tested in other locations around the world. [ABSTRACT FROM AUTHOR]

Nearly 50 years of research focused on large wood (LW) in rivers provide a basis for understanding how wood enters rivers; how wood decays, breaks, and is transported downstream; and how at least temporarily stable wood influences channel geometry, fluxes of water, sediment, and organic matter, and the abundance and diversity of aquatic and riparian organisms. Field-based studies have led to qualitative conceptual models and to numerical stimulations of river processes involving wood. Numerous important gaps remain, however, in our understanding of wood dynamics. The majority of research on wood in rivers focuses on small- to medium-sized rivers, defined using the ratio of wood piece size to channel width as channels narrower than the locally typical wood-piece length (small) and slightly narrower than the longer wood pieces present (medium). Although diverse geographic regions and biomes are represented by one or a few studies in each region, the majority of research comes from perennial rivers draining temperate conifer forests. Regional syntheses most commonly focus on the Pacific Northwest region of North America where most of these studies originate. Consequently, significant gaps in our understanding include lack of knowledge of wood-related processes in large rivers, dryland rivers, and rivers of the high and low latitudes. Using a wood budget as an organizing framework, this paper identifies other gaps related to wood recruitment, transport, storage, and how beavers influence LW dynamics. With respect to wood recruitment, we lack information on the relative importance of mass tree mortality and transport of buried or surficial downed wood from the floodplain into the channel in diverse settings. Knowledge gaps related to wood transport include transport distances of LW and thresholds for LW mobility in small to medium rivers. With respect to wood storage, we have limited data on longitudinal trends in LW loads within unaltered large and great rivers and on fluctuations in LW load over time intervals greater than a few years. Other knowledge gaps relate to physical and ecological effects of wood, including the magnitude of flow resistance caused by LW; patterns of wood-related sediment storage for diverse river sizes and channel geometry; quantification of channel-floodplain-LW interactions; and potential threshold effects of LW in relation to physical processes and biotic communities. Finally, knowledge gaps are related to management of large wood and river corridors, including understanding the consequences of enormous historical reductions in LW load in rivers through the forested portions of the temperate zone; and how to effectively reintroduce and manage existing LW in river corridors, which includes enhancing public understanding of the importance of LW. Addressing these knowledge gaps requires more case studies from diverse rivers, as well as more syntheses and metadata analyses. [ABSTRACT FROM AUTHOR]

With the increased recent attention on understanding the complex pathways and fluxes of material, energy, and organisms and the multidimensional coupling between various geomorphic process domains, the 47th Binghamton Geomorphology Symposium was organized around the theme of Connectivity in Geomorphology . Six key subthemes emerged: sediment connectivity, hydrologic connectivity, geochemical connectivity, riverine connectivity, landscape connectivity, and modeling of connectivity. Papers presented at the symposium and collected in this special issue elucidate the theoretical and conceptual underpinnings of connectivity but also provide field-based and analytical approaches to document the fundamental role of connectivity in geomorphic and ecological functioning. Among the consistent themes that emerged from the papers and from discussion during the symposium were (1) the interconnectedness of diverse forms of connectivity, (2) the appropriateness (or not) of conceptualizing connectivity as a gradient or continuum, and (3) the importance of an explicit recognition of disconnectivity as a mechanism to retain ecologically important materials and organisms within landscapes. Knowledge gaps identified in discussions during the symposium include: identifying questions that can be usefully addressed within a framework emphasizing connectivity; identifying feedbacks that enhance and limit connectivity; and quantification – of diverse aspects of connectivity, of thresholds of connectivity, and of interactions among different types of connectivity. [ABSTRACT FROM AUTHOR]

Human-induced landscape change is difficult to predict due to the complexity inherent in both geomorphic and social systems as well as due to the coupling relationships between them. To better understand system complexity and system response to changing inputs, “connectivity thinking” has become an important recent paradigm within various disciplines including ecology, hydrology and geomorphology. With the presented conceptual connectivity framework on geomorphic change in human-impacted fluvial systems a cautionary note is flagged regarding the need (i) to include and to systematically conceptualise the role of different types of human agency in altering connectivity relationships in geomorphic systems and (ii) to integrate notions of human-environment interactions to connectivity concepts in geomorphology to better explain causes and trajectories of landscape change. Geomorphic response of fluvial systems to human disturbance is shown to be determined by system-specific boundary conditions (incl. system history, related legacy effects and lag times), vegetation dynamics and human-induced functional relationships (i.e. feedback mechanisms) between the different spatial dimensions of connectivity. It is further demonstrated how changes in social systems can trigger a process-response feedback loop between social and geomorphic systems that further governs the trajectory of landscape change in coupled human-geomorphic systems. [ABSTRACT FROM AUTHOR]

Evolutionary trajectories and related control factors of the Fortore River (southern Italy) are analyzed over a 150-year period as to assess channel modifications. A multitemporal GIS analysis of topographic maps and aerial photographs together with topographic and geomorphological field surveys were performed. Attention was focused on the impact caused by human disturbance, above all the presence of the Occhito dam at only 40 km upstream of the Fortore mouth (central Adriatic coast). Results show that channel adjustments occurred in three distinct phases and were primarily driven by human disturbance that diversely affected reaches located upstream and downstream of the dam. From the last decades of the nineteenth century to the 1950s (phase 1), channel widening prevailed along upstream reaches whilst narrowing along downstream reaches. Major channel adjustments occurred from the 1950s until the end of the 1990s (phase 2), especially channel narrowing of up to 81% in upstream reaches and 98% in downstream reaches. Narrowing was accompanied by channel-bed lowering of 1 to 5 m and by pattern changes in prevalence from multithread to largely prevailing single-thread channel configurations. In-channel mining, channel works, and hydraulic interventions are considered key driving factors of observed channel adjustments. The closure of the Occhito dam in 1966 had significant and permanent effects on downstream reaches through overall discharge regulation and permanent sediment trapping as also proved by the progressive retreat of the Fortore river mouth area. From 2000 to 2015 (phase 3), a substantial trend inversion was observed with overall channel widening and partial aggradation of upstream reaches and total stabilization of downstream reaches. As highlighted by an integrated multitemporal analysis of recent channel changes and flood events, the latter have played an important role in channel recovery of upstream reaches. Comparison between the Fortore River and other rivers in southern Italy has allowed us to ascertain that the reconstructed evolutionary trajectories are quite similar and that control factors are essentially the same. In particular, it confirms the role of major hydraulic structures as to the amount of channel adjustments of downstream reaches and the ensuing scarce to nil potential to channel recovery of regulated reaches. [ABSTRACT FROM AUTHOR]

Palaeo–hydrological and sedimentary investigations were carried out in the Longmenxia Gorge of the middle Yihe River. Five bedsets of flood slackwater deposits (SWD) were found interbedded into Holocene aeolian loess–soil profiles in the river bank at the Longmenxia site. They were identified as the deposits of the suspended sediment load during the extreme flood events of the Holocene. The minimum flood peak discharges were estimated to be 12, 300–15, 300 m 3 /s using the slope–area method. These are about twice the largest gauged record (7180 m 3 /s) that has occurred since 1937. These flood events occurred at 3100–3000 a B.P., 1800–1700 a B.P., 700–550 a B.P. and 350–250 a B.P., as dated by optically stimulated luminescence (OSL) in combination with stratigraphic correlation, to which may be added the recorded events of the 223 and 1761 CE floods. These were associated with Holocene monsoonal shifts and abrupt climatic events. This research not only provides palaeoflood discharge estimates on the middle Yihe River, but also provides important data for understanding interactions between regional hydro–climatic systems and global climate change in humid and semi–humid monsoonal regions, such as China. [ABSTRACT FROM AUTHOR]

This study characterizes and provides ages for an extensive sedimentary record occurring in Lapa Doce and Torrinha caves, NE Brazil. With > 40 km of surveyed passages, these caves integrate a distributary cave system fed by allogenic recharge from the surrounding sandstone plateaus. Sediment petrography together with descriptions of depositional facies and architectural elements shows four depositional units related to fluvial and standing water environments. These include, from bottom to top: (1) a channel unit including lateral bars deposited during an ordinary flood regime; (2) a sandy flood unit including minor channel and scour fills derived from bank-full equivalent flood events; (3) mud caps deposited in standing water that often reach the ceiling; and (4) intraclast breccias associated with collapse of the mud caps under saturated conditions. The deposits were dated using a combination of cosmogenic nuclide burial dating and U-series dating of flowstone. Cosmogenic nuclide data point to fluvial aggradation being active since 1.91 + 0.12 My and extending until 0.36 ± 0.08 My, with intensive cave and valley aggradation events between 0.78 ± 0.10 My and 0.44 ± 0.12 My. Long term alluviation of the cave system seems to be important in forming passages, determining their configuration, and setting up a general distributary pattern evident in passage morphology and sedimentary sequences. Mud caps overlapping the fluvial deposits are interpreted as the products of successive rising and lowering of the water table (static level). Radiometric ages of interstratified flowstones and speleothems show that these oscillations were active at least since 115 ky ago and finally ceased around 12 ky ago, indicated by the recurrent age obtained from uneroded capping flowstones. These long-term water table oscillations may drive paragenetic expansion of the whole cave system. Valleys, caves and other landforms in our study area are part of an ancient landscape with multiple episodes of burial and exhumation. Despite the possibility of much older sediment being preserved somewhere in the cave system, our data indicate a younger Quaternary age for the bulk of the sediment filling the study caves. [ABSTRACT FROM AUTHOR]

Channel changes in meandering rivers naturally exhibit complex behaviour, and understanding the river dynamics can be challenging in environments also subject to cumulative human impacts. Planform changes were analysed on four reaches of the lower course of the Peixe River, Brazil, at decadal scales over the period 1962–2008 from aerial photographs and satellite imagery, complemented by a historical map from 1907. Analysis of the spatial and temporal patterns of channel change mechanisms and morphometry of bends and of the sinuosity and morphodynamic variations of the reaches demonstrates major changes in planform characteristics. Sinuosity in all reaches decreased from ~ 2.6 to ~ 1.7, average wavelength of bends has increased from ~ 200 to ~ 500 m, and the planform has become much simpler. Changes have been progressive from downstream to upstream, with higher intensities of processes, particularly cutoffs first in downstream reaches then more recently in upstream reaches. It is suggested that channel changes represent a morphological adjustment to human interventions, such as reservoir construction and land use. However, evidence of the autogenic behaviour of meanders is highlighted in which the existence of compound meanders reveals control over the spatial variation in the reaches. The results suggest that geomorphic thresholds associated with the compound meander formation and the bend evolution should be considered, even in impacted meandering rivers, because they exert primary controls on the spatial-temporal adjustment of channels. [ABSTRACT FROM AUTHOR]

This paper investigates post-dam geomorphic and vegetation changes in the Sauce Grande River, a meandering dryland river impounded by a large water-conservation dam. As the dam impounds a river section with scarce influence of tributaries, sources for fresh water and sediment downstream are limited. Changes were inspected based on (i) analysis of historical photographs/imagery spanning pre- (1961) and post-dam (1981, 2004) channel conditions for two river segments located above and below the dam, and (ii) field survey of present channel conditions for a set of eight reference reaches along the river segments. Whilst the unregulated river exhibited active lateral migration with consequent adjustments of the channel shape and size, the river section below the dam was characterized by (i) marked planform stability (93 to 97%), and by (ii) vegetation encroachment leading to alternating yet localized contraction of the channel width (up to 30%). The present river displays a moribund, stable channel where (i) redistribution of sediment along the river course no longer occurs and (ii) channel forms constitute a remnant of a fluvial environment created before closing the dam, under conditions of higher energy. In addition to providing new information on the complex geomorphic response of dryland rivers to impoundment, this paper represents the very first geomorphic assessment of the regulated Sauce Grande and therefore provides an important platform to underpin further research assessing the geomorphic state of this highly regulated dryland river. [ABSTRACT FROM AUTHOR]

While sediment tracing has been typically applied to identify sediment sources that are difficult to measure by gauging (monitoring), it can also be useful in estimating relative sediment yields from gauged river catchments. The major and trace element composition of river sediments from eleven locations in the 130000 km 2 Burdekin River catchment, northeastern Australia was analysed to examine relative contributions from upstream source areas in the 2011/12 water year. Sediment tracing results are compared against estimates derived from sediment load monitoring at three locations. Comparisons show that there is good agreement between tracing results and monitoring data at one of the tributary confluences. At the second site, notable contrasts were found between the load estimates from the monitoring and tracing data. At this site a large impoundment occurs between the upstream sampling/gauging sites for source sediments and the downstream sampling/gauging sites for target sediments. The contrast is likely caused by temporal variations in particle size distributions of suspended sediment from each river and differential trapping efficiencies in the impoundment for sediment derived from the different tributaries. In the absence of the detailed particle size data and trapping efficiency estimates, sediment tracing provides the unique opportunity to elucidate source contributions of the finer fractions of suspended sediment. At a third site, where there were recognised measurement gaps in the monitoring data during large discharge events, the relative load estimates from the tracing data provided a means of constraining the recognized uncertainty of monitored load estimates. We conclude that sediment tracing can be used as a valuable adjunct to monitoring data particularly in remote, large and data-sparse catchments. Both tracing results and monitoring data show that the Upper Burdekin River and Bowen-Bogie Rivers were the dominant source of the < 10 μm sediments being delivered to the GBR lagoon from the Burdekin River catchment in the 2011/12 water year. More substantial contribution from the Belyando-Suttor Rivers indicated by the tracing results than the monitoring data is attributed to preferential delivery of the 1–10 μm sediments through the impoundment and has uncovered a knowledge gap in sediment budgets in the catchment. [ABSTRACT FROM AUTHOR]

River management practices are often informed by theoretical expectations of downstream channel adjustment, which may not be valid in low relief, glacially conditioned watersheds such as those in the lower North American Great Lakes region. Downstream trends in channel morphology and bed material size within a low-relief, glacially conditioned watershed are explored here and compared to a theoretical watershed model where slope and grain size are expected to decline exponentially. The observed channel morphology is then tested against a theoretical concept of reach-scale channel grade. The downstream hydraulic geometry relations w bf ∝ Q bf 0.51 S − 0.02 and d bf ∝ Q bf 0.32 S − 0.21 were found to best describe downstream changes in channel morphology and are consistent with some prior studies. Bed material size varies irregularly down the channel. Slope-controlled downstream fining trends are evident where inputs from glacial materials and tributaries are negligible but are masked by cobble/boulder lag deposits where the channel is cut into these glacial deposits. The asynchronous variability in slope and grain size produces downstream variations in graded and nongraded, understeepened conditions separated at τ * ex = 0. Graded reaches exist where τ * ex > 0, but an upper boundary with nongraded, oversteepened reaches is less clear. The results emphasize the geomorphic legacy of inherited slopes and sediment sources in dictating the modern downstream patterns of fluvial characteristics and morphologies in glacially conditioned, and similarly complex, watersheds. [ABSTRACT FROM AUTHOR]

This special issue honors the contributions of William L. Graf to geomorphology and river science. A hallmark of Will's work over the course of his career has been a focus on the natural and human structuring of river systems. More broadly, Will has been an innovator and leader who has shaped the way in which geomorphologists conduct research. Through his work, he has made fundamental contributions to basic fluvial theory, to the understanding of human impacts on river systems, and to policy-relevant science. He has demonstrated by example how to pursue policy-relevant science and to participate in science-based policy formulation. His contributions to river science can be classified into several themes: (1) the hydrology and geomorphology of suburban drainage systems, (2) riparian vegetation and river systems, (3) the spatial structure and dynamics of incised channels, (4) the dynamics of dryland river systems, (5) heavy metals in river systems, (6) dams and dam removal, and (7) water and public policy. The papers in this special issue reflect many aspects of these themes and address topics related to (1) the understanding of rivers and other geomorphic systems in the midst of dynamic physical change, (2) human influences on geomorphic processes, (3) the intersection of geomorphology and public policy, and (4) the fusion of geomorphic analysis and GIScience. [ABSTRACT FROM AUTHOR]

Humans have become major geomorphological agents, effecting substantial change in the characteristics of Earth's physical landscapes. The agricultural Midwest of the United States is a region marked by pronounced human influence at the landscape scale. Humans undoubtedly have strongly influenced critical zone processes, including fluvial processes, in intensively managed agricultural landscapes, yet the exact nature of human alteration of these processes is unknown. This study documents historical changes in the extent of the stream channel network and in channel planform within the upper Sangamon River basin — an intensively managed agricultural watershed in Illinois. Results indicate that the modern channel network is nearly three times more extensive than the channel network in the 1820s. Most change in drainage density has occurred in headwater portions of the basin where numerous drainage ditches have been added to the network to drain flat uplands. No detectable change in channel position is evident between 1940 and 2012 along about 60% of the total length of the Sangamon River and its major tributaries. Nearly 30% of the total length exhibits change related to meander dynamics (cutoffs and lateral migration), whereas about 8% has changed as a result of channelization. Channelized sections typically remain straight for decades following human modification, supporting the notion that humans produce long-lasting catastrophic change in channel planform in this region. The findings confirm that humans are effective agents of morphological change in fluvial systems in this intensively managed watershed. Documenting human-induced versus natural changes in fluvial systems is important for evaluating how other critical zone processes in intensively managed landscapes have been affected by these changes. Human-induced changes in channel extent and planform most likely have altered this landscape from one dominated by biogeochemical transformations and storage of water and sediment prior to agricultural development into one now characterized by enhanced fluxes of water, sediment, and nutrients. [ABSTRACT FROM AUTHOR]

While human impacts on rivers and other landforms have long been a component of geomorphic research, little of this work explicitly includes insights into human agency from social science or recognises that in many cases rivers can be considered to be hybrid co-productions or ‘socio-natures’. A socio-geomorphic approach proposed here has parallels with some aspects of sociohydrology and can extend and enrich existing geomorphic explanations of the morphology of, for example, urban rivers by explicitly recognising and working with the co-evolution of the human and natural systems. Examples from recent literature illustrate ways in which these relationships can be understood and analyzed, showing a range of socio-natural influences in particular contexts that have material consequences for river morphology and recognising that events in the system have many forms. The approach recognises the importance of contingency in time and place together with the role and nature of both local and global knowledge. An important element of this approach is that it provides ways for understanding the nature, position and intention of geomorphic and other scientific interventions as part of the system, for example in the case of river restoration. This also leads to the need for reflexivity by geomorphologists and reconsideration of the nature of geomorphological knowledge by those involved in such work and with respect to sociogeomorphology as a whole. [ABSTRACT FROM AUTHOR]

The impact of extreme flood events is rarely considered in studies of long-term landscape evolution, despite the potential for catastrophic landscape change in a short period of time. Here, we use an integrated approach of geomorphological mapping, topographic analysis and geophysical surveys to identify and quantify the impact of extreme flood events (jökulhlaups) along the Jökulsá á Fjöllum, Iceland, where evidence for the action of such floods is widespread on microspatial to macrospatial scales. The apex of the 28-km-long Jökulsárgljúfur canyon is characterised by a complex network of palaeo-flood channels and large vertical knickpoints such as Dettifoss (54 m high) and Hafragilsfoss (20 m high). Downstream, the Forvoð valley contains large terraces of boulder-rich deposits (50 m thick, > 3 km long). Near the outlet of the canyon is Ásbyrgi, a dry canyon (3 km long, 1 km wide, up to 90 m deep) with eroded cataracts and scabland morphology immediately upstream and ~ 90 m above the current river channel. Topographic analysis and electrical resistivity tomography surveys show that 0.144 km 3 of rock was eroded from Ásbyrgi during its formation ~ 10,000 years ago, and just 4% of this eroded volume is currently filled with sediment deposits, up to 5 m thick. Deposited boulders across the canyon floor of Ásbyrgi demonstrate that the discharge of the jökulhlaup that formed the canyon was at least 39,000 m 3 s − 1 . We present a model for the evolution of the lower Jökulsá á Fjöllum and the Jökulsárgljúfur canyon during various stages of an extreme flood event. Reconstruction of the early Holocene flood event includes the initiation and development of different canyons before the capture of all floodwater within one canyon at the end. We tie the evolution of the lower Jökulsárgljúfur canyon to established chronology of flood events during the Holocene farther upstream and highlight the dominant impact of extreme flood events over background processes in this landscape. [ABSTRACT FROM AUTHOR]

The 2008 eruption of Chaitén volcano in southern Chile severely impacted several densely forested river catchments by supplying excess pyroclastic sediment to the channel networks. Our aim is to substantiate whether and how channel geometry and forest stands changed in the Rayas River following the sudden input of pyroclastic sediment. We measured the resulting changes to channel geometry and riparian forest stands along 17.6 km of the impacted gravel-bed Rayas River (294 km 2 ) from multiple high-resolution satellite images, aerial photographs, and fieldwork to quantify yield volume characteristics of the forest stands. Limited channel changes during the last 60 years before the eruption reflect a dynamic equilibrium condition of the river corridor, despite the high annual precipitation and the sediment supply from Chaitén and Michinmahuida volcanoes in the headwaters. Images taken in 1945, 2004, and 2005 show that total size of the vegetated channel islands nearly doubled between 1945 and 2004 and remained unchanged between 2004 and 2005. Pyroclastic sediment entering the Rayas River after the 2008 eruption caused only minor average channel widening (7%), but killed all island vegetation in the study reach. Substantial shifts in the size distribution of in-channel vegetation patches reflect losses in total island area of 46% from 2005 to 2009 and an additional 34% from 2009 to 2012. The estimated pulsed release of organic carbon into the channel, mainly in the form of large wood from obliterated island and floodplain forests, was 78–400 tC/km/y and surpasses most documented yields from small mountainous catchments with similar rainfall, forest cover, and disturbance history, while making up between 20% and 60% of the annual carbon burial rate of fluvial sediments in the northern Patagonian fjords. We conclude that the carbon footprint of the 2008 Chaitén eruption on the Rayas River was more significant than the measured geomorphic impacts on channel geometry for the first five years following disturbance. The modest post-eruptive geomorphic response in this river is a poor indicator of its biogeochemical response. [ABSTRACT FROM AUTHOR]

Bioerosion is an important process that destroys coastal rocks in the tropics. However, the rates at which this process occurs, the organisms involved, and the dynamics of rocky cliffs in tropical latitudes have been less studied than in temperate and subtropical latitudes. To contribute to the knowledge of the bioerosion process in rocky cliffs on the Pacific coast of Colombia (Eastern Tropical Pacific) we compared: 1) boring volume, 2) grain size distribution of the rocks, and 3) rock porosity, across three tidal zones of two cliffs with different wave exposure; these factors were related to the bioeroding community found. We observed that cliffs that were not exposed to wave action (IC, internal cliffs) exhibited high percentages of clays in their grain size composition, and a greater porosity (47.62%) and perforation (15.86%) than exposed cliffs (EC, external cliffs). However, IC also exhibited less diversity and abundance of bioeroding species (22 species and 314 individuals, respectively) compared to the values found in EC (41.11%, 14.34%, 32 and 491, respectively). The most abundant bioeroders were Petrolisthes zacae in IC and Pachygrapsus transversus in EC. Our findings show that the tidal zone is the common factor controlling bioerosion on both cliffs; in addition to the abundance of bioeroders on IC and the number of bioeroding species on EC. The integration of geology, sedimentology, and biology allows us to obtain a more comprehensive view of the patterns and trends in the process of bioerosion. [ABSTRACT FROM AUTHOR]

The research reported in this paper employs flume experiments to investigate the potential effects of living vegetation and large wood on river morphology, specifically aiming to explore how different wood input and vegetation scenarios impact channel patterns and dynamics. We used a mobile bed laboratory flume, divided into three parallel channels (1.7 m wide, 10 m long) and filled with uniform sand to reproduce braided networks subject to a series of cycles of flooding, wood input, and vegetation growth. Temporal evolution of river configuration (in terms of the braiding index), vegetation establishment and erosion, and wood deposition amount and pattern was recorded in a series of vertical images. The experiments reproduced many forms and processes that have been observed in the field, from scattered logs in unvegetated, dynamic braided channels to large wood jams associated with river bars and bends in vegetated, stable, single-thread rivers. Results showed that the inclusion of vegetation in the experiments changes wood dynamics, in terms of the quantity that is stored and the depositional patterns that develop. Vegetated banks increased channel stability, reducing lateral erosion and the number of active channels. This promoted the formation of stable wood jams, where logs accumulated continuously at the same locations during subsequent floods, reinforcing their effect on river morphology. The feasibility of studying these processes in a controlled environment opens new possibilities for disentangling the complex linkages in the biogeomorphological evolution of the fluvial system and thus for promoting improved scientific understanding. [ABSTRACT FROM AUTHOR]

Logjams significantly influence watershed hydrology, flow regime, channel morphology and stability, and processes in lowland rivers. Consequently, logjams play a major role in the existence and conservation of the riparian and aquatic ecosystems along major waterways. In this paper, we attempt to detect and quantify logjams in river channels using LiDAR technology in conjunction with traditional fieldwork. To the best of our knowledge, LiDAR-based analysis has not been used to characterize logjams in streams. Overall, when applied in a lowland river environment, LiDAR-based analysis demonstrates a comprehensive solution for detecting logjams in relation to the fieldwork, with a low rate of omission. A filtered approach predicted the presence of 95% of fieldwork-reported logjams (a 5% rate of omission), but also identified six logjams not identified in the field (a 10% rate of commission). A nonfiltered approach identified 87% of field-reported logjams, producing a 13% rate of omission and a 6.7% rate of commission. Dimension measurements were more consistent in the filtered LiDAR approach, showing 53%, 34%, and 90% of R 2 improvements for the length, width, and height, respectively, over the unfiltered LiDAR values. As vegetation cover hindered accurate delineation of logjam boundaries by LiDAR, field and LiDAR measurements of nonvegetation-obstructed logjams were more highly correlated than the field and LiDAR measurements of partially and completely vegetation-obstructed logjams. [ABSTRACT FROM AUTHOR]

The Pleistocene opening of the endorheic Duero River drainage basin (northwestern Spain and central Portugal) has led to river incision, creation of steep valley sides, and development of large (> 0.1 km 2 ) and episodically active rotational and roto-translational landslides along river reaches where a weak geological lithology has been exposed by river erosion. These landslides occur in the central part of the Duero basin despite low precipitation, weak contemporary seismicity, and low regional relief. These landslides occurred as a result of the downcutting of the Duero River and its tributaries through a sequence of Miocene basin-fill sediments. In the last few thousand years the incision reached a series of high-plasticity, low-strength clay layers within the sedimentary sequence. Owing to this mechanism, these landslides occurred in a specific area at a specific period of time. All of the large landslides are located at the outside of meander bends, suggesting that river lateral erosion facilitated slip failures. Recent anthropogenic activities to control river flows and to stabilize river banks have decreased the possibility of future landslides in this area. [ABSTRACT FROM AUTHOR]

In April 2000 a large-scale rock avalanche dammed the Yigong Zangpo River, forming an extensive rockslide-dammed lake. The impoundment lasted for 62 days before a catastrophic breaching caused a massive outburst flood in the Yarlung Zangpo (Tibet) and the Dihang rivers (India) that travelled downstream to the main floodplain of the Brahmaputra in northeastern India. In response to discrepancies in the published literature on the event, we present a review and re-evaluation of the characteristics of the rock avalanche and associated landslide-dammed lake. We use digital topographical data (SRTM-3) and dynamic landslide modelling (DAN-W and DAN3D) to determine the salient characteristics of the damming landslide and to characterise its behaviour. Our analysis indicates that the volume of the damming rockslide was ca. 115 Mm 3 , including 91 Mm 3 from the initial rockslope failure (bulked during disaggregation to 109 Mm 3 ) and 6 Mm 3 from entrainment during its 10.1 km travel down Zhamulong gully. The debris travelled with an average velocity of 15–18 m/s and resulted in a landslide dam on the Yigong River with a minimum height of about 55 m. Using LANDSAT-7 imagery (obtained before, during, and after impoundment) in conjunction with an SRTM-3 DEM, we reproduced the filling of the lake. We determine that the landslide dam formed an extensive reservoir with an impounded volume of 2.015 Gm 3 and a maximum possible lake level of 2264 m asl (rounded to 2265 m asl). Our figures differ from those previously published but are believed to be well-constrained verifiable estimates of the volumes of the 2000 Yigong events. The outburst occurred after an attempt by army personnel to manually dig a spillway over the landslide debris and resulted in the entire volume of the lake draining in about 12 h. The outburst flood travelled over 500 km south into India, with a recorded rise in river level of 5.5 m at the Pasighat gauging station, 462 km downstream. In terms of historical outburst volumes from rockslide-dammed lakes, the volume of the 2000 Yigong event is only exceeded by that of the 1841 outburst flood from the Indus River rockslide-dammed lake, northern Pakistan. [ABSTRACT FROM AUTHOR]

The Iberian Chain (central–eastern Spain) is characterized by a dome-shaped topography with poorly incised and relatively flat landscape in its interior at an elevation of ~ 1300 m. A recent regional tectonic event started during or after the Late Pliocene, inducing deep valley incision on the flanks of the Iberian Chain. The rate and timing of this deformation, as well as the magnitude of the uplift-induced erosion processes, still lack a quantitative validation. We used 3D (SIGNUM) and 1-D (river profile) numerical models to investigate the landscape evolution of the Iberian Chain from the Late Pliocene to the present and to study the response of topography and rivers to tectonically induced base level lowering. Our model results are supported by geological, geomorphological and geochronological data. The results of the SIGNUM experiments show that the Iberian Chain topography has experienced regional uplift since ca. 3 Ma with rates between 0.25 and 0.55 mm y − 1 . In response to this uplift, rivers have incised at an average long-term incision rate of about 0.22 mm y − 1 and have progressively captured drainage areas from the chain interior. To further validate the results of landscape evolution modeling, we use a 1-D river incision model to explore the incision history of several rivers draining the Iberian Chain. The results constrain the range of values of bedrock erodibility from 5.8 × 10 − 5 to 5.0 × 10 − 4 m 0.4 y − 1 and predict long-term incision rates similar to those from the SIGNUM experiments. [ABSTRACT FROM AUTHOR]

In-channel wood is a fundamental component of the riverine system. Its nature, abundance, and distribution as well as the role of wood in trapping sediment have been reported by many authors. However, a lack of knowledge still exists on how the geomorphic effects, quantity, and characteristics of in-channel wood may be altered by different human pressures. For this reason, in-channel wood was surveyed in the Brenta, Piave, and Tagliamento gravel-bed rivers (northeastern Italy), which are altered by different degrees of human pressures. Both single pieces of wood (> 0.1 m diameter, and/or > 1 m long) and accumulations of large wood were measured on cross sectional transects within the active channels. Overall, 3430 (8.4, 13.9 and 10.7 elements/ha in the Brenta, Piave, and Tagliamento rivers, respectively) of isolated pieces and 591 (9.8, 15.0, and 11.0 wood accumulations/ha in the Brenta, Piave, and Tagliamento rivers, respectively) accumulations were surveyed in the study sites. In the Brenta and Piave rivers, which feature the greater human pressures, logs appear in a worse state of conservation. In the less disturbed Tagliamento River, the logs appear to be smaller and in a better state of conservation with higher capacity for resprouting. In addition, higher geomorphic interactions were found between wood and sediments in the Tagliamento River. Because of its ability to create geomorphic effects, in-channel wood represents an important source of complexity that can increase habitat diversity in river systems. A better knowledge of the role of human disturbances on the characteristics and abundance of large wood in river systems could help in developing better river management and the practical application of river ecology. [ABSTRACT FROM AUTHOR]

The interaction between fluvial and aeolian processes can significantly change Earth surface morphology. When rivers and sand dunes meet, the interaction of sediment transport between the two systems can lead to change in either or both systems. However, these two systems are usually studied independently, which leaves many questions unresolved in terms of how they interact. This paper carries out a global inventory, using satellite imagery, to identify 230 sites where there are significant fluvial–aeolian interactions. At each location key attributes such as wind/river direction, net sand transport direction, fluvial–aeolian meeting angle, dune type and river channel pattern were identified and relationships between each factor were analysed. From these data, six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems. Results from this classification confirm that only certain types of interaction were significant: the meeting angle and dune type, the meeting angle and interaction type and finally the channel pattern and interaction type. However, the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images. [ABSTRACT FROM AUTHOR]

Abstract: Turbidity is commonly used as a proxy to estimate suspended sediment content in streams, and for hydroecological purposes. The scope of this paper is to give an outlook to wider applications of nephelometric turbidimetry as a method. Uncalibrated turbidity records in conjunction with water chemistry data prove useful in detecting watershed reaction to single hydrological events during the spring flood in Arctic Russia. The turbidimetric survey technique was applied to study the spatial variability of sediment yield features on small rivers of the south-eastern part of Sakhalin Island. Suspended sediment concentration (SSC) vs. turbidity relation follows the geological features of the terrain and reflects the land-use intensity within the watersheds. For our Igarka key site, a logarithmic regression model was developed as an instrument of SSC calculation with turbidity data for each of the four studied watersheds. A regional regression model was developed for this site, and supplementary water optics data (filtered sample turbidity) was employed to increase the reliability of SSC calculations. Our results show that factors influencing turbidity, namely water colour and sediment grain size, have to be considered in multivariate models, to minimize errors and acquire an understanding of what kind of physical response is actually measured by nephelometry-based instruments. [Copyright &y& Elsevier]

Abstract: While differences in catchment sediment yield (SY, [tkm−2 y−1]) are generally attributed to topography, lithology, climate and land use, recent studies have highlighted that also seismic activity may have an important impact on SY. Nonetheless, relatively little is known about the importance of this factor and the processes and mechanisms explaining its influence. Therefore, this study explores the role of seismic activity in explaining spatial and temporal variation in sediment export within the Siret Basin (Romania, 45,000km2), a catchment with a large variability in seismic activity. Based on previously unpublished long-term (>30years) SY measurements for 38 subcatchments of the Siret, we analyze the correlation between average SY, seismic activity and various other catchment characteristics. Our results showed that spatial variation in average SY was indeed strongly correlated with the degree of seismic activity in each catchment (R 2 =0.74). Also catchment lithology explained an important part of the differences in SY (R 2 =0.67). The combination of these two factors accounted for about 80% of the observed variation in SY, while other factors (e.g. topography, land use, climate, and runoff) did not significantly contribute to the explained variance in average SY. To explore the impact of a specific earthquake event on sediment export, we analyzed daily variations in suspended sediment concentrations of 10 subcatchments, five years before and after an earthquake of Mw =7.4 that affected the Vrancea region in 1977 and triggered a substantial number of landslides. Only one catchment showed a clear (3-fold) increase in sediment concentrations at unit discharge. For the other nine catchments, no consistent increase could be observed. This indicates that the impact of seismic activity on average SY is mainly indirect and not associated with sudden pulses of sediments, caused by earthquake-triggered landslides. Potential mechanisms that could explain such indirect responses are discussed. [Copyright &y& Elsevier]

Abstract: Fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades. Fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development. This paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to: conceptual models; fluvial features and environments being studied; tools used by fluvial geomorphologists; geomorphic specialty groups within professional societies; journals in which fluvial geomorphic research is published; and textbooks of fluvial geomorphology. During this half century, fluvial geomorphology broadened considerably in scope, from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range, to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient, substrate composition, and grain size. The array of tools for making basic observations, analyzing data, and disseminating research results also expanded considerably during this period, as did the diversity of the fluvial geomorphic community. [Copyright &y& Elsevier]

Abstract: We assess the sediment yield at 119 gauging stations distributed from Colombia to Patagonia, covering the different morphotectonic and morphoclimatic settings of the Andes. The most productive areas are the Meta River basin within the northern Andes and the Bolivian and northern Argentina-Chaco systems, which produce an average of 3345, 4909 and 2654tkm2 y−1 of sediment, respectively. The rivers of the northern and central Andes (excluding the Pacific watersheds of Peru, northern Chile, and central Argentina) have a weighted mean sediment yield of 2045tkm−2 y−1 and produce 2.25 GTy−1 of total sediment. A major constraint estimating the Andean continental budget of sediment yield lies in the lack of gauging data for the Peruvian region. Using the available gauge stations, the regional sediment yield appears underestimated. Assuming a higher value of sediment yield for the Peruvian Andes, the total budget for the whole central Andes could range between 2.57 GT y−1 and 3.44 GT y−1. A minimum of~0.55 GT y−1 and a probable maximum of~1.74 GT y−1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins. The magnitude of sediment yield in the Andes is comparable to other rivers draining orogenic belts around the world. [Copyright &y& Elsevier]

Abstract: Large rivers have anabranching channels with components that may be defined as braided, meandering or straight. This paper shows that application of such holistic terminologies is complicated by recognition of within-type and transitional-type variety, a confusingly varied use of terms, and a coverage of pattern characteristics that for many large rivers is incomplete. In natural states, big rivers can be plural systems in which main, accessory, tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics. A distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems. At any one time, even at flood stage, only some channels are geomorphologically active. Six types of geomorphological connectivity are described that range from coupled, through to partially-coupled and decoupled. The interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity. For improved understanding of the dynamics as well as the forms of these large composite systems, it is helpful to: (1) adopt element-level specification, not only for sediment bodies, but also for functioning channels; (2) track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers; and (3) recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates. Such augmenting information will provide an improved platform for both river management and ecological understanding. [Copyright &y& Elsevier]