A PRACTICAL GUIDE TO EFFECTIVE DISCHARGE CALCULATION
David S. Biedenharn1, Colin R. Thorne2, Philip J. Soar3,
Richard D. Hey4, Chester C. Watson5
ABSTRACT: This paper presents a procedure for calculating the effective discharge for rivers with
alluvial channels. An alluvial river adjusts the bankfull shape and dimensions of its channel to the wide range
of flows that mobilize the boundary sediments. It has been shown that time-averaged river morphology is
adjusted to the flow that, over a prolonged period, transports most sediment. This is termed the effective
discharge. While it may, under some circumstances, be possible to estimate the dominant discharge from
the bankfull discharge, in practice, identification of bankfull stage in the field is often problematic. The
dominant or channel-forming discharge may more reliably be found by calculating the effective discharge
provided that the necessary data are available, or can be synthesized, and the calculations are properly
performed. The procedure for effective discharge calculation presented here is designed to have general
applicability, have the capability to be applied consistently, and to integrate the effects of physical processes
responsible for determining the channel dimensions. An example of the calculations necessary and
applications of the effective discharge concept are presented.
KEYWORDS
Bankfull Discharge, Effective Discharge, Hydraulic Geometry, Regime Theory, River Engineering, River
Management, River Restoration, Stable Channel Design
INTRODUCTION: THEORIES AND CONCEPTS
While most engineers and river scientists recognize the conceptual limitations of dominant discharge
theory, its application remains popular due to the versatility and utility of approaches that incorporate the
principle that the cumulative effect of a range of discharges can be represented by a single flow. However,
there is a great deal of uncertainty regarding both the terminology concerning dominant discharge and the
best practice in its calculation. To alleviate both difficulties, this paper presents a definitive glossary of
terms (Appendix II) and outlines the best practical procedure for calculating the effective or channel-
forming discharge.
1
Engineer, US Army Corps of Engineers, Waterways Exp. Station, Vicksburg, MS 39180 USA.
2
Professor, School of Geography, University of Nottingham, Nottingham NG7 2RD, UK.
3
Graduate Student, School of Geography, University of Nottingham, Nottingham NG7 2RD, UK.
4
Reader, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
5
Assoc. Prof., Dept. Civil Engrg., Colorado State University, Fort Collins, CO 80523 USA.
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