Rational Method Time of Concentration Can Underestimate Peak Discharge for Hillslopes
Publication: Journal of Hydraulic Engineering
Volume 147, Issue 10
Abstract
The Rational Method remains one of the most widely used approaches for estimating peak discharge in small catchments. In one widely used interpretation of the Rational Method, the maximum possible peak discharge produced by a storm with a given return period is predicted by setting the storm duration equal to the time of concentration. Whether the time of concentration maximizes peak flow for a rainfall return period, however, depends on the relationship between contributing area and storm duration. Here, we show that under many conditions, using the time of concentration in the Rational Method leads to an underestimation of peak discharge. This underestimation is illustrated using two case studies on idealized hillslopes on which runoff occurs as sheet flow. We suggest that practitioners should become cognizant of the differences between the critical duration (the storm duration that maximizes peak discharge) and the time of concentration within the Rational Method and be alert to morphology and land-use patterns that are likely to cause these timescales to diverge.
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Data Availability Statement
Some or all data, models, or code generated or used during the study are available in a repository online in accordance with funder data retention policies. (https://github.com/lapidesd/Lapides-etal-2020-RationalMethod; Lapides et al. 2020b).
Acknowledgments
This work was supported by the Hellman Foundation (DAL), UC Berkeley (DAL), the National Science Foundation Grant Nos. EAR-1013339 and EAR-BSF1632494 (DAL, OC), Engineering Research Center for Reinventing the Nation’s Urban Water Infrastructure (ReNUWIt) (AS), and the Gledden Foundation at the University of Western Australia’s Institute for Advanced Studies (AS).
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Published In
Journal of Hydraulic Engineering
Volume 147 • Issue 10 • October 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Nov 18, 2020
Accepted: Mar 11, 2021
Published online: Aug 2, 2021
Published in print: Oct 1, 2021
Discussion open until: Jan 2, 2022
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