SWAT Setup with Long-Term Detailed Landuse and Management Records and Modification for a Micro-Watershed Influenced by Freeze-Thaw Cycles

In the widely used soil and water assessment tool (SWAT), the standard hydrological response units (HRUs) delineation method has low spatial resolution with respect to model inputs and outputs and renders difficulties in using long-term detailed landuse and management records. In addition, the modified universal soil loss equation (MUSLE) uses a constant K-factor which cannot address seasonal variation in soil erodibility caused by freeze-thaw cycles in cold regions. The current study presents a simple method to incorporate detailed landuse and management inputs in SWAT. The method delineates HRUs based on field boundaries and associates each HRU with a particular field. As a result, long-term detailed records can be incorporated into the SWAT management files. In addition, the existing MUSLE in SWAT was modified by introducing a variable K-factor to address effects of freeze-thaw cycles on soil erosion for cold regions. This modified version of SWAT was calibrated and validated for an agricultural micro-watershed, i.e., Black Brook Watershed in New Brunswick, Canada. The results showed that, compared with the standard HRU-delineation method, field-based HRU-delineation method was able to improve landuse and management practice input accuracy for SWAT and save time and effort for long-term simulation, and provide high resolution outputs in the watershed. As a result, the field-based HRU-delineation method can facilitate decision making not only at the subbasin scale but also at the field scale. In addition, results showed that sediment loading simulation accuracy was improved with the modified-MUSLE compared with the original-MUSLE.     

一种高效的SWAT模型参数自动率定方法

本文分析了SWAT模型和PSO算法的原理,将PSO算法引入SWAT模型中,构建了新的SWAT模型参数自动率定模块,通过在天津蓟运河流域实例研究,发现该方法率定精度较高,收敛速度快,运行结果稳定,整体率定效果优于模型自带的参数率定模块。如果用改进后的模块在Linux平台开展自动率定,可以使模型自动率定效率提高到当前水平的7倍,适用于大型流域或长时间系列模拟。而PSO算法作为一种通用的优化算法,可广泛用于各种水文模型的参数率定。     

Spatial and Temporal Variabilities of Sediment Delivery Ratio

Sediment contribution of specific areas of a watershed is an important consideration, but one that is often overlooked, when developing watershed management plans. Understanding sediment delivery to the watershed outlet is one method for identifying high contribution areas. In this study, a new methodology for calculating individual subbasin sediment delivery ratio (SDR) was developed within the Soil and Water Assessment Tool (SWAT) for two Michigan watersheds. Subbasins with the greatest SDR had two defining characteristics: high erosion rates and close proximity to the watershed outlet. The impact of best management practice (BMP) implementation (no-tillage and Conservation Reserve Program) on sediment yield reduction at the watershed outlet was compared for two targeting methods (SDR and erosion rate). Identifying SDR of individual subbasins for implementation of BMPs is more effective method for addressing water quality concerns at the watershed outlet than the widely used targeting high risk erosion areas. Watershed SDR was found to be highly variable on a monthly basis, due to changes in sediment yield, which is in turn affected by factors such as precipitation and surface runoff. Finally, watershed SDR calculated using the physically-based SWAT model was compared to four empirically-based areal relationships with SDR. While some area methods reproduced the SWAT-SDR, the variations between areal methods indicate that more detailed physical characteristics should be considered in watershed SDR calculation.     

淤地坝对流域水沙影响模拟研究

使用SWAT模型,结合淤地坝特点对模型自带的水库模型进行修正来设置淤地坝模块,研究淤地坝对流域径流和输沙的影响,并在内蒙古十大孔兑之一的西柳沟流域进行模拟和验证.以1980-1990年为率定期、2006-2015年为验证期,龙头拐水文站模拟径流量和输沙量与实测值拟合较好,线性拟合系数R2和纳什效率系数ENS均超过0.6...     

基于SWAT模型的陕西沣河流域非点源污染模拟

随着工业点源的大幅治理和农业的快速发展,陕西沣河流域非点源污染负荷在总负荷中所占比重日益加大。本文应用SWAT模型,对沣河流域的径流、泥沙及营养盐污染负荷的产输出过程进行模拟计算。利用沣河干流秦渡镇水文站2001-2006年的实测月径流、泥沙和污染物数据进行了模型的率定和验证。验证结果表明:模型在沣河流域具有较好的适应性,可用于流域非点源污染的模拟计算。流域非点源污染产出时空分布结果表明:非点源负荷产出集中在汛期;流域中部长安区的五星、滦镇、子午地区,以及流域西部户县的草堂镇和秦渡镇,是非点源污染产出的关键区域。流域非点源污染控制措施效果模拟表明:采取水土保持措施、改进化肥施用方式、合理减少施肥量可以有效减少流域非点源污染负荷。     

Development and Integration of Sub-hourly Rainfall–Runoff Modeling Capability Within a Watershed Model

Increasing urbanization changes runoff patterns to be flashy and instantaneous with decreased base flow. A model with the ability to simulate sub-daily rainfall–runoff processes and continuous simulation capability is required to realistically capture the long-term flow and water quality trends in watersheds that are experiencing urbanization. Soil and Water Assessment Tool (SWAT) has been widely used in hydrologic and nonpoint sources modeling. However, its subdaily modeling capability is limited to hourly flow simulation. This paper presents the development and testing of a sub-hourly rainfall–runoff model in SWAT. SWAT algorithms for infiltration, surface runoff, flow routing, impoundments, and lagging of surface runoff have been modified to allow flow simulations with a sub-hourly time interval as small as one minute. Evapotranspiration, soil water contents, base flow, and lateral flow are estimated on a daily basis and distributed equally for each time step. The sub-hourly routines were tested on a 1.9 km² watershed (70% undeveloped) near Lost Creek in Austin Texas USA. Sensitivity analysis shows that channel flow parameters are more sensitive in sub-hourly simulations (Δt = 15 min) while base flow parameters are more important in daily simulations (Δt = 1 day). A case study shows that the sub-hourly SWAT model reasonably reproduces stream flow hydrograph under multiple storm events. Calibrated stream flow for 1 year period with 15 min simulation (R ² = 0.93) shows better performance compared to daily simulation for the same period (R ² = 0.72). A statistical analysis shows that the improvement in the model performance with sub-hourly time interval is mostly due to the improvement in predicting high flows. The sub-hourly version of SWAT is a promising tool for hydrology and non-point source pollution assessment studies, although more development on water quality modeling is still needed.     

基于SWAT的灌区分布式水文模型——Ⅰ.模型构建的原理与方法

针对中国南方丘陵水稻灌区水文特点,在对自然流域水文模型SWAT改进的基础上,构建了灌区分布式水文模型,改进了SWAT的灌溉水运动模块、稻田水分循环模块、稻田水量平衡各要素和产量模拟的计算方法,改变了陆面水文过程的计算结构,增加了渠系渗漏模拟模块及其对地下水的补给作用、塘堰的灌溉模块等。以湖北省漳河灌区内的一个闭合小流域为例,对构建的灌区分布式水文模型进行校正和验证,模拟结果显示,该模型适合于水稻灌区水分循环的模拟。     

Application of dynamic contributing area for modelling the hydrologic response of the Assiniboine River Basin to a changing climate

The Prairie landscape consists of numerous pothole depressions which produce complex fill-and-spill runoff generation processes that result in intermittent hydrologic connectivity and dynamic contributing areas (DCA). We investigated the effect of including DCA in the modified version of the Soil and Water Assessment Tool (SWAT) model and its implication on future streamflow projection for the pothole dominated Assiniboine River Basin (ARB). The fill-and-spill processes that lead to DCA were captured using a physically-based approach, with a volumetric threshold to reduce the computational demand. Despite the challenges in accurately simulating prairie pothole hydrology, both in terms of timing and volume of runoff, the modified approach improved streamflow modelling performance, and reduced model uncertainty. Further, we evaluated the effects of representing DCA on projecting future streamflow by using eight statistically downscaled CMIP5 GCMs, forced with the RCP4.5 and RCP8.5 scenarios. End of century projections indicate increases in annual precipitation and temperature across the ARB, with decreasing summer precipitation relative to the 1976–2005 baseline period. Compared to the standard SWAT setup that does not allow for DCA, the modified model was found to be more responsive to climatic change with relatively larger projected increases in seasonal and annual flows at the majority of evaluated stations. This advance in DCA modelling will facilitate longer-term large basin-scale simulations that are more representative for the Prairie region.     

The Improvement in GWLF Model Simulation Performance in Watershed Hydrology by Changing the Transport Framework

The correct and reasonable delineation of actual hydrologic processes is a footstone for the effective simulation of pollutants in watershed models. In this study, a simple but comprehensive semidistributed modeling approach based on the generalized watershed loading function (GWLF) was modified to enable the accurate simulation of hydrology in watersheds. The frame of the original GWLF model (ORM), with a lumped hydrological parameter, was modified by adding channel routing processes, which made it possible to introduce the concept of subbasins. Then, the revised GWLF model was applied to the Luanhe watershed (30,000 km²) on a monthly bias in comparison with the ORM and the previously revised version. The sensitivity analysis and generalized likelihood uncertainty estimation (GLUE) uncertainty analysis were individually conducted to evaluate these modifications. Eventually, we compared four extreme conditions for the daily streamflow simulations of the three model versions in the Tunxi watershed but without calibration. All of the results indicated that the stability and accuracy of the model and the validity of the parameters were all enhanced and improved by the new revised version of the model, which provided reliable simulation results and indicated that it is a prospective tool to support watershed management.

     

基于物理过程的分布式流域水沙预报模型

将分布式水文模型与土壤侵蚀产沙模型相互嵌套,构建了一个分布式流域水沙预报模型。模型基于DEM,将流域离散为“坡面+ 沟道”系统,采用“+ 1 ”分级方法将沟道组织为河网,实现了流域水沙预报的并行计算。坡面单元划分为植被层、地表层、非饱和带和地下水层,模拟了降雨、截留、蒸散发、入渗、地表径流、壤中流和地下水、各种形式的侵蚀产沙及泥沙输移;沟道进行汇流演算以及泥沙输移。模型在李子溪流域对长系列降雨的模拟结果表明,模型的水文模块模拟精度良好,侵蚀产沙模块模拟效果基本令人满意。     

Application of the Soil and Water Assessment Tool for six watersheds of Lake Erie: Model parameterization and calibration

The Soil and Water Assessment Tool (SWAT), a physically-based watershed-scale model, holds promise as a means to predict tributary sediment and nutrient loads to the Laurentian Great Lakes. In the present study, model performance is compared across six watersheds draining into Lake Erie to determine the applicability of SWAT to watersheds of differing characteristics. After initial model parameterization, the Huron, Raisin, Maumee, Sandusky, Cuyahoga, and Grand SWAT models were calibrated (1998-2001) and confirmed, or validated (2002-2005), individually for stream water discharge, sediment loads, and nutrient loads (total P, soluble reactive P, total N, and nitrate) based on available datasets. SWAT effectively predicted hydrology and sediments across a range of watershed characteristics. SWAT estimation of nutrient loads was weaker although still satisfactory at least two-thirds of the time across all nutrient parameters and watersheds. SWAT model performance was most satisfactory in agricultural and forested watersheds, and was less so in urbanized settings. Model performance was influenced by the availability of observational data with high sampling frequency and long duration for calibration and confirmation evaluation. In some instances, it appeared that parameter adjustments that improved calibration of hydrology negatively affected subsequent sediment and nutrient calibration, suggesting trade-offs in calibrating for hydrologic vs. water quality model performance. Despite these considerations, SWAT accurately predicted average stream discharge, sediment loads, and nutrient loads for the Raisin, Maumee, Sandusky, and Grand watersheds such that future use of these SWAT models for various scenario testing is reasonable and warranted.     

昆明市松华坝水源区小流域土壤侵蚀分析

以1993-2009年松华坝水源区及昆明市的气象资料、2009年土地利用资料、第二次全国土壤普查资料、水源区牧羊河小流域的径流和泥沙观测资料为基础,用SWAT模型模拟分析了牧羊流域土壤侵蚀的空间差异。结果表明：牧羊河小流域输沙在年际上表现为与年降水量和输沙量峰谷变化具有较好的一致性,在年内表现出,输沙主要集中在6-9月;空间上牧羊河土壤侵蚀模数多年平均值介于21.4~4 586.5 t/(km²·a),且以中轻度为主,土壤侵蚀模数的空间变化与土地利用类型和地形坡度密切相关;土壤侵蚀模数与降水在年际变化上有较好的一致性。这一研究可为水源区土壤侵蚀空间分布的掌握和估算,以及制定有针对性的水土保持措施提供重要的理论依据。     

Developing a Snowmelt Forecast Model in the Absence of Field Data

In data poor regions predicting water availability is a considerable challenge for water resource managers. In snow-dominated watersheds with minimal in situ measurements, satellite imagery can supplement sparse data networks to predict future water availability. This technical note presents the first phase of an operational forecast model in the data poor Elqui River watershed located in northern Central Chile (30°S). The approach applies remotely-sensed snow cover products from the Moderate Resolution Imaging Spectrometer (MODIS) instrument as the first order hydrologic input for a modified Snowmelt Runoff Model. In the semi-arid Elqui River, snow and glacier melt are the dominant hydrologic inputs but precipitation is limited to up to six winter events annually. Unfortunately winter access to the Andean Cordillera where snow accumulates is incredibly challenging, and thus measurements of snowpack are extremely sparse. While a high elevation snow monitoring network is under development, management decisions regarding water resources cannot wait as the region is in its eighth consecutive year of drought. Our model applies a Monte Carlo approach on monthly data to determine relationships between lagged changes in snow covered area and previous streamflow to predict subsequent streamflow. Despite the limited data inputs the model performs well with a Nash-Sutcliffe Efficiency and R² of 0.830 and 0.833 respectively. This model is not watershed specific and is applicable in other regions where snow dominates hydrologic inputs, but measurements are minimal.

     

简化SWAT模型模拟漓江支流小流域的适用性评价

以漓江支流某小流域作为非点源污染流域研究对象,应用简化的SWAT模型,模拟示范区流域非点源污染的负荷量。通过对SWAT模型的简化,建立适用于漓江支流小流域的非点源污染模型,并对模型的适用性做出评价,得出月均值相对误差Re均小于25%,月相关系数R~2均大于0.7,月效率系数E_(ns)均大于0.5,拟合效果良好。本文研究结果表明,在漓江支流小流域建立简化的SWAT模型,对该流域进行非点源污染模拟是可行的。     

Artificial Neural Network Models of Watershed Nutrient Loading

This paper illustrates the use of artificial neural networks (ANNs) as predictors of the nutrient load from a watershed. Accurate prediction of pollutant loadings has been recognized as important for determining effective water management strategies. This study compares Haith??s Generalized Watershed Loading Function (GWLF) and Arnold??s Soil and Water Assessment Tool (SWAT) to multilayer artificial neural networks for monthly watershed load modeling. The modeling results indicate that calibrated feed-forward ANN models provide prediction which are always essentially as accurate as those obtained with GWLF and the SWAT, and some times much more accurate. With its flexibility and computation efficiency, the ANN should be a useful tool to obtain a quick simulation assessment of nutrient loading for various management strategies.     

Mitigating lake eutrophication through stakeholder-driven hydrologic modeling of agricultural conservation practices: A case study of Lake Macatawa,Michigan

Lake Macatawa is a hypereutrophic water body that connects with Lake Michigan via a navigation channel. Excess phosphorus (P) concentrations have resulted in a Total Maximum Daily Load (TMDL) for total phosphorus (TP) in the lake, which has not been met. To guide land management and water pollution control in the Macatawa watershed, a Soil and Water Assessment Tool (SWAT) model and scenarios of agricultural best management practices (BMPs) were developed in consultation with stakeholders. Modelling emphasized incorporating practices representative of local agricultural conditions. Approaches to initializing high legacy soil P levels in SWAT were tested. The validated model was used to evaluate the influence of BMPs on lake water quality and identify which practices are necessary for meeting the TMDL. The model showed that eliminating manure applications would have small effect on curbing TP loading, but continuous no-till and high residue combined with already used subsurface manure application would yield notable TP reductions. Achieving TMDL-mandated TP reduction of 72% is possible through a widespread adoption of multiple BMPs (continuous no-till with high residue, cover crops, filter strips, and conversion of some marginal croplands to perennial grasses) across all the watershed’s row croplands. The study highlights how guidance from a local community interested in watershed improvement was integrated with modeling towards addressing eutrophication with informed watershed management. The Lake Macatawa case study presents a tractable system from which management solutions could be transferred to similar small agricultural tile-drained watersheds with high legacy soil P levels in the Great Lakes basin.     

Coupling watershed modeling,public engagement,and soil analysis improves decision making for targeting P retention wetland locations

Constructed and restored wetlands can be effective sinks for particulate and dissolved phosphorus (P) if properly managed, but identifying suitable P retention wetland locations remains challenging. From a landscape perspective, Soil and Water Assessment Tool (SWAT) models identify locations within target watersheds with high nutrient loads that exhibit appropriate site characteristics and hydrodynamics. However, soil properties vary at the field scale, dictating the capacity of wetland systems to remove P and ultimately determining if a given wetland will operate as a sink or source of P over time. Land ownership and site access further complicate identification of P retention wetland locations. As a result, optimization and identification of P retention wetland locations requires analysis at both 1) watershed and 2) field scales, and 3) public engagement. In response, a survey effort linked SWAT model results that identified locations with target watersheds with field soil P storage capacity data and interested landowners. Results suggest that several locations recommended for their high SWAT-predicted P loading and landowner interest were in fact not well suited for project implementation due to soil P saturation and legacy P constraints. These findings highlight the need to couple watershed models with field scale soils analysis to identify locations for P retention wetlands in order to avoid unintended P release. Additionally, increased collaboration with social scientists and others familiar with public engagement strategies is needed to improve outreach activities targeting regional water quality improvements. Practical applications for nutrient retention wetland site selection are also discussed.     

SWAT和WetSpa Extension在罗玉沟流域的应用比较

近年来,运用水文模型来研究流域水文状况越来越普遍,本文以黄土高原丘陵沟壑区第三副区的典型小流域为例,基于SWAT和WetSpa Extension两个模型,从模型的输入数据、模型的参数和模型模拟结果等方面进行比较,以期为该区水沙模拟选择合适水文模型并为将来模型性能的改进提供参考。连续15年的校准验证表明:两个模型都能得到较好的结果,而SWAT模型能应用于水文及泥沙等模拟过程,相对来说功能更全面;WetSpa Extension模型目前仅能提供水文模拟的模块,优点在于模拟时间步长较任意,可进行洪水模拟。     

Groundwater Modeling Under Variable Operating Conditions Using SWAT,MODFLOW and MT3DMS: a Catchment Scale Approach to Water Resources Management

This paper presents an integrated modeling approach by linking soil and water application tool (SWAT), modular finite difference groundwater flow (MODFLOW) and modular 3-dimensional multi-species transport (MT3DMS) models capable of predicting a groundwater system response, in terms of flow and salt concentrations, to current and future development conditions. SWAT, a semi-distributed hydrologic model, estimates the spatio-temporal distribution of groundwater recharge rates. These rates are then input to MODFLOW using an interface module developed that maps the HRU-based spatial resolution of SWAT outflows into the cell-based spatial structure of inputs to MODFLOW and MT3DMS. The integrated SWAT-MODFLOW-MT3DMS model is used in modeling Dehloran aquifer system located in the arid western region of Iran, experiencing changes in land-use, irrigation system and pumping locations and loads. The results illustrate the significance of the developed integrated modeling tool in quantifying the impact of changes in land and surface water resources on its subsurface water system.     

不同管理措施对密云水库流域水量水质变化的影响

在密云水库上游控制流域建立SWAT(Soil and Water Assessment Tool)水文模型,根据实测水量-水质数据对模型的参数进行优化。识别流域土壤侵蚀和污染物关键区域,并对不同管理措施对流域水量-水质的影响进行定量研究。研究结果表明:密云水库流域土壤侵蚀强度较大的集中在流域中下游临近河道的区域;潮河流域非点源污染状况较为严重,潮河和白河总氮流失超高风险区分别占总面积的62.62%和43.09%,白河流域总磷均为低流失风险区,潮河流域总磷高流失风险区占17.81%;等高耕作和梯田种植对于产沙量和污染物都有较好的去除效果,其中等高耕作对于产沙量和总氮、总磷负荷的削减率,潮河分别为25.16%、10.79%和32.89%,白河为47.60%、34.92%和53.49%;通过对比退耕还林和退耕还草措施得知,退耕还林的效果更优。研究结果可为密云水库流域水土保持和水环境治理提供决策依据。