The HRON rainfall/outflow model used for simulating the outflow from the rainfall and snowfall has a character of a concept model with centralised parameters. It consists of the three subroutines, contains 15 parameters, and works with daily time step. The input data required for calculation comprise the average daily aggregate rainfall on the river basin, the average daily values of air temperature in the river basin, the values of long term average monthly potential evapotranspiration, and the values of long term average monthly air temperature. Calibration of the model parameters requires an order of values of average daily flows in the final profile of the pilot river basin. Also the initial values of some simulating values may be given to the model.
As a pilot river basin, the Hron river basin up to Banska Bystrica was elected, with available measured orders of rainfall, air temperature, and flows for the period of 1962 – 1998.
In order to assess the effect of the preceding condition of the river basin on the extreme rainfall, three different levels of saturation of the river basin were elected from the past, namely the level of high, low, and average saturation. The year 1965 was considered as a year with high aggregate rainfall and flow above average, the year 1992 as a year with low aggregate rainfall and flow, and the year 1998 as an average year. In these selected years, the measured rainfall values were always replaced by one combination of a rainfall event in the days on which they occurred in August 2002 in the Czech Republic. The aim of calibration was to find such parameter values which would well reflect the top of the flood wave and at the same time a period with lower flows.
Simulation of the response of the river basin to extreme rainfall was carried out in total 12 times.
For each preceding level of saturation of the river basin, 4 simulations were carried out in accordance with four scenarios of rainfall events.
The results of the study show that in all three simulated levels of saturation of the river basin and in the assumed extreme rainfall, flood would occur. They also confirmed strong effect of the preceding saturation of the river basin on the volume of outflow. In any event, flood flow would occur even at the average level of saturation of the river basin. During the historical flood in the river basin of the upper Hron river on October 22, 1974, the culmination level in Banska Bystrica reached the value of Hmax=494 cm and the flow was 560 m3.s_1, which represents, according to the information on maximum flows prepared by the Slovak Hydrometeorologic Institute, more than a 100-year flow. In case of assumed average saturation of the river basin and occurrence of assumed extreme rainfall, the resulting flow in the value of Qculm= 596 m3.s_1 would be higher than the 100-year one. Assuming higher preceding saturation of the river basin, the culmination flow might be much higher (Qculm= 757 m3.s_1).
Information & Contact:
Ing. Richard Kubes
Faculty of Civil Engineering of the Slovak Technical University
Department of Landscape Water Management
In: Water Management Journal – Year 46, No. 7/2003, p. 11.
