Olathe, Kansas

2018

Water Resources Solutions was subcontracted to meet a Kansas Department of Water Resources request for a dam breach analysis to be completed for two crossings over Coffee Creek and its tributary. The purpose of the breach analysis is to understand a breaching scenario that would occur in Coffee Creek at proposed embankments at Lindenwood Drive and Brougham Drive. The breaching map was developed based on the requirements in Kansas Administrative Regulation (K.A.R.) 5-40-24. The importance of this scenario is to understand the dam breach hydraulics that occur downstream compared to the 100-year 6-hour storm event.

WRS developed the dam breach hydrograph according to the parameters regulated by the state. A HEC-HMS model of Coffee Creek was developed by the prime contractor and used to establish the breach condition at the two embankments. Because Lindenwood Drive crosses two tributaries of Coffee Creek, the tributary with the highest peak breach discharge was used in the analysis, as required by state regulations. Additionally, because the proposed Brougham Drive is also acting as a dam, the hydrograph combines the peak breach flow of Lindenwood with the Brougham Drive peak water surface elevation hydrograph. The combined hydrograph for Lindenwood and Brougham Drive was used in a HEC-RAS model to establish the extent of the flooding should a dam breach occur.

Using the breach hydrographs of Lindenwood and Brougham Drive, an unsteady flow model was created to analyze the extent of the flood, to show the extent of the water surface elevation according to HEC-RAS output, detailing the breach flow rates, water surface elevation, minimum channel elevation, and top width at each river station.

Inundation contour maps of the Lindenwood and Brougham Drive breaches were developed to show the breach analysis. The maps are created according to the state regulatory requirements, including the elevation of each existing hazard and the water surface elevation at each existing hazard. Five homes were identified and mapped as potential hazards due to the Brougham dam breach.