WSP03460

• File Number: 8441.700
• Description: Colorado Big Thompson Project - Annual Operating Plans
• Basin: South Platte
• Water Division: 1
• Date: 1/1/1989
• Title: Annual Operating Plans - Colorado Big Thompson Project - Water Year 1989-1990
• Water Supply Pro - Doc Type: Report/Study

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

a
<:)
,....
-.J
C'"J
~

average. Due to much above normal temperatu...es. Apri 1 inflow was high
at 165 percent of ave...age. Howeve.... April was a dry month as
precipitation was 66 pe...cent of average. The May 1 snowpack was only
50 pe...cent of average, which further dec...eased the April-July runoff
forecast volumne to 155.000 acre-feet. Inflows rose sharply in mid-May
and peaked for the wate... year at 1,486 ft3/s on May 30.

With water pumped from Wi 11 ow C...eek and natura 1 i nfl ow on the ri se,
sto...age began a gradual climb reaching 343,245 ac...e-feet by May 31.
May continued to be dryas precipitation was only 57 pe...cent of ave...age.

Natu...al inflow decreased rapidly in late June to below 500 ft3/s by the
end of the month. P...ecipitation continued below no...mal fo... June at
73 pe...cent of average. as well as inflow at only 52 percent of average.
Lake Granby sto...age continued to rise ...eaching its maximum fo... the
season of 374.644 acre-feet on June 23. Thi s was 165.156 ac...e-feet
below maximum sto...age capacity.

Natu...al inflows continued to be low in July at only 47 pe...cent of
average. By mid-month, natural inflow averaged only 225 ft3/s. Total
release to the Colo...ado Rive... was equal to the bypass ...elease fo... minimum
required fish habitat release, and this was dec...eased by 25 percent
due to the low runoff.

During July. Adams Tunnel dive...sions remained high at 30.700 acre-feet
to meet project water del iveries which were much above ave...age and to
maintain desi...able sto...age levels in Carte... Lake and Ho...setooth
Reservoirs. Fo... August, dive...sions through Adams Tunnel were increased
to capacity at 33,800 acre-feet for the month to maintain terminal
reservoir storage and to meet nea... normal i...rigation delive...ies.
Conditions improved in August as inflows averaged 105 pe...cent of average
and precipitation was 79 percent of average.

Du...ing Septembe.... natural inflows we...e 79 pe...cent of average. and
p...ecipitation was only 53 percent of average. Adams Tunnel diversions
continued high at 30,700 ac...e-feet fo... the month, 180 percent of average.

A total of 4,020 acre-feet of wate... was pumped into lake Granby during
June via Windy Gap Pumping Plant for the 1989 wate... year.

The computed Ap...il-July natu...al inflow to Lake Granby totaled
133,500 ac...e-feet. This was between the May 1 ...easonable minimum
(120.000 acre-feet) and May most p...obab le (155,000 ac...e-feet) runoff
fo...ecasts for the April-July volume. The May-July precipitation was
only 70 percent of average which ...esulted in the low runoff.

Lake Granby ended the water yea... with 301.182 acre-feet of water in
storage. This was 118,318 acre-feet above average and 124,170 acre-feet
less than last yea....

Adams Tunnel diversions totaled 276,700 acre-feet fo... the wate... Year.
This was more than 42,200 acre-feet above average.

11