Modeling the Impacts of Lakes and Wetlands on Streamflow
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Lakes and wetlands cover a large portion of the earth’s surface and play a crucial role in hydrology. They provide permanent and temporary storage for water within the landscape allowing for greater infiltration and evaporation along with a reduction in peak flooding events. Lakes and wetlands also provide many other non-hydrological benefits such as their ability to improve water quality and provide wildlife and fisheries habitat. Despite their known benefits, wetland destruction has been a prominent issue for many years. This study quantifies the hydrologic effects of lakes and wetlands by introducing a parametrization method for hydrologic model simulations in the North American Land Data Assimilation System (NLDAS) domain. Lake profiles were created based on the geospatial lake depth-area relationship through interpolation of known lake depths and areas throughout the domain. Wetlands were parametrized based on topographic wetness index (TWI) calculated using high-resolution DEM imagery. Wetland profiles were created using a binning technique along with the DEM and land use classifications. The Variable Infiltration Capacity (VIC) macroscale hydrologic grid-based model and its associated lake and wetland algorithm were used to quantify the effects of lakes and wetlands on streamflow. Profiles were generated for every corresponding VIC grid cell in the NLDAS domain, but for this study two watersheds, the Buttahatchee River in Mississippi and the Black River in North Carolina, were selected to test the parametrization and quantify the impact of lakes and wetlands on watershed hydrology. The Buttahatchee River watershed contains 6.6% lakes and wetlands, which were predominantly clustered near the stream channel, and the Black River watershed contained 19.2% lakes and wetlands which were spread out across the entirety of the watershed. Simulated daily streamflow with and without the lake and wetland algorithm activated was used to evaluate impacts on flood frequency as well as components of the water balance. Flood magnitude decreased due to the presence of lakes and wetlands. This decrease was 5.8% and 29.6% for a 10-year return period flood for the Buttahatchee River and the Black River sites, respectively. Mean annual flowrate decreased significantly as a result of lakes and wetlands indicating storage of water in the lakes and wetlands allowed for a greater degree of evapotranspiration. There were 1.6% and 10.9% decreases in average streamflow rates as well as corresponding 0.3% and 4.1% increases in annual evapotranspiration in the Buttahatchee River and Black River watersheds, respectively. While lakes and wetlands reduce peak flood events and decrease average streamflow rates through increased storage and evapotranspiration, the magnitude of these impacts varies based on the quantity and distribution of lakes and wetlands in the watershed as well as the climate and vegetation present.