WMOD00288 ‎(2)‎

• Title: Twelve Basin Investigation - Volume I
• Prepared For: Bureau of Reclaimation
• Prepared By: Robert D. Elliot, Jack F. Hannaford, Russell W. Chaffer
• Date: 5/15/1973
• Weather Modification - Doc Type: Report

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this temperature, range, frequency of occurrence, and the low elevation of a seeding
effect as well as crest zone specifications either windward of leeward or both if
applicable.
1.3 Hydrologic Approach
The objective of the hydrologic analysis phase of the Twelve Basin Study was
to convert incremental precipitation quantities derived in the meteorologic phase
of the project into surface water runoff from mountain massifs subjected to a hypo-
thetical seeding program. Both the quantity and time distribution of runoff origi-
nating in and discharging from the pl~rtinent massif units in selected study water-
sheds have been developed and summarized by study watersheds.
Various investigators have prepared estimates of potential incremental runoff
from weather modification activities in portions of the western United States.
Burley ("Augmenting Upper Colorado River Basin Water Supply by Weather Modification",
Patrick A. Hurley, presented to ASCE annual meeting and national meeting on Water
Resources Engineering, New York City, October 18, 1967) estimated an average annual
incremental runoff in the order of 1,800,000 acre-feet from the Upper Colorado River
basin. This estimate was based upon. a fifteen percent increase in the average
November-April precipitation occurri.ng above the 9500 foot elevation throughout the
areas in the upper basin subject to weather modification. This increase was based
on average conditions, assuming the 85% of the precipitation which falls will result
in surface runoff to supplement water available downstream. The estimate was based
on an average November-April precipitation of 19.4 inches (493 rom) over the entire
area above 9500 feet.
In 1971, Elliott and Hannaford ("A Hydrometeorological Data Appraisal and
Design Study in Certain River Basins in the Western United States", Report No. 15-15)
made similar estimates of average incremental runoff for the Snake, Missouri, Bear,
North Platte, and Rio Grande basins based upon a 10% increase in precipitation over
the entire seeding units or massifs tributary to the individual watersheds. Analysis
varied from the Colorado study in that variation in precipitation and forest cover
within the seeding units was considered. Elevation bands were used to define the
physical and hydrologic characteristics of the seeding units. Loss rates (and the
percentage of precipitation resulting in runoff) varied with respect to average pre-
cipitation within the elevation zones, permitting identification of the most pro-
ductive areas within the major watersheds.
A simple precipitation-runoff relationship might at first appear as the easiest
and most straightforward way of computing incremental runoff from the study watersheds.

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