محمد ابراهیم یخکشی

The Voshmgir dam with a height of 21 meters, is one of the oldest dams in the country and is located in Golestan Province. The Voshmgir Dam is built with one main reservoir and three sub-reservoirs with a total initial volume of 96 MCM. But in the current situation, with the end of the useful life of the dam and the filling of the dam reservoir due to the influx of sediments from numerous floods, it has decreased to 45 MCM. The available topographic maps show that it is not possible to increase the height of the main body of the dam and its side walls, and all the potential of the area has been used for the construction of the dam. Therefore, the only available solution to increase the volume is to increase the overflow’s height. In order to increase the dam height, according to the calculations, one- meter increase in height of the dam’s spillway, dam has been done. The purpose of this research is to investigate the hydraulics of the flow on the Voshmgir dam spillway with a rubber valve and compare it with sharp-edged, wide-edged and cylindrical spillways using physical modeling.

In this research, Anwar's mathematical model, which is the modeling of the upstream part of rubber dams, was tested on a flexible object. Then, the rubber dam with 4 different internal pressures (the ratio of internal pressure to the height of the rubber dam) was made with a rigid body and installed on the main spillway model of the dam. Experiments were conducted in 7 different flow rates between 12.69 and 30.45 liters per second in a concrete channel with a width of one meter and a length of 6 meters in non-submerged and clear water conditions in the water and sediment laboratory of Gorgan University of Agricultural Sciences and Natural Resources. Finally, to take advantage of these studies in the design of rubber dams, various linear and non-linear equations were extracted and presented to estimate the discharge coefficient using SPSS software.

The results showed that the hydraulic behavior of the rubber dam is more similar to the broad-crested weir than to the sharp-crested and cylindrical weirs. In all models, the flow coefficient increases with the increase of the hs/P ratio. Additionally, when the internal pressure of the dam increases from 0.5 to 1.3 at a constant hs/p, the discharge coefficient shows an average increase of 19%. Moreover, it has been observed that at a constant Froud number, the discharge coefficient experiences a 13.7% increase as the ratio of internal pressure to the height of the rubber valve increases.

Based on the obtained results, Anwar's mathematical model can model the geometry of rubber dams well. The geometry of the rubber valve is a function of its internal pressure and the flow rate changes with the change of the geometry. It can also be concluded that the flow rate, the height of the rubber valve and its internal pressure, the height of the flow relative to the crest of the dam and the height of the upstream water are among the factors affecting the flow hydraulics, including the flow coefficient.