Water Resources Solutions complete the dam breach analysis for three dams on the Jeffrey Energy Center (JEC) property. The existing Emergency Action Plan (EAP) is being revised and updated, including the breach inundations maps. The breach analysis will provide the understanding of a breach scenario that would occur in the tributaries downstream of the existing dams.
The JEC property is in Pottawatomie County near Belvue, Kansas. The three dams on the JEC property include JEC Tower Hill Lake Dam, JEC Make-Up Lake Dam, and JEC Auxiliary Make-Up Lake Dam. All three dams are in Pottawatomie County, Kansas, northeast of Belvue, Kansas. The Tower Hill Lake Dam and Make-Up Lake Dam were constructed in the late 1970s, and the Auxiliary Make-Up Dam was constructed in the mid-1980s. The Tower Hill Lake Dam is classified as a significant hazard class “B” structure, and the Make-Up Lake Dam and Auxiliary Make-Up Lake Dam are classified as high hazard class “C” structures, as determined by the Kansas Department of Agriculture (KDA) Division of Water Resources (DWR).
The watershed boundaries to each of the dams were delineated using the 2012 Digital Elevation Models (DEMs) acquired from the United States Geological Survey (USGS). Peak runoff flowrates for each of the watersheds were determined using the Natural Resource Conservation Service (NRCS) Curve Number Method. The composite curve number was determined using aerial imagery, the National Land Cover Database (NLCD), and the United States Department of Agriculture (USDA) Web Soil Survey. The flow paths were determined, and the time of concentrations were calculated using the DEM topographic data in Hydraulic Engineering Center Hydrologic Modeling System (HEC-HMS).
HEC-HMS was used to generate the dam breach hydrographs for each of the dams. One dam breach hydrograph was developed for the Tower Hill Lake Dam, and one was developed for the combined dam breach of the Make-Up Lake Dam and Auxiliary Make-Up Lake Dam. The 100-year 6-hour storm event was chosen as the design event
Inundation contour maps of the Tower Hill Lake Dam breach and the combined dam breach of the Make-Up Lake Dam and the Auxiliary Make-Up Lake Dam were developed to show the breach analyses. The maps are created according to the requirements of K.A.R. 5-40-24(j) (1) and (2), which mandates:
Contour intervals of 10 feet or less
A scale of not less than 1-to-24,000
The inundation area determined from the breach
The location of each existing hazard
Each cross section entered in the hydraulic flow model with a label identifying the cross section
The elevation of each existing hazard
The water surface elevation at each existing hazard
The elevation of the streambed at the point nearest each existing hazard
The hazards were determined using aerial imagery and the breach inundation limits as calculated by the 2-D HEC-RAS dam breach modeling. Seven existing bridges, including one highway and two railroad bridges, and nine homes and businesses are hazards because of the Tower Hill Lake dam breach. Nine existing bridges, including three highway and three railroad bridges, and 110 homes and businesses are hazards because of the Make-Up Lake and Auxiliary Make-Up Lake combined dam breach.