Streamflow Yield Research Articles

Viability of investing in ecological infrastructure in South Africa’s water supply areas

Ecological infrastructure (natural ecosystems that provide important services and save on built infrastructure costs) can have an important role in securing water supply, particularly in water-scarce areas, but this importance is not reflected in investment decisions, partly due to a lack of evidence. In South Africa, one of the main threats to water supply is the proliferation of woody invasive alien plants which significantly reduce stream flow and water yields. We used existing spatial data and estimates of the impact of woody invasive plants on flows and water yields and on restoration costs to analyse the viability of investing in ecological infrastructure at the scale of major water supply areas. The analysis involved comparison of the costs and effects on water yields of catchment restoration with those of planned built infrastructure interventions designed to meet increasing water demands in the medium to long term. The cost-effectiveness analysis used the unit reference value as a measure of comparison, which is based on the discounted flows of costs and water supplied over a defined time. Restoration could supply 24% of the combined yield of planned built infrastructure interventions by 2050, and is not only cost-effective but has the added advantage of a range of co-benefits delivered by improving ecosystem health. This finding suggests that investing in ecological infrastructure should be considered ahead of new built-infrastructure projects.

Prioritization of sub-watersheds and subsequent site identification for soil water and conservation practices using the SWAT-AHP integrated model in the Lower Sutlej Sub-basin, India.

Prioritization of watersheds is a crucial step in integrated river basin management. It guides resource allocation, planning, decision-making, stakeholder engagement, targeted interventions, and monitoring and evaluation efforts. By identifying and addressing priority watersheds, comprehensive and sustainable management of water resources can be achieved within a river basin. The aim of the current study is to prioritize watersheds using the Soil and Water Assessment Tool (SWAT) and site suitability analysis for the implementation of soil and water conservation structures (SWCS) in the prioritized watersheds by using an analytical hierarchy process (AHP) of the Lower Sutlej Sub-basin, India. The model was calibrated with observed data from 2017 to 2019 with the first 2years (2015-16) as a warm-up period. Furthermore, validation of the model was done using 2-year data from 2020 to 2021. The model showed successful performance in terms of the R2 range from 0.72 to 0.89, the NSE range from 0.67 to 0.73, the PBIAS range from - 26.70 to 11.30, and the RSR range from 0.51 to 0.57 for stream flow and sediment yield during calibration and validation period. The basin's average annual soil loss ranged from 3.08 to 21.63 t/ha/year, a watershed with the WS2 index seeing the highest rate of soil erosion (21.63 t/ha/year). Hence, WS2 was found to be a top priority. In addition, the site suitability analysis of the prioritized watershed (WS2) reveals that about 1.42% of the area is extremely suitable, 16.14% is highly suitable, and 35.58% is moderately suitable for SWCS. According to the site suitability map validation, both dam locations were found in highly suitable areas, so the developed site suitability map is accurate. This research will help sustainability planners and managers make more informed decisions when building SWCS at suitable sites for better land and water conservation.

Estimating Sediment Yield at Sungai Pusu Watershed using Soil and Water Assessment Tool (SWAT) Model

Sediment yield is the net result of soil erosion and sediment deposition processes. In the watershed, sediment yields are dominantly determined by stream flow, drainage area, and channel size. Land-use activity conducted by human is one of the major contributions to the sediment yield in the watershed. The study area covered in this study is the Sungai Pusu which flows through International Islamic University Malaysia (IIUM). Significant amount of sediments is deposited in Sungai Pusu due to the improper land clearing activities that are taking place along the river’s main tributaries. As a result, the water quality of Sungai Pusu is rapidly deteriorating. Sediment yield estimation is crucial in order to design suitable measure to rehabilitate the river. The aim of this study is to estimate sediment yield at Sungai Pusu watershed using SWAT model. Remote sensing and Geographic Information System (GIS) were used to evaluate sedimentation over time in the Sungai Pusu watershed. The SWAT model was performed to simulate water balance, stream flow, and sediment yield. The annual sediment yield obtained by the model is 427-ton ha-1 year-1.

Sediment yield estimation and evaluating the best management practices in Nashe watershed, Blue Nile Basin, Ethiopia

Sediment yield estimation along with identification of soil erosion mechanisms is essential for developing sophisticated management approaches, assessing, and balancing different management scenarios and prioritizing better soil and water conservation planning and management. At the watershed scale, land management practices are commonly utilized to minimize sediment loads. The goal of this research was to estimate sediment yield and prioritize the spatial dispersion of sediment-producing hotspot areas in the Nashe catchment using the Soil and Water Assessment Tool (SWAT). Moreover, to reduce catchment sediment output, this study also aims to assess the effectiveness of certain management practices. For calibration and validation of the model, monthly stream flow and sediment data were utilized. The model performance indicators show good agreement between measured and simulated stream flow and sediment yields. The study examined four best management practice (BMP) scenarios for the catchment’s designated sub-watersheds: S0 (baseline scenario), S1 (filter strip), S2 (stone/soil bunds), S3 (contouring), and S4 (terracing). According to the SWAT model result, the watershed’s mean yearly sediment output was 25.96 t/ha. yr. under baseline circumstances. The model also revealed areas producing the maximum sediment quantities indicating the model’s effectiveness for implementing and evaluating the sensitivity of sediment yield to various management strategies. At the watershed scale, treating the watershed with various management scenarios S1, S2, S3, and S4 decreased average annual sediment yield by 34.88%, 57.98%, 39.55%, and 54.77%, respectively. The implementations of the soil/stone bund and terracing scenarios resulted in the maximum sediment yield reduction. The findings of this study will help policymakers to make better and well-informed decisions regarding suitable land use activities and best management strategies.

Wildfire-induced shifts in groundwater discharge to streams identified with paired air and stream water temperature analyses

Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning.

Can annual streamflow volumes be characterised by flood events alone?

Can total annual streamflow in any given year be largely characterised by a relatively small number of high flow events? A comprehensive assessment of this is of high value as there is evidence to suggest that as flood events increase in rarity a more consistent response between streamflow extremes and temperatures increases can be established — providing greater reliability in projections of rare events. We propose here a novel methodology to characterise streamflow regimes in the context of total annual streamflow for water supply. Using the Australian Bureau of Meteorology’s Hydrologic Reference Station database, we developed annual event flow distributions that standardise the relationship between total annual streamflow and event flows. It was found that the annual event flow distributions are primarily a function of local climate and catchment size and were largely insensitive to interannual variability represented by the El Niño Southern Oscillation Index, mean annual temperature, or total annual rainfall volume. Statistically significant trends were found in the timeseries of annual event flow distribution values, signalling a move to a less even distribution in the southern latitudes and a more even distribution in the northern latitudes. Our results show that total annual streamflows can be characterised by a small number of high flow events. This suggests that for Australia’s most critical surface drinking water supply catchments the streamflow yields can be represented by changes in a few, high flow events, independent of interannual variability. As these relationships are non-stationary, they may provide a basis for understanding changes in water supply into the future.

Modifying the SWAT Model to Simulate Eco-Hydrological Processes in an Arid Grassland Dominated Watershed

Grasslands are the main land cover type and one of the most important ecosystems in arid and alpine endorheic basins. The vegetation coverage of grasslands is spatially heterogeneous in arid and alpine areas and it may lead to variations in water allocation. The Soil and Water Assessment Tool (SWAT) is one of the most widely used semi-distributed catchment-scale eco-hydrological models. The leaf area index (LAI) is one of the vegetation coverage indexes and is incorporated in the SWAT model. However, in SWAT, the LAI accumulation is controlled by heat, and neglects other relevant factors such as precipitation and terrain. To address the drawbacks of the SWAT in simulating vegetation coverage and plant patterns, several studies have focused on improving LAI estimation. However, they still have been limited to arid and alpine grasslands with different vegetation coverages. In this study, we modified the SWAT model using remotely sensed LAI data with high temporal and spatial resolution. We used this to better simulate eco-hydrological processes in grassland basins with different vegetation coverages in the upper reaches of the Bayin River Basin. Results showed that for the original SWAT model, the simulated LAI was homogeneous within each land use/cover type, whereas the remotely sensed LAI was spatially heterogeneous and better captured the vegetation coverage of the entire basin. The proper estimation of the LAI was reflected in the improved simulation of the monthly streamflow and sediment yield at the basin outlet and the monthly ET. These findings indicate that the modified SWAT could better simulate hydrological processes in arid and alpine grasslands with different vegetation coverages.

Sediment Yield Estimation and Identifying the Soil Erosion Prone Areas in Koysha Dam Watershed of Omo-Gibe Basin

Sedimentation is huge problems that have threatened many reservoirs in Ethiopia. Koysha dam watershed is conditioned densely populated with intensive traditional agricultural practice and low soil and water conservation practice in left side. The left side of watershed is gentle slope terrain topography. This study has been conducted to estimate mean annual sediment yield of watershed, to identify and prioritize the most sensitive sub-watersheds with the help of Arc SWAT 2012 for planning reservoir sedimentation mitigating strategies at the watershed level. Based on a digital elevation model the catchment was divided in to 23 sub-basins using the dam axis as the main outlet. The current LULC map was downloaded from satellite. The pre-processing and both unsupervised and supervised classification was conducted in ERDAS Imagine 2015. By overlaying land use, soil and slope maps, sub-watersheds were further divided in to 241 HRUs. Arc SWAT Model was calibrated and validated using SUFI-2 SWAT-CUP optimization algorithms for stream flow rate and sediment yield data observed at dam axis, which transposed from other gauging stations. The model performance was evaluated by using both stream flow and sediment yield data. The study has revealed that Koysha dam residual watershed has mean annual sediment yield of 7.22 t/ha/year. Out of the 23 sub-watersheds, seven sub-basins produce above average sediment yields ranging from 8.79 -56.70 t/ha/yr, while the others yield below the average value. Out of the 23 sub-basins two sub-basins were prioritized for immediate implementation of watershed management interventions. The maximum sediment outflow of these two sub-basin are 26.33 and 56.7 t/ha/year and are characterized dominantly by cultivated land with average land slope of 31.45% and 28.74% respectively and with the dominant soil type of Humic Nitisols. The soil erosion was sensitive to cultivation land use and terrain steepness. Keywords: Koysha dam watershed, Sediment yield, SWAT, Prioritization DOI: 10.7176/CER/14-2-01 Publication date: April 30 th 2022

Evaluation of the Impact of Best Management Practices on Streamflow, Sediment and Nutrient Yield at Field and Watershed Scales

Evaluating Best Management Practices (BMPs) in watersheds using hydrologic and water quality models can help to establish an effective watershed water management. Soil and Water Assessment Tool (SWAT) was applied to Big Sunflower River Watershed (BSRW) and the Stovall Sherard Watershed (SSW) to evaluate BMP’s impact at watershed and field scale watersheds respectively. SWAT was calibrated and validated for streamflow, sediment yield, total nitrogen (TN), and total phosphorous (TP) at outlets of three sub-basins of the BSRW, and within the SSW. BMP scenarios of check-dam, tail water pond, vegetative filter strips (VFS), nutrient management, and tillage management were evaluated for their efficacy in reducing streamflow, sediment yield, and nutrient loads at field and watershed scales. The VFS was determined as the most effective BMP in decreasing sediment yield, TN, and TP at both field and watershed scales. At field scale, reduction of sediment yield, TN, and TP by VFS ranged from 8 to 12%, 71% to 98%, and 72% to 99% respectively and at watershed scale, reduction of sediment yield, TN, and TP by VFS ranged from 12 to 38%, 29% to 87%, and 42% to 99% respectively. The application of conservation and zero tillage operation showed reduction in sediment yield by 1% to 2% respectively but increased TN and TP by 2% to 25% at field and watershed scale watersheds. This study will help in managing water at field and watershed scale watersheds regarding BMPs selection and implementation.Graphical

Evaluating Streamwater Dissolved Organic Carbon Dynamics in Context of Variable Flowpath Contributions With a Tracer‐Based Mixing Model

AbstractThis study focuses on characterizing the contributions of key terrestrial pathways that deliver dissolved organic carbon (DOC) to streams during hydrological events and on elucidating factors governing variation in water and DOC fluxes from these pathways. We made high‐frequency measurements of discharge, specific conductance (SC), and fluorescent dissolved organic matter (FDOM) during 221 events recorded over 2 years within four Vermont (USA) watersheds that range in area from 0.4 to 139 km2. Using the SC measurements, together with statistical information on discharge, we separated the event hydrographs into contributions from three terrestrial pathways, which we refer to as riparian quickflow, subsurface quickflow, and slow‐flow groundwater. The pathway discharges were used as input to a mixing model that closely approximated sub‐hourly streamwater DOC concentrations as measured with the FDOM sensors. Subsurface quickflow, comprised of pre‐event water, was the leading contributor to streamwater DOC fluxes, while riparian quickflow, comprised of event water, was the second‐leading contributor to streamwater DOC fluxes, despite comprising the smallest proportion of streamflow yield among the three end‐member pathways. Fixed‐effects regression analysis revealed that the relationship between DOC fluxes from the end‐member pathways and event magnitude was consistent across the four watersheds. This analysis also showed that DOC fluxes from the quickflow pathways increased significantly with temperature and varied inversely, but weakly, with catchment antecedent wetness. We believe that our approach, which leverages in‐stream sensors that enable high‐frequency measurements over extended periods, may be applicable for evaluating controls on DOC export from other watersheds within and beyond our study region.

Modelling streamflow and sediment yield using Soil and Water Assessment Tool: a case study of Lidder watershed in Kashmir Himalayas, India

Abstract The conjunction of heavy snowfall during winters and intensive rainfall during monsoons along with the mountainous topography expose the Lidder watershed to serious erosion and flood aggravation issues. Barely any attempts have been made for an in-depth examination of the Lidder watershed for precise estimation of sub-basin level runoff and erosion. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated using the Sequential Uncertainty Fitting algorithm (SUFI-2) for modelling streamflow and sediment yield of the Lidder watershed. Daily runoff and sediment event data from 2003–2013 were used in this study; data from 2003–2008 was used for calibration and 2009–2013 for validation. Model performance was evaluated using various statistical tools, which showed good results revealing excellent potential of the SWAT model to simulate streamflow and sediment yield for both calibration and validation periods. The annual rate of average upland sediment drawn from the watershed was approximately 853.96 Mg/ha for an average surface runoff of 394.15 mm/year. This study identifies the vulnerable areas of the Lidder watershed, which can be thoroughly examined by decision-makers for effective management and planning. Further, the calibrated model can be applied to other watersheds with similar characterization to influence strategies in the management of watershed processes.

Review of Yield Comparison Options for Planning Irrigation Reservoirs in Ungauged Watersheds

Irrigation reservoir design is often associated with ungauged watersheds. Irrigation system planners have the option of selecting either traditional institutional guidelines or more recently calibrated and verified hydrologic models to compute watershed yield. A design watershed yield is the key for sustainable irrigation reservoir development. Design values not only should lead to reliable estimates but also require the incorporation of safety factors for both rainfall uncertainty and modelling uncertainties. Empirical design yield calculation options in guidelines require explicit rationalization to determine appropriate design levels. Use of popular watershed models , developed and calibrated with other datasets, too requires the guidance to convert the estimations as design watershed yield with the use of safety factors. Therefore, both options need to clearly express the reliability of yield estimations and the associated safety factors for a sustainable practice of water management. Comparison of available alternatives in the light of methods and incorporation of safety is a necessity to select the appropriate option for water resources design in ungauged watersheds. Accordingly, the objective of the present work is to carry out a critical review of available methods to recommend a selection for estimation of streamflow yield from ungauged watersheds. A comprehensive literature review is carried out considering available text books, guidelines and other literature. The study looked at the runoff estimation methods, strengths and difficulties, incorporation of safety factors etc., when deriving design watershed yield from watershed yield. The review of 110 related documents revealed that, although there is literature on models for the estimation of watershed yield, there is a gap in the applicability at various locations and in the conversion to design watershed yield. Irrigation Department Sri Lanka has reported the most detailed direct yield model with threshold considerations. Unit Hydrograph model has many text book references while HEC HMS is the most commonly cited process-based model for runoff estimations. The review shows that, amidst the drawbacks in the present documentation, the best available optionfor a practicing engineer to compute design watershed yield is to use a similar approach that is indicated in the guidelines of Irrigation Department of Sri Lanka. There is an urgent necessity to verify guideline recommended design watershed yield estimation methods by using observed data and take measures to incorporate explicit safety factors.

Impact of Climate Change on the Spatiotemporal Distribution of Stream Flow and Sediment Yield of Darbandikhan Watershed, Iraq

The impact of climate change on stream flow and sediment yield in Darbandikhan Watershed is an important challenge facing the water resources in Diyala River, Iraq. This impact was investigated using five Global Circulation Models (GCM) based climate change projection models from the A1B scenario of medium emission. The Soil and Water Assessment Tool (SWAT) was used to compute the temporal and spatial distribution of streamflow and sediment yield of the study area for the period 1984 to 2050. The daily-observed flow recorded in Darbandikhan Dam for the period from 1984 to 2013 was used as a base period for future projection. The initial results of SWAT were calibrated and validated using SUFI-2 of the SWAT-CUP program in daily time step considering the values of the Nash-Sutcliffe Efficiency (NSE) coefficient of determination (R2) as a Dual objective function. Results of NSE and R2 during the calibration (validation) periods were equal to 0.61 and 0.62(0.53 and 0.68), respectively. In addition, the average future prediction for the five climate models indicated that the average yearly flow and sediment yield in the watershed would decrease by about 49% and 44%, respectively, until the year 2050 compared with these of the base period from 1984 to 2013. Moreover, spatial analysis shows that 89.6 % and 90 % of stream flow and sediment come from the Iranian part of Darbandikhan watershed while the remaining small percent comes from Iraq, respectively. However, the middle and southern parts of Darbandikhan Watershed contribute by most of the stream...

Hydrological Impacts of Climate Change in Tikur Wuha Watershed, Ethiopian Rift Valley Basin

According to Intergovernmental Panel on Climate Change (IPCC) rising of global surface temperature, sea level rises, arctic and land ice decrease, erratic precipitation and increase of CO2 concentration are the main indicators of climate change. The main objectives of the study was to investigate the possible hydrological impacts of climate change on stream flow and sedimentation in Tikur Wuha watershed, by downscaling canESM2 (Canadian Earth System Model of second generation) global climate model using Statistical Downscaling Model (SDSM). Based on IPCC recommendation baseline periods (1987–2016) were used for baseline scenario analysis. Future scenario analysis was performed for the 2020s, 2050s, and 2080s. canESM2 model consists of Representative Concentration Pathway (RCP) RCP2.6, RCP4.5 and RCP8.5 scenarios. Impact assessment on stream flow and sediment yield was done by Soil and Water Assessment Tool (SWAT) hydrological model. SWAT model performance in simulating monthly stream flow for the study area was satisfactory with R 2 (0.77 and 0.87), N SE (0.70 and 0.77) and D (-16 and -9) for calibration and validation periods respectively. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for all three scenarios; RCP2.6, RCP4.5 and RCP8.5 scenarios. These increases in climate variables are expected to result in increase in mean annual stream flow of 8%, 13%, and 15 % for RCP2.6 scenario, 17%, 24%, and 31% for RCP4.5 scenario and 14%,24% and 35% for RCP8.5 scenario for the 2020s, 2050s, and 2080s, respectively. This leads to increment of sediment yield from different sub watershed. The estimated soil loss rate from different sub-watersheds had ranged from 0.42 tons/ha/yr to 28.31 tons/ha/year (1987-1999), whereas the annual weighted average soil loss rate from the watershed was estimated 16.80 tons/ha/year (2000-2100). Future work need to consider studying the effects of different climate change adaptation strategies. Keywords: Climate change Scenarios, Ethiopia, Hydrological impact, SWAT model DOI: 10.7176/JEES/10-2-04 Publication date: February 29 th 2020

Evaluation of the Performance of SWAT Model to Simulate Stream Flow of Mojo River Watershed: In the Upper Awash River Basin, in Ethiopia

The assessment of the accessibility of water in the basin and significance setting of its use is essential before planning for the expansion and development of additional sectors which poses pressure on water availability. The main purpose of this study was to evaluate the performance of SWAT model to simulate stream flow of Mojo River. The performance evaluation of the model was to obtain the water balances was conducted. In this study both secondary and primary data were used. The SWAT model was used for data analysis. In this study for stream flow yield simulation the parameters involving surface runoff (CN2.mgt) and ground water (ALPHA_BNK.rte was found to be the most sensitive parameters. A good agreement between observed and simulated discharge were observed, which was verified using both graphical technique and quantitative statistics. The value of R2=0.80, NSE=0.75, RSR=0.5 and PBIAS=-10.6 obtained during calibration and R2 value 0.76, NSE value 0.69, RSR value 0.56 and PBIAS -14.4 obtained during validation as well as the uniformly scatter points along the 1:1 line during calibration and validation justify that the model is very good in simulating observed steam flow. From the results the total annual surface water available yields is estimated around 0.401Billion Cubic Meters (BCM).

A case study for the assessment of the suitability of gridded reanalysis weather data for hydrological simulation in Beas river basin of North Western Himalaya

The major problem of estimating snowmelt runoff for Beas river basin is inadequacy of observed meteorological data distributed across the basin. In this study, ERA-Interim global reanalysis data have been used for assessing the stream flow and sediment yield in Beas river basin of North Western Himalaya. The snow module of ARCSWAT hydrology model has been simulated by integration of subbasin-wise elevation band files for modeling snowmelt runoff process including sediment yield due to rainfall and temperature change for different elevation bands varying from 361 to 6188 m. The gridded reanalysis (0.125° × 0.125°) dataset produces a decreased maximum and minimum temperature and increased precipitation at higher elevation in comparison with IMD gridded weather data. The outcome of this study conveys that the reanalysis data represent better snowmelt runoff (NSE = 0.76, 0.70 and R2 = 0.80, 0.70) and sediment yield (NSE = 0.50, 0.53 and R2 = 0.72, 0.57) mechanism at Pong and Pandoh dams than IMD gridded weather data (NSE = 0.50, 0.47 and R2 = 0.65, 0.60) for stream flow and (NSE = 0.50, 0.53 and R2 = 0.65, 0.60) sediment yield during the period 1996–1999 and 1999–2002 for these two locations.

Impacts of land use/land cover change on stream flow and sediment yield of Gojeb watershed, Omo-Gibe basin, Ethiopia

Land use/land cover (LULC) change is an important landscape process capable of altering the fluxes of water, sediment, contaminants and energy. In this study, Soil and Water Assessment Tool (SWAT) model was used to examine the effects of LULC on the hydrological process of Gojeb Watershed in the Omo-Gibe basin. The performance of the model was evaluated through sensitivity, uncertainty analysis, calibration and validation. The LULC change analyses for three periods (1989, 2000 and 2013) were performed using ERDAS Imagine 2014 with a maximum likelihood classifier. The time series LULC changes results were used for estimation of stream flow and sediment yield. The result has shown that during the study period most parts of the forest land were converted into cultivated land with an increase of cultivated land by 14.97% over the study periods which resulted in an increase of stream flow and sediment yield by 8.6 m3/s and 41.07ton/km2 respectively. The Nash sutcliff efficiency (NSE), coefficient of determination (R2) and percent of bias (PBIAS) were used for evaluating the model performance. The model results have shown a good agreement with the observed values with NSE > 0.75, R2 > 0.78, and PBIAS < 0.5 values. Based on the validated sediment yield results of 2013 land use, high potential source of spatial variability of sediment was found at middle and downstream of the watershed. Hence, for the critical sub-watersheds, the design and development of three best management practices (BMPs) were performed. These best management scenarios include: S1 (filter strip), S2 (terrace/ bund) and S3 (reforestation). Based on these scenarios, the findings have shown a sediment yield reductions by 22.9%, 29.4% and 32.3% with the implementation of S1, S2 and S3 respectively. Therefore, based on the findings, implementing S3 is the best management strategy as compared to other options and hence, such intervention should be encouraged at a wider scale for efficient sediment reductions of Gojeb watershed.

SIMULATION OF SEDIMENT YIELD AT THE UPSTREAM WATERSHED OF JEBBA LAKE IN NIGERIA USING SWAT MODEL

In this study, we focused on the applicability and suitability of Soil and Water Assessment Tool (SWAT) embedded in Geographical Information Systems (GIS) environment in the prediction of sediment yield of a watershed (12,992km2 ). The watershed is drained by Rivers Niger, Kontagora, Awun and Eku and is located at the upstream of Jebba Reservoir in north central Nigeria . SWAT was run daily for 26 years (1985 to 2010 ) using climatic data representing three weather stations located within the watershed. The model was calibrated and validated using measured flow data from 1990 to 1995. Also due to the unavalilability of observed sediment data for the area, sediment samples were collected from three locations in the watershed from May to December, 2013 using suspended sediment sampler USDH-2A. The sediment samples were analysed and used to spatially calibrate and validate the model. The model was statistically evaluated using coefficient of determination, R 2 and Nasch-Sutcliffe Efficiency, NSE. Evaluation of the model revealed that it performed satisfactorily for stream flow and sediment yield predictions in the watershed. The model predicted the annual sediment yield in the watershed as 255.8 tons/ha/yr producing about 8.31x 109 tons of sediment between 1985 and 2010. Sediment concentration (mg/l) in the reach during the period of simulation showed that the highest sediment concentration was obtained in subbasins 29, 20 and 19 with values 446.3, 376.8 and 365.4 mg/l respectively. However, lowest sediment concentration occurred in subbasin 73 with a value of 108.6 mg/l. The results from the study showed that a properly calibrated SWAT embedded in GIS environment is suitable for modelling the hydrology and predicting the sediment yield in a watershed. In the light of this, SWAT can be adopted by water engineers and hydrologists in Nigeria and other sub sahara Africa countries in the region as a decision support tool to assist policy makers in achieving sustainable sediment and water management at watershed level.

On the Sensitivity of Hillslope Runoff and Channel Transmission Losses in Arid Piedmont Slopes

AbstractChannel transmission losses alter the streamflow response of arid and semiarid watersheds and promote focused groundwater recharge. This process has been primarily studied in dryland channels draining large areas that are displaced away from hillslope runoff generation. In contrast, small watersheds on arid piedmont slopes allow the investigation of interactive hillslope and channel processes that control the partitioning between surface and subsurface flows. In this study, we utilize high‐resolution, long‐term measurements of water balance components in an instrumented watershed of the Chihuahuan Desert to set up, parameterize, and test a process‐based, distributed hydrologic model modified to account for channel losses. A transient method for capturing capillary effects in channels results in simulations with a reliable representation of the watershed energy balance, soil moisture dynamics, hillslope infiltration, channel transmission (or percolation) losses, and streamflow yield over the study period. The simulation also reproduces a conceptual model of hillslope infiltration‐excess runoff generation linked to downstream channel percolation losses that depend on the rainfall event size. Model‐derived thresholds were obtained for the amount of hillslope runoff (6 mm) and rainfall (12.5 mm) necessary for streamflow yield, such that 40% of percolation occurs for small events that do not reach the outlet. Using a set of scenarios, we identify that hillslope infiltration controls the rainfall threshold necessary to initiate percolation, while channel infiltration affects the partitioning into percolation and streamflow yield. Thus, the connectivity along hillslope‐channel pathways is deemed an essential control on the streamflow generation and groundwater recharge in arid regions with complex terrain.

Predicting future land cover change and its impact on streamflow and sediment load in a trans-boundary river basin

Abstract. Sediment load can provide very important perspective on erosion of river basin. The changes of human-induced vegetation cover, such as deforestation or afforestation, affect sediment yield process of a catchment. We have already evaluated that climate change and land cover change changed the historical streamflow and sediment yield, and land cover change is the main factor in Red river basin. But future streamflow and sediment yield changes under potential future land cover change scenario still have not been evaluated. For this purpose, future scenario of land cover change is developed based on historical land cover changes and land change model (LCM). In addition, future leaf area index (LAI) is simulated by ecological model (Biome-BGC) based on future land cover scenario. Then future scenarios of land cover change and LAI are used to drive hydrological model and new sediment rating curve. The results of this research provide information that decision-makers need in order to promote water resources planning efforts. Besides that, this study also contributes a basic framework for assessing climate change impacts on streamflow and sediment yield that can be applied in the other basins around the world.