| Abstract: | Abstract Highwater stages of frequently very long duration which commonly develop on plain-land watercourses having flat slopes, constitute a fatigue loading on the flood levees built along such streams. In order to describe by a single parameter the magnitude of this fatigue load, the concept of flood exposure has been introduced and defined as the area under the flood hydrograph exceeding a certain stage (the toe of the levee). Consequently both stage and duration of highwater are taken into consideration. Positive relationships have been found to exist between the magnitude of flood exposure and adverse phenomena associated with highwaters (groundwater emergence, underseepage, leakage, boil formation, saturation slumping and wave action). The magnitude of the labour force, fleet of mechanical equipment and materials used in flood fighting, consequently the costs thereof depend to a significant extent on the magnitude of flood exposure, which can thus be used conveniently for economic analysis as well. Mathematical statistical analysis has shown the logarithmic normal distribution to fit best to the empirical distribution of flood exposure. The full set of data was found to be homogeneous in the gaging sections examined on the Danube and Tisza Rivers. Sets of data have been grouped according to the dates of major interference into the life of the watercourse. It was found further that in the sections considered the duration of highwaters could also be regarded as a homogeneous random variable. |
