00802529

Component

https://doi.org/10.3141/1720-11

http://scholar.google.com...avis&publication_year=2000

The time of concentration (TC) is an important input to most hydrologic models and is usually estimated by travel-time computations or by using rainfall-runoff data. Average TCs were determined for 78 rural and urban watersheds in Maryland and related to watershed characteristics using regression analysis. The regression equation is based on the channel length and slope; the percentage of the watershed covered with forests, lakes, and ponds; and the percentage of the watershed with impervious areas. The equation is applicable for estimating TCs for rural and urban watersheds in Maryland with watershed characteristics similar to the gauging station data. TC values computed at Maryland gauging stations were compared with estimates from an equation developed by Kirpich and the Soil Conservation Service (SCS) lag equation, and with basin lag times determined by the U.S. Geological Survey (USGS). The average TC values computed in this analysis were about 5% higher than the basin lag-time estimates, which is consistent with the USGS's definition of lag time. TC estimates from the Kirpich or SCS equations were consistently lower than the values computed from gauging station data. The tendency to underestimate TCs is a major reason why hydrologic models often provide conservative estimates of design discharges compared with regional regression equations and gauging station data.

This paper appears in Transportation Research Record No. 1720, Roadside Safety Features and Hydraulic, Hydrology, and Water Quality Issues.

English

p. 95-99

2000

Transportation Research Record

0309066980

Figures (5) ; References (7) ; Tables (1)

Equations; Estimating; Flood hydrographs; Hydrology; Mathematical models; Rainfall; Regression analysis; Runoff; Rural areas; Streams; Urban areas; Watersheds

Maryland

Data and Information Technology; Highways; Hydraulics and Hydrology; I26: Water Run-off - Freeze-thaw

TRIS, TRB

Nov 16 2000 12:00AM

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