ASABE Technical Library - Abstract
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Insight on the Variable Nature of Channel and Bank-Forming Discharges
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 032279, 2003 ASAE Annual Meeting . (doi: 10.13031/2013.13824) @2003Authors: Andy Ward, Dan Mecklenburg, Dawn Farver, Jon Witter, Anand Jayakaran
Keywords: Bankfull, Effective Discharge, Sediment, Recurrence Interval, Fluvial Geomorphology
The goal of the paper is to provide insight on why various terms are used to describe the
channel forming discharge and how these discharges are related to recurrence interval, sediment
transport, channel dimensions, and drainage area. Results are presented of studies by the authors
on low gradient streams in Ohio. A review is presented of studies of discharges that are most
influential in shaping streams. Historically, there are many examples of stream modifications that
paid little attention to the discharges that naturally shape a stream. To some extent this oversight has
been alleviated in the last decade by also considering a bankfull or effective discharge. These discharges are sometimes incorrectly identified or evaluated and we have a societal fixation in tying
them to a 1 to 2 year recurrence interval. Inadequate attention has been paid to reports in the
literature by eminent geomorphologists who provide extensive discussion on the relationship
between the effective discharge, bankfull discharge, other discharges, sediment transport, and
recurrence interval. For the streams in this study there was close agreement between bank-forming
discharges associated with effective discharge and bankfull discharge concepts. All of the streams
suggested that the bank-forming discharges are associated with a range of discharges. Calculation
of the effective discharge was sensitive to the subdivision of the sediment and discharge data into
unequal bin sizes. The bank-forming discharges were primarily related to the transport of the middle
50% of the total sediment load. The recurrence interval of the bank-forming discharges generally
ranged from 0.8 to 1.0-years. A study of the frequency of daily discharges that equal or exceed the
bank-forming discharges suggests that for these streams these flows occur several times annually
and the annual peaks approach is a poor indicator of the actual frequency of the flows. eave the
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