El Dorado Lake
Introduction
El Dorado Lake is a Corps of Engineers reservoir located in the Walnut River Basin, in southeastern Kansas (figure 7). The El Dorado Reservoir watershed encompasses an area of 234 square miles, and includes portions of Chase and Butler Counties (KWO, 2012a)(figure 8). Land use in the El Dorado watershed consists of: 81% grasslands, 12% crop production, with the remaining 7% divided between other minor land uses (KDHE(b))(figure 9).
El Dorado Lake was authorized by congress under the Flood Control Act of 1965 (KBS, 2012). Initial construction of the lake began in September of 1973, and it was deemed fully operational for flood control in June 1981 (KBS, 2012). Two lakes, Lake Bluestem and Lake El Dorado, used to exist in the area of present-day El Dorado Lake (KBS, 2012). The dams of these two lakes were breached and the lakes were incorporated into larger El Dorado Reservoir (KBS, 2012). Aside from flood control, El Dorado Lake is also authorized for water quality, water supply, fish and wildlife conservation, and recreation (Powell, 2011a).
Figure 7. Map of the Walnut River Basin (KWO, 2011)
Figure 8. Map of the El Dorado Lake Watershed (Powell, 2011a)
Figure 9. Map of El Dorado Lake Land Use (KDHE(b))
Sediment
El Dorado Lake was surveyed by the Corps of Engineers in 1981. This survey revealed the area of the conservation pool at 1,339 feet to be 8,495 acres, and the storage capacity to be 163,942 acre-feet (KWO, 2012a). In 2004, the Oklahoma Water Resources Board conducted a bathymetric survey of the lake (KBS, 2011). This survey indicated the area of the conservation pool at 1,339 feet to be 7,478 acres, and the storage capacity to be 158,159 acre-feet (KBS, 2012). When compared to the 1981 survey this represents a total capacity loss of 3.5% over 23 years. Another bathymetric survey was conducted by the Kansas Biological Survey in August-July 2010 (figure 10). The survey revealed the area of the conservation pool at 1339 feet to be 7408 acres, with a storage capacity of 153,641 acre-feet (KBS, 2012). Comparison of the 1981 and 2010 surveys indicate a total area loss of 1,087 acres with a 10,301 acre-feet loss in capacity (KBS, 2012). This represents a total capacity loss of 6.28% over 29 years.
Figure 10. Bathymetric Map of El Dorado Lake, depth in feet (KBS, 2012)
As part of the 2010 KBS survey, core samples were taken at 25 sites throughout the reservoir to determine the areas of highest sediment accumulation (figure 11)(KBS, 2012). The survey revealed the areas of highest sediment accumulations occurred upstream of the now inundated dams of Lake Bluestem and Lake El Dorado (KBS, 2012). High sediment accumulation was also found near the current reservoirs dam, which is typical for most reservoirs in the area (KBS, 2012). Sediment accumulation was low throughout the rest of the reservoir (KBS, 2012).
Figure 11. Sediment thickness (cm) at 25 coring sites at El Dorado Lake (KBS, 2012)