Draft EIS_072312.pdf - Middle Fork American River Project ...

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20120723-4002 FERC PDF (Unofficial) 07/23/2012 Table 3.3.3-4. Summary of riparian vegetation around project reservoirs and diversion pools (Source: PCWA, 2011a, as modified by staff). Location Total Acreage Riparian Vegetation 140 Total Miles of Vegetated Shoreline Total Miles of Shoreline Large Reservoirs Hell Hole reservoir 6.1 9.1 11 French Meadows reservoir 2.5 8.5 9 Medium Reservoirs Middle Fork interbay 1.7 0.6 1 Ralston afterbay 6.1 1.3 4 Diversion Pools Duncan Creek diversion pool 0.2 0.1
20120723-4002 FERC PDF (Unofficial) 07/23/2012 unimpaired river reach on the North Fork American River. On Duncan Creek, the abundance of riparian vegetation was a little greater and occurred in larger patches upstream of the diversion compared with downstream. Riparian Resources and Hydrologic Regime Relationships PCWA assessed the influence of the current hydrologic regime on riparian vegetation in the vicinity of the project, the hydrology associated with successful recruitment events (scouring and recruitment flows and recession rates) and the position of vegetation along the channel (frequency, duration, and width and depth of inundation). Tree cores from the bypassed and peaking reaches and comparison reaches from nearby unregulated rivers were analyzed as was the lateral distribution of riparian trees adjacent to the channel which was compared with that on the comparison unregulated river reaches and upstream of the project diversions. Riparian recruitment flows (i.e., the flow at which additional increases in flow provide very little additional width and depth of inundation of the channel) were evaluated for the spring and early summer (May through June) time period. Successful recruitment events were often preceded by large magnitude scouring flows in the bypassed and peaking reaches. Furthermore, sediment and channel conditions in the bypassed and peaking reaches were being maintained by the current flow regime and berm development was not observed. Scouring flows generally occurred during the 6 wetter water years in the bypassed and peaking reaches for a total of 14 to 22 days (depending on the reach) during the period of record. The majority of trees in the bypassed, peaking, and unregulated comparison river reaches became established during years with low to moderate magnitude spills following particularly high magnitude winter events (e.g., 1986 and 1996 to 1997) that scoured banks and bars, and prepared seed beds. PCWA stated that it is possible that other recruitment events occurred during or prior to the period of record evaluated (1975 to 2007), but the trees were removed (scoured) during more recent events. In general, riparian recruitment flows in the larger bypassed reaches occurred during wet and above normal water years, with an average duration of 7 to 28 days in wet water years and 3 to 14 days in above normal water years. On the smaller bypassed reaches, recruitment events also typically occurred in wet and above normal water years, with an average duration of 3 to 22 days in wet water years and 0 to 6 days in above normal water years. In the peaking reach, recruitment flows were less frequent and of shorter duration compared with the bypassed reaches (2 days on average). However, hundreds of seedlings and young individuals were observed by PCWA on bars with suitable substrates during field surveys. On the larger bypassed reaches, particularly immediately downstream of the large dams, and in Duncan Creek, recession rates of the spring high flow (early May to late June) were typically faster than those identified in the literature (2 to 3+ inches per day) and typically decreased with distance downstream as a result of accretion and tributary 141
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41 Table 3.3.1-1. Average number of
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43 Site/Release Location Gravel Ini
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45 a Q 1 - TSR, Table G-1 (PCWA, 20
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69 Table 3.3.2-3. Hydrology for sel
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71 Exceedances and Summary Statisti
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Page 121 and 122: 91 Figure 3.3.2-6. Fish passage bar
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195 Figure 3.3.5-1. French Meadows
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197 Figure 3.3.5-3. Long Canyon, re
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253 Table 3.3.6-1. Archaeological a
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255 Resource Number Type a Descript
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275 Table 4-2. Summary of annual co
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279 Enhancement/Mitigation Measures
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303 c Base 2010 costs were provided
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307 Resource No-Action Alternative
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319 Table 5-2. Staff-recommended mi
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321 Location Middle Fork American R
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