APPROXIMATION OF THE BOUNDARY CONDITIONS AT THE COMPUTATION OF FLOOD WAVES

Abstract

The computation of wave phenomena belongs to the subject of the unsteady flow problems. To the computations boundary conditions are required. The initial conditions, usually, can be very easily produced. Generally, the upstream boundary condition is given, and this presents the actual wave for the effected and calculated lower river stretch. It is a general and difficult problem to produce the downstream boundary condition - especially for shorter river stretches - which is often substituted by the normal (steady flow) discharge curve: Q₀=Q₀(h). This approach - depending on the type of the flood wave - is very often not precise enough. The goal of this study is to justify that the downstream boundary condition, instead of the Q₀=Q₀(h) discharge curve, can be substituted by the Q=Q(h) loop, which is also a rating curve, but for unsteady flow. The computational results justified the statements of the authors. It was also numerically justified, that during a total wave flow the maximum time order of the main hydraulic parameters is: S_max, v_max, h_max (or Z_max) and Q_max.