Summary:

Within the framework of the small retention program location of 65 reservoirs and 4 polders was determined. Their total capacity will permit retention of 38 hm2 water and the estimated cost of building was about 1,03 mld złote [„Program małej retencji…” 2004]. Small water reservoirs undergo quick silting and the time laps of their silting is hazard to define. The paper presents possibilities of forecasting of small water reservoirs silting basing upon data gained from measurements of silting quantity from years 1969–1983 and 1999–2006. Two reservoirs at Zesławice i.e. the main reservoir before and after desiltation and the sidereservoir which was passed over for exploitation after desiltation of the main reservoir. The paper aims at determination of the influence of the side-reservoir on silting intensity decrease in the main reservoir. The time laps after which the reservoirs will be silted in 80% was calculated. Forecasting of water reservoir silting was made according to Gončarov’s formula. Determination of the quantity of load deposition after the first years of exploitation - R1 cause of principal difficulties in elaboration of forecasts. Disposing of measurements of silting quantities in consequent years this quantity was calculated after transformation of the equation to the form permitting calculations of the quantity R1 basing upon measurements results. It was shown that the side-reservoir contributes to the decrease of silting of the main reservoir by taking over a part of the inflowing sediment load. A comparison of volume of load deposits in the main reservoir before and after desiltation when side-reservoir was switched to exploitation permitted to state that in the tenth years of exploitation a decries in the quantity of deposits in the main reservoir exceeded 30% and in the seventeenth – 33%. The decrease in the quantity of sediment load retained in the main reservoir is not a measurable effect caused by the side-reservoir. The calculated sum of load sediment accumulated in two reservoirs after desiltation is bigger than the volume which was retained in the main reservoir before desiltation. The determined time laps after which main reservoir capacity before desiltation would be reduced by 80% is 38 years. Due to building a side-reservoir retaining a part of the sediment load entering the reservoirs siltation of the main reservoir equaling 80% will be reached after 66 years and that of the side-reservoir after 138 years. Attainment of prolonged exploitation time is result of cooperation of two reservoirs supplied with water from a common water mode gives in consequence retention of a bigger quantity of load in two reservoirs that in the main before desiltation in a comparable equaling exploitation period. In the existing system of cooperating reservoirs necessary desiltation works can be undertaken after a longer exploitation period, however, in the scope of works connected with desiltation renovation of the side-reservoirs must also be taken into consideration.