A simple formula for estimating backwater at bridge constrictions

Abstract

The past experimental studies to investigate the backwater effects due to bridge constrictions have been mostly performed in setups of single rectangular channels with fairly smooth surfaces. Therefore, there is a need to investigate more realistic cross-sectional shapes and roughness conditions. The most obvious case is to consider bridges in natural channels with floodplains. This paper reports the findings of model testing of arch and straight deck bridge constrictions in a compound channel flume with both smooth and roughened surfaces. Four different types of bridge models, namely single opening semicircular, multiple opening semicircular, single opening elliptic, and straight deck models with and without piers, were used in the testing program. An attempt was made to develop a simple formula for estimating bridge backwater as a function of Froude number and opening ratio.Key words: bridge backwater, hydraulic model testing, open channel flow, flood control.