Streamflow Yield Research Articles

Impact of Land Use Change on Flow and Sediment Yields in the Khokana Outlet of the Bagmati River, Kathmandu, Nepal

Land use changes are a key factor for altering hydrological response, and understanding its impacts can help to develop a sustainable and pragmatic strategy in order to preserve a watershed. The objective of this research is to estimate the impact of land use changes on Bagmati river discharge and sediment yield at the Khokana gauging station of the Kathmandu valley outlet. This study analyzes the impact of land use changes from the year 2000 to 2010 using a semi-distributed hydrological, Soil Water Assessment Tool (SWAT) model. The Load Estimator (LOADEST) simulates sediment loads on limited available sediment data. Sensitivity analysis is performed using the ParaSole (Parameter Solution) method within SWAT Calibration and Uncertainty Procedure (SWAT-CUP), which shows that Linear parameters for calculating the maximum amount of sediment that can be re-entrained during channel sediment routing is a most sensitive parameter that affect the hydrological response of the watershed. Monthly discharge and sediment data from 1995 to 2002 are used for calibration and remaining monthly discharge and sediment data from 2003 to 2010 are used for validation. Four statistical parameters including the Coefficient of Determination (R2), Nash–Sutcliffe Efficiency (NSE), RMSE-observations’ standard deviation ratio (RSR), and Percentage Bias (PBIAS) are estimated in order to evaluate the model performance. The results show a very good agreement between monthly measured and simulated discharge data as indicated by R2 = 0.88, NSE = 0.90, RSR = 0.34, and PBIAS = 0.03. The model shows nearly the same performance also with sediment data. The land use change data shows about a 6% increase in built-up areas from the years 2000 to 2010, whereas the remaining areas such as Forest, Shrub, Grass, Agriculture, Open Field, and Rivers/Lakes are decreased. The surface runoff contribution to stream flow and sediment yields are increased by 27% and 5% respectively. In the contrary, lateral flow contribution to stream flow and groundwater contribution to stream flow are decreased by 25% and 21%, respectively.

Uncertainty Analysis and Calibration of Swat Model for Estimating Impacts of Conservation Methods on Streamflow and Sediment Yield in Thika River Catchment, Kenya

Despite their imperative role in water resources management, distributed hydrological models like SWAT require calibration that can be challenging due to uncertainties of parameters involved. Prior to modelling of hydrological processes, these parameters and their uncertainty range need to be identified. The objective of this study was to conduct uncertainty analysis of hydrological processes and to calibrate the Soil and Water Assessment Tool (SWAT) for stream flow and sediment yield modelling in Thika River catchment. Sequential Uncertainty Fitting program (SUFI-2) was used to conduct sensitivity and uncertainty analysis. Stream flow was calibrated and validated between the years 1998 to 2013 for gauging stations 4CB05 and 4CB04. Manual sediments calibration was achieved by constraining the MUSLE parameters using the bathymetric survey data. Two uncertainty indices, p and r factor, were obtained as 0.72 and 0.65, 0.65 and 0.45 during calibration and validation, respectively. Statistical performance indicators showed a good match between the observed and simulated values which indicated that the model was well calibrated for simulation of stream flow and sediments yield in the catchment.

Stream Flow and Sediment Yield Modeling: A Case Study of Beles Watershed, Upper Blue Nile Basin

Stream Flow and Sediment Yield Modeling: A Case Study of Beles Watershed, Upper Blue Nile Basin

Hydrological modelling of upper Ebonyi watershed using the SWAT model

In this study, soil and water assessment tool (SWAT) model was applied to the upper Ebonyi Watershed to simulate streamflow and sediment yield. Results of sensitivity analysis, model calibration and model validation showed that the SWAT model performed reasonably for this study area. Streamflow and sediment discharge predictions were calibrated and validated against the daily flow using observed data. The simulated daily flow fit the observed data for the calibrated period with R2, NSE and PBIAS values of 0.68, 0.58 and –0.871% respectively while the simulated daily sediment yield fit the observed data with R2, NSE and PBIAS values of 0.53, 0.51 and 24.11% respectively. For the validation period, the values of R2, NSE and PBIAS values are 0.747, 0.719 and 5.16% for streamflow while, the values of R2, NSE and PBIAS values are 0.647, 0.606 and 4.92% for sediment yield. Thus, SWAT is an effective tool for watershed management.

Modelling the impacts of structural conservation measures on sediment and water yield in Thika-Chania catchment, Kenya

Recently, there has been a growing need to implement soil and water conservation measures in order to control sediment and water yield from agricultural areas. The objective of this study was to use a modeling approach to evaluate the impacts of structural conservation measures on water and sediment yield from Thika Chania catchment in Central Kenya. The SWAT model was calibrated and validated for stream flow and sediment yield at a gauging station in the catchment. The calibrated model was run to create a base scenario for the simulation of structural conservation methods, i.e. terraces and grassed waterways. Model simulation results indicated that terraces and grassed waterways would significantly impact water and sediment yield at the catchment outlet. Terraces were found to provide the greatest reduction in sediment yield, by 81% from the baseline scenario, while grassed waterways reduced sediment yield by 54%. Terraces indicated a reduction in surface runoff by 30% from the base annual average value of 202 mm. This was attributed to the increased infiltration that was indicated by increase in base flow by 8%. However, grassed waterways did not indicate any significant reduction in water yield. The results of this study show that structural conservation measures could reduce sediment yield from cultivated areas by more than 50% at the sub catchment level. Results also indicated that the effectiveness of structural conservation measures can be increased by implementing more than one method. Structural conservation measures studied in the current study were found to have a positive impact in controlling water and sediment yield in the catchment. However, further studies need to be conducted to evaluate the costs and benefits of implementing them at a small scale.

Impact of Abandoned Opencast Mines on Hydrological Processes of the Olidih Watershed in Jharia Coalfield, India

The Olidih watershed hydrology was affected by opencast mines for the past five decades. This study explores the potential hydrological effect of these mines using Soil and Water Assessment Tool (SWAT2012). The calibration and validation of the model was performed using daily streamflow and sediment yield data (2005–2008) at the outlet of the water shed. The model performed satisfactorily during simulation when tested with statistical indicators. The alternative scenario of no-mines was also modelled to assess the potential impact of abandoned opencast mines for the period 2005–2010. Results show that the abandoned opencast mines play a crucial role in altering hydrological processes of the watershed with 16% increase in the annual sediment yield and reduction of 51% and 6% in annual surface flow and water yield, respectively. This may be due to surface soil disturbance and accumulation of surface runoff in large depressions that resulted in less surface runoff and 13% more groundwater flow. The contribution of this analysis is the application of SWAT in modelling potential hydrological effect of abandoned opencast mines by defining large opencast mines as pothole during simulation.

Modeling stream flow and sediment yield using the SWAT model: a case study of Ankara River basin, Turkey

The Soil and Water Assessment Tool (SWAT) was tested for prediction of stream flow and sediment yield in the Ankara basin, Turkey. The overall objective of this study was to evaluate the performance and applicability of the SWAT and generate a soil erosion map. Thirteen years of daily/monthly flow and monthly sediment data were used for calibration and validation. Model performance was evaluated using statistical measures to assess the applicability of the model in simulating stream flow and sediment yield during calibration (1989–1996) and validation (1982–1984) periods. Nash Sutcliffe efficiency (NSE), relative error (RE), and R² (coefficient of determination) for daily flow were computed as 0.61, −0.55, and 0.78, respectively; and as 0.79, −0.58, and 0.89 for monthly flow during the calibration. Statistical comparisons of sediment yield produced values for NSE, RE, and R² of 0.81, −1.55, and 0.93, respectively, during the calibration. The resulting map suggests that significant portions of urbanized and highly cultivated areas in the vicinity of stream channels are particularly vulnerable to soil erosion. SWAT satisfactorily simulated hydrology and sediment yield and can be used as a tool in decision-making for water resources planning in a basin with similar characteristics.

Sediment inflow estimation and mapping its spatial distribution at sub-basin scale: the case of Tendaho Dam, Afar Regional State, Ethiopia

Sedimentation is a major problem of reservoir operation in Ethiopia. Deforestation, overgrazing and poor land management practices are some that accelerate the rate of erosion. The topography of Ethiopia in general and TDW in particular is undulating and local farmers commonly cultivate on the hilly sides causing easy topsoil wash away. This study aims to determine the sediment yield at Tendaho dam reservoir, identify the high sediment source sub-basins and check the applicability of SWAT model in the area. To achieve these goals, the hydro-meteorological, sediment, topographic, land use and soil map data were used as inputs for the model. The model was successfully calibrated and validated for measured stream flow and sediment yield of AR at Wonji, Melka Werer and Tendaho stations. It was thus found applicable in this watershed with acceptable performance evaluation statistics values. From the model simulated output, sub-basins 27, 34, 29 and 50 were found to be the top four severely eroded sub-basins with average annual sediment yield of 26.66t/ha, 24.22t/ha, 23.79t/ha and 19.13t/ha, respectively. While, sub-basins 31, 18 and 21 were found to be the least sediment sources with annual averaged sediment yield of 0.02t/ha, 0.04t/ha and 0.04t/ha, respectively. In general, the results found in this study are very important inputs in selecting appropriate watershed management strategies and the methodologies used can also be valuable guides for the researchers in similar studies.Keywords: SWAT Model; Sediment yield modeling; Sub-basins; Tendaho reservoir

Prediction of sediment yield at storm period in Northwest Algeria

This paper studies the hydrodynamics and variability of stream flow and sediment yield in Wadi El Hammam, located in the semi-arid region of Algeria. In this location, hysteresis effects are obvious especially during high discharge periods. The sediment concentration and load maxima go several months before discharge maxima, while decreased sediment concentrations are noticed during the discharge peaks. In order to explain these phenomena, we have adopted a methodology that consists of finding a simple regression model capable of explaining the sediment load as a function of the water discharge measured at gauging stations of three rivers at various scales, e.g., annual and seasonal. Suspended sediment concentrations are measured during a 22-year period (1986/1987–2007/2008). The results have shown that the power model explains the greatest part of the variance (80%). The changes in sediment availability result in so-called hysteresis effects. In this work, we have described different loops: clockwise or positive hysteresis loops and anti- or counter-clockwise hysteresis loops. The analysis of the seasonal sediment yields has shown that the autumn season contributes a large proportion of the annual sediment yield (62%).

Effect of land use land cover dynamics on hydrological response of watershed: Case study of Tekeze Dam watershed, northern Ethiopia

Land use change is a very important issue considering global dynamics and their response to hydrologic characteristics of soil and water management in a catchment. A significant land use change has been observed in the Tekeze dam catchment. The main objective of this study was to estimate the potential impacts of the land use land cover (LULC) dynamics on hydrological response (stream flow and sediment yield). This was done by integrating SWAT model with GIS. The simulation and sensitivity analysis for each land use was done by dividing the catchment in to 47 sub-catchments and assigning HRUs based on multiple HRU definition. After a sensitivity analysis, calibration and validation of SWAT model, the impact of LULC dynamics on hydrological response were evaluated with three scenarios (climate of 2000s & 2008 LULC, climate of 2000s & 1986 LULC and climate of 1980s & 1986 LULC). In the Tekeze dam watershed, land cover change had a beneficial impact on modeled watershed response due to the transition from grass and shrub land to agricultural land. Simulation results for the Tekeze dam watershed indicates that increasing bare land and agricultural areas resulted in increased annual and seasonal stream flow and sediment yield in volumes. The mean annual stream flow was increased by 6.02% (129.20–137.74m3/s) and the impact on sediment yield amounts to an increase of 17.39% (12.54–15.18t/ha/yr) due to LULC dynamics. The hydrological response was more sensitive to LULC dynamics for the months of August to October than others in the year. These results demonstrate the usefulness of integrating remote sensing and distributed hydrologic models through the use of GIS for assessing watershed conditions and the relative impacts of land cover transitions on hydrologic response in a continuous manner.

Prediction of Stream Flow and Sediment Yield of Lolab Watershed Using SWAT Model

The SWAT model was used to estimate the runoff and sediment yield of Lolab watershed. The model was calibrated, validated, and assessed for evaluation to model ambiguity using Nash–Sutcliffe coefficient (NSE) and coefficient of determination (R2). Ten highly sensitive parameters were recognized for stream flow simulation of which CN2 (Initial SCS CN II value) factor was the most sensitive one and four highly sensitive parameters were recognized for sediment yield simulation of which SPCON (Linear parameters for sediment re-entrainment) was most sensitive one. The model was calibrated for a time period between 1993 to 2000 and validated from 2001 to 2004 for flow and sediment yield. The predicted and observed stream flow and sediment yields generally matched well. The results of the model calibration and validation showed reliable estimates of monthly stream flow (R2=0.74 and ENS=0.68) and yearly stream flow (R2=0.90 and ENS=0.68) during the calibration period and monthly stream-flow (R2=0.85 and ENS=0.83) and yearly stream-flow (R2=0.99 and ENS=0.91) during the validation period. For sediment yield, this study shows antremendous model efficiency of monthly sediment yield (R2=0.80 and ENS=0.79) and yearly sediment yield (R2=0.86 and ENS=0.78) during the calibration period and monthly sediment yield (R2=0.88 and ENS=0.86) and yearly sediment yield (R2=0.83 and ENS=0.58) during the validation period. This study showed that the SWAT model is competent of predicting sediment yields and hence can be used as a tool for water resources planning and management in the study watershed.

Assessment of the Influence of Rainfall and River Discharge on Sediment Yield in the Upper Tana Catchment in Kenya

Sediment yield in the Upper Tana Basin in Kenya has implications on the sustainability of Hydro-Electric Power (HEP) dams and water resources development projects. Therefore, a study was undertaken in the basin to establish the extent to which rainfall and river discharges influence the sediment yield in the catchment. The study was based on hydrological data obtained from the Water Resources Management Authority (WARMA) and Kenya Meteorological Department (KMD). The river discharge data was obtained from three RGS Maragua (4BE01), Gura (4AD01) and Tana Sagana (4BC02) and rainfall data was obtained from Sagana Fish Farm and Nyeri Ministry of Works for the of period 1960-2013.The study also applied the Soil Water Assessment Tool (SWAT) Model to determine the extent to which the model can be used to simulate streamflow and sediment yield in the basin. The results of the study showed that there is a significant variability in streamflow and sediment yield in the Upper Tana Basin. In the period between 1960 and 2015, the mean total annual river discharge of Tana Sagana was 128 m3s-1, and the maximum and minimum river discharges were 29.94 m3s-1 and 3.15 m3s-1, respectively. There was an indication of increasing trend in rainfall and subsequently sediment yield in the basin, which may be attributed to alteration of land use and climatic change. The results showed that SWAT model was quite good in simulating the variability of river discharge. The analysis revealed a poor relationship between sediment yield and rainfall. However, the relationship between rainfall and stream flow was strong with r value of 0.9 which is significant at p=0.05. Relationship between simulated and observed river discharge had a R2 of 0.442, r of 0.665 and NSE of -89.43. The relationship between simulated and observed sediment yield had a R2 of 0.733, r of 0.86 and NSE of 0.69. The results of this study showed that SWAT model can be used to predict sediment yield in the Upper Tana catchment. The model had good performance when daily rainfall, stream flow and sediment yield data were used. Thus, the model can be used to establish the relationship between rainfall, discharge, and sediment yield in a highly human-impacted tropical catchment area. The study puts also forward various recommendations on land and water resources management in the basin.

A dynamic multiple regression approach for quantifying the relative impact of precipitation variations and streamflow generation conditions on runoff

Based on the observed data of monthly precipitation and runoff from 1960 to 2011 in the catchment controlled by the Sandaohezi hydrological station, the double mass curve of precipitation-runoff and Kolmogorov–Smirnov dual sample test were applied to divide the years 1960–2011 into four periods: 1960–1979, 1980–1991, 1992–1999 and 2000–2011. And then, through several trial calculations, a water year of the catchment was divided into wet season and dry season, and the precipitation-runoff dynamic multiple regression (DMR) models were constructed for the four periods. The computed annual runoff values of the DMR models all passed the Fisher test. Besides, the four models' average residuals were all less than 14.15%, and the determination coefficients were all greater than 77.96%. Using the established models, we quantified to what extent the runoff was affected by precipitation variations and streamflow yield capability changes. The result showed that compared with the period of 1960–1979, the annual runoff in 1980–2011 decreased by 14.42% due to precipitation variations and by 23.11% due to streamflow generation condition changes. Furthermore, we found that the runoff of the dry season was dominantly related to the precipitation during the flood season in the previous year.

Identification and prioritization of subwatersheds for land and water management in Tekeze dam watershed, Northern Ethiopia

Sedimentation and/or soil erosion are huge problems that have threatened many reservoirs in the Northern Ethiopian highlands, particularly in the Tekeze dam watershed. This study has been conducted to identify and prioritize the most sensitive subwatersheds with the help of a semi-distributed watershed model (SWAT 2009) for improved management of reservoir sedimentation mitigating strategies at the watershed level. SWAT 2009 was chosen for this study due to its ability to produce routed sediment yield and identify principal sediment source areas at the selected point of interest. Based on a digital elevation model (DEM) the catchment was divided in to 47 subwatersheds using the dam axis as the main outlet. By overlaying land use, soil and slope of the study area, the subwatersheds were further divided in to 690 hydrological response units (HRUs). Model calibration (for the period of January 1996 to December 2002) and validation (for the period of January 2003 to December 2006) were carried out for stream flow rate and sediment yield data observed at Emba madre gage station. The results of model performance evaluation statistics for both stream flow and sediment yield shows that the model has a high potential in estimation of stream flow and sediment yield. Tekeze dam watershed has mean annual stream flow of 137.74m3/s and annual sediment yield of 15.17t/ha/year. Out of the 47 subwatersheds, 13 subwatersheds (mostly located in the north eastern and north western part of the catchment) were prioritized. The maximum sediment outflow of these 13 subwatersheds, ranges from 18.49 to 32.57t/ha/year and are characterized dominantly by cultivated land, shrub land & bare land with average land slope ranging from 7.9 to15.2% and with the dominant soil type of Eutric cambisols. These results can help to formulate and implement effective, appropriate and sustainable watershed management which in turn can help in sustaining the reservoir storage capacity of the dam.

Improved reservoir sizing utilizing observed and reconstructed streamflows within a Bayesian combination framework

AbstractReservoir sizing is a critical task as the storage in a reservoir must be sufficient to supply water during extended droughts. Typically, sequent peak algorithm (SQP) is used with observed streamflow to obtain reservoir storage estimates. To overcome the limited sample length of observed streamflow, synthetic streamflow traces estimated from observed streamflow characteristics are provided with SQP to estimate the distribution of storage. However, the parameters in the stochastic streamflow generation model are derived from the observed record and are still unrepresentative of the long‐term drought records. Paleo‐streamflow time series, usually reconstructed using tree‐ring chronologies, span for a longer period than the observed streamflow and provide additional insight into the preinstrumental drought record. This study investigates the capability of reconstructed streamflow records in reducing the uncertainty in reservoir storage estimation. For this purpose, we propose a Bayesian framework that combines observed and reconstructed streamflow for estimating the parameters of the stochastic streamflow generation model. By utilizing reconstructed streamflow records from two potential stations over the Southeastern U.S., the distribution of storage estimated using the combined streamflows is compared with the distribution of storage estimated using observed streamflow alone based on split‐sample validation. Results show that combining observed and reconstructed streamflow yield stochastic streamflow generation parameters more representative of the longer streamflow record resulting in improved reservoir storage estimates. We also generalize the findings through a synthetic experiment by generating reconstructed streamflow records of different sample length and skill. The analysis shows that uncertainty in storage estimates reduces by incorporating reconstruction records with higher skill and longer sample lengths. Potential applications of the proposed methodology are also discussed.

Simulation of hydrosedimentological impacts caused by climate change in the Apucaraninha River watershed, southern Brazil

Abstract. Climate change can cause significant modifications in hydrosedimentological processes. Climate projections indicate the occurrence of extreme events, in terms of precipitation, droughts, floods and temperature. By increasing temperatures and altering precipitation regimes, climate change is expected to affect sediment dynamics. Predictions of the effects of climate change on streamflow and sediment yield vary widely, depending on the geographical location and climate scenarios used. Mathematical modelling can be used to simulate the hydrosedimentological processes in watersheds and enable the simulation of climate change effects on sediment yield. This paper aims to simulate the impacts of climate change hydrosedimentological dynamics in the Apucaraninha River watershed (504 km²), southern Brazil, considering the climate change scenarios A2 (pessimistic about the emissions of greenhouse gases) and B2 (optimistic about the emissions of greenhouse gases), developed by the IPCC. The Soil and Water Assessment Tool (SWAT) was used to evaluate the impacts of climate projections on the sediment yield in the Apucaraninha River watershed. The model was calibrated and validated using daily streamflow and sediment data from 1987 to 2012. The model presented satisfactory fit to the observed data allowing the reproduction of the current hydrological conditions of the watershed. Based on the satisfactory results in calibration and validation, the climate scenarios A2 and B2 were inserted to simulate streamflow and sediment conditions for the period 2071–2100. The results for both scenarios indicate that simulations of both climate scenarios resulted in changes in hydrosedimentological dynamics in the Apucaraninha River watershed, mainly in terms of decrease in average sediment yield due to the reduction in precipitation amount and increase in evapotranspiration. Our results also indicate that every 1% change in precipitation has resulted in 2.8% change in soil erosion and 1.6% change in runoff under scenario A2, and 2.3% change in erosion and 1.1% in runoff under scenarios B2, thus suggesting that climate change tends to affect sediment yield more than streamflow, although seasonally both could be impacted in similar ways.

Rangeland watershed study using the Agricultural Policy/Environmental eXtender

Information on grazing land conservation practices and their effectiveness in controlling nonpoint source pollution and watershed health at the watershed/landscape scale is necessary for future planning and resource allocation. The objectives of this study were to test the ability of the Agricultural Policy/Environmental eXtender (APEX) model to simulate hydrologic and soil processes at the watershed scale and utilize the model to evaluate the benefit of rangeland in reducing sediment loading and the benefit of potential conservation practices within a rangeland watershed. The model was calibrated and validated for stream flow and sediment yield for two watersheds within the Cowhouse Creek Watershed in north-central Texas: Cowhouse Creek Watershed upstream of Pidcoke (CCUP) Watershed (1,178 km2 [290,966 ac]) and Clear Creek (CC) Watershed (57.3 km2 [14,153 ac]). Nash-Sutcliffe efficiencies for the watersheds ranged from 0.62 to 0.71 and 0.71 to 0.81 for monthly and annual stream flow, and from 0.51 to 0.84 and 0.60 to 0.84 for monthly and annual sediment yields, respectively. The percent errors ranged from −9.3% to 12.7% for stream flow and from −22.6% to 11.5% for sediment yield. In addition to APEX model calibration/validation, various modeling scenarios (e.g., cropland expansion and brush control/reduced grazing rate conservation practices) were derived and analyzed for the CCUP watershed. The cropland expansion scenario analysis (less than 0.1% continuous corn to 39% continuous corn) indicated that the current rangeland has the benefit of reducing sediment loading by 65%. Rangeland conservation practice scenario modeling identified substantial reductions in overland sediment losses for conversion of range brush to range grass on Evant soil areas, with an average reduction of 58.8% from treated areas. However, the sediment loading to the CCUP watershed outlet at Pidcoke was only reduced by 7% due to the low treated area of 6%. The reducing stocking rate scenario was less effective compared with brush removal since the current 10 ha cattle−1 (24 ac cattle−1) was not considered a heavy stocking rate. Reducing the current stocking rate to 15 ha cattle−1 (37 ac cattle−1) reduced sediment loading by 5%. This study shows that the APEX model is able to replicate measured stream flow and sediment yields for rangeland watersheds with satisfactory performance based on well-accepted statistical criteria.

Hydrospatial assessment of streamflow yields and effects of climate change: Snowy Mountains, Australia

Summary Hydrospatial analyses of catchment topographic indices for 112 unregulated (unimpaired) gauging stations show that mean catchment elevation is the primary control on annual precipitation, runoff depth, runoff coefficients and evapotranspiration in the Snowy Mountains. Catchments with mean elevations greater than 1850 m show a steep increase in yield over the trend for lower elevation catchments and have runoff coefficients greater than one. Precipitation undercatch because of high winds and winter snowfall is the cause for this unusual situation, with deep accumulations of blown and drifted snow contributing significantly to runoff from small, high elevation catchments. Climate change effects on precipitation, runoff, runoff coefficients and the timing of peak snowmelt discharges vary across an elevational gradient. Annual precipitation shows strongly significant declines of up to 11.0 mm yr −1 from 1944 to 2009, with the magnitude of precipitation declines increasing with increasing elevation. Lower elevation catchments show greater sensitivity to drought than higher elevation catchments, exhibiting sharp declines in annual runoff coefficients due to smaller average differences between evapotranspiration and precipitation, and switching from energy (demand) to supply (precipitation) limited water balances. Climate change effects on the timing of peak winter–spring (June to November) snowmelt discharges for the highest elevation gauged catchments in Australia are pronounced with average shifts toward earlier peak discharges of 6.2 and 4.0 days per decade for the Snowy and Geehi Rivers, respectively. A lapse rate model using elevation as a substitute for temperature change highlights the sensitivity of mean annual runoff coefficients in the Snowy Mountains to changes in mean annual temperature, declining by 15% and increasing by 17% per degree centigrade rise and fall, respectively. Runoff coefficient sensitivity is driven by elevation (temperature) driven controls on the proportion of precipitation falling as snow vs. rain, combined with decreasing evapotranspiration with increasing elevation. Temperature (elevation) driven decreases in evapotranspiration resulting from changes in rain–snow precipitation balances, widespread snowpack accumulation and largely treeless catchments dominated by alpine vegetation during cool phases of the last glacial cycle offer a simple but comprehensive explanation for the greater runoff volumes in the Murray-Darling basin from the SE Australian highlands preserved by palaeochannels considerably larger than present river systems.

Evaluating the impact of land use uncertainty on the simulated streamflow and sediment yield of the Seyhan River basin using the SWAT model

As a result of the increased availability of spatial information in watershed modeling, several easy to use and widely accessible spatial datasets have been developed. Yet, it is not easy to decide which source of data is better and how data from different sources affect model outcomes. In this study, the results of simulating the stream flow and sediment yield from the Seyhan River basin in Turkey using 3 different types of land cover datasets through the soil and water assessment tool (SWAT) model are discussed and compared to the observed data. The 3 land cover datasets used include the coordination of information on the environment dataset (CORINE; CLC2006), the global land cover characterization (GLCC) dataset, and the GlobCover dataset. Streamflow and sediment calibration was done at monthly intervals for the period of 2001-2007 at gauge number 1818 (30 km upstream of the Catalan dam). The model simulation of monthly streamflow resulted in good Nash-Sutcliffe efficiency (NSE) values of 0.73, 0.71, and 0.68 for the GLCC, GlobCover, and CORINE datasets, respectively, for the calibration period. Furthermore, the model simulated the monthly sediment yield with satisfactory NSE values of 0.48, 0.51, and 0.46 for the GLCC, GlobCover, and CORINE land cover datasets, respectively. The results suggest that the sensitivity of the SWAT model to the land cover datasets with different spatial resolutions and from different time periods was very low in the monthly streamflow and sediment simulations from the Seyhan River basin. The study concluded that these datasets can be used successfully in the prediction of streamflow and sediment yield.

Efeitos de cenários de uso do solo sobre o regime hidríco e produção de sedimentos na bacia do Ribeirão Concórdia - SC

O uso inadequado dos solos agrícolas vem causando a perda gradual da sua capacidade produtiva e a degradação dos recursos hídricos por sedimentos e poluentes. O uso do solo pode afetar os processos hidrológicos e a erosão do solo na bacia. O objetivo do trabalho foi simular diferentes cenários de uso do solo para a bacia hidrográfica do ribeirão Concórdia, utilizando o modelo SWAT, e analisar os efeitos dessas mudanças no fluxo de água e de sedimentos. Os cenários gerados foram agricultura, mata nativa e pastagem. A bacia está localizada no sul do Brasil e possui uma área de drenagem de 30,74 km². Na etapa de calibração, obteve-se coeficente de eficiência Nash-Sutcliffe mensais de 0,82 para escoamento e 0,83 para sedimento. O cenário mata nativa apresentou o maior decréscimo na vazão média, em relação ao cenário atual, cerca de 8,70%. O cenário agricultura produziu a maior taxa de produção de sedimentos, aproximadamente 3 vezes maior que o cenário atual.Observou-se que alterações no uso do solo impactam o regime e a disponibilidade hídrica da bacia.