Laserfiche WebLink
<br />at this cross section (Appendix 2, Table 8). <br /> <br />Strata 8 <br /> <br />Cluster 3 (rm 94.0) <br /> <br />This cluster was surveyed at a flow of 330 cfs. A bed profile was done across the shallowest <br />part of the riffle below the control cross section. This cross section had a notch in the bed profile <br />which had a depth of 1.96 ft. Flows would have to drop below 50 cfs for the depth in the notch to <br />drop below 1.0 ft. <br /> <br />Cross section 4 described a slow riffle about midway in the station. Maximum depth found at <br />this cross section was 1.28 ft. To attain a maximum depth of at least 1.0 ft, a flow of 190 cfs would <br />be required (Appendix 2, Table 10). <br /> <br />Cross section 8 was the upper terminus of the station and traversed a shallow riffle. Maximum <br />depth at 330 cfs was 1.57 ft. A flow of 118 cfs would provide a depth of at least 1.0 ft that this area. <br /> <br />Cluster 6 (rm 115.5) <br /> <br />This cluster was surveyed at a flow of 332 cfs (Table 6). The shallowest profile taken in this <br />cluster was cross section 1. This was a wide riffle with velocity over 4.4 ft/sec at the 332 flow. The <br />deepest point on this cross section was 0.9 feet. At flow of 400 cfs is needed to provide a depth of <br />1.0 ft at this cross section. <br /> <br />The riffle at the upstream end of the sequence (cross section 4) was not a problem to fish <br />passage. The right two-thirds of the channel was a raised cobble riffle and the left side of the <br />channel was narrow and deep. The left side (deep channel) should maintain a depth of 1.0 ft at <br />flows as low as 20 cfs, but the upstream cross section (5) needs 52 cfs for a 1.0 maximum depth. <br /> <br />Discussion <br /> <br />To recover endangered fishes, the objective is to maintain a sustainable <br />populations size compatible with current base flow conditions. Figure 3, the hydro graph for the 20, <br />50, and 80% exceedence flow, indicates that base flow drops to 180 cfs in 50% of the years, based <br />on the Maybell gage. Ifwe accept the readings for the Maybell gage as representative of the river <br />reach, then we can determine the percent of clusters that have riffles that will maintain the desired <br />depth at some base flow. <br /> <br />Of seven riffles with bed profiles in Strata 6, the highest flow required to produce <br />a 1 foot depth, or 100% access across riffles, was found to be 336 cfs. A flow of230 cfs would <br /> <br />44 <br />