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sluice gates. Some fish are also expected to travel upstream near the <br />right bank. Fish will approach the diversion dam, which is a barrier to <br />their upstream passage, and begin searching for a passage route. Any <br />facility should readily attract fish to an entrance without presenting <br />any physical barriers such as high velocity jets or large structures. <br />The auxiliary attraction flow available should be three times the maximum <br />ladder flow to produce a strong attraction current, especially during <br />high flow periods. This large amount of attraction flow provides adequate <br />operational flexibility due to the uncertainty of the target species <br />behavior. Once inside the passage facility, the target species may <br />prefer to swim through an orifice or a vertical slot, so both should be <br />provided. Also, screens with 1.0- to 1.5-inch spacing are required to <br />preclude adult fish from undesirable areas (water intakes and the power <br />canal). <br />3. Specifically, the razorback sucker is a bottom dweller and, <br />like most suckers, will travel along the bottom of a fish ladder. So <br />their progress will be minimally impeded, the floor of the ladder should <br />be sloped from the entrance up to the exit, and orifices and slots should <br />have an invert flush with the floor of the ladder. Also, entrances <br />should have an invert flush with the river bottom. <br />4. Colorado squawfish size has been recorded up to 80 pounds. <br />Therefore, orifices should be no smaller than 12 inches wide by 18 inches <br />high. Slots should be at least 12 inches wide and extend from the ladder <br />floor to at least 6 inches above the water surface at high flow operation. <br />B. Technical Considerations and Recommended Criteria. <br />1. After review of several ladder types (refer to Appendix A <br />for technical review), the vertical slot/orifice ladder can be modified <br />to fulfill most of the biological requirements. Many smaller fish lad- <br />ders of this type are designed for a 1-foot head drop between pools, <br />8 feet wide by 10 feet long by 3 feet deep, and pass similar squawfish <br />and sucker species. This volume of water in each pool helps dissipate <br />energy and reduce turbulence. However, the slope of the ladder can be <br />changed to create the desired head drop per pool and the desired pool <br />length. To provide a lower velocity flow through each orifice and ver- <br />tical slot, a 1/2-foot drop per pool is recommended. Provisions for <br />experimentation with different head drops per pool (and different veloci- <br />ties through the slot and orifice) will allow a 1/4-foot drop or a 1-foot <br />drop per pool within the ladder. The flexibility to change slot and ori- <br />fice velocities is required due to uncertainties of biological criteria. <br />This experimental installation should help develop more specific criteria <br />• for the two target species. This type of ladder has the advantage of a <br />constant flow pattern at all operating depths. It also adapts very well <br />5 <br />