Modeling Water Quantity and Sulfate Concentrations in the Devils Lake Watershed Using Coupled SWAT and CE‐QUAL‐W2

Abstract

Devils Lake is an endorheic lake in the Red River of the North basin in northeastern North Dakota. During the last two decades, the lake water level has risen by nearly 10 m, causing floods that have cost more than 1 billion USD in mitigation measures. Another increase of approximately 1.5 m in the lake water level would cause spillage into the Sheyenne River. To alleviate this potentially catastrophic spillage, two artificial outlets were constructed. However, the artificial drainage of water into the Sheyenne River raises water quality concerns because the Devils Lake water contains significantly higher concentrations of dissolved solids, particularly sulfate. In this study, the Soil and Water Assessment Tool (SWAT) was coupled with the CE‐QUAL‐W2 model to simulate both water balance and sulfate concentrations in the lake. The SWAT model performed well in simulating daily flow in tributaries with ENS > 0.5 and |PBIAS| < 25%, and reproduced the lake water level with a root mean square error of 0.35 m for the study period from 1995 to 2014. The water temperature and sulfate concentrations simulated by CE‐QUAL‐W2 for the lake are in general agreement with the field observations. The model results show that the operation of the two outlets since August 2005 has lowered the lake level by 0.70 m. Furthermore, the models show pumping water from the two outlets raises sulfate concentrations in the Sheyenne River from ~100 to >500 mg/L. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

Mitigating Impact of Devils Lake Flooding on the Sheyenne River Sulfate Concentration

“…In response, an East Outlet with a capacity of 10 m 3 /s was built in 2012 on the east side of the lake. However, sulfate concentration in Devils Lake increases from west to east, and therefore the East Outlet discharged higher concentrations of sulfate than the West Outlet (Shabani et al ).…”

“…In this study, the Soil and Water Assessment Tool (SWAT model) was used to simulate the Sheyenne River natural discharge and a flood frequency analysis was performed to evaluate the flood risk of the river during outlet operation. To simulate the sulfate concentration in the river, we connected our SWAT model with a coupled SWAT and CE‐QUAL‐W2 model that was developed for a previous study of the Devils Lake watershed (Shabani et al ). A conceptual optimization model was then designed and implemented to improve management of the Devils Lake outlets.…”

“…For calibration, the SWAT Calibration Uncertainty Program (Abbaspour ) was used to run the model for 2000 iterations using SUFI‐2 algorithm to evaluate the sensitivity of daily discharge simulated at the four gauging stations for the 22 parameters listed in Table . This set of parameters was used to properly characterize snowmelt, soil and land management, channel conditions, wetlands, and potholes within the watershed (Wang et al ; Kharel et al ; Shabani et al ; Tahmasebi Nasab et al ). Among the parameters, the simulated discharge was found to be sensitive to the following seven: threshold temperature for snowmelt, snowmelt lag factor, curve number, baseflow recession constant, soil evaporation compensation coefficient, effective hydraulic conductivity, and Manning’s roughness coefficient for the main channel.…”

“…In the previous study (Shabani et al ), SWAT and CE‐QUAL‐W2 models were coupled to simulate the water level and sulfate concentration of Devils Lake from 2008 to 2014. CE‐QUAL‐W2 is a two‐dimensional (longitudinal‐vertical), laterally averaged hydrodynamic and water quality model for lakes, rivers, estuaries, and reservoirs (Cole and Wells ).…”

“…Therefore, it is best suited for simulating large and narrow water bodies such as Devils Lake. In the coupled model, SWAT was used to simulate Devils Lake water levels and provided the inflows for the lake tributaries, which were used as input data for the CE‐QUAL‐W2 model to simulate lake sulfate concentrations (Shabani et al ). For the current study, the original simulation was extended to 2018 in order to match the study period.…”