Modelling gravel-bed topography from sediment transport

A simple queueing model which generates bed topography consistent with the mechanics of gravel motion is presented. The equations on which it is based are derived from the application of simple theoretical ideas and an analysis of published flume data (Meland and Norrman, 1966; Francis, 1973; Abbott and Francis, 1977). The simulation produces an extremely variable bed topography in which at least two scales of bedform may be identified. Features of 5–10 grain wavelengths, similar to pebble clusters, are superimposed on other forms whose wavelength is up to 30–40 grains and which resemble step-pools systems and antidunes. Sediment transport shows many of the characteristics found in the field and the model is, therefore, thought to provide a useful starting point from which to examine the interaction between flow, sediment transport, and bedforms in gravel-bed and cobble streams.     

Impacts of projected climate change on sediment yield and dredging costs

Changes in climate may significantly affect how sediment moves through watersheds into harbours and channels that are dredged for navigation or flood control. Here, we applied a hydrologic model driven by a large suite of climate change scenarios to simulate both historical and future sediment yield and transport in two large, adjacent watersheds in the Great Lakes region. Using historical dredging expenditure data from the U.S. Army Corps of Engineers, we then developed a pair of statistical models that link sediment discharge from each river to dredging costs at the watershed outlet. Although both watersheds show similar slight decreases in streamflow and sediment yield in the near‐term, by Mid‐Century, they diverge substantially. Dredging costs are projected to change in opposite directions for the two watersheds; we estimate that future dredging costs will decline in the St. Joseph River by 8–16% by Mid‐Century but increase by 1–6% in the Maumee River. Our results show that the impacts of climate change on sediment yield and dredging may vary significantly by watershed even within a region and that agricultural practices will play a large role in determining future streamflow and sediment loads. We also show that there are large variations in responses across climate projections that cause significant uncertainty in sediment and dredging projections.     

Impact of climate change on sediment yield for Naran watershed,Pakistan

In this paper, the site-specific impact of climate change on sediment yield has been assessed for the Naran watershed, Pakistan. Observed data has been gathered for period 1961–2010 and HaDCM3 GCM predictors of SRES scenarios A2 and B2 have been downloaded. Future precipitation and temperature time series have been statistically downscaled for time horizon 2011–2040 and 2041–2070. Downscaled data show both increasing and decreasing changes with respect to the observation. Potential sediment yield for future related to climate change has been simulated. The results show that the both snowy and monsoon seasonal stream discharges are expected to increase. This will lead to increase in annual sus-pended sediment yields. Percentage-wise, a less discharge and more sediment yield are expected during the early summer. The study concluded that the climate change and variability are influencing the watershed, and suspended sediment yield is likely to increase in the future.     

Predicting catchment sediment yield in Mediterranean environments: the importance of sediment sources and connectivity in Italian drainage basins

Predicting sediment yield at the catchment scale is one of the main challenges in geomorphologic research. The application of both physics‐based models and regression models has until now not provided very satisfying results for prediction of sediment yield for medium to large sized catchments (c. >50 km²). The explanation for this lies in a combination of the large data requirements of most models and a lack of knowledge to describe all processes and process interactions at the catchment scale. In particular, point sources of sediment (e.g. gullies, mass movements), connectivity and sediment transport remain difficult to describe in most models. From reservoir sedimentation data of 44 Italian catchments, it appeared that there was a (non‐significant) positive relation between catchment area and sediment yield. This is in contrast to what is generally expected from the theory of decreasing sediment delivery rates with increasing catchment area. Furthermore, this positive relation suggests that processes other than upland erosion are responsible for catchment sediment yield. Here we explore the potential of the Factorial Scoring Model (FSM) and the Pacific Southwest Interagency Committee (PSIAC) model to predict sediment yield, and indicate the most important sediment sources. In these models different factors are used to characterize a drainage basin in terms of sensitivity to erosion and connectivity. In both models an index is calculated that is related to sediment yield. The FSM explained between 36 and 61 per cent of the variation in sediment yield, and the PSIAC model between 57 and 62 per cent, depending on the factors used to characterize the catchments. The FSM model performed best based on a factor to describe gullies, lithology, landslides, catchment shape and vegetation. Topography and catchment area did not explain additional variance. In particular, the addition of the landslide factor resulted in a significantly increased model performance. The FSM and PSIAC model both performed better than a spatially distributed model describing water erosion and sediment transport, which was applied to the same catchments but explained only between 20 and 51 per cent of the variation in sediment yield. Model results confirmed the hypothesis that processes other than upland erosion are probably responsible for sediment yield in the Italian catchments. A promising future development of the models is by the use of detailed spatially distributed data to determine the scores, decrease model subjectivity and provide spatially distributed output. Copyright © 2006 John Wiley & Sons, Ltd.     

Impact of climate change on stream discharge and sediment yield in Northern Viet Nam

The purpose of this paper is to apply “Soil and Water Assessment Tool (SWAT)” model to assess the impacts of climate change on stream discharge and sediment yield from Song Cau watershed in Northern Viet Nam. Three climate change scenarios B1, B2, and A2; representing low, medium, and high levels of greenhouse gas emission, respectively, were considered in this study. The highest changes in stream discharge (up to 11.4%) and sediment load (15.3%) can be expected in wet season in 2050s according to the high emission scenario (A2), while for the low emission scenario the corresponding changes equal to 8.8% and 12.6%. The results show that the stream discharge is likely to increase in the future during the wet season with increasing threats of sedimentation.     

Assessing the impacts of land cover and climate on runoff and sediment yield of a river basin

ABSTRACT

This study investigated the impacts of changes in land cover and climate on runoff and sediment yield in a river basin in India. Land Change Modeler was used to derive the future land cover and its changes using the Sankey diagram approach. The future climatic parameters were derived from five general circulation models for two emission scenarios with representative concentration pathways (RCPs) 4.5 and 8.5. The land cover and climate change impacts on runoff and sediment yield were estimated using SWAT model. The results show important changes in land cover and indicate that urban and agricultural areas strongly influence the runoff and sediment yield. Among the land cover and climate change impacts, climate has more predominant (70%–95%) impact. Runoff and sediment yield are likely to decrease in both RCP scenarios in the future period. The impacts of land cover changes are more prominent on sediment yield than runoff.     

Interpreting sediment yield scaling

Terrestrial sediment yield – often measured as suspended sediment load in stream channels – commonly scales with drainage area within homogeneous land surface regions. But the effect of drainage area has not usually been recognized in comparative sediment yield analyses, rendering most comparisons of sediment yield from disparate source areas invalid. The procedure to discount scale differences for comparative purposes is presented. Mathematical scaling varies according to landscape condition and provides a physical interpretation of that condition. The results open the way for rational construction of a ‘sediment delivery ratio’. Copyright © 2017 John Wiley & Sons, Ltd.     

Predicting streamflow distributions and flow duration curves from landscape and climate

Characterizing the probability distribution of streamflows in catchments lacking in discharge measurements represents an attractive prospect with consequences for practical and scientific applications, in particular water resources management. In this paper, a physically-based analytic model of streamflow dynamics is combined with a set of water balance models and a geomorphological recession flow model in order to estimate streamflow probability distributions based on catchment-scale climatic and morphologic features. The models used are described and the novel parameterization approach is elaborated on. Starting from rainfall data, potential evapotranspiration and digital terrain maps, the method proved capable of capturing the statistics of observed streamflows reasonably well in 11 test catchments distributed throughout the United States, east of the rocky mountains. The method developed offers a unique approach for estimating probability distribution of streamflows where only climatic and geomorphologic features are known.     

Predicting cumulative sediment depostition in large reservoirs

Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data.     

Predicting cumulative sediment depostition in large reservoirs

Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data.     

Interannual variation of suspended sediment load and sediment yield in an alpine catchment

Abstract

The results are described of 16 years operation of a measuring station for the automatic recording of water discharge, bed load and suspended sediment transport in the Rio Cordon catchment, a small alpine basin (5 km²) located in northeastern Italy. Hillslope erosion processes were investigated by surveying individual sediment sources repeatedly. Annual and seasonal variations of suspended sediment load during the period 1986–2001 are analysed along with their contribution to the total sediment yield. The results show that suspended load accounted for 76% of total load and that most of the suspended sediment transport occurred during two flood events: an extreme summer flash flood in September 1994 (27% of the 16-years total suspended load) and a snowmelt-induced event in May 2001 accompanied by a mud flow which fed the stream with sediments. The role of active sediment source areas is discussed in relation to the changes in flood peak—suspended load trends which became apparent after both the 1994 and the 2001 events.     

Estimation of soil erosion and sediment yield using GIS

Abstract

A Geographical Information System (GIS) based method is proposed and demonstrated for the identification of sediment source areas and the prediction of storm sediment yield from catchments. Data from the Nagwa and Karso catchments in Bihar (India) have been used. The Integrated Land and Water Information System (ILWIS) GIS package has been used for carrying out geographic analyses. An Earth Resources Data Analysis System (ERDAS) Imagine image processor has been used for the digital analysis of satellite data for deriving the land cover and soil characteristics of the catchments. The catchments were discretized into hydrologically homogeneous grid cells to capture the catchment heterogeneity. The cells thus formed were then differentiated into cells of overland flow regions and cells of channel flow regions based on the magnitude of their flow accumulation areas. The gross soil erosion in each cell was calculated using the Universal Soil Loss Equation (USLE) by carefully determining its various parameters. The concept of sediment delivery ratio (SDR) was used for determination of the total sediment yield of each catchment during isolated storm events.     

Modeling the sediment yield from landslides in the Shihmen Reservoir watershed,Taiwan

Landslides generate enormous volumes of sediment in mountainous watersheds; however, quantifying the downstream transport of landslide‐derived sediment remains a challenge. Landslide erosion and sediment delivery to the Shihmen Reservoir watershed in Taiwan was estimated using empirical landslide frequency–area and volume–area relationships, empirical landslide runout models, and the Hydrological Simulation Program‐ FORTRAN (HSPF). Landslide erosion rates ranged from 0.4 mm yr^‐1 to 2.2 mm yr^‐1 during the period 1986–2003, but increased to 7.9 mm yr^‐1 following Typhoon Aere in 2004. The percentage of landslide sediment delivered to streams decreased from 78% during the period 1986–1997 to 55% in 2004. Although the delivery ratio was lower, the volume of landslide sediment delivered to streams was 2.81 × 10⁶ Mg yr^‐1 in 1986–1997 and 8.60 × 10⁶ Mg yr^‐1 in 2004. Model simulations indicate that only a small proportion of the landslide material was delivered downstream. An average of 13% of the landslide material delivered to rivers was moved downstream during the period 1986–1997. In 2004, the period including Typhoon Aere, the annual fluvial sediment yield accounted for approximately 23% of the landslide material delivered to streams. In general, the transfer of sediment in the fluvial system in the Shihmen Reservoir watershed is dominantly transport limited. The imbalance between sediment supply and transport capacity has resulted in a considerable quantity of landslide material remaining in the upper‐stream regions of the watershed. Copyright © 2012 John Wiley & Sons, Ltd.     

The responses of hydrological processes and sediment yield to land‐use and climate change in the Be River Catchment,Vietnam

In this study, we investigated the responses of hydrology and sediment yield with impacts of land‐use and climate change scenarios in the Be River Catchment, using the Soil and Water Assessment Tool (SWAT) hydrological model. The calibration and validation results indicated that the SWAT model is a powerful tool for simulating the impact of environmental change on hydrology and sediment yield in this catchment. The hydrologic and sediment yield responses to land‐use and climate changes were simulated based on the calibrated model. The results indicated that a 16.3% decrease in forest land is likely to increase streamflow (0.2 to 0.4%), sediment load (1.8 to 3.0%), and surface runoff (SURQ) (4.8 to 10.7%) and to decrease groundwater discharge (GW_Q) (3.5 to 7.9%). Climate change in the catchment leads to decreases in streamflow (0.7 to 6.9%) and GW_Q (3.0 to 8.4%), increase in evapotranspiration (0.5 to 2.9%), and changes in SURQ (?5.3 to 2.3%) and sediment load (?5.3 to 4.4%). The combined impacts of land‐use and climate changes decrease streamflow (2.0 to 3.9%) and GW_Q (12.3 to 14.0%), increase evapotranspiration (0.7 to 2.8%), SURQ (8.2 to 12.4%), and sediment load (2.0 to 7.9%). In general, the separate impacts of climate and land‐use changes on streamflow, sediment load, and water balance components are offset each other. However, SURQ and some component of subsurface flow are more sensitive to land‐use change than to climate change. Furthermore, the results emphasized water scarcity during the dry season and increased soil erosion during the wet season. Copyright © 2012 John Wiley & Sons, Ltd.     

Sources and sediment yield from a rural catchment in humid temperate environment,northwest Spain

A study was carried out on a rural catchment located in northwest Spain to examine the sediment yield from the catchment by measuring suspended sediments during rainfall events. Within the catchment regular surveys were conducted to obtain data on the suspended sediment sources. Important variations in sediment load were detected at event scale (0·3–21·0 Mg); some of these can be explained in terms of event size, antecedent conditions, rainfall distribution and soil surface erosion. To study the variables controlling suspended sediment yield during the events in the catchment, several event and pre‐event variables were calculated for all events. The sediment load is strongly influenced by discharge variables. During the events discharge–suspended sediments were also analysed. When the soil surface was unprotected, the formation of rills and ephemeral gullies on agricultural land at the catchment head was an important source of suspended sediments in the catchment. Copyright © 2010 John Wiley & Sons, Ltd.     

Identifying threshold storm events and quantifying potential impacts of climate change on sediment yield in a small upland agricultural watershed of Ontario

Agricultural zones are significant sediment sources, but it is crucial to identify critical source areas (CSAs) of sediment yield within these zones where best management practices (BMPs) can be applied to the best effect in reducing sediment delivery to receiving water bodies rather than the economically nonviable alternative of randomly or sweepingly implementing BMPs. A storm event of a specific magnitude and hyetograph profile may, at different times, generate a greater or lesser sediment yield. The widely used agricultural nonpoint source (AGNPS) model was used to identify CSAs for sediment losses in Southwestern Ontario's agriculture‐dominated 374‐ha Holtby watershed. A storm threshold approach was adopted to identify critical periods for higher sediment losses. An AGNPS model for the Holtby watershed was set up, calibrated, and validated for run‐off volume, peak flow rate, and sediment yield for several storms. The calibrated and validated model was run for storms of increasing return periods to identify threshold storm events that would generate sediment yield greater than an acceptable value for early and late spring, summer, and fall seasons. Finally, to evaluate the potential impacts of climate change, we shifted shorter duration summer storms into spring conditions and quantified the changes in sediment yield dynamics. A 6‐hr, 7.5‐year early spring storm would generate sediment losses exceeding the acceptable limit of 0.34 t ha^?1 for the season. However, summer storms (2 hr, up to 100 years) tended to generate sediment yields below those of an identifiable threshold storm. If such shorter duration summer storms occurred in spring, the sediment yield would increase by more than fivefold. A 5‐year future storm would generate an equivalent effect of a 100‐year current spring event. The high sediment delivery to be expected will have significant implications regarding the future management of water quality of receiving waters. Appropriate placement of BMPs at CSAs will thus be needed to reduce such high sediment delivery to receiving waters.     

A semi-physical sediment yield model for estimation of suspended sediment in loess region

Sediment yield is a complex function of many environmental factors including climate,hydrology,vegetation,basin topography,soil types,and land cover.We present a new semi-physical watershed sediment yield model for the estimation of suspended sediment in loess region.This model is composed by three modules in slope,gully,and stream phases.For slope sediment yield,a balance equation is established based on the concept of hydraulic erosion capacity and soil erosion resistance capacity.According to the statistical analysis of watershed characteristics,we use an exponential curve to approximately describe the spatial variability of watershed soil erosion resistance capacity.In gully phase,the relationship between gully sediment concentration and flow velocity is established based on the Bagnold'stream power function.In the stream phase,we assume a linear dependence of the sediment volume in the reach on the weighted sediment input and output.The proposed sediment yield model is operated in conjunction with a conceptual hydrologic model,and is tested over 16 regions including testing grounds,and small,medium and large watersheds in the loess plateau region in the mid-reach of Yellow River.Our results indicate that the model is reasonable in structure and is able to provide a good simulation of sediment generation and transportation processes at both flood event scale and inter-annual time scale.The proposed model is generally applicable to the watersheds with soil texture similar to that of the loess plateau region in the Yellow River basin in China.     

Effect of parameter uncertainty on calculated sediment yield

The modified Universal Soil Loss Equation combined with the U.S. Soil Conservation Service runoff calculation method is analysed with respect to parameter uncertainty. The case of agricultural watersheds, where the above method gives quite accurate estimates on the multiannual sediment yield, illustrates the methodology. Parameter uncertainty results in a coefficient of variation of the calculated sediment yield in the range (0.14–0.21). For the general case, five groups of statistical error bound for the parameters are distinguished, based on available information such as the scale of maps.     

Prediction of sediment yield by coupling Kalman filter with instantaneous unit sediment graph

An instantaneous unit sediment graph (IUSG) model in conjunction with Kalman filter was investigated for prediction of sediment yield from an upland watershed in Northwestern Mississippi. The state vector of the watershed sediment yield system was constituted by the IUSG and then the sediment yield was estimated by the IUSG model using Kalman filter. The initial values of the state vector were assumed as the average of the IUSG values and the initial sediment yield estimated from the average IUSG. The IUSG model using Kalman filter with a recursive algorithm accurately predicted sediment yield from watershed W‐5, Mississippi. The filter allowed the IUSG to vary in time, increased the accuracy of the IUSG model, and reduced physical uncertainty of the sediment yield process in the watershed. Copyright © 1999 John Wiley & Sons, Ltd.     

Water and sediment evolution in areas with high and coarse sediment yield of the Loess Plateau

In the past few years, the amount of sediment entering the Yellow River decreased significantly in areas with high and coarse sediment yield of the Loess Plateau. Some researchers considered that it was owing to the soil and water conservation project, while others believed that it was caused by the low precipitation. The observation data showed -2 that the ultimate sod erosion modulus m 1960s could reach 150,000 t km . However some experts preferred to believe that the ultimate soil erosion modulus in 1960s was wrong due to some uncertain mistakes. This paper quantitatively analyzed the spatial-temporal evolution pattern of sediment yield in areas with high and coarse sediment yield of the Loess Plateau over the past 50 years, by simulating the precipitation-runoff and soil erosion in 12 sample years with the digital watershed model. Some preliminary conclusions have been drawn as following： since the 1960s and 1970s, the rainstorm center had moved southward and the intensity of rainfall center became weaker and spread into dispersed rainfall distribution in areas with high and coarse sediment yield; the decrease of the amount of sediment entering the Yellow River was caused by the changes of rainfall type in recent years; the rainstorm of 1967 was concentrated in the re~ion nearby ＂Shenmu-Fugu＂ in Shaanxi Province, and the annual maximum transport modulus （150,000 t km-2 ） measured in Bullpen Ditch of the left bank tributary between ＂Shenmu＂ and ＂Fugu＂ in 1967 is reasonable.