Bank‐full discharge of rivers

TLDR

Eleven definitions of “bank‑full” exist, with geomorphologists favoring the active floodplain and engineers focusing on valley‑flat banks. Bank‑full discharge at gaged sites should be derived from the rating curve using a longitudinal floodplain profile; at ungaged sites it can be estimated with an empirical equation from this study or the Gauckler‑Manning equation, using a site‑specific resistance coefficient n. Bank‑full discharge shows no common recurrence frequency among rivers, and the 1.5‑year recurrence interval discharge rarely corresponds to the true bank‑full discharge.

Abstract

Eleven possible definitions of ‘bank‐full’ have been used by various investigators. The active floodplain is the most meaningful bank‐full level to the fluvial geomorphologist, whereas the banks of the valley flat are the most important to engineers. Comparison of 16 ways of determining bank‐full discharge suggests that bank‐full discharge at gaged sites should be obtained from the station's rating curve, where bank‐full gage height is determined from a longitudinal profile of the floodplain along the entire reach. At ungaged sites, bank‐full discharge can be estimated from the empirical equation of this study or from the Gauckler‐Manning equation. In the latter case the resistance coefficient n should be estimated at the field site for bank‐full flow; a measured low‐flow n should not be used. Bank‐full discharge does not have a common recurrence frequency among the rivers studied, and the discharge corresponding to the 1.5‐year recurrence interval in most cases does not represent the bank‐full discharge.