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• No discussion is presented on the hydrologic regime that the structures are being <br /> designed for. Is the project designed to handle a 100, 50 or 25 year event? What <br /> are those flow event levels? <br /> • Has an instream flow study been done to evaluate potential changes to the fish <br /> populations that may occur with this development? CDOW has done some work <br /> in the San Juan River in Pagosa yet there is no reference to their input in the <br /> design of the structures. <br /> 2. Probable Impacts <br /> • Stream Dynamics <br /> o What will happen to the routing of flood flows through Pagosa Springs <br /> with the hardening of the stream channel? Will the elevation of the 100 <br /> year flood increase or stay the same? Will the flow be routed to "less <br /> hard"areas in the event of a flood? <br /> o No discussion occurs of the fluvial geomorphic controls that occur <br /> upstream and downstream of the planned whitewater features. The <br /> success or failure of the project is dependent upon the hydrologic controls <br /> upstream and downstream and the ability of the river to absorb high flow <br /> events. Change occurs at the extremes, not at the average flow conditions. <br /> Stream dynamics will change with the proposed project. A stress- <br /> response evaluation that includes possible fluvial geomorphic shifting <br /> should occur before construction begins so that all people understand the <br /> possible risks. <br /> o What is the hydraulic and sediment Carrying Capacity of the San Juan <br /> River through Pagosa Springs? Has the proposed white water park been <br /> evaluated and designed in respect to these capacities? <br /> o The addition of 60 6-ft diameter"riffle roughness boulders" is an <br /> interesting suggestion. How will these RRBs be anchored into the river <br /> bed? What types of rock will be used? What shape will the rocks be? <br /> (Round rocks roll at lower flows). Has an evaluation been made as to <br /> what happens when the areas behind the boulders erode and the rocks drop <br /> into the holes? Will they still be effective in the creation of whitewater <br /> play holes? Is this sort of habitat needed by the fish in this stretch of the <br /> San Juan River? <br /> o How much sediment is expected to collect in the plunge pools over the <br /> year? What maintenance will be required to remove the sediment? How <br /> are these structures designed to pass sediment? They look like they will <br /> capture sediment rather than pass it along. Sediment passes when you <br /> have a hard channel with fast hydraulics and no eddies. This is not well <br /> explained in the proposal. <br /> o Has a probable stream response analysis been completed to look at where <br /> the San Juan River may migrate under high flow conditions IF the <br /> hardened channel is harder than the surrounding areas? The river will <br /> look for the path of least resistance under flood conditions and as such <br /> those folks who might be directly impacted by this may want the city to <br /> 2 <br />