Estimating Design Discharges for Drainage Structures in Western Kansas

Kansas Department of Transportation (KDOT) engineers have expressed concern that the hydrologic methods in the current KDOT Design Manual (Volume I, Part C, 2011) may lead to over-sizing of drainage structures in Western Kansas. Some new structures designed by the current methods are much larger than the previous structures at these locations or existing structures directly upstream or downstream, where the older structures had no known history of overtopping. There are reasons to suspect that current methods may not be well suited to small watersheds in Western Kansas, particularly for areas with high soil permeability. This report examines the applicability of KDOT’s current hydrologic methods to Western Kansas and develops new Rational C values and flood-frequency regression equations for this region. In addition, KDOT’s current hydrologic methods are compared with those of nearby state DOTs. In order to develop new flood-frequency regression equations and recommendations for Rational C values for Western Kansas, the authors assembled a data set of all U.S. Geological Survey (USGS) gaging stations that met the following criteria: (1) at least 10 years of peak flow records, (2) watershed area less than 100 mi², (3) unregulated watersheds (no major lakes or reservoirs), and (4) watersheds within 100 miles of the Kansas border and west of 97.5° longitude. The resulting data set contains 156 stations, 62 of which are in Kansas. Regional flood frequency analyses were performed on this data set using Generalize Least Squares regression in WREG 1.0. Soil permeability was found not to be a significant predictor variable. Regression equations were developed for Western Kansas, but comparisons show that these equations are not a substantial improvement over existing regression equations. Based on an evaluation of available methods, the authors recommend the Extended Rational method for watershed areas > 640 ac and < 30 mi² and the USGS four-parameter regression equation for watersheds ≥ 30 mi² in both Western and Eastern Kansas. An analysis of Rational C values indicates that C values currently used for design in Western Kansas are too high for recurrence intervals below 100 years. New Rational C values for Western Kansas were developed and checked against regression methods for consistency. The proposed C values for Western Kansas are lower than the current values for all recurrence intervals below 100 years. The authors also propose certain adjustments to the Rational C values for Eastern Kansas. They recommend that urban open spaces and pervious surfaces within the right-of-way be considered equivalent to pasture/range rather than cropland in both Western and Eastern Kansas.

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  • Supplemental Notes:
    • This research was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    University of Kansas, Lawrence

    Department of Civil, Environmental and Architectural Engineering
    1530 West 15th Street
    Lawrence, KS  United States  66045-7609

    Kansas Department of Transportation

    Bureau of Materials and Research, 2300 SW Van Buren
    Topeka, KS  United States  66611-1195

    Kansas State University Transportation Center

    Kansas State University
    Department of Civil Engineering
    Manhattan, KS  United States  66506

    Research and Innovative Technology Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • McEnroe, Bruce M
    • Young, C Bryan
    • Williams, Aaron R
    • Hinshaw, Matt
  • Publication Date: 2013-6


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 84p

Subject/Index Terms

Filing Info

  • Accession Number: 01485999
  • Record Type: Publication
  • Report/Paper Numbers: K-TRAN: KU-12-4
  • Contract Numbers: C1912
  • Created Date: Jul 8 2013 1:07PM