Large hazardous floods as translatory waves

The theory for non-stationary flow in translatory waves is developed for an inclined plane in a prismatic channel and a funneling channel. The existence of translatory waves traveling over dry land or superimposed on constant flow is established, and the dependance on the initial flow value is discussed. Inherent instabilities of the wave tail are discussed. Data from a CFD simulation of a jokulhlaup (volcanic glacial burst) down the Markarfljot valley in Iceland are shown, and the similarities to the translatory wave established. Geological evidence of such large floods exists, and it is concluded that some historical floods like Katla 1918 have most likely been of this type. It is concluded that in simulation and hazard assessment of great floods, the translatory flow theory has an advantage over estimates based on Manning and alike methods, since the often subjective determination of the Manning n is avoided.