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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be subject to some depletion or regulation before reaching the downstream gaging
stations representing the study watersheds.
Estimates of the time-distribution of runoff for each season have been made
based upon time-distribution from watersheds typic~l of the massif units. These
sub-watersheds represent the massifs in terms of quantity of precipitation, eleva-
tion distribution, forest coyer, and other factors apt to influence the time-distri-
bution of runoff. Adjustments have been made for precipitation falling outside of
\
the October-April seeQ:i.ng_p$r:!-QQ.~d
~..... _..--"-

1.3.2 Description of Techni~~. Following is a brief description of techni-
ques used in the development of the hydrologic phase of this report.
1.3.2.1 Areal distribution of increases in cold orographic precipitation.
A technique was required to determine the average and seasonal distribution of the
increase in precipitation from seeding cold orographic storms. Meteorologic input
was based upon precipitation occurring during the October 1 - April 30 season. ~he
areal distribution of incremental precipitation, primarily in the form of sncrwp:~]
within massif units has been ~sed =u~n i~ohy~~!_. m~~ _d_~li~~~ting~~~!ra~e October' .
1 - April 30 precipit~.tJo!1_. ~' . -~, ' ._~- .
1.3.2.2 Physical and hydrologic characteristics. Maps were prepared
delineating the various study watersheds within major basin boundaries and the area
of effect of the various massif units influencing runoff from the study watersheds.
This information was delineated on 1:1,000,000 World Aeronautical Charts and is
shown in the Map Appendix.
A~~leva.ti~~ata were deve~~~ed for each massif unit by planimetering~
foot contours on the World Aeronautfcal Charts. Where more detail was required, work
was done using 1:250,000 Western Untted States Topographic Maps or USGS 15 minute
Quadrangles.
Maps delineating forested area were used to distinguish forested from alpine
regions where runoff characteristics would differ. Generalized soil and geologic
maps were utilized as available.
Average seasonal (October 1 - April 30) precipitation by elevation zone within
,~~c_~_~,:s~if_.~n~t_~a~.d~termined fr.o.~!!...!~?l1ye_!,~l. maps, Although some ~b; ectiv~y
entered into evaluation of precipitation by elevation zones, provision was made in
the procedure for entry of more than one precipitation quantity if precipitation
within the elevation zone and massi:E unit varied considerably. In several instances
where October-April isohyetals were not available, average annual isohyetals were
used and adjusted for the variation. In some west coast basins, October-April

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