WSP06476

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1978
• Title: Salinity Management Options for the Colorado River -- Part 1 of 2 -- Title Page - Page 168
• Water Supply Pro - Doc Type: Report/Study

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. CHAPTER II

ESTIMATES OF AGRICULTURAL DAMAGES

INTRODUCTION

This chapter is limited to an estimation of crop
yield losses due to increasing salinity of the irrigation
water in areas below Lee Ferry served by the
Colorado River. Areas presently receiving Colorado
River water are considered in detail, and a few
irrigation districts which might receive water from
the Central Arizona Project are considered hypotheti.
cally. In the latter instance, some possible blends of
Colorado River water with that presently supplied to
the districts concerned are used for estimating the
crop yields to be expected as the salinity of the
Colorado River increases. Expected blends of Colora.
do River water with northern California water were
used in estimating crop yields in the Pacific Coast
area.

These estimates are based upon: 1) yield decre.
ment to be expected for certain crops due to the
salinity of the soil solution, as worked out by the U.S.
Salinity Laboratory and modified by a University of
California Committee of Consultants: 2) the salinity
expected to develop in soils having a given infiltration
rate and drainage capability and irrigated with water
having a given salt content, as determined on the
Imperial Valley Field Station: 3) soil drainage classes
and acreages in the areas involved, as determined
from maps of soil series and associations prepared by
the U.S. Soil Conservation Service; and 4) annual crop
reports of the irrigation districts.

In each irrigation district, the cropland was
divided into "well," dmoderate, n and "poor" drainage
classes (based upon infiltration rate and drainage
capability) and equated to similar soils on the Imperial
Valley Field Station for which mean salinity levels
(electrical conductivity of soil extracts) to be expected
had been established under irrigation with given
water quality (TDS), given irrigation intensity, and
best cultural practice for the soil. The principal crops
were then partitioned on the different soil classes and
projected on the basis of irrigation practice and
expected salinity of the irrigation water as it
progressea to about 1,200 mg/I TDS predicted for the
river by the year 2000.

Estimates of yield reduction for a given crop were
obtained by imposing the effective soil solution

conductivity expected for the drainage class, salinity
level of the irrigation water, and irrigation practice
upon the yield declination curve supplied by the
California Committee of Conaultants. For the areas
which receive all of their water from the river t crop
yields were computed directly on tbe expected river
salinities. For the areas wbicb may receive water from
tbe Central Arizona Project or tbe Metropolitan
Water District facilities, yields were computed on
salinities of possible blends of water with that
presently available to the irrigation districts con.
cerned.

Gila ad Yuma Projecto

Tbe Gila and Yuma projects comprise a total of
approximately 150,000 acres of irrigated cropland
which was divided into 109,210 acres of well drained,
14,580 acres of moderately drained, and 25,020 acres
of poorly drained soil (Appendix 1). Yield losses to be
expected for the 10 major crops are projected on tbe
basis of salinity level and irrigation metbod and
summarized over soil drainage classes in Table 1.

CeIorado Kinr IrrIgation Project
(Colorado River indian
Re80rvation, Parker, Arizo....)

A total of 105,734 acres of the Colorado River
flood plain bas heen mapped and will be under
cultivation within 15 years. Expected crop looses from
increasing salinity are based upon this projection
broken down into 57,096 acres of well drained, 32,778
moderately drained, and 15,860 poorly drained soil.
Yield losses for tbe different salinity levels and
irrigation methods, averaged over drainage classes,
are sbown in Table 2.

Central Arizo.... Project

The CAP is expected to deliver an annual average
of 1,200,000 acre feet of Colorado River water from
Lake Havasu through the Granite Reef Aqueduct to
the area of Central Arizona generally between
Phoenix and Tucson. The present indication is that the
major portion of this water will be required for
municipal and industrial uses. But for the purpose of
indicating bow the Colorado salinity might affect crop
production if CAP water is used for agriculture, some
probable allotments are assumed for irrigation

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