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

Streamflow Hydrology, Reservoir Inflow and Inflow Duration Curve. Synthetic
flow records were developed by the Applicant based on 18 years of gaged
streamflow records from the USGS Gage No. 1504800, Sheep Creek near Juneau.
The Sheep Creek dra i nage ba sin was chosen due to its simi 1 ari ty ins i ze and
other physical characteristics with the Annex Creek basin. In addition, it
has the longest period of record of unregulated flows in the vicinity of the
Project.
Based on the synthetic monthly average streamflow record, the average
unregulated inflow to Annex Creek Reservoir is approximately 68 cfs. The
maximum monthly average inflow is 280 cfs, and the minimum monthly average
inflow is 0 cfs. A reservoir inflow duration curve for Annex Creek Reservoir
is shown in Fig. B-1.
Reservoir Rule Curve, Downstream Flow Requirements and Area-Capacity
Curve. The power operations study was based on a rule curve release schedule
designed to provide maximum power generation during the critical winter months
of December through April. For Annex Creek Reservoir, the rule curve releases
were as follows:
B-3
Month
August through November
December and January
February through April
May through July
Release
(cfs)
73.4
47.7
44.0
51 .4
When the reservoir was full, all reservoir inflow was released
through the penstock, up to the hydraulic capacity of the power plant.
There are no minimum instream flow release requirements for Annex
Creek downstream of the dam.
The area-capacity curve for Annex Creek Reservoir is shown in
Fig. B-2. As shown in the exhibit, active storage at the maximum pool (E1 844
MSL) is 23,400 acre-feet.
Turbi ne Capabi 1 i ty. Hydrau 1 i c Capac i ty and Hydrau 1 i c Head Los ses. An
estimated constant overall plant efficiency of 72% was used in the operation
studies. The maximum plant capacity at full reservoir ;s 4,050 kVA, and the
max i mum hydrau 1 i c capac i ty of the plant is 76.8 cfs. The head los ses in the
penstock were calculated based on a Manning's II nil roughness value of 0.015,
yielding a head loss coefficient of 0.01131. A curve showing power plant
capability versus head and power plant discharge is shown in Fig. B-3.