Wanhong Yang

Integrating economic, environmental and GIS modeling to target cost effective land retirement in multiple watersheds

Abstract An integrated framework of economic, environmental and GIS modeling is developed to study cost-effective retirement of cropland within and across multiple watersheds to achieve environmental goals. This framework is applied to 12 contiguous agricultural watersheds in the Illinois Conservation Reserve Enhancement Program region of the United States. A key goal of this program is to reduce sediment loadings in the Illinois River by 20% by retiring land from crop production. The characteristics of land parcels to be targeted for retirement within each watershed and the criteria for cost-effective allocation of abatement responsibility across watersheds are analyzed. Our analysis suggests that program costs are minimized when the abatement standard is set for the region rather than uniformly for each watershed. For both policy scenarios, the land parcels targeted for retirement should be those that are highly sloping and adjacent to a water body.

Simulated wetland conservation-restoration effects on water quantity and quality at watershed scale.

Wetlands are one of the most important watershed microtopographic features that affect hydrologic processes (e.g., routing) and the fate and transport of constituents (e.g., sediment and nutrients). Efforts to conserve existing wetlands and/or to restore lost wetlands require that watershed-level effects of wetlands on water quantity and water quality be quantified. Because monitoring approaches are usually cost or logistics prohibitive at watershed scale, distributed watershed models such as the Soil and Water Assessment Tool (SWAT), enhanced by the hydrologic equivalent wetland (HEW) concept developed by Wang [Wang, X., Yang, W., Melesse, A.M., 2008. Using hydrologic equivalent wetland concept within SWAT to estimate streamflow in watersheds with numerous wetlands. Trans. ASABE 51 (1), 55-72.], can be a best resort. However, there is a serious lack of information about simulated effects using this kind of integrated modeling approach. The objective of this study was to use the HEW concept in SWAT to assess effects of wetland restoration within the Broughtons Creek watershed located in southwestern Manitoba, and of wetland conservation within the upper portion of the Otter Tail River watershed located in northwestern Minnesota. The results indicated that the HEW concept allows the nonlinear functional relations between watershed processes and wetland characteristics (e.g., size and morphology) to be accurately represented in the models. The loss of the first 10-20% of the wetlands in the Minnesota study area would drastically increase the peak discharge and loadings of sediment, total phosphorus (TP), and total nitrogen (TN). On the other hand, the justifiable reductions of the peak discharge and loadings of sediment, TP, and TN in the Manitoba study area may require that 50-80% of the lost wetlands be restored. Further, the comparison between the predicted restoration and conservation effects revealed that wetland conservation seems to deserve a higher priority while both wetland conservation and restoration may be equally important.

Multi-Objective Sensitivity Analysis of a Fully Distributed Hydrologic Model WetSpa

The application of fully distributed watershed models has the advantage of providing location-specific outputs. However, the calibration of these models is very challenging due to over-parameterization. A typical strategy is to aggregate parameters and screen out insensitive parameters in order to decrease the dimension of the problem for calibration. To ensure the validity of calibration, it is important to identify important physical processes and parameter interactions, and examine how different model setups affect model simulation. In this paper, a two-step multi-objective sensitivity analysis approach is applied to a distributed hydrologic model, the WetSpa (Water and Energy Transfer between Soil, Plant and Atmosphere), with case studies in the Chaohe Basin in China and the Margecany Basin in Slovakia respectively. This two-step global sensitivity analysis technique, incorporating the Morris method and the SDP (State Dependent Parameter) method, has proved to be effective in the two case studies. The results of two case studies show that (i) a warm-up period is essential for minimizing the impact of initial state variables to the model simulation, (ii) different objective functions lead to different sensitivity results, (iii) evapotranspiration is the most sensitive process to the model result in the two study watersheds followed by the groundwater and soil water process, and (iv) the sensitivity of snowmelt process is case dependent.

Development of a robust runoff-prediction model by fusing the Rational Equation and a modified SCS-CN method

Abstract The objective of this study is to develop a Modified Rational Equation (MoRE) that combines the advantages of the Rational Equation (e.g. simplicity and global acceptance) and those of the standard US Department of Agriculture (USDA) Soil Conservation Service (SCS) curve number (CN) method (e.g. easy parameterization and extensive verification across the world). Herein, the hypothesis is that the MoRE is more accurate, consistent and robust than the SCS-CN method and its improved versions in predicting runoff in watersheds with limited data. The MoRE was designed to have a simple structure that is described by four intrinsic parameters: CN, permanent wilting point, field capacity and saturation soil moisture, and does not include initial abstraction as a variable. An evaluation of 77 USDA small agricultural watersheds indicated that CN of the MoRE has different physical meanings from CN of the SCS-CN method. The MoRE (mean Nash-Sutcliffe coefficient, E > 0.73) performed better than the SCS-CN (mean E < 0.32) and the four improved models (mean E < 0.56) in reproducing the runoff of the study watersheds. Performance of all six models varied greatly between watersheds, as well as between events, but was independent of watershed drainage area. However, the model performances tend to be better for watersheds and/or events with a runoff-to-rainfall ratio of between 0.1 and 0.3 than for those with a ratio outside this range. The MoRE has the most consistent and robust performance. Editor D. Koutsoyiannis; Associate editor I. Nalbantis Citation Wang, X., Liu, T., and Yang, W., 2012. Development of a robust runoff-prediction model by fusing the rational equation and a modified SCS-CN method. Hydrological Sciences Journal, 57 (6), 1118–1140.

Assessing Effects of Small Dams on Stream Flow and Water Quality in an Agricultural Watershed

Small dams and associated reservoirs have notable effects on soil and water dynamics in prairie streams. In this study, we developed a simulation module of small dams in the soil and water assessment tool (SWAT) to evaluate their long-term effects on stream flow and water quality at a watershed scale. To overcome the challenges in characterizing small storage and short retention time in small reservoir routing, concepts of equivalent reservoir storage and equivalent reservoir discharge are applied by which the average daily storage and daily discharge of the small reservoirs are calculated. Accordingly, the sediment deposition and nutrient abatement within the reservoir are computed using available SWAT routines. The effects of small dams in reduction of daily peak flow, sediment, and nutrient loads at the watershed outlet are obtained by summing the effects of all small dams within the watershed considering both reservoir and channel processes. The model is applied to the 74.6-km(2) South Tobacco Creek watershed located in Southern Manitoba of Canada. A total of 26 small dams exist in the watershed with surface area ranging from 0.002 to 0.492 km(2) and storage capacity from 3,380 to 642,000 m(3). The simulation results show that the combined effect of these small dams can reduce daily peak flow by 0-14% at the watershed outlet depending on climate and initial reservoir storage conditions. The estimated average annual sediment, total nitrogen and total phosphorus reductions at the watershed outlet are about 4.51, 3.59, and 2.96%, respectively. However, the on-site effects of individual small dams are much higher depending on its size, location, shape, drainage area, and land use compositions in the contribution area. The simulation results also show that snowmelt-flooding events have higher reduction amounts but lower relative reduction rates compared to rainfall storm events and the back-flood small dams have greater impact on sediment, nitrogen, and phosphorous abatement followed by multipurpose small dams and dry dams in the study watershed

Cost-effective targeting of riparian buffers to achieve water quality and wildlife habitat benefits

ABSTRACT This study develops an integrated economic, hydrologic, and ecological modelling framework to examine cost-effective targeting of riparian buffers to achieve water quality and wildlife habitat benefits. The framework is empirically applied to the Canagagigue Creek watershed in Ontario, Canada to compare the economic costs for establishing riparian buffers under three alternative environmental and ecological constraints: sediment abatement only, habitat improvement only, and riparian buffer acreage only. The results show that riparian buffers targeted for achieving sediment abatement goal are not effective in improving habitat quality. Similarly, riparian buffers identified through habitat improvement goal achieve less sediment abatement as compared to those targeted in the sediment abatement scenario. The trade-offs suggest that agricultural stewardship programmes with joint water quality and habitat improvement goals may need to allocate funds independently for targeting two pools of riparian buffers: for improving water quality only or for improving habitat only.

Hydrologic Modelling of an Agricultural Drained Micro-Watershed: Performance Analysis of Coupled Surface Water/Groundwater Models

The objective of this study is to quantitatively assess the impact of subsurface drainage and soil properties on the hydrological behaviour of a headwater micro-watershed located in the Bras d’Henri watershed, Quebec (Canada). The studied 2.4-km² micro-watershed is characterized by intensive livestock production supported by forages and annual crops such as corn grain or soybeans. It is one of Agriculture and Agri-Food Canada’s WEBs watersheds (Water Evaluation of Beneficial management practices). Hydrometeorological monitoring has shown that soil properties and subsurface drainage could negatively affect the expected behaviour of beneficial management practices at the watershed scale. Therefore there is a need to understand the influence of these properties on hydrology and one way to study this problem is to set up a physically-based hydrological modelling investigation. Specifically, this project focuses on evaluating the ability of two or three coupled hydrological models (surface flow/subsurface flow) to simulate flows at the micro-watershed outlet and water table depth fluctuations while quantifying the surface and subsurface contributions to flows. The models under consideration are: CATHY (Camporese et al., 2010), DRAINMOD (Skaggs, 1978) and PESTDRAIN (Branger et al. 2009).