Investigating Potential Wetland Development in Aging Kansas Reservoirs

Abstract

Reservoirs around the world are losing their storage capacity due to sediment infilling; and with this infilling, the quality or value of some reservoir uses such as boating, fishing and recreation are diminishing. However, the sediment accumulating in the upper ends of reservoirs, particularly around primary inflows with well-defined floodplains, could potentially be developing into wetland ecosystems that provide services such as sediment filtration, nutrient sequestration, and habitat for migratory birds and other biota. The objectives of this study are as follows: 1) use water level management data and topography to delineate the primary zone of potential wetland formation around the reservoir perimeter, 2) examine the relationship between ground slope in this area and wetland delineations found in the U.S. Fish and Wildlife Service National Wetlands Inventory (NWI), and 3) investigate if these potential wetland locations have water quality, sediment, and vegetation that indicate a wetland ecosystem. To achieve these objectives, high quality LiDAR elevation data and bathymetry data were used to create reservoir basin topography for 20 large federally operated reservoirs in the state of Kansas located in the central U.S. Historical reservoir water surface elevation data were used to determine the water level and inundation extents associated with the 25th (dry), 50th (normal) and 75th (wet) water surface elevation percentiles for each reservoir, and the area between the 50th and 75th percentile boundaries was used to define the zone of potential wetland formation. Field work was also conducted to collect water, sediment, and vegetation samples from these potential wetland areas. Results showed that using the median slopes of the NWI yielded potential wetland development areas within the upper fluctuation zone (the area between the 50th -75th percentiles excluding areas of zero slope) that were comparable to the NWI coverages for each reservoir, and that slopes between 4.9 and 7.7 produced similar NWI coverages throughout this dataset. The results also indicated that four water quality variables (Total Nitrogen, Total Suspended Solids, Volatile Suspended Solids, and Turbidity) were unique in the riverine sites compared to the main basin sites, and when all the variables were analyzed cumulatively the main basin sites and the riverine sites grouped together, except for two main basin sites and two riverine sites