Qualification of the distribution of bottom sediments in small water reservoir using the relative depth shape function

Praca dotyczy określenia rozmieszczenia osadów dennych w małym zbiorniku wodnym Zesławice. Zbiornik ten zlokalizowany jest na rzece Dłubni w okolicach Krakowa i charakteryzuje się wysoką intensywnością zamulania. Obliczony średni roczny stopień zamulenia przed odmuleniem wynosił 3,0%, a po odmuleniu 2,0%. W celu prognozy rozmieszczenia osadów w zbiorniku wodnym wykorzystano metodę Rahmaniana i Banihashemiego polegającą na założeniu, że rozmieszczenie odkładów rumowiska w zbiorniku wodnym określa się po tzw. długim okresie eksploatacji. Do określenia długiego okresu eksploatacji posłużono się charakterystyką zamulania, tj. stopniem zamulenia, i wykazano, że gdy stopień zamulenia osiągnie co najmniej 50%, rozmieszczenie osadów w zbiorniku można opisać za pomocą krzywej odłożonego osadu, określoną jako funkcja względnego kształtu dna (Relative Depth Shape Function - RDSF). Na podstawie wstępnej oceny stwierdzono, że metoda określenia rozmieszczenia osadów w zbiorniku wodnym za pomocą RDSF umożliwia uzyskanie wyników zbliżonych do określonych na podstawie pomiarów. Określenie możliwości zastosowania metody wymaga jej weryfikacji w oparciu o wyniki pomiarów zamulania dla różnej wielkości zbiorników.The attempt of the application of the new method of forecasting the sediment distribution in the water reservoir was introduced in this work. The researches of silting and the sediment distribution were conducted in the small water reservoir at Zesławice near Cracow. Reservoir came into operation in 1966. After sixteen years of exploitation it was silted in 50%. The side reservoir, which took over the functions of the main reservoir during the period of its desilting, was built in 1989. After desilting of the main reservoir the side reservoir was supplied with water from the common water knot on river Dłubnia. A change in water flow conditions in main reservoir at Zesławice, as a consequence of redirecting part of water flow and sediment to the side reservoir Zesławice alters the conditions of transport and sedimentation, and may affect the distribution of sediments in the reservoir. The quantity of sediment deposited in parts nearer dam of the reservoir being got smaller in this effect. Decrease of the water flow intensity and water flow velocity resulted in intensive layering of sediment in the inlet part of main reservoir. The examined small water reservoir at Zesławice is characterized by high silting rate. The calculated average annual silting ratio equals: 3.0% - before desilting, 2.0% - after desilting. Having the results of long-term silting measurements of the small reservoirs at Zesławice, an attempt was made to apply the method presented by Rahmanian and Banihashemi for prediction of sediment distribution in small reservoirs. Rahmanian and Banihashemi stated that distribution of sediment deposition in water reservoir is defined for a long duration operation. Silting characteristics - i.e. silting ratios were used in order to determine the long duration operation, and it was demonstrated that when the silting ratio has reached at least 50%, the sediment deposition in the reservoir may be described by empirical reservoir Relative Depth Shape Function (RDSF). According to this method for a long duration operation, relative volume divided by relative level gives relative cumulative sediment volume concept for each point on relative curve of volume-depth, where Relative Depth Shape Function (RDSF) is related to cumulative sediment deposition in different heights from reservoir bed. It was affirmed on the basis of the preliminary appraisal that the method of the qualification of the sediment distribution in the water reservoir using the Relative Depth Shape Function (RDSF) made possible the obtainment of approximate results to determined on the basis measurements. The qualification of the possibility of the use of this method requires execution of next verification on basis of the results of the measurements of silting of not only small, but average and large water reservoirs