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velocity, substrate and cover, usually choosing traJilsition areas between pools and riffles where the velocity and depth are suitable. Brown trout aUd brook trout spawn in the fall when water temperatures drop below 50 degrees F, In Snowmass Creek most spawning occurs in late September through October with some still occurring in early November, The female cuts into the substrate by flexing her body and turning side to side. This creates a depression in the substrate in which the female deposits her eggs, which are immediately fertilized by the male, The female moves upstream and repeats the operation, which covers the downstream eggs with substrate creating a small mound over the eggs, the mating sequence is repeated until the final depression is created which covers the last egg deposit The last depression is termed the redd pit and the mound covering the egg pockets is termed the redd tailspilL Trout are selective in the physical conditions of redd locations as breeding success is completely dependent on those physical parameters at the redd site. Depth is rather obvious as even naturally decreasing winter flows could expose the redd tailspill thus freezing the eggs, or expose enough of the tailspill to reduced temperatures enough that hatching would be delayed, Trout eggs require a certain number of degree-days (one degree-day occurs for each degree above 32 degrees F per 24-hour period) to hatch. :Velocity at the redd is also critical for delivering adequate oxygen to the incubating eggs and to keep the tailspill free of fine sediments, If velocity decreases below suitable levels, insufficient oxygen will be delivered to the eggs thus reducing viability of the eggs, Also, as velocity decreases the deposition of fine sediments (sands, silts and clay particles) will occur in the tailspill, which fills the interstitial spaces in the gravels, This degrades the success of spawning in two ways. First, the filling of the interstitial spaces blocks the delivery of oxygen and second,ithe filling could block the emergence of the sac-fry upon hatching, Hatching usually occurs in April, again depending on the degree-days accumulated, but the sac-fry remain in the gravel$ until just before high water. The physical parameters of spawning sites for different trout species are known from the work of others including depths, substrate size and velocity requirements for successful incubation. Walsh & Walsh (1995) discuss those documented requirements, and compare the physical parameters they measured at redds on Snowmass Creek during on,e year through the existing winter decreasing flows with those documented requirements, This is the great benefit of the Walsh & Walsh study; we have actual data for potential resource Impacts of the proposed project to compare with published data on the same resources, Walsh & Walsh (1995) identified 35 redds downstream of the SWSD diversion in November of 1994, They measured depths, velocities, substrate and temperatures at the redds at fixed locations for each redd over the winter from November to March. Depth and velocity were recorded at 5 fixed locations at each redd: 3 points upstream of the redd, 1 in the deepest point of the redd (red pit), and 1 at the highest point on tl1e redd (redd tailspill), For the three points upstream ofthe redd, one was closest to the chaJinel, one directly above the redd, and one close to the stream bank. Measurements were taken monthly at each redd from November to March. Substrate was assessed by estimating the percent composition of substrate by an accepted breakdown of sediments by size, An initial substrate composition was taken in November and a second in February, For stream discharge, they used data collected at the SWSD diversion gauge, the Zeigler bridge staff gauge and during each monthly field visit, they developed their own transects and calculated discharge at three locations downstream of the diversion, 10 e e e