Challenges Calibrating Hydrology for Groundwater-Fed Wetlands: a Headwater Wetland Case Study
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Challenges Calibrating Hydrology for Groundwater-Fed Wetlands: a Headwater Wetland Case Study R. Ramesh 1 & L. Kalin 1 & M. Hantush 2 & M. Rezaeinzadeh 3 & C. Anderson 1 Received: 28 September 2018 / Accepted: 10 October 2019 # Springer Nature Switzerland AG 2020
Abstract This study aims to adapt the Soil and Watershed Assessment Tool (SWAT), a ubiquitously used watershed model, for groundwater dominated surface waterbodies by accounting for recharge from the aquifers. Using measured flow to a headwater slope wetland in Alabama’s coastal plain region as a case study, we present challenges and relatively simple approaches in using the SWAT model to predict flows from the draining watershed and relatively simple approaches to model groundwater upwelling. SWAT-simulated flow at the study watershed was limited by precipitation, and consequently, simulated flows were several times smaller in magnitude than observed flows. Thus, our first approach involved a separate stormflow and baseflow calibration which included the use of a regression relationship between observed and simulated baseflow (ENASH = 0.67). Our next approach involved adapting SWAT to simulate upwelling groundwater discharge instead of deep aquifer losses by constraining the range of deep losses, βdeep parameter, to negative values (ENASH = 0.75). Finally, we also investigated the use of artificial neural networks (ANN) in conjunction with SWAT to further improve calibration performance. This approach used SWAT-calibrated flow, evapotranspiration, and precipitation as inputs to ANN (ENASH = 0.88). The methods investigated in this study can be used to navigate similar flow calibration challenges in other groundwater dominant watersheds which can be very useful tool for managers and modelers alike. Keywords Wetland . Model . SWAT . Headwater slope wetland . High baseflow . Artificial neural networks
1 Introduction The biogeochemical state or nutrient content of a drainage network is dictated by that of its headwaters which form the beginning of water movement from uplands into * R. Ramesh [email protected] L. Kalin [email protected] M. Hantush [email protected] C. Anderson [email protected] 1
School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA
2
Center for Environmental Solutions and Emergency Response, U.S. Environmental Protection Agency, 26 West Martin Luther King Dr., Cincinnati, OH 45268, USA
3
Lynker, 3002 Bluff St., Suite 101, Boulder, CO 80301, USA
streams [6]. Headwater streams also comprise the highest proportion of stream miles [17, 32, 33], which explains their disproportionately high influence in the drainage [6, 32, 33]. Wetlands of headwater streams provide important ecosystem services such as habitat for aquatic life; nutrient uptake and cycling; clean drinking water; downstream temperature regime regulation; and reduce loads of nitrogen, phosphorous, and sediment to coastal waters [32, 33, 35]. As a class, wetlands on lower order streams have higher capacity for water quality
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