Search

The complex and unique riverbank erosion characteristics of the Brahmaputra River in India, the fourth largest river in the world in terms of average discharge at the mouth and second only to the Yellow River in China in the amount of sediment transported per unit drainage area, is highlighted with illustrations of the severity of erosion caused at various bank locations. First, the source and the entire course of the river are described. Riverbank erosion mechanisms and existing erosion control measures and their effectiveness in the Assam reach of the Brahmaputra River are described. As part of a joint effort for the first time between U.S. and Indian (local) investigators to understand and find solutions to this mega unique problem of the Brahmaputra River, a set of recommendations, including a phase-wise multiple solutions to the acute and potential riverbank erosion sites along this large river, is forwarded for discussion and getting feed back from international experts. [ABSTRACT FROM AUTHOR]

A field study was conducted in man-made ditches in a tidal saltmarsh in Lewes, Delaware, USA. Ditches are prevalent throughout tidal marshes along the Atlantic US coast, and influence hydrodynamics and sediment transport. The field study focused on measuring near-bed velocity, shear stress, sediment concentration, and bed level variability at 5 stations over a 3-week period. Velocities in the ditch (2–5 m wide, 1 m deep) peaked between 0.4 and 0.6 m/s and were slightly ebb dominated. Velocity and shear stress were maximum during a storm event, with peak shear stresses of 2 N/m 2 . Bed levels were estimated from acoustic amplitude return of a downward-looking velocity profiler. The bed level in the ditch at the landward locations increased ∼ 0.03 m over 3 weeks, while there was ∼ 0.01 m bed level decrease at the most seaward site suggesting a net import of sediment into the channel. At all sites, erosion ( ∼ 0.005–0.015 m) occurred during the accelerating phase of the flood tide, and accretion of a similar magnitude occurred during the decelerating phase of the ebb tide. This erosion-deposition sequence resulted in small net changes in bed level at the end of each tidal cycle. The intratidal behavior of the bed level was simulated using erosion and deposition flux equations based on shear stress, critical shear stress, and suspended sediment concentration. Erosion was predicted well with RMS errors on the order of 2 ⋅ 10 −3 m. The bed level during the deposition phase could not be reproduced using the simple approach. Model inaccuracies for deposition were attributed to advection and variations in fall velocity due to flocculation that were not modeled due to lack of ground-truth observations. [ABSTRACT FROM AUTHOR]

Erosion of rock masses by water typically involves unraveling of blocks of rock along existing defects in a manner that is not represented by analytical solutions for sediment transport or rockfill (rip-rap). A pragmatic approach to this complex problem is found by using a rock mass index to represent the erodibility of the rock-mass. The likelihood of erosion is then assessed by comparison against case studies in similar rock masses. A new independent data set of rock-mass erosion was gained from inspection of 26 unlined spillways in Australia, South Africa, and the United States. It was found that erosion can be usefully correlated against various published rock mass indices and hydraulic indices. A modified rock mass index, developed specifically to represent erodibility, is presented, and is applied to prepare a new comparative erosion assessment method for rock masses. [ABSTRACT FROM AUTHOR]

Establishing background (geologic) rates of erosion is prerequisite to quantifying the impact of human activities on Earth's surface. Here, we present 10Be estimates of background erosion rates for ten large (10,000-100,000 km²) river basins in the southeastern United States, an area that was cleared of native forest and used intensively for agriculture. These 10Be-based rates are indicative of the pace at which the North American passive-margin landscape eroded before European settlement (~8 m/m.y.). Comparing these background rates to both rates of post-settlement hillslope erosion and to river sediment yields for the same basins, we find that following peak disturbance (late 1800s and early 1900s), rates of hillslope erosion (~950 m/m.y.) exceeded 10Be-determined background rates more than one-hundred fold. Although large-basin sediment yields during peak disturbance increased 5-10x above pre-settlement norms, rivers at the time were transporting only ~6% of the eroded material; work by others suggests that the bulk of historically eroded material remained and still remains as legacy sediment stored at the base of hillslopes and along valley bottoms. Because background erosion rates, such as we present here, reflect the rate at which soil is generated over millennial time scales, they can inform and enhance landscape-management strategies. [ABSTRACT FROM AUTHOR]

Abstract: The ability to predict the effects of dam removal in highly sediment-filled systems is increasingly important as the number of such dam removal cases continues to grow. The cost and potential impacts of dam removal are site-specific and can vary substantially depending on local conditions. Of specific concern in sediment-impacted removals is the volume and rate of reservoir deposit erosion. The complexity and potential accuracy of modeling methods used to forecast the effects of such dam removals vary substantially. Current methods range from predictions based on simple analysis of pre-dam channel geometry to sophisticated data-intensive, three-dimensional numerical models. In the work presented here, we utilize data collected from past dam removals to develop an additional tool for predicting the rate and volume of sediment deposit erosion. Through the analysis of sediment, discharge, deposit, removal timeline, channel, and watershed data, in conjunction with post-removal monitoring data from a wide range of dam removal projects, some significant trends in the evolution of reservoir deposits following dam removal can be seen. Results indicate that parameters such as median grain size, level of cohesion, spatial variability of the deposit, and removal timeline are among the most influential factors in determining the rate and volume of sediment erosion. By comparing local conditions of dams and reservoirs slated for removal with those of past removals, we hope that predictions of the rate and volume of sediment deposit erosion can be usefully constrained. [Copyright &y& Elsevier]

A detailed description of how recently-developed sediment dynamics formulations are incorporated into the United States Environmental Protection Agency's Environmental Fluid Dynamics Code is presented. The new approach is an extension of previous models and accounts for multiple sediment size classes, has a unified treatment of suspended load and bedload, and appropriately replicates bed armouring. The resulting flow, transport, and sediment dynamics model is an improvement to previous models because it may directly incorporate site-specific data, while maintaining a physically consistent, unified treatment of bedload and suspended load. Experimental data from a noncohesive sediment erosion experiment in a straight channel help validate the numerical model. In this simulation, unknown parameters representing the active layer thickness and the erosion rates of the two largest sediment size classes when they are newly deposited are identified from the available data. [ABSTRACT FROM AUTHOR]

Abstract: This paper details the historical coastal evolution of the Columbia River littoral cell in the Pacific Northwest of the United States. Geological data from A.D. 1700 and records leading up to the late 1800s provide insights to the natural system dynamics prior to significant human intervention, most notably jetty construction between 1885 and 1917. All reliable surveys, charts, and aerial photos are used to quantify decadal-scale changes at the three estuary entrances and four sub-cells of the littoral cell. Shoreline, bathymetric, and topographic change over three historical intervals—1870s–1920s, 1920s–1950s, and 1950s–1990s—are integrated to provide an understanding of sediment-sharing relationships among the littoral cell components. Regional morphological change data are developed for alongshore segments of approximately 5km, enabling comparisons of shoreline change to upper-shoreface and barrier volume change within common compartments. The construction of entrance jetties at the Columbia River (1885–1917) and Grays Harbor (1898–1916) has profoundly affected the evolution of the littoral cell, and has accentuated the morphological coupling between the inlets, ebb-tidal deltas, shorefaces, and barriers. The jetties induced erosion of the inlets and offshore migration of ebb-tidal deltas. The change in boundary conditions at the entrances enabled waves to rework the flanks of ebb-tidal deltas and supply enormous quantities of sand to the adjacent coasts. Over several decades the initial sand pulses have been dispersed alongshore up to tens of kilometers from the estuary entrances. Winter waves and coastal currents produce net northward sediment transport across the shoreface while summer conditions tend to induce onshore sediment transport and accumulation of the upper shoreface and barriers at relatively high rates. Historical shoreline progradation rates since jetty construction are approximately double the late prehistoric rates between 1700 and the 1870s. Erosion rates of the mid- to lower shoreface to the south of the jettied estuary entrances have typically been greater than the accumulation rates of the upper shoreface and barrier, suggesting that the lower shoreface has been an important source of littoral sediments over decadal and longer time scales. Until recent decades, sediment supply from the ebb-tidal delta flanks and lower shoreface has largely masked the decline in Columbia River sediment supply resulting from flow regulation and dredging disposal practices. With the contemporary onset and expansion of coastal erosion adjacent to the jettied estuary entrances, proper management of dredged sediment is imperative to mitigate the effects of a declining sediment budget. [Copyright &y& Elsevier]

Knight, Kris W., Richard C. Schultz, Cathy M. Mabry, and Thomas M. Isenhart, 2010. Ability of Remnant Riparian Forests, With and Without Grass Filters, to Buffer Concentrated Surface Runoff. Journal of the American Water Resources Association (JAWRA) 46(2):311-322. DOI: 10.1111/j.1752-1688.2010.00422.x Riparian forest buffers established according to accepted conservation practice standards have been recommended as one of the most effective tools for mitigating nonpoint source pollution. The midwestern United States is characterized by many kilometers of narrow, naturally occurring forests along streams. However, little is known about the relative effectiveness of these remnant forests compared with these newly established buffers. This study compared the ability of naturally occurring remnant forests with and without adjacent planted grass filters to buffer concentrated flow paths (CFPs) originating in crop fields along first- and second-order streams in three northeast Missouri watersheds. Remnant forests breached by runoff through CFPs were narrower than those that dispersed 100% of the CFPs. Remnant forests with adjacent grass buffers were nearly twice the width as those without grass filters. We also found that CFPs, which developed within remnant forests and at the base of in-field grass waterways, were potential sources of sediments to streams. Methods to mitigate these CFPs warrant further investigation. Our study suggests that although these natural remnant forests provide substantial buffering capacity, both improved management and/or the addition of an adjacent grass filter would improve water quality by reducing sediment loss to streams. Inferences can be used to inform the design and management of similar conservation buffer systems within the region. [ABSTRACT FROM AUTHOR]

Various methods are used to estimate sediment transport through riparian buffers and grass filters, with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to integrate some of the factors influencing sediment delivery heuristically. This study independently tested the Forest Service sediment delivery ratio contrasted with artificial neural networks to represent the multiple nonlinearities between important factors and sediment delivery. The Forest Service sediment delivery ratio was not adequate when compared to published sediment yields from 30 small experimental buffers from three countries, including four forested buffers. However, artificial neural networks gave estimates of the delivery ratio that were highly correlated to the observations. The 30 buffer observations produced such good estimates of the sediment delivery ratio with both seven and five buffer parameters that this study suggests that as few as 30 sediment yield observations can be the basis for applying neural networks to interpolate the complex, multiple nonlinearities of hydrology and sediment transport on riparian buffers. [ABSTRACT FROM AUTHOR]

The article discusses the experiment which explores threshold conditions for motion of coarse uniform sediments in the U.S. It was aimed at investigating the importance of threshold flow conditions for incipient motion of streambeds as a tool in predicting erosion and sedimentation. It was conducted with 2.8 millimeters gravel in a 7.5 meters long by 0.3 meters wide flume and they measured the hydraulic characteristics and rate of bed particle movement for the flows at different bed slopes. Results of the experiment show that three critical shields stress for motion of coarse uniform sediment vary with both grain size and bed slope.

Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short-term variations in post-fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post-fire sediment dynamics in a semi-arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km². Surface water samples were collected in an affected watershed using an event-based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time-invariant set of sediment rating parameters. A sediment mass-balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm-based sampling in areas with intense monsoon activity to characterize post-fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high-intensity rainstorms. These findings can be used to constrain rapid assessment fire-response models for planning mitigation activities. [ABSTRACT FROM AUTHOR]

Abstract: The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island''s evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bi-directional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island. [Copyright &y& Elsevier]

Contemporary three-dimensional numerical sediment transport models are often computationally expensive because of their complexity and thus a compromise must be struck between accurately modeling sediment transport and the number of effective sediment grain (particle) size classes to represent in such a model. The Environmental Fluid Dynamics Code (EFDC) was used to simulate the experimental results of previous researchers who investigated sediment erosion and gradation around a 180° bend subject to transient flow. The EFDC model was first calibrated using the eight distinct particle size classes reported in the physical experiment to find the best erosion formulations to use. Once the best erosion formulations and parameters were ascertained, numerical simulations were carried out for each experimental run using a single effective particle size. Four techniques for evaluating the effective particle size were investigated. Each procedure yields comparable effective particle sizes within a factor of 1.5 of the others. Model results indicate that particle size as determined by the weighted critical shear velocity most faithfully reproduced the experimental results for erosion and deposition depths. Subsequently, model runs were conducted with different numbers of effective particle size classes to determine the optimal number that yields an accurate estimate for noncohesive sediment transport. Optimal, herein, means that numerical model results are reasonably representative of the experimental data with the fewest effective particle size classes used, thereby maximizing computational efficiency. Although modeling with more size classes can be equally accurate, results from this study indicate that using three effective particle size classes to estimate the distribution of sediment sizes is optimum. [ABSTRACT FROM AUTHOR]

Abstract: Channel pattern effectively stratifies the dynamics of rivers and floodplains in forested mountain river systems of the Pacific Northwest, USA. Straight channels are least dynamic, with relatively slow floodplain turnover and floodplains dominated by old surfaces. Braided channels are most dynamic, with floodplain turnover as low as 25 years and predominantly young floodplain surfaces. Island-braided and meandering channels have intermediate dynamics, with moderately frequent disturbances (erosion of floodplain patches) maintaining a mix of old and young surfaces. Return intervals for the erosion of floodplains increase in the order of braided, island-braided, meandering, and straight (8, 33, 60, and 89 years, respectively). A threshold for the lateral migration of a channel occurs at a bankfull width of 15–20 m. The most likely mechanism underlying this threshold is that larger channels are deep enough to erode below the rooting zone of bank vegetation. Above this threshold, channels not confined between valley walls exhibit channel patterns distinguishable by slope and discharge, and slope–discharge domains can be used to predict channel patterns. Meandering and braided patterns are most consistently identified by the model, and prediction errors are largely associated with indistinct transitions among channel patterns that are adjacent in plots of slope against discharge. Locations of straight channels are difficult to identify accurately with the current model. The predicted spatial distribution of channel patterns reflects a downstream decline in channel slope, which is likely correlated with a declining ratio of bed load to suspended load. Ecological theory suggests that biological diversity should be highest where the intermediate disturbance regime of island-braided channels sustains high diversity of habitat and successional states through time. [Copyright &y& Elsevier]

Single-barrel culverts are a common means of roadway crossings for smaller streams. While this culvert design provides an economical solution for a crossing, the adverse effects of conveying the stream through a single opening can be far reaching. The single-barrel culvert is typically sized for a design storm much greater than the channel forming discharge. This oversizing causes an interruption of the normal flow patterns and sediment transport for the system. Shallow depths at low flow in the pipe and perching at the outlet can impede fish passage. Multicell culverts (where the main culvert at the channel invert is sized for bankfull discharge, and additional pipes are placed at the floodplain elevation to convey overbank flow up to the design discharge) have been recommended as a best management practice to minimize erosion and improve fish passage. This flume study scaled a prototype single-barrel culvert to both a single-cell model, and a multicell design to compare outlet scour and flow depths within the culvert. The results provide designers and planners with evidence of the benefits of multicell culverts to justify the higher cost of installation compared to single-barrel culverts. [ABSTRACT FROM AUTHOR]

Agricultural practices dominate over climatic variability in determining temporal variability in dust blowing on cropland in the USA. Farming operations that increase wind erosion and dust emissions include plowing, leveling beds, planting, weeding, seeding, fertilizing, mowing, cutting, baling, spreading compost or herbicides and burning fields. Methods of controlling sediment loss include planting windbreaks and special crops to alter wind flow; retaining plant residue after harvesting; tilling soil to bury erodible particles, create aggregates that resist entrainment, and increase surface roughness; improving farm equipment; and stabilizing soil surfaces using water or commercial products. Government programs prescribe air quality standards, provide education programs, and cost-share and incentive payments to assist farmers in controlling erosion and dust production. Problems continue because farmers do not consider wind erosion a significant problem. Dust events have nevertheless decreased in some areas, indicating that improved management practices may be effective where accepted by farmers. [Copyright &y& Elsevier]

A conceptual model of fine sediment transport between a river and a bay is proposed, based on observations at two rivers feeding the same bay. The conceptual model consists of river, transitional, and bay regimes. Within the transitional regime, resuspension, advection, and deposition create a mass of sediment that oscillates landward and seaward. While suspended, this sediment mass forms an estuarine turbidity maximum. At slack tides this sediment mass temporarily deposits on the bed, creating landward and seaward deposits. Tidal excursion and slack tide deposition limit the range of the sediment mass. To verify this conceptual model, data from two small tributary rivers of San Pablo Bay are presented. Tidal variability of suspended-sediment concentration markedly differs between the landward and seaward deposits, allowing interpretation of the intratidal movement of the oscillating sediment mass. Application of this model in suitable estuaries will assist in numerical model calibration as well as in data interpretation. A similar model has been applied to some larger-scale European estuaries, which bear a geometric resemblance to the systems analyzed in this study. [Copyright &y& Elsevier]

In this paper, we re-examine the question of identification of source areas using optimization methods for two Iowa watersheds. The question of nonuniqueness is addressed first, with the result that only eight sediment contributing regions are allowed to be active simultaneously as in the companion study. Tukey's procedure is utilized to examine if the differences in erodibility of the different regions are statistically significant. Results were presented in the form of maps to obtain a spatial picture of the potential of sediment generating areas. Comparisons with physical characteristics of the watersheds showed good agreement between erosion potential and properties associated with erosion. [ABSTRACT FROM AUTHOR]

Identification of sediment source areas within a watershed is useful for designing appropriate management alternatives that reduce sediment losses. In most watersheds, data collection programs are present at the stream gauging station, and sediment source identification must be treated as an inverse problem. A physically based watershed-scale surface flow and erosion model, KINEROS was utilized as the modeling tool in this study. A modified unit sedimentograph approach was used for source identification based on hydrograph and sedimentograph data collected at the watershed outlet. Data from several events were examined over two small watersheds, and a statistical procedure was employed to assess the erosion vulnerability of different regions in the two watersheds. These results were presented in the form of maps to obtain a spatial picture of potential sediment generating areas. A statistical analysis was also utilized to determine if erosion potentials of different regions of a watershed were significantly different. It appears that identification of source areas is possible when a limited number of regions are contributing sediments. [ABSTRACT FROM AUTHOR]

Hydrogemorphic linkages related to sediment transport in headwater streams following basin wide clear-cut logging on Prince of Wales Island, southeast Alaska, were investigated. Landslides and debris flows transported sediment and woody debris in headwater tributaries in 1961, 1979, and 1993. Widespread landsliding in 1961 and 1993 was triggered by rainstorms with recurrence intervals (24 h precipitation) of 7·0 years and 4·2 years respectively. Occurrence, distribution, and downstream effects of these mass movements were controlled by landform characteristics such as channel gradient and valley configuration. Landslides and channelized debris flows created exposed bedrock reaches, log jams, fans, and abandoned channels. The terminus of the deposits did not enter main channels because debris flows spread and thinned on the unconfined bottom of the U-shaped glaciated valley. Chronic sediment input to channels included surface erosion of exposed till (rain splash, sheet erosion, and freeze–thaw action) and bank failures. Bedload sediment transport in a channel impacted by 1993 landslides and debris flows was two to ten times greater and relatively finer compared with bedload transport in a young alder riparian channel that had last experienced a landslide and debris flow in 1961. Sediment transport and storage were influenced by regeneration of riparian vegetation, storage behind recruited woody debris, development of a streambed armour layer, and the decoupling of hillslopes and channels. Both spatial and temporal variations of sediment movement and riparian condition are important factors in understanding material transport within headwaters and through channel networks. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Soil erosion has both on-farm and off-farm impacts. Reduction of soil depth can impair the land's productivity, and the transport of sediments can degrade streams, lakes, and estuaries. Since 1933, soil conservation policies have existed in the United States. Originally they focused on the on-farm benefits of keeping soil on the land and increasing net farm income. Beginning in the 1980s, however, policy goals increasingly included reductions in off-site impacts of erosion. As a consequence of conservation efforts associated with explicit U.S. government policies, total soil erosion between 1982 and 1992 was reduced by 32% and the sheet and rill erosion rate fell from an average of 4.1 tons per acre per year in 1982 to 3.1 tons per acre in 1992 while the wind erosion rate fell from an average of 3.3 tons per acre per year to 2.4 tons per acre per year over the same period. Still, soil erosion is imposing substantial social costs. These costs are estimated to be about $37.6 billion annually. To further reduce soil erosion and thereby mitigate its social costs, there are a number of policy options available to induce farmers to adopt conservation practices including education and technical assistance, financial assistance, research and development, land retirement, and regulation and taxes. [ABSTRACT FROM AUTHOR]

Focuses on a study on the sediment erodibility in Boston Harbor, Massachusetts. Reasons for the selection of flume on the assessment of sediment erosion; Opinion on the measurement of erodibility during steady and unsteady flow conditions; Methodology of the study; Results and discussion of the study; Conclusions.

A 30-year simulation of fine-grained, cohesive sediment transport in Watts Bar Reservoir, located in Tennessee, demonstrated that the SEDZL model realistically predicts overall patterns of erosion and deposition throughout this large reservoir. Good qualitative agreement was achieved between the predicted and observed trends in the net sediment-bed-elevation change during the model-calibration period, from 1961 to 1991. Quantitative comparison of predicted and measured bed elevation changes indicated that the model was generally able to accurately simulate local erosion and deposition within Watts Bar Reservoir, yielding a median absolute relative error of 46% in the cohesive sediment bed areas of the reservoir. The model predicted that 76% of the incoming sediments during this 30-year period would be trapped in the reservoir, which is in excellent agreement with the observed trapping efficiency of 72 ±6% (95% confidence interval). [ABSTRACT FROM AUTHOR]

• Prescribed fire promoted herbaceous growth in bare interspaces. • Litter enhanced infiltration and provided protection against erosion. • Increased vegetation cover altered flow paths and reduced runoff and soil loss. • Reduced soil surface connectivity post-fire improved hydrologic function. • Hydrologic function continues to improve 9 yr after fire. Woody species encroachment into herbaceous and shrub-dominated vegetations is a concern in many rangeland ecosystems of the world. Arrival of woody species into affected rangelands leads to changes in the spatial structure of vegetation and alterations of biophysical processes. In the western USA, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.) tree species into sagebrush steppes poses a threat to the proper ecohydrological functioning of these ecosystems. Prescribed fire has been proposed and used as one rangeland improvement practice to restore sagebrush steppe from pinyon-juniper encroachment. Short-term effects of burning on the ecohydrologic response of these systems have been well documented and often include a period of increased hydrologic and erosion vulnerability immediately after burning. Long-term ecohydrologic response of sagebrush steppe ecosystems to fire is poorly understood due to lack of cross-scale studies on treated sites. The aim of this study is to evaluate long-term vegetation, hydrologic, and erosion responses at two pinyon-juniper-encroached sagebrush sites 9 years after prescribed fire was applied as a restoration treatment. Thirty-six rainfall simulation experiments on 6 m × 2 m plots were conducted for 45 min under two conditions: a dry run (70 mm h−1; dry antecedent soils) and a wet run (111 mm h−1; wet antecedent soils). Runoff and erosion responses were compared between burned and unburned plots. Overall, increases in herbaceous cover in the shrub-interspace areas (intercanopy area between trees) at both sites 9 years post-burn resulted in runoff- and erosion-reduction benefits, especially under the wet runs. While the initially more degraded site characterized by 80% bare ground pre-burn, registered a higher overall increase (40% increase) in canopy cover, greater post-fire reductions in runoff and erosion were observed at the less degraded site (57% bare ground pre-burn). Runoff and erosion for the wet runs decreased respectively by 6.5-fold and 76-fold at the latter site on the burned plots relative to control plots, whereas these decreases were more muted at the more degraded site (2.5 and 3-fold respectively). Significant fragmentation of flow paths observed at the more-degraded site 9 years post-fire, suggests a decreased hydrologic connectivity as a mechanism of runoff and erosion reduction during post-fire recovery. [ABSTRACT FROM AUTHOR]

Presents research which measured stream channel erosion for San Diego Creek, southern California, from 1983 to 1993. Role of stream channel erosion in long-term sediment yield from urbanizing watersheds; Results in sediment yield; Channel stabilization a priority in managing sediment yield.

A sediment budget was developed for a representative rural southeastern Piedmont watershed to estimate the relative importance of various sediment sources, particularly the contribution of agricultural sediments introduced to stream systems during the cotton-farming era (approximately 1820 to 1930 A.D.). The Murder Creek basin containing Monticello, Georgia was chosen because: 1) forestry and agriculture were and continue to be dominant land uses; 2) a U.S. Geological Survey (USGS) gage provided flow and suspended sediment records; and 3) the creek discharges into the Lake Sinclair reservoir (constructed 1949 to 1953), which could be used as a bedload sediment trap. Sediment rating curves, reservoir sediment deposition, and the Water Erosion Prediction Project (WEPP) and Universal Soil Loss Equation (USLE) erosion models were used to estimate suspended sediment export, bedload export, unpaved road erosion, and other surface erosion, respectively. Depths of historical agricultural sediment deposits were measured in stream cutbanks and floodplain auger holes. Historical row-crop agriculture led to floodplain deposition of a nearly-uniform 1.6 m (5.3 ft) of sediment, equivalent to 12.2 cm (0.40 ft) of topsoil over the watershed. The mass of cotton-farming sediments in valley storage was extremely large compared to current sediment export rates. At present sediment export rates, it would take six to ten millennia to remove all of the cotton-farming sediment in storage. This study suggests that the unstable streambanks, mobile sandy streambeds, and turbid conditions characteristic of modern Piedmont streams are largely a legacy of poor farming practices in the late 1800s and early 1900s. Estimated sediment exports exceed estimates of current inputs, and floodplain accretion rates and streambank conditions suggest streams have been in a state of net sediment export over the last 50 years. [ABSTRACT FROM AUTHOR]