Experimental comparing the hydraulic performance of one- and three-dimensional porous bottom intakes

One of the most critical problems in using bottom intake is the accumulation of sediments on the garbage catch network and immediately after this network. Also, sediments whose size is smaller than the distance between the bars pass through the bars and settle in the intake channel. Accumulation of sediments on the garbage collection network and in the water intake channel, as well as sediments getting stuck in the space of the garbage collection network, will reduce the efficiency and increase the operating costs of this water collection system. To solve these problems, replacing the mesh floor with a porous medium is proposed. Although the latter method has limitations, its numerous and significant advantages confirm its replacement. This type of intake is called a porous bottom intake. In the simplest case, a trench is dug at the river's bottom to build it. This trench is filled with a material with appropriate granularity, and water is directed to this trench through an end structure to the transmission line or diversion channel. Due to the greater use of this intake in the headwaters of rivers with steep slopes and the lack of access to concrete materials in such conditions, this type of intake can be technically and economically efficient. This research mainly compares the hydraulic performance of one- and three-dimensional floor intakes. For this purpose, two one-sided and three-sided water intake samples have been tested in different hydraulic conditions. Also, the effect of the main channel slope and the granularity of the materials of the porous media around the intake has been investigated. In the first part, the performance results of the three-dimensional water intake, and in the second part, the hydraulic performance of the corresponding one-dimensional model has been examined. The performance results of these two intake types have been compared in the third part. Also, in the final part, their discharge coefficient is compared.

This research experiment was carried out in a laboratory flume with a length, width, and height of 11, 0.5, and 0.5, respectively. In this research, two models of one and three-dimensional intakes were tested. Three different granulations of particles with an average diameter of 1.94, 2.5, and 4.13 mm were used for the porous part. Also, to investigate the effect of the slope of the main channel, according to the ability to change the slope of the laboratory flume, tests were performed for two slopes of 1 and 1.67%.

The results show that the changes in the water intake discharge compared to the total discharge are increasing at the beginning with a higher slope and then with a gentle slope as a power function. Although it is expected that with the increase in the size of the materials, the amount of water intake will be higher, in the sample used in this research, due to the distribution of granularity, materials with an average diameter of 2.5 mm have more water passage than the total flow. The results show that the percentage of membrane discharge from the 2.5 mm granulation is higher than the other two. The slope effect is minimal in all three gradings, and no significant difference is seen from the slope effect. The changes in the percentage of water passing about the total flow are reduced exponentially. Due to the specific capacity of porous media, a higher percentage passes through the intake at low flow rates and decreases with increasing flow rates. In this model, for the slope of 1% of the main channel, the highest flow rate from the porous intake is related to the material size of 2.5 mm and the lowest for the material with a granularity of 1.94 mm. Like the M1 model, the one-sided intake has no noticeable slope effect. The ratio of discharges is between 2 and 10% for a 1% slope and between 2 and 8% for a 1.67% slope. On average, the flow through the M1 model is 72% higher than the M2 model. On average, the ratio of internal flow rate to total flow rate for the M1 model is 6% higher than the M2 model. The difference in this ratio is more in low flow rates and is about 21%, and with the increase in the flow rate of the main channel, it gradually decreases and reaches about 2%.The results show that the discharge coefficient of the single-sided water intake is higher than the three-sided water intake. The average value of the discharge coefficient of the single-sided intake is about 70% higher than that of the three-sided intake.