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:
  Concentration Runoff Stormwater Streamflow Watershed Lag Times Watersheds
• 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.
  
  
• Format:
  PDF
• Funding:
  C2027
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:07ea30546c41a7b3e2c190dadfbe3ddecf23a2a42e0085984500f835b3af5247
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/30790/dot_30790_DS1.pdf
• File Type:
  [PDF - 1.51 MB ]