A mathematical model of dam-break shock waves, or flood waves, in channels
of trapezoidal cross section is presented. When the model is applied to cha
nnels of rectangular cross section, a new theoretical solution expressed us
ing one independent multinominal algebraic equation is derived. In the past
, the solution had to be described using three interrelated equations. The
new equation indicates that the hydraulic parameters of a shock wave-such a
s depth and velocity of flow, and velocity of discontinuity-are determined
only by the ratio of initial downstream depth to initial upstream depth. Th
e model shows that results from the new equation are completely equivalent
to those of the set of old equations. In addition, the hood hydrograph prod
uced by a dam break at any time or any site can be described by a single cu
rve in terms of dimensionless variables.