# Hydraulic Analysis of a Passive Wedge Wire Water Intake Screen for Ichthyofauna Protection
## 5 Conclusions  
Large-volume water intakes for municipal, cooling, or hydroelectric purposes, which consist of the intake pipe alone without an installed screen, can pose a serious threat to local or migrating ichthyofauna. For these types of intakes, maintaining intake velocities below maximum allowable values that are safe for small-length fry is very difficult. This requires very large inlet pipe diameters, which is often impossible or uneconomical. With an inlet capacity of 4.5 L/s during the experiments and an inlet pipe diameter without an installed screen equal to 50 mm, the inlet velocity of 2.17 m/s and approach velocities at 2.5 cm, 5.1 cm, and 7.6 cm from inlet surface were determined to be 0.5 m/s, 0.11 m/s, and 0.07 m/s, respectively. These values far exceeded those allowed by American, Canadian, and British standards for the protection of ichthyofauna. Mounting the screen model at the end of the inlet pipe in the form of a cylindrical wedge wire screen with a diameter of 15 cm increased the area of the inlet and significantly reduced the inlet and approach velocity while maintaining similar water intake capacity. The highest determined inlet velocity decreased by almost 20 times and amounted to 0.08 m/s, while approach velocities decreased by 3 to 10 times and amounted to 0.05 m/s, 0.03 m/s, and 0.02 m/s, respectively. These values meet most global standards. Still, the intake could pose a threat to smaller individuals, especially \"eel\" type fish moving. Measurements of inlet and approach velocities showed large heterogeneity in their distribution around the cylindrical screen. The heterogeneity of inlet and approach velocities expressed in quotients (\(V_{max}/V_{avr}\)) were 1.8, 1.6, 1.4, and 1.5, respectively, and expressed in quotients (\(V_{max}/V_{min}\)) were 10, 5, 5.5, and 3.5, respectively. In order to reduce the heterogeneity of inlet and approach velocities, an elaborate deflector with uniform openings of 6 mm diameter was installed inside the cylindrical screen. The mounted deflector reduced the quotients (\(V_{max}/V_{avr}\)) to the values of 1.5, 1.4, 1.35, and 1.3, respectively, and expressed by the quotient (\(V_{max}/V_{min}\)) to the values of 4.5, 3, 2.2, and 2.1, respectively. As a result, the highest determined value of the inlet velocity decreased by \(\frac{1}{4}\) and was 0.06 m/s, and the approach velocities depending on the distance from the screen decreased to values of 0.045 m/s, 0.025 m/s, and 0.012 m/s. Based on the measured distributions of inlet and approach velocity heterogeneity around the screen, a deflector was developed with openings of varying sizes from 3 mm on the pump side to 10 mm on the opposite side. With the deflector developed in this way, the inlet velocity heterogeneity expressed in quotients (\(V_{max}/V_{avr}\)) and (\(V_{max}/V_{min}\)) decreased by 5% and 20%, respectively. While the highest inlet velocity decreased by almost 20% to a value of 0.05 m/s. Analysis of the results showed that inlet velocities and approach velocities to the surface of the cylindrical screen were smallest above the screen (at 0\({}^{\circ}\) to vertical), and highest at the axillary level, (at 90\({}^{\circ}\) to vertical). This means less risk of pulling in fish flowing over the intake and floating ice and drift during winter periods, and more for fish flowing at the screen level. Wanting to check the effect of the developed deflectors on the operating costs associated with the pumping screen, the head losses with the deflectors installed were determined. Installing at a similar throughput of 4.5 dm\({}^{3}\)/s inside the inlet screen, a deflector with equal openings increased the head loss from 0.183 m to 0.207 m (by about 13 percent), and for a deflector with unequal inlet openings to 0.218 m (by about 19 percent). Numerical calculations conducted with ANSYS Fluent using computational fluid mechanics methods yielded velocity values similar to those measured during laboratory tests.