Estimation of watershed lag times and times of concentration for the Kansas City Area.

Details

• Creators:
  McEnroe, Bruce M. ; Young, C. Bryan ; Gamarra Zapata, Ricardo A.
• Corporate Creators:
  University of Kansas. Dept. of Civil, Environmental and Architectural Engineering
• Corporate Contributors:
  Kansas. Dept. of Transportation. Bureau of Research ; Johnson County Public Works and Infrastructure. Stormwater Management Program
• Subject/TRT Terms:
  • Watersheds
  • Streamflow
  • Runoff
  • Watershed lag times
  • Concentration
  • Stormwater
• Publication/ Report Number:
  KS-16-01
• Resource Type:
  Tech Report
• Geographical Coverage:
  Missouri
• Corporate Publisher:
  Kansas. Dept. of Transportation. Bureau of Research
• Abstract:
  Lag time (TL) and time of concentration (TC) are two related measures of how quickly a stream responds to ; runoff-producing rainfall over its watershed. In this report, a general relationship for lag time is derived from the ; Manning equation for frictional resistance, the rational formula for bankfull discharge, and a generalized rainfall ; intensity-duration relationship. This relationship accounts for the length, average slope, and average Manning n value ; for the longest flow path and three watershed characteristics: average width, a rational runoff coefficient, and a ; reference rainfall intensity. A simpler form of this relationship is derived for regional calibration. The regional form of ; the lag-time equation accounts for the impacts of urbanization through two inputs: the fraction of the longest flow path ; that is paved or enclosed, and the fraction of the drainage area covered by impervious surfaces. The relationships ; indicate that lag time is strongly related to the length, slope, and roughness of the main channel and less strongly ; related to other watershed characteristics that affect the bankfull discharge in the channel. ; The regional lag-time equation was calibrated for the Kansas City area with observed lag times and channel ; and watershed characteristics for 30 gage sites in the Automated Local Evaluation in Real Time (ALERT) flash-flood ; warning system. Average lag times for the gaged watersheds were determined from archived rainfall and water-level ; records for significant runoff events. The new lag-time equation for the Kansas City area performs better than the 2001 ; KU-KDOT equation for urban lag time, which was developed from a study of 14 gaged watersheds in Johnson County ; (McEnroe & Zhao, 2001). The main advantage of the new lag-time equation is that it accounts directly for the higher ; velocities in the paved and enclosed segments of the flow path. The new equation’s solid theoretical foundation is also ; an advantage. ; Because time of concentration cannot be determined from gaging data, direct calibration of an equation for TC ; is not possible. However, time of concentration and lag time are closely related, so TC can be estimated from TL. The ; Natural Resources Conservation System (NRCS, 2010) recommends the approximation TC = 5/3 TL. The ; recommended time-of-concentration equation for the Kansas City area incorporates this approximation.
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• Format:
  PDF
• Funding:
  C2027
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/30790/dot_30790_DS1.pdf
• File Type:
  [PDF - 1.51 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:07ea30546c41a7b3e2c190dadfbe3ddecf23a2a42e0085984500f835b3af5247