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Feasibility Study for the Plaza Project - Phase 2: McDonald Ditch Implementation Project boaters. It was recognized that a side channel could be added to allow fish passage. This would add to the costs of the diversion. 6.3.2 Diversion Alternative #2: Steel and Grouted Rock Diversion A steel and grouted rock dam would span the entire width of the river, checking the water behind it. The steel and rock structure would have lower installation costs than the concrete dam, but greater maintenance needs and costs. While this structure is more "natural looking" than concrete, it is impassable by fish and boaters. Similar to Alternative #i, a side channel could be added to allow fish passage. 6.3.3 Diversion Alternative #3: Hybrid Rock and Concrete Diversion A hybrid rock and concrete diversion would be half concrete and half rock. The concrete would be adjacent to the headgate and extend half way across the river. The rocks would comprise the other half of the dam and include a series of drop structures, allowing for fish and boat passage. This structure would be comparable to the grouted rock and steel diversion in terms of installation cost. It would have higher maintenance than the concrete structure and lower maintenance than the grouted rock and steel structure. Because this alternative provides boat and fish passage, it would fulfill numerous nonconsumptive needs including recreation and habitat improvement. This option was the most favorable of the diversion alternatives. 6.3.4 Diversion Alternative #4: Pipeline The final alternative was specific to the Silva, Atencio 2, and McDD diversions. This alternative would include the removing the current McDD diversion and moving its headgate upstream to the location of the Silva and Atencio 2 headgates. The Silva and Atencio 2 diversion would be replaced with the most favorable diversion option, Alternative #3, and all water for the Silva, Atencio 2, and McDD would be diverted from this location. The Silva and Atencio 2 would divert their water into their ditches at the location of their current headgates. The McDD would divert their water (14.4 cfs) into the Silva Ditch for 0.5 mile, then divert it into a pipeline, which would travel approximately o.5 miles along County Road 5N, over the river, and into the current McDD concrete lined ditch. Combining the Silva, Atencio 2, and McDonald diversions, would reduce overall maintenance. Furthermore, the current diversion structure at the Sevenmile Plaza bridge would be removed, which was a priority project identified by the 2001 Study. Installing the concrete and grouted rock hybrid structure would have the advantages and disadvantages discussed above. The McDD would have to go through Colorado Water Court to change their point of diversion. Additional complications include the evaporative losses of transporting water in an open ditch before the pipeline, lack of sufficient right -of -way along County Road 5 North, and the need for the pipeline to cross the Rio Grande. Finally, engineers from the Colorado NRCS State Office raised issue with removing the McDD diversion structure entirely as this diversion dam is controlling the grade of the river in the area. The concern is that without grade control, scour could occur at the bridge, causing instability. As such, it would be necessary to install a grade control structure at the current diversion. The cost of installing two check structures, three headgates, and a pipeline would make Alternative #4 twice the cost of all other alternatives. 6.4 Headgate Alternatives Through the Plaza Plan, efforts to improve diversion efficiency, reduce maintenance costs, and explore the possibilities of including automation in the McDD headgate were explored. 6.4.1 Automated Gates and Precise Water Management To research automated gates, the stakeholders met with Kyle Clair, engineer of the Prairie Ditch automated gate system, and Rubicon Systems America, Inc. (Rubicon Water). Clair's system uses the data transmitted by the Prairie Ditch gauging station to the Colorado Division of Water Resources. The ditch superintendent programs the desired flow rate into the automated gate system, which then triggers a motor to raise and lower the headgate until the flow the gauging 15