City of Leavenworth, Kansas
The watershed that drains to Ottawa Street between 7th Street and Broadway, a subwatershed of ThreeMile Creek, was experiencing flooding. The City of Leavenworth hired Water Resources Solutions to develop an improvements plan that will be used to guide the city’s stormwater improvements in the watershed over the next few years.
WRS performed a hydrologic analysis for the watershed using the methods outlined in Technical Release 55 (TR-55) and the NRCS Curve Number Method. The watershed was delineated into seven subwatersheds, to better analyze the hydrology. The depth of direct runoff and peak flowrate from each subwatershed were determined. The runoff hydrographs from each sub-basin within the watershed were modeled using the U.S. Corps of Engineers Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS). The EPA Storm Water Management Model (SWMM) was used to analyze the existing enclosed pipe system, identifying flooding locations at different model simulations.
WRS used the watershed modeling to develop improvement alternatives that included an emphasis on local system maintenance, individual areas noted for infrastructure improvements, and suggested use of drainage facilities. The three alternatives, which each included an opinion of probable constructions costs, were a replacement of undersized conduits, use of bio-retention storage and increased pipe sizes, and use of underground detention and increased pipe sizes.