Much more precipitation falls on the high mountains than in the low lands and valleys, but after the low salinity runoff from the mountains has converged with the runoff and seepage from the low lands, a large amount of salt has been added to the river system. It is estimated that about 80 percent of the naturally occurring salts added to the river are from diffuse sources. This amounts to an estimated 4.2 million tons annually under average water conditions in the Upper Basin and 0.5 million tons in the Lower Basin.

Man-made sources-agricultural

Irrigation is the major consumer of water in the basin and is responsible for the largest of the increases in salinity caused by man's activities. Irrigation contributes to both salt loading and salt concentration. Water is removed by evaporation and consumption by the plants but practically all of the dissolved salts are returned to the river, concentrating the salts in a smaller volume of water. When irrigation water is applied to land overlying saline shales, large quantities of soluble salts are dissolved from the shales and returned to the river.

Studies indicate that as much as 3.5 million tons of salt are added annually by irrigation return flows in the Upper Basin. Salt loading and salt concentration effects of irrigation account for an estimated 270 ppm of the salinity at Imperial Dam, or 14 ppm for each 100,000 acre-feet consumed.

Reservoir evaporation and out-of-basin export

During the 1973 water year, Upper Basin reservoir evaporation was 550,000 acre-feet, which approximates the estimates of long term evaporation. This caused an increase of 30 ppm in salinity at Imperial Dam, or 6 ppm for each 100,000 acre-feet evaporated.

The Lower Basin reservoirs, Lake Mead, Mohave, and Havasu, have a longterm average annual evaporation rate of about 1,050,000 acre-feet, which would be responsible for 60 ppm of the river's salinity at Imperial Dam. This amounts to an increase of 6 ppm for each 100,000 acre-feet evaporated.

Diversions from the Upper Colorado River Basin into surrounding basins occur at or near the headwaters, where the river's water has a very low salt content. Thus, the effect on downstream salinity of Upper Basin transmountain diversions is very similar to the effect resulting from increased reservoir evaporation. In 1973, 690,000 acre-feet of water and about 70,000 tons of salt were diverted out of the Upper Basin. The net effect was to increase the salinity at Imperial Dam by 40 ppm. This amounts to an increase of 5 ppm for each 100,000 acre-feet of water diverted.

Municipal and industrial uses

Municipal and industrial water uses amount to less than 200,000 acre-feet annually above Imperial Dam. Of the approximately 350,000 tons of salt load added during 1973 assignable to these uses, about 40 percent is due to salt additions from former operations of an industrial complex in Nevada. Omitting the impact of that salt load, these uses cause a total increase of 22 ppm at Imperial Dam, or 11 ppm for each 100,000 acre-feet of water used.

HISTORICAL AND PRESENT SALINITY

The U.S. Geological Survey has estimated that, under natural conditions, the Colorado River at Lee Ferry contained an average annual salt load of 5.1 million tons, with a salinity of 250 ppm. Man's activities have increased the river's salt load at Lee Ferry by about 3.7 million tons and the average annual salinity to about 600 ppm. Man's addition of 3.7 million tons annually to the river amounts to about 40% of the total annual salt load of 8.8 million tons. Man's activities, the consumptive use of water plus salt loading, accounts for 350 ppm out of 600 ppm, or nearly 60% of the river's salinity at Lee Ferry.

The river's average annual salinity at Lee Ferry for the 5 years, 1968 through 1972, was 606 ppm. Average annual salinities at other major points along the river in the Lower Basin for the 5 years ending in 1972 were Hoover Dam, 739 ppm; Parker Dam, 744 ppm; and Imperial Dam, 881 ppm.

Table 1 presents sources of salinity discussed earlier and shows how each source contributes to the river's present salinity at Imperial Dam.

TABLE 1.—Approximation of contributions to salinity at Imperial Dam

Lower Basin: Naturally occurring salt additions__

52

Lower Basin: Salinity increase, Parker to Imperial Dams (from irrigation and phreatophyte losses)

137

Total.

875

NOTE. Salinity impacts for sources are estimated based on current levels of use, except for the Parker to Imperial Dam analysis which is based on average difference over 5 years, 1968-72.

LAND USE AND OWNERSHIP RELATED TO NATURAL SOURCES OF SALINITY

sources.

The largest contributions to salinity are from natural runoff and natural point The following tabulation shows that over two-thirds of the lands in the Colorado River Basin are owned by the federal government. Federally owned lands contribute substantially to the salinity problem:

The Colorado River will increase in salinity in future years unless control measures are implemented. The amount of increase is dependent upon the growth of municipal, domestic, industrial (including mining and energy production), irrigation, and recreational uses which tend to add dissolved minerals and to deplete the river's flow. Water exports from Upper Basin headwaters will further deplete the river's flow.

Even if the timing and amount of all salt loading and concentrating activities were known, the river's future salinity still could not be predicted with exactness, as the salinity is also affected by the river's annual runoff, which fluctuates widely. Reasonable approximations of future salinities may be calculated, however, by assuming average water supply conditions.

Over the last few years, it has become very evident that the Upper Basin's vast mineral energy resources will be further called upon to assist in meeting the nation's energy requirements. Large electric generating plants that use coal mined within the Basin are either being placed in operation or are nearing completion. Plans for major coal gasification plants are proceeding past the design stage into contract negotiations. The costs of mining and processing oil shale deposits in Colorado, Wyoming, and Utah are rapidly becoming competitive with the costs of other sources of petroleum. Development of these energy resources will require the use of water for evaporation cooling, for chemical interactions in manufacturing gas fuel, for extracting oil from oil shale and for support of the increased population associated with the industry.

Approximately 20% of the depletions of the river caused by Upper Basin states are due to the export of Colorado River system water to areas outside the basin. It is expected that the quantity of water exported outside the basin will increase in the future. Denver, for example, recently passed a $160 million bond issue which will enable the construction of works that will increase Denver's diversions out of the Colorado River Basin by about 100,000 acre-feet/year. In addition, there are several transmountain diversion projects that have either been recently completed or are nearly completed, that will be diverting additional quantities in future years.

In-basin municipal and industrial uses, other than those associated with energy development, are not expected to greatly increase. Irrigation, the present major user of water in the Upper Basin, will continue to constitute the principal use of water in the future.

Most of the Lower Basin's supply is presently being used, and projects that will consume the remaining portion are either completed or under construction.

The Central Arizona Project, on which construction is just getting under way, will, when completed in 10-12 years, enable Arizona to withdraw its full apportionment from the river. Nevada's use is steadily increasing and should reach its full apportioned use between the years 1990 and 2000.

Upon completion of the Central Arizona Project in the mid-1980's, California's uses will have to be reduced to 4.4 maf/yr, except during those years when the Secretary may declare a surplus.

Estimates of future salinity at Lee Ferry were derived by adding to present conditions of depletions and salt load at Lee Ferry, the depletions projected for future years together with the changes in salt load associated with the different types of depletion. The resulting projections are listed in Table 2.

TABLE 2. CURRENT AND PROJECTED FUTURE SALINITY OF THE COLORADO RIVER ASSUMING NO SALINITY

2 Projected salinities at northerly international boundary assume that Minute 242 will be implemented, limiting the differential salinity increase between Imperial Dam and the northerly international boundary to 115 ppm.

PHYSICAL AND ECONOMIC IMPACT OF SALINITY

The major harmful impacts of increasing salinity are felt by municipal, industrial and agricultural users of Colorado River Water.

Effects of salinity on urban users of water

The major harmful economic impacts on urban water users caused by using waters of a high salinity and hardness are as follows:

1. Reductions in the useful lives of (a) water utility distribution_facilities; (b) home, business, and industry piping and fixtures; (c) water using devices within homes, businesses and industries; and (d) home and industry heating vessels. 2. Increases in water treatment and conditioning costs. Some of these impacts represent current expenses, but most are included in the decreased service lives of the affected facilities.

Economic detriments experienced by urban users of Colorado River water have been studied and reported by several investigators. Numerical values of damages to urban users were estimated by the Colorado River Board of California based largely on recent studies of the coastal plain of Southern California performed by the consulting firms of Daniel, Mann, Johnson and Mendenhall and Koebig and Koebig for the Califonria Water Resources Control Board. Because of the difficulty in obtaining valid estimates of the economic detriments associated with all of

the factors enumerated above, the estimates of salinity detriments were limited to impacts on those items for which valid studies have been made. Accordingly, the estimates include the impact of items 1(a), 1(d), 2 and only a partial evaluation of the detriments associated with item 1(b), and nothing on item 1(c). Evaluation of item 2 was based on the estimated costs of operating municipal water softening plants plus residual hardness detriments.

The damages to urban users were computed on a unit-use basis to be 15g/af/ppm increase in salinity.

Effects of salinity on agricultural users of water

Irrigators using high salinity water are faced with high expenses to overcome a variety of harmful impacts upon their operations. Crop yields decline and plants and trees die as the salinity within the root zone increases. The higher value crops are generally most susceptible to such damage. To reduce salt buildup within the root zones of crops, increasing quantities of water must be passed through the soil in order to leach salts accumulating in the root zone. The soil must be able to accept an increased amount of the applied water without becoming permanently saturated. Often it is required to install expensive pipe drainage systems.

The additional quantities of applied water also leach fertilizers past root zones, thus resulting in increased fertilizer requirements. Labor costs, capital outlays, and fertilizer costs are all increased. Additional costs are involved during the seed germination period when special irrigation and cultivation measures are necessary to achieve seed germination.

The Bureau of Reclamation has analyzed the penalty costs associated with the use of Colorado River water within Arizona, California, and Nevada, extending its analyses beyond the studies conducted by the Environmental Protection Agency and other investigations. The Bureau study represents the most comprehensive analysis to date. The findings are reported to be that the total annual direct cost to irrigators in these states amount to $66,400 for each ppm increase in the river's salinity. The annual indirect costs were estimated to be $42,000 per ppm salinity increase. Thus, total annual direct and indirect costs are $108,400 for each ppm increase.

This estimate of salinity costs to irrigators was converted into a unit cost per acre-foot of irrigation water delivered. The result, 1.7¢/af/ppm, is used herein as the best estimate of salinity detriments to irrigators using Colorado River water.

Total salinity detriments

Using forecasted use of Colorado River water in Arizona, California, and Nevada, the projections of salinity increases, and unit values of urban and agricultural salinity penalties, the increases in damages to Colorado River water users in these states, over and above damages currently being experienced, were computed for the years 1980, 1990, and 2000. The total annual detriments to Colorado River water users in the three states due to the projected increases in salinity, amounted to $14 million in 1980, $44 million in 1990, and $80 million in 2000. About 80% of these values are direct damages, and the balances are indirect. The total detriments amount to $240,000 per year per ppm increase for the year 2000. These potential damages indicate the stake the people of the Colorado River Basin have in measures to control the River's salinity. The beneficiaries of salinity control and the causes of salinity increases are dispersed widely throughout the Basin States.

HISTORICAL ACTIONS RELATED TO THE RIVER'S SALINITY

During the 1950's, Congress in authorizing major new developments in the basin recognized that there would be associated salinity increases. The acts that authorized the Colorado River Storage Project, the Navajo Indian Irrigation Project, the San Juan-Chama Project, and the Fryingpan-Arkansas Project directed the Secretary of the Interior to collect data and make analyses relating to the salinity of the Colorado River. As a result of these Acts, the Bureau of Reclamation has reported on the data collected and its analysis in a series of biennial reports on the quality of the river. To date, six reports have been issued covering sources of salinity, data on flows and levels of salt concentration.

The Colorado River Board of California began a comprehensive review of the entire salinity problem in early 1969, and in August, 1970, published a report on