Summary:

Erosive processes are the limitative vitality of water reservoirs in catchment areas. Considerable quantity of the delivered erosion products to rivers are deposited in artificial barrage reservoirs. Qualification of the silting volume of small retention reservoirs in time of their operation and indication of the proper methods of silting forecast is a particularly essential engineering question especially in relation of the realized programme of small retention. The measurements results of silting of twelve small retention reservoirs being in the river-basin of the Upper Vistula were introduced in this paper. The determined mean silting degree of studied reservoirs carries out from 0,06 % to 6,38 %. Detailed silting forecast of four chosen water reservoirs was presented, two situated on water-courses with hydrological control - reservoirs Krempna and Maziarnia, and two situated on water-courses not included hydrological observations. The aim of the paper is appraisal of the possibility of silting forecast of small retention reservoirs by help of Gončarov’s and Šamov’s empirical formulas and on the basis of the determined intensity of silting according to Schoklitsch’s and Piečinov’s formulas. The capacity- inflow ratios - α, capacity-watershed ratios – C/W of studied water reservoirs were marked. This coefficients made it possible to qualify of ability to trapping of sediments according to nomographs of Lopatin, Brune, Drozd, Brune and Allen, Brown, Gottschalk and Churchill. It was affirmed, that sediment trap efficiency of small retention reservoirs closest real value, determined from the balance the sediment incoming and deposited in the reservoir, can be received from Churchill’s nomograph. In the result of carried out calculations it was stated, that the results of silting forecast of studied retention reservoirs by help of Gončarov’s and Šamov’s formulas, in which β was determined from Churchill’s nomograph are closest to the value obtained from measurements. However Schoklitsch’s and Piečinov’s methods should be not applied in the calculations of silting of small retention reservoirs. Investigations of the silting process should not be restricted to appraise of material quantity flowing into the reservoir or fish ponds but physical, chemical and rheological properties of sediments should also be considered. Determination of these properties of sediments may contribute to undertaking a decision as to the system of their removal, subsequent management or utilization. With regard the high silting rate of small water reservoirs and fish ponds these must be desilted after a relatively short period of operation. Long years’ investigations permitted presentation of investigation study results on physical, chemical and rheologicalponds. Physical and rheological properties can decide about the possibilities and way of sediment removal from the bottom, whereas chemical properties decide about their possible utilization in nature (an exact analysis of heavy metal presence in sediments is very important). The examined fish ponds are located in the vicinity of Krakow and Bielsko-Biała, and water reservoirs of storage volume from 60 thousand to 3,8 million m³ are located on the Little Poland and Subcarpathian territory. The investigation results permit to state that rheological properties give evidence of fast progress of mud consolidation (a few to over ten days) and in consequence of no possibility of sediment removal from the bottom by the stream. On the other hand, the content of heavy metal in sediments is low and presence of micro- and macro elements in them is positive. In connection of it the removed sediments may be used in agriculture in the possible plant cultivations. Enrichment of agricultural soils under grain and root crops and on pastures is admitted.