In the world professional literature can find many formulae and the nomograph using to apprise of sediment trap efficiency of water reservoirs. Sediment trap efficiency of water reservoirs, introduces in the form of nomograph or formulae, is defined in the function of the coefficients which they are the most often: capacity- inflow ratio – C/I and capacity-watershed ratio – C/W. The reservoir sediment trap efficiency is determined from Łopatin’s, Drozd’s, Karaušev’s, Brune’s formulae in dependence on the capacity-inflow ratio. The C/W ratio is used methods of Brune-Allen’s, Brown’s and Gottschalk’s. Churchill defined the reservoir sediment trap efficiency in function of sedimentation index. Qualification of sediment trap efficiency of small water reservoirs creates considerable difficulties, because the majority of existing formulae and nomograph using to apprise of sediment trap efficiency was worked out in the result of the investigations of large and middle water reservoirs. The results of real sediment trap efficiency of the small water reservoir βrz in the following years of operation were introduced in this work. Sediment trap efficiency was qualified on the basis of several the measurements of silting and on the basis of calculations of the quantity of suspended sediment delivered to the water reservoir. The reservoir at locality Krempna on the river Wisłoka was chosen to investigations. Calculated sedimentation index of the studied reservoir, taking into account the change of the reservoir capacity in the result of silting, equals 5.0⋅10^{5}÷1.4⋅10^{6} s^{2}⋅ft^{-1}. The sediment trap efficiency reservoir at Krempna in first year of operation, definite on the basis of measurements of silting carries out 77.1 % and is higher than the definite value according to the Churchill’s formula, equal to 65%. Churchill’s formula can be used to approximate qualification of the initial value β. Reduction of the value β_{Ch} in period eighteen years of the exploitation of the reservoir at Krempna is above twice lower than the reduction of real sediment trap efficiency - β_{rz}. Regression relationship in form β_{rz} = 21.044Ln(SI)-222.35 makes possible the qualification of the sediment trap efficiency of the reservoir at Krempna in the several years of operation. Introduced by Churchill sedimentation index can be used to the study of dependence enabling delimitation of the sediment trap efficiency of small water reservoirs. This requires however executing the systematic measurements of silting and the possibility of the qualification of the quantity of suspended sediment delivered to the reservoir on the basis of the hydrological data.

- Dr inż. Bogusław Michalec
- Uniwersytet Rolniczy w Krakowie
- Wydział Inżynierii Środowiska i Geodezji
- Katedra Inżynierii Wodnej i Geotechniki

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