Semi-distributed Watershed Model Research Articles

가뭄이 농업유역의 하천 유량에 미치는 영향 분석: 준분포형 유역모델 STREAM의 논산천 유역 적용 사례

금강하구유역은 한반도의 중부지방에 위치하며, 상류는 산림지역, 중하류는 농업지 하천의 유량은 하천 수질과 수생태계 건강성에 영향을 미치는 주요 요소이기 때문에 가뭄이나 과도한 관개로 인한 하천 유량의 감소는 매우 심각한 수생태계 위해요인으로 작용할 수 있다. 본 연구에서는 준분포형 유역모델 STREAM을 이용하여 논산천 유역을 대상으로 가뭄 시기의 하천유량 변화 경향과 그 원인을 분석, 평가하였다. 논산천 유역은 유역면적의 약 44.5%가 농업지역으로 2015년에 심각한 가뭄의 영향을 받았다. 논산천 유역에서 2015년의 강우량과 하천유량은 2011년과 비교하여 각각 42.5%, 17.5% 수준으로 감소하였다. 한편, 2011년과 비교하여, 2015년 하천에서 취수된 관개용수는 43.4% 증가하였다. 즉, 2011년과 비교하여 2015년 강우량의 감소폭보다 하천유량의 감소폭이 25.0% 더 큰 것은 하천의 관개용수 취수량이 증가하고, 논의 유출량이 감소하였기 때문인 것으로 분석되었다.

유역모델 STREAM을 이용한 강우조건에 따른 금강하구 유입 오염부하량 산정

유역모델 STREAM을 이용한 강우조건에 따른 금강하구 유입 오염부하량 산정

Comprehensive simulation of nitrate transport in coupled surface-subsurface hydrologic systems using the linked SWAT-MODFLOW-RT3D model

This paper presents SWAT-MODFLOW-RT3D, a model that couples the semi-distributed watershed model SWAT (Soil and Water Assessment Tool) with the groundwater flow model MODFLOW and the groundwater solute reactive transport model RT3D to simulate nitrate (NO3) fate and transport in a watershed system. The model is based on a recently developed SWAT-MODFLOW model, with RT3D now called as a subroutine within the MODFLOW code to provide a single, stand-alone model code. RT3D uses NO3 concentration of deep percolation water from SWAT and groundwater heads and flows from MODFLOW to simulate spatially-varying groundwater NO3 concentration and NO3 loading to/from streams, with the latter used by SWAT to route NO3 mass through the network. Model use is demonstrated through an application to the Sprague River Watershed (4100 km2) in Oregon. Other chemical species of interest can be included in the RT3D reaction module in applications of the model to other watersheds.

Watershed modeling for reducing future non-point source sediment and phosphorus load in the Lake Tana Basin, Ethiopia

Agricultural intensification to meet the food needs of the rapidly growing population in developing countries affects water quality. In regions such as the Lake Tana basin, knowledge is lacking on measures to reduce non-point source pollutants in humid tropical monsoon climates. The aim of this paper was, therefore, to develop a non-point model that can predict the placement of practices to reduce the transport of sediment and phosphorus (P) in a (sub) humid watershed. In order to achieve the objective, hydrometeorological, sediment, and P data were collected in the watershed since 2014. The parameter efficient semi-distributed watershed model (PED-WM) was calibrated and validated in the Ethiopian highlands to simulate runoff and associated sediments generated through saturation excess. The P module added to PED-WM was used to predict dissolved (DP) and particulate P (PP) loads aside from discharge and sediment loads of the 700 ha of the Awramba watershed of Lake Tana basin. The PED-WM modules were evaluated using the statistical model performance measuring techniques. The model parameter based prediction of source areas for the non-point source sediment and P was also evaluated spatially and compared with the Topographic Wetness Index (TWI) of the watershed. The water balance component of the non-point source model performed well in predicting discharge, sediment, DP, and PP with NSE of 0.7, 0.65, 0.65, and 0.63, respectively. In addition, the predicted discharge followed the hydrograph with insignificant deviation from its pattern due to seasonality. The model predicted a sediment yield of 28.2 t ha−1 year−1 and P yield of 9.2 kg ha−1 year−1 from Awrmaba. Furthermore, non-point source areas contributed to 2.7 kg ha−1 year−1 (29%) of DP at the outlet. The main runoff and sediment source areas identified using PED-WM were the periodically saturated runoff areas. These saturated areas were also the main source for DP and PP transport in the catchment. Using the PED-WM with the P module enables the identification of the source areas as well as the prediction of P and sediment loading which yields valuable information for watershed management and placement of best management practices.

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.

Modeling Climate and Management Change Impacts on Water Quality and In-Stream Processes in the Elbe River Basin

Eco-hydrological water quality modeling for integrated water resources management of river basins should include all necessary landscape and in-stream nutrient processes as well as possible changes in boundary conditions and driving forces for nutrient behavior in watersheds. The study aims to assess possible impacts of the changing climate (ENSEMBLES climate scenarios) and/or land use conditions on resulting river water quantity and quality in the large-scale Elbe river basin by applying a semi-distributed watershed model of intermediate complexity (SWIM) with implemented in-stream nutrient (N+P) turnover and algal growth processes. The calibration and validation results revealed the ability of SWIM to satisfactorily simulate nutrient behavior at the watershed scale. Analysis of 19 climate scenarios for the whole Elbe river basin showed a projected increase in temperature (+3 °C) and precipitation (+57 mm) on average until the end of the century, causing diverse changes in river discharge (+20%), nutrient loads (NO3-N: −5%; NH4-N: −24%; PO4-P: +5%), phytoplankton biomass (−4%) and dissolved oxygen concentration (−5%) in the watershed. In addition, some changes in land use and nutrient management were tested in order to reduce nutrient emissions to the river network.

Examining the Possibilities: Generating Alternative Watershed-Scale BMP Designs with Evolutionary Algorithms

Recent studies in water resources planning and management show a gradual shift in the state of the art from numerous on-site structural stormwater Best Management Practice (BMP) designs to watershed-scale BMP design approaches that meet both target water quantity (peak flow) and quality (sediment reduction) criteria. Such regionally-strategic approaches are not only cost-effective but emphasize comprehensive, holistic watershed-scale management, an idea strongly promoted by the U.S. Environmental Protection Agency (US EPA) since the early 1990s. Implementing a watershed-scale design can prove difficult when decision-makers have differing and sometimes conflicting objectives. We present a methodology that integrates the semi-distributed watershed model Soil and Water Assessment Tool (SWAT) with an evolutionary algorithm, Species Conserving Genetic Algorithm (SCGA). In addition to identifying an optimal watershed-scale BMP design (e.g., type, size, location), SCGA simultaneously produces several near-optimal design alternatives using a user-specified distance metric. We demonstrate this decision-oriented framework on a watershed in southern Illinois. Results of this application yield several high-quality alternative designs appropriate for solving integrated watershed management problems.

Calibration and evaluation of a semi-distributed watershed model of Sub-Saharan Africa using GRACE data

Abstract. Irrigation development is rapidly expanding in mostly rainfed Sub-Saharan Africa. This expansion underscores the need for a more comprehensive understanding of water resources beyond surface water. Gravity Recovery and Climate Experiment (GRACE) satellites provide valuable information on spatio-temporal variability in water storage. The objective of this study was to calibrate and evaluate a semi-distributed regional-scale hydrologic model based on the Soil and Water Assessment Tool (SWAT) code for basins in Sub-Saharan Africa using seven-year (July 2002–April 2009) 10-day GRACE data and multi-site river discharge data. The analysis was conducted in a multi-criteria framework. In spite of the uncertainty arising from the tradeoff in optimising model parameters with respect to two non-commensurable criteria defined for two fluxes, SWAT was found to perform well in simulating total water storage variability in most areas of Sub-Saharan Africa, which have semi-arid and sub-humid climates, and that among various water storages represented in SWAT, water storage variations in soil, vadose zone and groundwater are dominant. The study also showed that the simulated total water storage variations tend to have less agreement with GRACE data in arid and equatorial humid regions, and model-based partitioning of total water storage variations into different water storage compartments may be highly uncertain. Thus, future work will be needed for model enhancement in these areas with inferior model fit and for uncertainty reduction in component-wise estimation of water storage variations.

Semiarid watershed response in central New Mexico and its sensitivity to climate variability and change

Abstract. Hydrologic processes in the semiarid regions of the Southwest United States are considered to be highly susceptible to variations in temperature and precipitation characteristics due to the effects of climate change. Relatively little is known about the potential impacts of climate change on the basin hydrologic response, namely streamflow, evapotranspiration and recharge, in the region. In this study, we present the development and application of a continuous, semi-distributed watershed model for climate change studies in semiarid basins of the Southwest US. Our objective is to capture hydrologic processes in large watersheds, while accounting for the spatial and temporal variations of climate forcing and basin properties in a simple fashion. We apply the model to the Río Salado basin in central New Mexico since it exhibits both a winter and summer precipitation regime and has a historical streamflow record for model testing purposes. Subsequently, we use a sequence of climate change scenarios that capture observed trends for winter and summer precipitation, as well as their interaction with higher temperatures, to perform long-term ensemble simulations of the basin response. Results of the modeling exercise indicate that precipitation uncertainty is amplified in the hydrologic response, in particular for processes that depend on a soil saturation threshold. We obtained substantially different hydrologic sensitivities for winter and summer precipitation ensembles, indicating a greater sensitivity to more intense summer storms as compared to more frequent winter events. In addition, the impact of changes in precipitation characteristics overwhelmed the effects of increased temperature in the study basin. Nevertheless, combined trends in precipitation and temperature yield a more sensitive hydrologic response throughout the year.

지표수-지하수 통합모형을 이용한 무심천 유역의 수문과정 해석

지표수와 지하수의 통합모델링은 지속가능한 수자원과 수질개선에 대한 점증하는 요구를 만족시키기 위해 점차 중요성을 더해가고 있다. 본 연구에서는 준분포형 유역유출모형인 SWAT과 완전분포형 지하수 모형인 MODFLOW의 통합모형을 무심천 유역에 작용하여 유역단위의 수문과정을 재생하였다. 모의결과 2001-2004년의 관측수문곡선과 모의유량수문곡선간의 적합이 잘 나타나는 한편 계산된 지하수위 분포와 관측지하수위와의 보정결과도 양호하게 나타났다. 통합모형은 서로 다른 기간의 강수평균이 하천유출, 침루, 함양, 지하수 유출의 동적과정에 미치는 영향을 평가하는데도 활용되었다. 나아가, 윌별강수와 각 수문성문간의 관계를 살펴보고 함양량의 시공간적 변동성을 분석하기 위한 종합적인 모의를 수행한 결과, 수문성분 상호간에 높은 상관성을 보이며 소유역경사, 토지이용, 토양종류 같은 유역특성의 비균질성이 함양량의 공간변화에 주요 원인인 것으로 확인됐다. 통합모형은 시공간적으로 변모하는 유역단위의 지표수와 지표하 수문과정을 전반적으로 잘 표현하는 것으로 나타났다. Integrated modelling of surface water and groundwater has become important to satisfy the growing demands for sustainable water resources and improved water quality. In this study, the integrated model of the semi-distributed watershed model, SWA T and the fully-distributed groundwater flow model, MODFLOW is applied to Musirn river basin for the purpose of investigating its applicability to reproduce watershed-scale hydrological processes. This objective is accomplished by first demonstrating good agreement between the simulated discharge hydrographs with the measured hydrographs for the period of 2001 -2004 while simultaneously calibrating the calculated groundwater level distribution to observation wells. Next, the integrated model is used to evaluate the effect of different temporal precipitation averages on hydrodynamic processes of streamflow, percolation, recharge and groundwater discharge. Moreover, comprehensive simulations are performed to present the relationships between monthly precipitation and each hydrological component, and to analyze the temporal-spatial variability of recharge. The results show that the components are highly interrelated, and that the heterogeneity of watershed characteristics such as subbasin slope, land use, soil type causes a significant spatial variation of recharge. Overall it is concluded that the model is capable of reproducing the temporally and spatially varied surface and subsurface hydrological processes at the watershed scale.

Multi-objective automatic calibration of SWAT using NSGA-II

This paper presents a diagnostic study on multiobjective, automatic calibration of a physically based, semi-distributed watershed model known as Soil and Water Assessment Tool (SWAT). Unlike lumped models, distributed models involve large number of calibration parameters, representing the spatial heterogeneity of inputs and various physical processes within a watershed. An automatic calibration routine is developed using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) that has been proved to be an effective and efficient multiobjective search technique in various applications. The automatic routine is capable of incorporating multiple objectives into the calibration process and also employs parameterization to help reduce the number of calibration parameters. In this study, SWAT is calibrated for daily streamflow and sediment concentration. Two calibration scenarios have been considered; the first scenario uses specific objective functions to fit different portions of the time series whereas in the second scenario, the calibration is performed using data from multiple gauging stations, simultaneously. In addition, two cases of parameter distribution have been considered in the second scenario during parameterization. The application results show that the approach is consistent and effective in estimating parameters of the model. The use of multiple objectives during the calibration process resulted in improved model performance and the second scenario, in particular, provided better results partly due to the respective location of the gauging stations within the watershed. Further distribution of parameters during parameterization also resulted in better sediment simulation.

Automatic Calibration and Predictive Uncertainty Analysis of a Semidistributed Watershed Model

Semidistributed models are commonly calibrated manually, but software for automatic calibration is now available. We present a two‐stage routine for automatic calibration of the semidistributed watershed model Soil and Water Assessment Tool (SWAT) that finds the best values for the model parameters, preserves spatial variability in essential parameters, and leads to a measure of the model prediction uncertainty. In the first stage, a modified global Shuffled Complex Evolution (SCE‐UA) method was employed to find the “best” values for the lumped model parameters. In the second stage, the spatial variability of the original model parameters was restored and a local search method (a variant of Levenberg–Marquart method) was used to find a more distributed set of parameters using the results of the previous stage as starting values. A method called “regularization” was adopted to prevent the parameters from taking extreme values. In addition, we applied a nonlinear calibration‐constrained method to develop confidence intervals for annual and 7‐d average flow predictions. We calibrated stream flow in the Etowah River measured at Canton, GA (a watershed area of 1580 km2) for the years 1983 to 1992 and used the years 1993 to 2001 for validation. The Parameter Estimator (PEST) software was used to conduct the two‐stage automatic calibration and prediction uncertainty analysis. Calibration for daily and monthly flow produced a very good fit to the measured data. Nash‐Sutcliffe coefficients for daily and monthly flow over the calibration period were 0.60 and 0.86, respectively. They were 0.61 and 0.87, respectively, for the validation period. The nonlinear prediction uncertainty analysis worked well for long‐term (annual) flow in that our prediction confidence intervals included or were very near to the observed flow for most years. It did not work well for short‐term (7‐d average) flows in that the prediction confidence intervals did not include the observed flow, especially for low and high flow conditions.

Integrated use of GIS-based field sampling and modeling for hydrologic and water quality studies

Enhancements to traditional catchment-scale water quality assessments can be realized by leveraging geographical information systems (GIS) for both field data collection and hydrologic and water quality (H/WQ) modeling. In this study, we describe a GIS-based data collection system for geo-referenced environmental sampling utilizing mobile, wireless and Internet technologies. Furthermore, sampled field data is combined with historical measurements within a GIS-based semi-distributed watershed model for simulating water quantity and quality in a large regional catchment. The GIS-based sampling and modeling system is intended to streamline water quality assessments as compared to current practices. We describe an application and field study in the Williams River, New South Wales, Australia designed to assess the impacts of point and non-point source pollution on water quality. Historical data were utilized for calibrating and validating the Hydrologic Simulation Program – Fortran (HSPF) with the BASINS GIS interface over the 1988–2000 period. Results from the study indicate that short-duration, spatially extensive field campaigns provide useful data for enhancing modeling studies based on historical measurements at sparse sites. In addition, the study suggests that the conjunctive use of data collection and modeling is a step towards real-time integration of field data in hydrologic and water quality modeling efforts.

A geomorphology-based semi-distributed watershed model

A semi-distributed watershed model was developed that conceptualizes the catchment as a cascade of nonlinear storage elements whose geometric dimensions are derived from the Horton–Strahler ordering of the stream network. Each storage element represents quick storm runoff over land or in a channel segment. The physically based groundwater submodel is parameterized through the application of the Brutsaert–Nieber recession flow analysis and it provides continuous baseflow separation. The model requires the calibration of seven parameters from a one year rainfall–runoff record. It was tested on the Mahantango Creek watershed in the Susquehanna River basin, Pennsylvania.

REMOTE SENSING ESTIMATES OF SNOW WATER EQUIVALENT FOR HYDROLOGIC MODELLING

Hydrological models are used by water managers and power utilities to simulate and to forecast streamflows. These models often use snow course data to estimate snow water equivalent over the basin. Passive microwave data from satellite may also be used to estimate areal snow water equivalent. Both methods involve assumptions as to the representativeness of the measured data. The paper compares the effectiveness of the two types of snow water equivalent data for simulating streamflow using a semi-distributed watershed model.