WSP03837

• File Number: 8210.140.20
• Description: Colorado River Basin Organizations and Entities - Colorado River Basin States Forum - California
• State: CA
• Basin: Western Slope
• Date: 1/1/1980
• Author: Myron B Holburt
• Title: Appendix to Annual Report of the Colorado River Board of California for the Calendar Year 1979
• Water Supply Pro - Doc Type: Annual Report

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The Nater and Power Resources Service has assumed that the amount
of water that percolates into the areas adjacent to Lake Powell is not
lost but has gone into ground water storage or "bank storage". It is
the residual resulting from a hydrologic balance of Lake Powell inflow,
outflow, change in surface storage, and evaporation. Evaporation and
a portion of the inflow must be estimated; thus, the estimated bank
storage is subject to wide variation and possible error. The 1979 year-
end bank storage in Lake Powell was estimated to be 10.9 maf, representing
an increase in bank storage from 1978 of about 0.7 maf.

Water Uses

Colorado River Basin depletions in the Upper Basin are classified
by the !'later and Power Resources Service as inbasin consumptive uses,
transbasin diversions, and reservoir evaporation. Irrigated agriculture
is responsible for most of the inbasin consumptive uses. The quantity
of these uses is estimated by applying unit water use factors to estimates
of the land areas being irrigated. The Water and Power Resources Service's
estimates of Colorado River water depletions above Lee Ferry for the
1979 water year are:

Acre-feet

Inbasin Depletions
Transbasin Diversions
Reservoir Evaporation

2,318,000
723,000
617,000

Total, Upper Basin
Depletions

3,658,000

Table 6 shows diversions less measured return flows for the
major water users in the Lower Basin during the past five calendar
years. As can be seen, Lower Basin use during 1979 was 265,000 acre-
feet more than the previous year's use.

Table 7 shows the annual deliveries to Mexico since 1970 and
includes data on both total excess deliveries to Mexico and deliveries
which are in excess of control schedules. These weekly control schedules
of deliveries to Mexico are made up of estimated return flows from the
settling basins and river regulation, and additional releases required
from upstream storage. The releases from upstream storage are normally
held to the minimum necessary for the sum of all deliveries to meet the
United States' commitments for water delivery pursuant to the Mexican
Water Treaty and the Minutes of the International Boundary and Water
Commission. However, in 1979, large amounts of water in excess of
the treaty requirements were delivered to Mexico as a result of
controlled flood releases from the normally dry Gila River into the
Colorado River below Imperial Dam (1,369,000 acre-feet), and because
of the release of close to 1,000,000 acre-feet of extra water from
Hoover Dam for anticipatory flood control operations and for power
generation.

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