WSP02851

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/19/1982
• Author: LJ Paulsen
• Title: Use of Hydroelectric Dams to Control Evaporation and Salinity in the Colorado River System
• Water Supply Pro - Doc Type: Report/Study

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(Figure 4) were not related to changes in river discharges
or reservoir volumes (Figure 5). Rather, it appears these
variations were caused by changes in methods of estimating
evaporation.

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54 56' 58 60 62 64 66 68 70 72 74 76 78
Waler Vear

Figure 5.

Average Annual Volumes for Lake Mead and
Inflows from Grand Canyon [USGS Data].

Evaporation rates in Lake Mead have historically been
estimated with the mass transfer method using equations
developed by Harbeck et al. [4]. Evaporation rates were
routinely adjusted for changes in energy advection and stor-
age. This was discontinued in October, 1974, and evaporation.
rates rose sharply in 1975 and 1976. The mass transfer meth-
od "JaS still used to estimate evaporation, but, in February
of 1976, the coefficient in the equation was changed, and
evaporation rates immediately decreased. This indicates that
the abnormally high evaporation rates for 1975 and 1976 .,ere
caused by failures to adequately compensate for advection.
Although evaporation rates for 1977 and 1978 appear reason-
able in comparison to other post-Lake Powell years, recent
data collected in limnological studies of I,ake !>lead [5]
indicate that evaporation rates are still being overesti-
mated.
Temperatures in the Upper Basin of Lake Mead are gener-
ally colder than in the Lower Basin [5]. In 1980, surface
temperatures in Virgin Basin were often 1-20C colder than in

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