engleski

Estimation of High Water Discharge on the Basis of Stochastic Water Level Analysis

In the 1970s, in the Karašica and Vučica catchment areas (right-side tributaries of the Lower Drava) staff gauges were placed at some fifty locations. Daily water level measurements were started within the framework of long-term hydrologic measurements with the aim of estimating discharge, i.e., water balancing in the catchment area. Due to the difficult economic situation the measurements were suddenly stopped at the majority of locations. Thus, today water level measurements are only still being done at some ten locations. The existing collected data cover a period from 15 to 36 years. According to the available information, no professional analysis of the performed measurements and collected data has been done so far. The fact that some measurements were suddenly stopped, that no adequate reference to the work done has been made, and that there was no evaluation of the need for a continuation of the measurements, at some locations at least, in accordance with future allocations to be made for that purpose have created circumstances in which the work, efforts and investments made so far can be easily underestimated or even devalued. This paper is intended as a cause for reflection about the importance of some measurements and the damage caused by their unplanned interruption. The paper presents a hydrological procedure for the estimation of high water discharges as an example for simifar research on the basis of existing data. The stochastic analysis of high water levels is done on the basis of water level data collected on four small rivers over a 35-year period. Independent water levels that exceed the selected threshold value were chosen. For the estimation of the distribution of the data on high waters, five theoretical functions were used for each location. The best agreement with the empirical distribution is achieved by the Log-Pearson III function. The relation between water level and discharge is defined on the basis of channel geometry. To that end, high discharges are systematised according to the return periods of infrequent occurrence, which can find practical application in water management. It is concluded that a comparison with the earlier obtained data on the basis of precipitation indicates grater deviations for longer return periods. Also, the need for urgent measurements of flow velocities and channel characteristics for the sake of the definition of discharge rating curves is pointed out.

estimation; water discharge; measurement; water level; stochastic analysis

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