Laboratory experiments related to open channel hydraulics are generally int
ended to be carried out in the fully developed flow region of a rectangular
flume. The developing region, in channels as well as in ducts, is a comple
x three-dimensional flow region influenced by secondary circulation and fre
e surface effects, and is therefore not amenable to analytical solution. La
boratory data and a numerical model have been used to study the variation o
f the length of flow establishment in rectangular channels.