WSP05700

• File Number: 8278.400
• Description: Title I - Mexican Treaty
• Basin: Colorado Mainstem
• Date: 2/17/1973
• Author: IWBC by Harshbager
• Title: Memorandum Report MR-73-1 Appendices, A - Groundwater Conditions in the Colorado River Delta Area, United States and Mexico and Appendix B - Pumping Regimens, Effects and Prediction Analysis
• Water Supply Pro - Doc Type: Publication

o

.1.1

NATURAL SOURCES, \VATER LEVELS A.N"D FLOlvS

Prior to development of water by man, the direction of
groundh'ater flo'~ ,.;as generally soutlward from Yuma and componcnts
of flow westward from the Colorado River towGrd the Salton
trough aud Nexicali Valley. Significant water development by
man took plaee in the early 19/10' s follm.;ing construction of
Boulder Dam and attendant canal system for delivery of,.;ater to
southern California and Nexico, in accordanee ,dth the International
Treaty of 1944. The development of irrigated agriculture in both
United States and Hexico by diversion of Colorado River waters
has created significant modifications of the natural Colorado
delta hydrologie system.

A revie,.; of several groundll'ater contour maps provides a basis
to observe the influence of the change in the groundwater as
caused by the diversion of Colorado River ,'raters. Figure A-7
Sh01~S the conditions in the Yuma Area for the year 1925. These
1Ya tel' level contours are typieal of virgin conditions and 5110';
the reeharge to the groundwater b,eneath Yuma Nesa was derived
from the Gila River and the Colorado River flows, in the South
Gila Valley area.

I
i

The gradient was relatively small and somewhat uniform.
North of the international boundary, between Sonora and Arizona,
the gradient \.;as about 1.3 feet per mile. It is estimated the
virgin groundwater flow across the boundary l'laS about 20,000 acre-
feet per year.

Figure A-S Sh01'lS the 1939 groundwater levels, prior to the
diversion of flO1'; frat:! the Colorado River via the AII-A:~eriean
Canal system. The conditions beneath Yuma Hesa are very similar
to those in 1925 \.;itl1 perhaps a sligllt incrcase in the f';radient
in the south,,'estenl part. Tile north-south aligullIent of the con-
tours "cst of 'the ColoTiHlo lliver in United States and ~lexico
elenrly indieute the l~estwnl'll flO1! of grollIllhmter was cilllsed by