Estimation Discharge Cifficient in New System of Bottom Intake with Porous Media

Background and Objectives: Bottom intake is one of the suitable methods for diverting water in mountainous rivers. Different forms of bottom intake, which have so far been less studied, are the use of bottom intake with porous media which can be considered as a suitable substitute for bottom rack intakes due to the reduction difficults of bottom rack and low cost of design and execution. Since the idea of using bottom intake with porous media is new and information is limited to design and construct this kind of intake, the present research tried to consider the condition of the hydraulic behavior of these intakes in accordance with the reality.
Materials and Methods: In order to model a bottom intake with porous medium and conduct experiments, a main flume with the walls of the glass materials in the dimensions of the 10* 0.30* 0.50 cube meter and a diverted flum by the dimensions of the 1* 0.45* 0.50 cube meter was used. To prepar an intake in the distance of 5 m at the beginning of main flume, the space has been considered so that the possibility of conduction is with three length, height and slope (L1=15 cm, L2=30 cm, L3=45 cm) (H1=10 cm, H2=15 cm, H3=20 cm) (S1=0%, S2=10%, S3=20%). The inner surrounding of intake was filled with four different types of gravel with average diameter P1=9.72mm, P2=13.41mm, P3=15.30 mm, P4=17.75mm. In every experiment by passing different discharges over intake,was measured the rate of diverted discharge for different models of intake was drawn and the effect of different parameters on the rate diverted discharge was studied, by bottom porous intake. We used rectangular weir at the end and beginning of main flume to measure discharge.
Results and Conclusions: The results showed that inflow discharge increases the rate of diverted discharge but the proportion of diverted discharge to inflow discharge is on the decrease. By increasing the grain size, the diverted discharge increase, so that grain size P4 has most rate of diverted discharge. It ,s the result of void space increasing in this kind of grain size. By increasing uniform coefficient grain of intake, the porosity and void space of granular material decreases, and consequently diverted discharge decreases between 4 and 6 percent. Researching on diverted discharge with different length and height showed increasing intake length from L1 to L3 for intake with height H1 for P2 (d50=13.41mm) gradation and Qt=12.25 lit/s, the Qd/Qt is increased up to 23 percent. Increasing intake height from 10 cm to 30 cm for intake with length 30 cm for P4 (d50=17.75mm) gradation and Qt=17 lit/s, the Qd/Qt is increased up to 10 percent. By incearsing the slope of intake surface from 0% to 20% , diverted discharge decrease, this kind of decrease is the result of unexpected change in th surface slope of intake and separating flow in the in enterance of porous media intake. The minimum and maximum the rate of diverted discharge in the experiments in this study was 13% and 90% respectively.
Conclusion: The results showed that by increasing the inflow discharge, the diverted discharge increases too; however, for larger values of the discharge, the ratio of the diverted to the upstream flow approaches a final constant value. Grain size of the porous media has a great influence on the diverted flow. By increasing the grain size, the diverted flow increases. By increasing the surface slope of bottom intake with porous media, the diverted flow decreases. Maximum diverted flow occurs at zero surface slope of the intake. Increasing intake length and height, causes increasing in diverted discharge.