Tw. Sturm et A. Sadiq, WATER-SURFACE PROFILES IN COMPOUND CHANNEL WITH MULTIPLE CRITICAL DEPTHS, Journal of hydraulic engineering, 122(12), 1996, pp. 703-709
Water surface profiles measured in a laboratory compound channel that
has rough floodplains and multiple critical depths are compared with c
omputed water surface profiles obtained by numerical solution of the o
ne-dimensional equation of gradually varied flow in a form that includ
es a compound channel Froude number. Manning's n is found to vary with
depth in the floodplain, and the interaction between the main channel
and floodplain is represented as a correction to the main channel res
istance coefficient. Outside the discharge range of multiple critical
depths, good agreement is demonstrated between measured and computed w
ater surface profiles. Within the discharge range of multiple critical
depths, the measured water surface profile near a free overfall canno
t be computed as a one-dimensional flow because it separates into dist
inctly different drawdown profiles in the main channel and floodplain.
A method is proposed for identifying the discharge range within which
multiple critical depths exist in order to identify potential problem
s with interpretation of water surface profiles computed by one-dimens
ional methods in this range.