Before the FERC Application for New License for the Annex Creek ...

The reservoir elevation, which averages 1104 feet (USCD), ranges
from 1019 to 1140, the maximum permitted because of dam safety considerations
(see the Dam Safety Report in the Supporting Design Report). The surface area
at maximum pool [E1 1140 (USCD)] is about 205 acres. The maximum level is
typi ca 11 y achi eved by autumn and ma i nta i ned through December. In the wi nter ,
wi th increased power generation and reduced runoff, the reservoi r e 1 evati on
typically drops gradually throughout, reaching its minimum level by May.
Data on the unregulated streamflow in the bypassed reach of Salmon
Creek are unavailable, since streamflow data were not recorded in that reach
prior to Project construction. Synthetic hydrological analyses of unregulated
streamflow have considered only inflow to the reservoir and are not available
for the lower portion of the stream. It seems likely that flows in this reach
would be slightly greater than those recorded at the dam site. The only data
available on this issue were provided by the USGS (Balding, 1974). They
exami ned di scharge measurements made in February 1973 when 1 eakage from the
flume was considered negligible due to icing and concluded that base flow into
the stream below Salmon Reservoir is about 17 cfs.
Streamflow in Salmon Creek has been recorded by the USGS since July
1982 at a gage located 0.3 mile upstream from the mouth of Salmon Creek. Data
collected from July 1982 to September 1984, when only the Upper Powerhouse was
operating, have been analyzed to estimate future streamflow in Lower Salmon
Creek.
The analysis, which was based on assumed values of turbine and generator
efficiencies, indicated that flow often drops to zero during dry
spells, a conclusion which has been contested by the USFWS. Owing to the
uncerta i nt i es of the synthet i c data, the USGS data recorded after the Lower
Powerhouse went on-line in December 1984 provide a more accurate indication of
the flows that can be expected duri ng Project operation. Monthly average
flows during this period varied from 18 to 95 cfs (see Appendix E-4). During
the lowest flow period, March 1985, mean daily flow dropped as low as 7.2 cfs,
and was less than 9 cfs for a period of 7 days.
In accordance wi th an agreement wi th ADFG (Appendi x E-1), streamflow
in Salmon Creek is to be maintained at a level of 1.4 feet as measured on
the staff gage 1 oca ted near the Salmon Creek Hatchery (see Append 1 x E-10 for
exact location). Analysis of available records indicates that this level corresponds
to about 9 cfs.
Water Use. Salmon Creek waters are currently serving three major purposes:
(1) development of hydroelectric power at AELP facilities; (2) provis
i on of 1 i mi ted pub 1 i c water supp 1 y for CBJ; and (3) maintenance of natura 1
anadromous fishery habitat in the lower reaches of Salmon Creek.
An agreement between AELP and CBJ allows for 4.64 cfs to be
delivered to the CBJ for domestic water from the Lower Penstock. The agreement
also includes removal of up to 10 mgd by pumping from the tailrace of the
Lower Powerhouse.
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