Search

The primary source of drinking water in Ethiopia's semi-arid mountainous regions is groundwater. The present study aims to assess the hydrogeochemical characteristics of low-grade basement rocks dominated by mountainous catchments. Moreover, it examines the suitability of the groundwater quality for drinking purposes in Irob, Tigray, northern Ethiopia. However, relatively little is known about the water chemistry and groundwater quality of the resources in the area. Fifteen samples of groundwater were collected and examined for ions according to standard procedures. The outcomes were assessed against the World Health Organization (WHO) drinking water quality criteria. To identify the source of dissolved ions and the process involved, graphic interpretations were applied. The results show that Ca–Mg–SO4–HCO3 and Ca–SO4–HCO3 were the dominant water types. Gibbs plots and ionic ratios reveal that silicate weathering, carbonate dissolution and ion exchange control water chemistry. Furthermore, the findings reveal that 60, 80, 46.67, 46.67, 60, 6.67, 60 and 53.33% of samples are above the safe limits of the WHO for hardness, alkalinity, total dissolved solids, electrical conductivity, calcium (Ca2+), potassium (K+), bicarbonate (HCO3-) and sulfate (SO42-), respectively. Consequently, the groundwater quality assessment demonstrates that the water sources in lower parts of the catchment are unsuitable for drinking. HIGHLIGHTS The study area is a mountainous and geologically complex setting.; Groundwater is the main source for drinking in semi-arid regions.; Dissolution, silicate weathering and ion exchange processes are responsible water quality.; Anthropogenic processes also control the water chemistry.; The groundwater chemistry is changing from Ca–Mg–SO4–HCO3 in the mountainous area to Ca–Na–HCO3–SO4 in the flat areas.;

Floods pose a significant threat to the safety of countries with severe societal, economic, and environmental consequences, especially the flash floods in mountainous regions. Previous studies have shown that many floods were caused by intense rainfall with highly saturated soil. In this study, we applied a physically-based distributed hydrological model (Integrated Hydrology Model, InHM) to a warm humid mountainous catchment in Southwest China, the Shouxi River. The main objective of our research is to investigate the relative importance of rainfall and antecedent soil moisture on flood generation in our study region. Our results show that an increase in rainfall return period and antecedent soil saturation ratio significantly increased peak flow and shortened peak time. There is a correlation between the ratio of antecedent soil saturation ratio to rainfall (SPR) and peak flow. When SPR <1, there is a positive correlation; when SPR >1, there is a negative correlation. Additionally, with the increase in drainage area, the relative importance of rainfall tends to decrease, while the relative contribution of soil saturation ratio tends to increase. The findings could provide support for the determination of the dominant factors influencing runoff generation in humid regions, offering scientific support for the timely and effective flood prevention and mitigation measures in mountainous regions. [ABSTRACT FROM AUTHOR]

Rainfall temporal patterns significantly affect variability of flash flood behaviors, and further act on hydrological model performances in operational flash flood forecasting and warning. In this study, multivariate statistical analysis and hydrological simulations (XAJ and CNFF models) were combined to identify typical rainfall temporal patterns and evaluate model simulation capability for water balances, hydrographs, and flash flood behaviors under various rainfall patterns. Results showed that all the rainfall events were clustered into three types (Type 1, Type 2, and Type 3) in Anhe catchment in southeastern China. Type 1 was characterized by small total amount, high intensity, short duration, early peak moment, and concentrated hourly distribution. Type 3 was characterized by great total amount, low intensity, long duration, late peak moment, and uniform hourly distribution. Characteristics of Type 2 laid between those of Type 1 and Type 3. XAJ and CNFF better simulated water balances and hydrographs for Type 3, as well as all flash flood behavior indices and flood dynamics indices. Flood peak indices were competitively simulated for all the types by XAJ and except Type 1 by CNFF. The study is of significance for understanding relationships between rainfall and flash flood behaviors and accurately evaluating flash flood simulations. [ABSTRACT FROM AUTHOR]

Floods pose a significant threat to the safety of countries with severe societal, economic, and environmental consequences, especially the flash floods in mountainous regions. Previous studies have shown that many floods were caused by intense rainfall with highly saturated soil. In this study, we applied a physically-based distributed hydrological model (Integrated Hydrology Model, InHM) to a warm humid mountainous catchment in Southwest China, the Shouxi River. The main objective of our research is to investigate the relative importance of rainfall and antecedent soil moisture on flood generation in our study region. Our results show that an increase in rainfall return period and antecedent soil saturation ratio significantly increased peak flow and shortened peak time. There is a correlation between the ratio of antecedent soil saturation ratio to rainfall (SPR) and peak flow. When SPR 1, there is a negative correlation. Additionally, with the increase in drainage area, the relative importance of rainfall tends to decrease, while the relative contribution of soil saturation ratio tends to increase. The findings could provide support for the determination of the dominant factors influencing runoff generation in humid regions, offering scientific support for the timely and effective flood prevention and mitigation measures in mountainous regions.

Snow in the mountains is essential for the water cycle in cold regions. The complexity of the snow processes in such an environment makes it challenging for accurate snow and runoff predictions. Various snow modelling approaches have been developed, especially to improve snow predictions. In this study, we compared the ability to improve runoff predictions in the Överuman Catchment, Northern Sweden, using different parametric representations of snow distribution. They included a temperature-based method, a snowfall distribution (SF) function based on wind characteristics and a snow depletion curve (DC). Moreover, we assessed the benefit of using distributed snow observations in addition to runoff in the hydrological model calibration. We found that models with the SF function based on wind characteristics better predicted the snow water equivalent (SWE) close to the peak of accumulation than models without this function. For runoff predictions, models with the SF function and the DC showed good performances (median Nash–Sutcliffe efficiency equal to 0.71). Despite differences among the calibration criteria for the different snow process representations, snow observations in model calibration added values for SWE and runoff predictions. HIGHLIGHTS Models with a snow distribution based on wind and topography in addition to precipitation and temperature improved snow predictions.; Models with a snow distribution based on wind and topography could use snow information and perform similarly to models with a depletion curve for runoff.; The robustness of model calibration increased by including spatially distributed snow observations in addition to runoff data.;

Assessment of environmental flow, that has to be maintained along a waterway to keep up health of riverine biological systems, is a key challenge in alleviating impact of establishing hydropower projects especially in mountainous ungauged catchment under limited data conditions. This study addresses the data scarcity issue by prediction of runoff from a Himalayan catchment, India, using HEC-HMS model and then estimating environmental flow based on daily rainfall data of 39 years (1980–2018). The soil conservation service–curve number method is employed for surface runoff estimation that utilizes spatially distributed maps of soil types, drainage, stream order, 4-year land use/land cover (1990, 2000, 2010, and 2020), and hydrologic soil group (HSG). Steep slopes (more than 60%), high annual rainfall (1377 mm), large area under C class of HSG (477.94 km2), and moderate values of curve number (70.51, 70.36, 70.16, and 70.54) revealed high potential for surface runoff generation in the catchment. Predicted runoff depicted a gradually increasing trend during 1980–1995 and decreasing trend during 1995–2008 and 2011–2017. In addition, an abrupt change was observed in annual runoff values in years 1992, 1998, and 2018 when the peak rate of runoff crossed the value of 2000 m3 s−1. The HEC-HMS model is validated by close agreement between peaks and troughs of runoff and rainfall values, and with reasonable values of correlation coefficient (0.57) and coefficient of determination (0.33). The annual values of environmental flow is obtained as 75 and 55 m3 s−1 from the flow duration curves at 70th and 90th percentiles, respectively. Findings of this study are useful for management of flood water in other ungauged mountainous catchment of Himalayan region as well as in other parts of the world under data scarcity conditions. [ABSTRACT FROM AUTHOR]

Snow in the mountains is essential for the water cycle in cold regions. The complexity of the snow processes in such an environment makes it challenging for accurate snow and runoff predictions. Various snow modelling approaches have been developed, especially to improve snow predictions. In this study, we compared the ability to improve runoff predictions in the Överuman Catchment, Northern Sweden, using different parametric representations of snow distribution. They included a temperature-based method, a snowfall distribution (SF) function based on wind characteristics and a snow depletion curve (DC). Moreover, we assessed the benefit of using distributed snow observations in addition to runoff in the hydrological model calibration. We found that models with the SF function based on wind characteristics better predicted the snow water equivalent (SWE) close to the peak of accumulation than models without this function. For runoff predictions, models with the SF function and the DC showed good performances (median Nash-Sutcliffe efficiency equal to 0.71). Despite differences among the calibration criteria for the different snow process representations, snow observations in model calibration added values for SWE and runoff predictions. [ABSTRACT FROM AUTHOR]

As the world is changing, mainly due to climate change, extreme events such as floods and droughts are becoming more frequent and severe. Considering this, the predictive modeling of flow in small mountain catchments that are particularly vulnerable to flooding is critical. Rainfall data sources such as rain gauges, meteorological radars, and satellites provide data to the hydrological model with a lag. Only numerical weather predictions can achieve this in advance, but their estimates are often subject to considerable uncertainty. This article aims to verify whether Global Environmental Multiscale numerical precipitation prediction can be successfully applied for event-based rainfall–runoff hydrological modeling. These data were verified for use in two aspects: the flow modeling and determination of antecedent moisture conditions. The results indicate that GEM data can be satisfactorily used for hydrological modeling, and particularly good simulation results are obtained when significant rainfall occurs. In addition, these data can be used to correctly estimate the AMC groups for each sub-catchment in advance, which is one of the key elements flowing into the amount of projected outflow in the catchment. It is worth noting that, according to the literature review conducted by the article's author, this is the first published attempt to use GEM data directly in applied hydrological applications. [ABSTRACT FROM AUTHOR]

Soil water movement is an important component in water cycle, which is also closely correlated with the transport of nutrients and contaminants in the catchment. Although there have been many studies in quantifying the water residence in soil, the understanding of the controlling factors is limited and could be controversial. Here, stable isotopes of water to explore the water age distribution in a mountainous catchment in the southwest China are used. The results are consistent with the regional climate pattern that the water vapor of the study catchment is brought by monsoons from Pacific Ocean in summer and prevailing westerly winds in winter. The estimated young water fraction is found to be strongly correlated with topographic gradient but presents no significant correlation with drainage area or vegetation coverage. Comparison between the difference in young water fraction of two adjacent sub‐catchments suggests that soil water in the steeper sub‐catchment tends to favor deep vertical infiltration, resulting in longer flow path, longer mean residence time, and smaller young water fraction. This difference between the soil water movement and the hydrological response revealed in this study has impacts on the biogeochemical cycles in the catchment. [ABSTRACT FROM AUTHOR]

In a mountainous catchment, understanding the interaction between DEM resolution and climatic variables is essential for the accurate spatial interpolation of areal mean monthly and annual rainfall and temperature, which is required as an input for further applications such as hydrological and hydraulic modeling, agriculture, and environmental conservation. This case study applied the geostatistical interpolation technique, kriging with external drift (KED), with a digital elevation model (DEM) with various horizontal resolutions, which were used to assess the effects of the DEM horizontal resolutions on the spatial distributions of rainfall and temperature by focusing on interpolating the mean monthly and annual rainfall and temperature over a spatially diversified catchment. The assessment was undertaken using spatially and temporally complete sampled historical climatic datasets, and consequently, the spatial pattern of monthly and annual rainfall (temperature) from east to the west gradually increases or decreases following the DEM elevation increment along the same direction. As a result, the finer-resolution DEM (90-m SRTM-DEM) had a considerable impact on predicting the mean monthly minimum and maximum temperatures, whereas the resampled 500-m SRTM-DEM performed relatively better in mean monthly and annual rainfall and annual minimum temperature estimation values. [ABSTRACT FROM AUTHOR]

• A subsurface storm flow-based hydrological model was created for mountainous regions. • A method determining rainfall threshold for extreme flood was proposed. • A relationship between forest cover and the rainfall threshold was established. • The rainfall threshold significantly increased when forest coverage exceeded 70%. Floods frequently occur in mountainous regions and threaten lives and property worldwide. Forest cover usually plays an important role in regulating and preventing floods. However, the rainfall thresholds for forest cover to effectively regulate extreme flood are still unclear. In this study, we developed the topography-based subsurface storm flow hydrological (Top-SSF) model, which generally exhibited precise simulation performances in five typical mountainous catchments in southwest China. Then, the Top-SSF model was combined with a frequency analysis method to set different forest cover scenarios, investigating the relationship between rainfall threshold and forest cover in mountainous catchments. The results showed that under the control of soil saturated hydraulic conductivity (Ks) and maximum soil water storage capacity (Szm), the rainfall threshold of an extreme flood (the 100-year return period) increased significantly, especially when forest cover was larger than 70% of a catchment. Under the same forest cover, high initial soil water content ( Sw i) weakened the mitigating effect of forest cover on the extreme flood. In addition, a non-linear regression relationship between forest cover and rainfall threshold of a catchment was developed considering the impacts of Ks , Sw i and annual mean precipitation ( P ¯ ) of the catchment. The significant impact of forest cover change on extreme floods was not only due to changing the amount of forest cover but also the soil properties. These results contribute to the understanding of the impact of forest cover changes on extreme floods and may provide valuable insights for flood defence in mountainous catchments. [ABSTRACT FROM AUTHOR]

Purpose: Analysis of sediment transport is an effective approach for identifying sediment sources and for catchment management. However, a long-term analysis of sediment variability at multiple time scales is less available, especially in mountainous catchments. This study aims to determine sediment sources and to identify sediment transport dynamics, as well as the influencing factors, through analyzing long-term sediment fluxes at different time scales. Materials and methods: In this paper, 32 years of sediment flux in an instrumented mountainous catchment in eastern Zhenjiang Province, China, was investigated at multiple time scales (i.e., monthly, seasonal, annual, and event). Sediment yields (SYs) during three time periods (i.e., 1964–1977, 1978–1989, and 2010–2015) were first classified by the Mann-Kendall and cumulative anomaly tests, and then sediment fluxes for each period were investigated and compared at multiple time scales. Results and discussion: Annual SYs ranged from 29 to 308 t year−1 during the recording period and were significantly influenced by several high magnitude flood events. The mean annual SYs decreased from 153.82 t year−1 in 1964–1977, to 97.79 t year−1 in 1978–1989, and to 91.08 t year−1 in 2010–2015 due to improved soil conservation measures and increased reservoirs. At the seasonal scale, over 92% of the sediment was transported in spring and summer over the recording period. Heterogeneous sediment sources, partial areal distribution of rainfalls, and other factors led to complex suspended sediment concentration versus water discharge hysteresis loop patterns at the event and monthly scales. Conclusions: The improved soil conservation measures and increased reservoirs over the recent decades decreased sediment availability, and the number and the magnitude of flood events from 1964 onward. However, the flood sediment fluxes in a few months were still high due to extreme precipitation events in recent years. The work can provide guidance for addressing sediment problems in this and/or other similar catchments. [ABSTRACT FROM AUTHOR]

The contribution of quarrying in the context of multiple catchment sources of fine‐grained sediment has rarely been investigated. This study assessed the relative importance of quarrying as a sediment source alongside rangeland surface soils and channel banks in a mountainous catchment in northern Tehran, Iran, using fingerprinting. Eight geochemical tracers were measured on 24 potential sediment source samples and four fine‐grained sediment samples. Statistical analysis to select three different composite fingerprints for discriminating the potential sediment sources comprised: (a) the Kruskal–Wallis H test (KW‐H), (b) a combination of KW‐H and discriminant function analysis (DFA), and (c) a combination of KW‐H and principal components and classification analysis (PCCA). A Bayesian unmixing model was used to apportion sediment source contributions using the three composite fingerprints. Using the KW‐H composite signature, the respective relative contributions (with uncertainty ranges) from channel banks, rangeland surface soils, and quarrying were estimated as 28.4% (10.9–46.8), 15.1% (6.6–22.7), and 56.6% (38.3–74.2), compared with 35.4% (11.9–60.1), 13.4% (4.1–22.2), and 51.3% (26.5–74.3) using a composite signature selected using a combination of KW‐H and DFA, or 20.7% (3.9–41.7), 17.2% (4.4–29.9), and 61.4% (44–78.8) using a fingerprint selected using KW‐H and PCCA. The different composite signatures therefore all consistently suggested that quarrying is the dominant source of the fine‐grained sediment samples. Potential mitigation measures targeting this land use include closure to permit revegetation to reduce exposure of bare surfaces to sediment mobilization. Limitations and uncertainties associated with this preliminary investigation are briefly discussed. [ABSTRACT FROM AUTHOR]

Within the framework of the project "Flood Prevention and Nature Conservation in the Weisseritz area" ("HochNatur"), a method including landscape metrics was developed and applied to assess and to compare different land use scenarios with regard to flood prevention and nature conservation. For the analysis, two sub-catchments strongly differing in land use within the Weisseritz catchment (Eastern Erzgebirge, Saxony, Germany) were selected. The first step of the evaluation procedure was a biotope assessment using three assessment criteria (naturalness, substitutability, rareness/endangerment). However, the biotope assessment did not yield any information about spatial distribution or the structural composition of the landscape. Therefore, landscape metrics were applied to analyse the structural and biotope type diversity at the landscape scale. Different landscape metrics (Shannon/Weaver diversity index, mean patch size index, Interdispersion/Juxtaposition index) and a weighting system were used to compare the different land use scenarios and the current state. The analysed catchment areas differ substantially in terms of their current state and potential measures regarding flood prevention and nature conservation depending on the location and distribution of biotope types. It was demonstrated that this method can be used for small catchment areas regardless of their land use for assessing, analysing and comparing different land use scenarios for a specific area.

The new challenges in assessment of water resources demand new approaches and tools, such as the use of hydrologic models, which could serve to assist managers in the prediction, planning and management of catchment water supplies in view of increased demand of water for irrigation and climatic change. Good characterization of the spatial patterns of climate variables is of paramount importance in hydrological modelling. This is especially so when modelling mountain environments which are characterized by strong altitudinal climate gradients. However, very often there is a poor distribution of climatic stations in these areas, which in many cases, results in under representation of high altitude areas with respect to climatic data. This results in the poor performance of the models. In the present study, the Soil and Water Assessment Tool (SWAT) model was applied to the Barasona reservoir catchment in the Central Spanish Pyrenees in order to assess the influence of different climatic characterizations in the monthly river discharges. Four simulations with different input data were assessed, using only the available climate data (A1); the former plus one synthetic dataset at a higher altitude (B1); and both plus the altitudinal climate gradient (A2 and B2). The model's performance was evaluated against the river discharges for the representative periods of 2003-2005 and 1994-1996 by means of commonly used statistical measures. The best results were obtained using the altitudinal climate gradient alone (scenario A2). This study provided insight into the importance of taking into account the sources and the spatial distribution of weather data in modelling water resources in mountainous catchments. [ABSTRACT FROM AUTHOR]

La Trucha is a granitic, second-order catchment (~1.9 km, average slope 5 %) placed at ~1400-m elevation in the Sierra de Comechingones (Argentina, 31°54′ S, 64°45′W; 31°53′, 64°44′W). The main geochemical characteristics were studied during a hydrological year (March 2005-February 2006), attending mainly seasonal and spatial variability and weathering-induced carbon consumption. Subjected to a weathering- limited denudation regime, the catchment is representative of hundreds of the second-order streams that dissect the Achala Batholith. Water chemistry is typical of streams draining F rich granites. High discharges (austral summer) determine the dilution of Na, Ca, Mg, HCO, SO, and F. Conversely, high summer rainfall increases Cl concentrations. The rainfall-induced mobilization of K is likely masked by its affinity for adsorption onto fine-grained particles and that of SiO by its biological consumption. La Trucha's upper catchment shows that steep slopes and a shallow regolith layer result in a more diluted water flow, chemically closer to rainfall. Subsurface flow increases the downriver positive rate of La Trucha's electrical conductivity twice as much in winter (6.7 µS cm per 1000 m) than during wet summer (3.9 µS cm per 1000 m). PHREEQC allowed the calculation of free CO and the likelihood of its evasion in different seasons and areas of the catchment. A mean carbon efflux of ~180 mg C m year has been estimated for La Trucha catchment. The first- and second-order streams, which occupy ~62.5 km of the Achala Batholith's surface area, are significant sources in the Sierra de Comechingones' carbon cycle. [ABSTRACT FROM AUTHOR]

A two-parameter transfer function with an infinite characteristic time is proposed for conceptual rainfall-runoff models. The large time behaviour of the unit response is an inverse power function of time. The infinite characteristic time allows long-term memory effects to be accounted for. Such effects are observed in mountainous and karst catchments. The governing equation of the model is a fractional differential equation in the limit of long times. Although linear, the proposed transfer function yields discharge signals that can usually be obtained only using non-linear models. The model is applied successfully to two catchments, the Dud Koshi mountainous catchment in the Himalayas and the Durzon karst catchment in France. It compares favourably to the linear, non-linear single reservoir models and to the GR4J model. With a single reservoir and a single transfer function, the model is capable of reproducing hysteretic behaviours identified as typical of long-term memory effects. Computational efficiency is enhanced by approximating the infinite characteristic time transfer function with a sum of simpler, exponential transfer functions. This amounts to partitioning the reservoir into several linear sub-reservoirs, the output discharges of which are easy to compute. An efficient partitioning strategy is presented to facilitate the practical implementation of the model. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recent advances in computer with geographic information system (GIS) technologies have allowed modelers to develop physics-based models for modeling soil erosion processes in time and space. However, it has been widely recognized that the effect of uncertainties on model predictions may be more significant when modelers apply such models for their own modeling purposes. Sources of uncertainty involved in modeling include data, model structural, and parameter uncertainty. To deal with the uncertain parameters of a catchment-scale soil erosion model (CSEM) and assess simulation uncertainties in soil erosion, particle filtering modeling (PF) is introduced in the CSEM. The proposed method, CSEM-PF, estimates parameters of non-linear and non-Gaussian systems, such as a physics-based soil erosion model by assimilating observation data such as discharge and sediment discharge sequences at outlets. PF provides timevarying feasible parameter sets as well as uncertainty bounds of outputs while traditional automatic calibration techniques result in a time-invariant global optimal parameter set. CSEM-PF was applied to a small mountainous catchment of the Yongdam dam in Korea for soil erosion modeling and uncertainty assessment for three historical typhoon events. Finally, the most optimal parameter sets and uncertainty bounds of simulation of both discharge and sediment discharge at each time step of the study events are provided. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to implement and test routing algorithms in the distributed Hydrologiska Byråns Vattenbalansavdelning (HBV) model with the emphasis of obtaining a most suitable routing algorithm for large mountainous catchments. Two routing algorithms were built into the grid-based HBV model and tested on the Losna (11,213 km2) and the Norsfoss (18,932 km2) catchments in central southern Norway. In the first algorithm, runoff is first routed from cell to cell and hydrographs are re-calculated at each cell, and then runoff is routed by the Muskingum--Cunge method in river channels. The second algorithm is a source-to-sink method, which routes runoff of all cells to the catchment outlet as a function of local slope and a calibrated velocity parameter. The routing approaches were compared at different spatial resolutions (i.e. 1, 5 and 10 km) in daily streamflow simulation. Additionally, the elevation band-based semi-distributed model was also compared with the distributed models. The results show that the distributed HBV models are able to perform better than the elevation band-based model, and hillslope routing is crucial in the mountainous catchments. However, incorporating the Muskingum--Cunge channel routing does not add value to the simulation of daily runoff in the mountainous catchments. [ABSTRACT FROM AUTHOR]

Purpose: Understanding hydro-sedimentary dynamics at the catchment scale requires high temporal resolution data on suspended sediments such as their origin, in addition to the common measurements of sediment concentrations and discharges. Some rapid and low-cost fingerprinting methods based on spectroscopy have recently been developed. We investigated how visible spectra could be used to predict the proportion of various source materials in suspended sediment samples, paying particular attention to the potential alteration of spectrocolorimetric signatures between soils and suspended sediments during transport. Materials and methods: The 22-km Galabre catchment, France, is composed of black marls, limestones, molasses, undifferentiated deposits and gypsum. Forty-eight source materials were sampled and 328 suspended sediment samples were collected at the outlet during 23 runoff events. Measurements were taken with a diffuse reflectance spectrophotometer on dried samples. As the erosion processes are particle size selective, five particle size fractions of source material were measured in order to assess the potential alteration of the fingerprint signatures. As the biogeochemical processes occurring in the river could also affect the signatures, source materials were immersed in the river for durations ranging from 1 to 63 days and subsequently measured. Finally, partial least-squares regression models were constructed on 81 artificial laboratory mixtures to predict the proportions of source materials. Results and discussion: The spectrocolorimetric measurements discriminated the primary source materials but not the Quaternary deposits. As the gypsum was not conservative, only the black marls, molasses and limestones were used in the fingerprinting procedure. The construction of the partial least-squares regression models led to a median absolute error of 1.1%. This error increased to 3.9% when the models were applied to source samples with: (1) different particle sizes; (2) different durations spent in the river; or (3) different origins than those used for their construction. The effect of particle size on the fingerprinting procedure was larger than the effect of biogeochemical reactions or the spatial variability of the spectrocolorimetric signatures. Half of the 23 runoff events analysed exhibited huge variations in the source proportions from one sediment sample to another. Conclusions: The spectrocolorimetric fingerprinting approach was able to quantify routinely the proportion of primary source materials in all suspended sediment samples collected during runoff events. The high temporal resolution of the predicted proportions revealed that only analysing three or four suspended sediment samples during a runoff event could lead to a misunderstanding of the hydro-sedimentary processes for more than half of the investigated runoff events. [ABSTRACT FROM AUTHOR]

This paper studies the influence of afforestation on the water regime in two catchments in the Jizera Mountains that are similar in size and altitude but have different afforestation pattern. In this paper a range of different modelling tools is used to establish whether the differences in catchment water regime can be quantified and attributed to differences in catchment characteristics. Frequency analysis of low and high flows and a number and duration of flows over a threshold value are used to look for the differences in flow regime in both catchments. Low flow conditions are modelled using the Wittenberg nonlinear store approach. A rainfall-runoff process is modelled using a Data Based Mechanistic approach. The results indicate that the differences in the catchment response to external climatic factors outweigh the influence of land use apart from the low flows, where the changes in the response might be attributed to afforestation. [ABSTRACT FROM AUTHOR]

Summary: The effect of snow cover and snowmelt on suspended sediment (SS) runoff at a mountainous catchment in the temperate zone was investigated. The observation was carried out from March 1999 to May 2002 (3years) at an experimental catchment with the area of 0.347km2 ranging from 280m to 618m above mean sea level with average stream gradient of 1/4. It was concluded that the snow accumulation and ablation process in the catchment had a significant impact on SS runoff characteristics especially during the snow-melting period. It was estimated that more than 60% of the annual SS load flowed out during the snow-melting period because of the enhanced water discharge. The daily average SS flux during the snow-melting period was calculated to be 2.54gs−1 km−2, corresponding to a 6–7 times greater SS flux than that during other periods. The C–Q relation analysis in each runoff event revealed a dynamic change in the SS runoff mechanism during the snow-melting period. Strong clockwise hysteresis in C–Q relation in the early stage of the snow-melting period may be explained by consumption of the bed load by the first flush followed by quick depletion of the material on the stream bed due to suppression of further SS supply by thick snow cover. Counterclockwise hysteresis in C–Q relation was observed only in the late stage of the snow-melting period. SS production at steep slopes beside the stream by avalanches and surface soil slides, induced by an abundance of meltwater, was considered to be one of the main causes of the counterclockwise loops. It would be hypothesized that exposure of other steep slopes or bluffs in the catchment apart from the stream and stream bank failure by repeating surges of the stream water stage could also be other possible SS sources causing counterclockwise hysteresis in the late snow-melting period. [ABSTRACT FROM AUTHOR]

Abstract: Total atmospheric Hg contamination in a French mountainous catchment upstream from a chlor-alkali industrial site was assessed using Hg concentrations in the deepest soil horizon, in the stream bottom sediments, in river waters and in bryophytes. The natural background level of Hg content deriving from rock weathering was estimated to 32 ng g−1 in the deepest soil layers. The soils appear to be Hg contaminated in two stages: atmospheric deposition and leaching through the soil profiles of Hg-organic matter complexes. The Hg enrichment factor (EFHg Sc) which could be calculated by normalization to a conservative element like Sc, allows to estimate the major contribution (63% to 95%) of the atmospheric inputs, even in the upper part of the basin. This contribution may be attributed to diffuse regional atmospheric deposition of Hg and is mainly due to the geographic location of the chlor-alkali plant. This study shows for the first time that the mercury enrichment is proportional to the carbon content indicating that most of the atmospheric mercury deposition is trapped by the organic matter contained in the soils and in the stream sediments. The Hg stock in the soils of the upper catchment and the soil erosion contribution to the riverine Hg fluxes are estimated for the first time and allow to assess the Hg residence time. It indicates that Hg is trapped in the soils of such a polluted catchment for probably several thousand years. [Copyright &y& Elsevier]

A typhoon in 1993 induced major aggradation along Oyabu Creek, a steep, gravel bed mountain stream in Kyushu, Japan. Processes of sediment reworking are inferred from a 7-year monitoring program that measured adjustments to channel cross-sections, the longitudinal profile, and the extent/distribution of bedrock outcrops along a 3-km study reach. Over time, the reach adopted a riffle and pool structure, with notable increase in the area of exposed bedrock on the bed. This adjustment process was characterised by progressive reduction in sediment storage change per unit flow. The relaxation pathway following disturbance induced by the typhoon was shaped by the magnitude and frequency of subsequent rainfall events, the capacity of these events to transport available sediments, and physical linkages between reaches. Adjacent subreaches demonstrated differing relaxation pathways in response to these influences, induced by spatial and temporal variability in threshold conditions along the channel. Longer-term evidence indicates that responses to major disturbance, such as the 1993 typhoon, occur as ‘cycles’ of around 20-year duration. A relaxation period of 7 years is required to attain a quasi-equilibrium bed configuration and rate of sediment flux. The timeframe of cycles is considered to reflect changes to hillslope–channel bed coupling, marking the period required to generate sufficient sediment stores to reactivate phases of aggradation and subsequent degradation. [Copyright &y& Elsevier]

Site-specific information about the level of protection that mountain forests provide is often not available for large regions. Information regarding rockfalls is especially scarce. The most efficient way to obtain information about rockfall activity and the efficacy of protection forests at a regional scale is to use a simulation model. At present, it is still unknown which forest parameters could be incorporated best in such models. Therefore, the purpose of this study was to test and evaluate a model for rockfall assessment at a regional scale in which simple forest stand parameters, such as the number of trees per hectare and the diameter at breast height, are incorporated. Therefore, a newly developed Geographical Information System (GIS)-based distributed model is compared with two existing rockfall models. The developed model is the only model that calculates the rockfall velocity on the basis of energy loss due to collisions with trees and on the soil surface. The two existing models calculate energy loss over the distance between two cell centres, while the newly developed model is able to calculate multiple bounces within a pixel. The patterns of rockfall runout zones produced by the three models are compared with patterns of rockfall deposits derived from geomorphological field maps. Furthermore, the rockfall velocities modelled by the three models are compared. It is found that the models produced rockfall runout zone maps with rather similar accuracies. However, the developed model performs best on forested hillslopes and it also produces velocities that match best with field estimates on both forested and nonforested hillslopes irrespective of the slope gradient. [Copyright &y& Elsevier]

To clarify the sediment yield processes following a disturbance by a forest fire in a mountainous catchment, and considering the hydrological and geomorphological processes in the headwater, we measured bedload sediment yield at rainfall events in disturbed and secondary forest catchments in the western part of Japan. The three catchments were under different hydrogeological conditions. The IK, TB and TY catchments were disturbed by forest fires in 2000, 1994, and 1978, respectively. In the IK catchment, although runoff response to rainfall was fastest with high peak flows, the catchment also had the highest base flow. Moreover, the annual sediment yield there was about ten times as high as in the other two catchments, and it was found that there was a steep linear curve in the relationship between precipitation and bedload sediment yield. This is thought to be caused by overland flow generation following water repellency on the slopes, and by the accumulated sediment that forms the thick soil layer on the valley bottom. On the other hand, in the TB catchment runoff experienced high peak flows at rainfall events and low base flows, and there was a gradual linear curve in the precipitation–sediment yield relationship. This might be the result of there being a thin soil layer on the hillslope and on the valley bottom because of successive erosion after the fire. In the TY catchment, runoff had a low peak flow at rainfall events and a high base flow; and the bedload sediment yield increased exponentially with increasing precipitation. Therefore, sediment yield in the TB catchment was more than that in the TY during storm events with precipitation of less than 100 mm, whereas it was the opposite during heavier rainfalls. It indicates that there is a thick soil layer on the slope and a thin soil layer on the valley bottom in the TY catchment following the recovering of vegetation, and that the sediment yield process predominates only during big rainfall events, only then does subsurface flow generate. [ABSTRACT FROM AUTHOR]

The long-term trends and seasonal patterns of stream water chemical composition in a small remote forested karst catchment, were investigated from 1978 to 2018. Calcium, magnesium, and bicarbonates, the dominant ions, increased over the period together with temperature, while sulfates decreased. Carbonate and sulfate mineral dissolution was the main source of these elements. These trends and the seasonal opposite patterns of discharge vs. temperature, calcite saturation index vs. pCO2 and bicarbonate vs. sulfates, suggested the influence of discharge, of reduced long-range atmospheric pollution, and of increasing air temperature on biological activity and carbonate dissolution. Furthermore, the hydrological regime controlled the seasonal stream water chemical composition and fluxes by: (i) a dilution during the high discharge period, (ii) a change in the contribution rate of the waters draining different lithological areas in the catchment, e.g., the increased sulfates to bicarbonates ratio during summer low flows, with a maximum alkalinity decrease of 24%, and (iii) a "piston" and a "flushing" effects of dissolved elements stored in soils and epikarst with the first autumn heavy rains. Long-term stream water hydrochemical surveys of karst system have proved to be powerful indicators of biogeochemical processes, water sources and pathways under variable natural and anthropogenic environmental pressure conditions. [ABSTRACT FROM AUTHOR]

The temporal variability of transit-time distributions (TTDs) and residence-time distributions (RTDs) has received particular attention recently, but such variability has barely been studied using distributed hydrological modeling. In this study, a low-dimensional integrated hydrological model is run in combination with particle-tracking algorithms to investigate the temporal variability of TTDs, RTDs, and StorAge Selection (SAS) functions in the small, mountainous Strengbach watershed belonging to the French network of critical-zone observatories. The particle-tracking algorithms employed rely upon both forward and backward formulations that are specifically developed to handle time-variable velocity fields and evaluate TTDs and RTDs under transient hydrological conditions. The model is calibrated using both traditional streamflow measurements and magnetic resonance sounding (MRS)—which is sensitive to the subsurface water content—and then verified over a ten-year period. The results show that the mean transit time is rather short, at 150–200 days, and that the TTDs and RTDs are not greatly influenced by water storage within the catchment. This specific behavior is mainly explained by the small size of the catchment and its small storage capacity, a rapid flow mainly controlled by gravity along steep slopes, and climatic features that keep the contributive zone around the stream wet all year long. [ABSTRACT FROM AUTHOR]

In Taiwan, the steep landscape and highly vulnerable geology make it difficult to predict soil erosion and sediment transportation via variable transport conditions. In this study, we integrated the Taiwan universal soil loss equation (TUSLE) and slope stability conditions in the soil and water assessment tool (SWAT) as the SWAT-Twn model to improve sediment simulation and assess the sediment transport functions in the Chenyulan watershed, a small mountainous catchment. The results showed that the simulation of streamflow was satisfactory for calibration and validation. Before model calibration and validation for sediment, SWAT-Twn with default sediment transport method performed better in sediment simulation than the official SWAT model (version 664). The SWAT-Twn model coupled with the simplified Bagnold equation could estimate sediment export more accurately and significantly reduce the overestimated sediment yield by 65.7%, especially in highly steep areas. Furthermore, five different sediment transport methods (simplified Bagnold equation with/without routing by particle size, Kodoatie equation, Molinas and Wu equation, and Yang sand and gravel equation) were evaluated. It is suggested that modelers who conduct sediment studies in the mountainous watersheds with extreme rainfall conditions should adjust the modified universal soil loss equation (MUSLE) factors and carefully evaluate the sediment transportation equations in SWAT. [ABSTRACT FROM AUTHOR]

Precipitation is one of the essential variables in rainfall-runoff modeling. For hydrological purposes, the most commonly used data sources of precipitation are rain gauges and weather radars. Recently, multi-satellite precipitation estimates have gained importance thanks to the emergence of Integrated Multisatellite Retrievals for Global Precipitation Measurement (IMERG GPM), a successor of a very successful Tropical Rainfall Measuring Mission (TRMM) mission which has been providing high-quality precipitation estimates for almost two decades. Hydrological modeling of mountainous catchment requires reliable precipitation inputs in both time and space as the hydrological response of such a catchment is very quick. This paper presents an inter-comparison of event-based rainfall-runoff simulations using precipitation data originating from three different sources. For semi-distributed modeling of discharge in the mountainous river, the Hydrologic Engineering Center-Hydrologic Modelling System (HEC-HMS) is applied. The model was calibrated and validated for the period 2014–2016 using measurement data from the Upper Skawa catchment a small mountainous catchment in southern Poland. The performance of the model was assessed using the Nash–Sutcliffe efficiency coefficient (NSE), Pearson's correlation coefficient (r), Percent bias (PBias) and Relative peak flow difference (rPFD). The results show that for the event-based modeling adjusted radar rainfall estimates and IMERG GPM satellite precipitation estimates are the most reliable precipitation data sources. For each source of the precipitation data the model was calibrated separately as the spatial and temporal distributions of rainfall significantly impact the estimated values of model parameters. It has been found that the applied Soil Conservation Service (SCS) Curve Number loss method performs best for flood events having a unimodal time distribution. The analysis of the simulation time-steps indicates that time aggregation of precipitation data from 1 to 2 h (not exceeding the response time of the catchment) provide a significant improvement of flow simulation results for all the models while further aggregation, up to 4 h, seems to be valuable only for model based on rain gauge precipitation data. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess soil erosion changes in the mountainous catchment of the Portaikos torrent (Central Greece) under climate change. To this end, precipitation and temperature data were derived from a high-resolution (25 × 25 km) RegCM3 regional climate model for the baseline period 1974–2000 and future period 2074–2100. Additionally, three GIS layers were generated regarding land cover, geology, and slopes in the study area, whereas erosion state was recognized after field observations. Subsequently, the erosion potential model (EPM) was applied to quantify the effects of precipitation and temperature changes on soil erosion. The results showed a decrease (−21.2%) in annual precipitation (mm) and increase (+3.6 °C) in mean annual temperature until the end of the 21st century, and the above changes are likely to lead to a small decrease (−4.9%) in soil erosion potential. [ABSTRACT FROM AUTHOR]

Runoff components of the Zastler catchment (18 x 4 km2, southern Black Forest, Germany) were analysed with hydrograph separations using stable oxygen isotopes and dissolved silica. It was shown that event water and components with low silica contributed only smallamounts to total runoff. In addition, comparison of the two-component hydrograph separations showed that the low-silica components are generated by both event water and pre-event water fractions, depending on the state of the system. A modified three-component hydrograph separation method was introduced using dissolved silica and 18O. During storm events an interaction of three runoff components having distinct silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was appropriate to assign (i) the low silica component to the riparian zones and impermeable areas, (ii) the medium silica component to the periglacial debris cover and (iii) the high silica component to the crystallinedetritus and crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium silica concentrations reacted very sensitively and intensely. Thecontribution of this component to total runoff is comparatively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runoff generation processes occurring in this reservoir. [ABSTRACT FROM AUTHOR]