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1 1 Mitigation and Modification Alternatives The pumps would be relocated to a point on the right bank, upstream of the new diversion with a new pump suction arrangement. The pump could probably be housed in the same structure as the new side-channel gravity diversion. All construction material would have to be transported to the site from outside sources. However, the site is easily accessible and construction could proceed using conventional heavy equipment. Maybell Canal The distinguishing characteristics of the Maybell Canal diversion are: 1) its difficult canyon access, 2) its height (5' drop), and 3) the physical dominance of large rock. These and other characteristics of this structure are summarized in Appendix F. This information was used to develop four possible options for modification of this structure. • No action - leave the structure unchanged except for routine maintenance. • Construct a defined low-flow passage over the diversion but otherwise leave it unchanged. • Seal the existing diversion and make it more structurally stable with concrete/grout and build a chute-run fishway along the left abutment. • Construct a concrete diversion tied to bedrock and a concrete weir-pool fishway as a replacement to the existing structure. The third of these options was considered reasonably representative of what a future structure at this site could be. Moving the location of the existing structure or changing the primary material of construction are not considered feasible modification options. Figure 4-2 presents a schematic of this design concept. Figure 4-3 presents a typical schematic of fishway components. The current low point in the "J" shaped diversion dam is at the far left (river left) upstream end, a logical location for a fishway. A seven-stage fishway tied to the left abutment is proposed there. An instream divider wall would train low flow into the fishway. Each stage would consist of a concave concrete weir followed by a five-foot long, twenty-foot wide grouted rock chute. A twenty-foot long run would follow each chute. In order to contain low flows to the fishway, the entire existing diversion would be grouted and an upstream cutoff wall to bedrock constructed. The fishway would be designed to handle up to approximately 200 cfs, above which flow would generally be overtopping the existing diversion structure. With higher flows the plunging flow regime changes to more of a shooting or streaming flow regime, which still permits passage, but as a single stage rather than seven distinct stages. On-site rock could be used to supplement that already in the structure. Because of the difficult access, the other primary construction materials, concrete and grout, would have to be delivered from the north canyon rim by pumping. Structural steel would probably be flown in by helicopter. 4-5