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

B-7
Dur i ng adverse water years, when the reservoi r 1 eve 1 drops be 1 ow
the minimum pool, only minimum releases for fisheries and municipal water
supply will be made.
3.2 ANALYSIS OF ESTIMATED DEPENDABLE
CAPACITY AND AVERAGE ANNUAL ENERGY
General Methodology. The methodology used to estimate dependable capacity
and average annual energy of the Salmon Creek facility is the same as that
described previously for Annex Creek in Section 2.2.
Streamflow Hydrology, Reservoir Inflow and Inflow Duration Curve. No
long term record of unregulated Salmon Creek streamflows is available.
Streamf10ws were recorded at the present site of Sa 1 mon Creek Dam from May
1911 through April 1914. Also, runoff in the Salmon Creek flume below the
Upper Powerhouse was recorded from October 1914 through September 1917.
Streamflows were recorded at the present site of Sa 1 mon Creek Dam for a
23-month per i od . Due to the 1 i mi ted extent of th iss treamf1 ow record, synthetic
flow records were developed by the App1 icant for Salmon Creek. The
synthetic monthly average inflows are based on 22 years of gaged streamflow
records from local basins with similar characteristics, namely Sheep Creek,
Gold Creek, and Carlson Creek. Relationships between these basins and Salmon
Creek were established based on the period 1914 through 1920, where streamflow
records for a 11 four sites are ava i 1 ab 1 e. Sheep Creek resu1 ted in the best
correlation and was primarily used to develop the Salmon Creek streamf10ws.
The 22-year study period January 1940 through December 1961 was
selected as the critical study period because it includes the driest 2-year
period on record, January 1950 through December 1951. Since Sheep Creek runoff
records are only available for water years 1947 through 1962, the runoff
from January 1940 through September 1946 was developed using a correlation
with precipitation at Juneau. Using the actual and synthetic Sheep Creek
streamf10ws, the Salmon Creek streamflows were developed for the 22-year critical
study period. The complete methodology used is documented in "Feasibility
Study - Replacement of Salmon Creek Flume and Lower Powerhouse Penstock,1I
James M. Montgomery, Consulting Engineers, Inc., 1980.
Based on the synthetic streamflow record, the average unregulated
inflow to Salmon Creek Reservoir is approximately 63 cfs. The maximum monthly
average i nfl ow i s 227 cfs, and the mi n i mum month 1 y average i nf1 ow i s 0 cfs.
An inflow duration curve for Salmon Creek Reservoir is shown in Fig. 8-4.
Reservoir Rule Curve, Downstream Flow Requirements and Area-Capacity
Curve. The power operations study was based on a rule curve release schedule
designed to maximize power generation during the critical winter months of
December through Apri 1 . For Sa 1 mon Creek Reservoi r, the ru 1 e curve re 1 eases
were as follows: