Reclamation Determines Beneficial Use of Water by California’s Imperial Irrigation District

August 2003

The Water Resources Committee Newsletter

On July 2, 2003, the U.S. Bureau of Reclamation (Reclamation) issued its evaluation of the estimated quantity of water that California’s Imperial Irrigation District (IID) could put to beneficial use during the 2003 water year. Acting pursuant to Section 417 of its regulations, Reclamation determined that IID could only put to beneficial use approximately 91 percent of the water that it had requested Reclamation deliver during the 2003 water year. The effect of this determination was to reduce proposed deliveries during the 2003 water year to IID by approximately 280,000 acre-feet, from 3.1 million acre-feet (IID’s requested deliveries during the 2003 water year) to 2.82 million acre-feet. IID had until Aug. 1, 2003 to submit objections to Reclamation’s determination and has the right to appeal the determination to Interior Secretary Gale Norton.


The current situation on the Colorado River is well-known and was treated at length in the January 2003 edition of this Newsletter. In brief, California has for a number of years diverted water in quantities significantly greater than its allocation of 4.4 million acre- feet/year, averaging about 5.2 million acre- feet/year. After lengthy efforts by the other six states in the Colorado River Basin, California agreed, by Dec. 31, 2002, to develop a plan that would reduce its use of water from the Colorado River to 4.4 million acre-feet by 2015. This so-called “soft-landing” was in large part premised on a long-term transfer of water from IID to San Diego because IID is the California water agency with a claim to the largest quantity of water from the Colorado River. The IID/San Diego water transfer collapsed last December due to concerns on the part of IID that: (i) the transfer would require its growers to fallow land (as opposed to merely implementing water conservation measures), thereby destroying the economy of the Imperial Valley and (ii) the reduction in the discharge of tailwater into the Salton Sea through either water conservation measures or fallowing could dry up the Salton Sea, thereby potentially creating liability on the part of IID or its growers for impacts to listed species that reside in or migrate through the Sea.

Because California was unable to prepare a plan to limit its diversions from the Colorado River to 4.4 million acre-feet, Interior Secretary Norton, acting in her role as watermaster of the Colorado River, issued an order limiting IID’s diversions during the 2003 water year to 2.86 million acre-feet from the 3.1 million acre- feet IID had requested Reclamation deliver. Litigation inevitably followed. In the course of that litigation, IID secured a preliminary injunction blocking implementation of Reclamation’s reduction in diversions on the ground that Reclamation had not complied with the provisions of Section 417 of its regulations. That section authorizes the Regional Director for Reclamation’s Lower Colorado Region to make “annual determinations of each Contractor’s estimated water requirements for the ensuing calendar year to the end that deliveries of Colorado River water to each Contractor will not exceed those reasonably required for beneficial use under the respective Boulder Canyon Project Act contract or other authorization for the use of Colorado River water.” (emphasis added). The federal district court remanded the matter to Reclamation to comply with the requirements of Section 417. Reclamation’s July 2, 2003 decision represents Reclamation’s effort to comply with Section 417.

The Section 417 Determination

Section 417.3 describes the manner in which the regional director for Reclamation’s Lower Colorado Region is to make his “recommendations and determinations” about the water required to meet each contractor’s beneficial uses. Specifically, Section 417.3 lists a series of sixteen factors as items that Reclamation shall use in determining the beneficial use of water: “area to be irrigated, climactic conditions, location, land classifications, the kinds of crops raised, cropping practices, the types of irrigation system in use, the condition of water carriage and distribution facilities, record of water orders, and rejections of ordered water, general operating practices, the operating efficiencies and methods of irrigation of the water users, amount and rate of return flows to the river, municipal water requirements and the pertinent provisions of the Contractor’s Boulder Canyon Project Act water delivery contract.” The Regional director is not limited to these factors but, in the case of the July 2, 2003 determination, Reclamation did not consider other factors.

Most of the 67-page determination is devoted to analyzing the potential effects of these sixteen factors on the beneficial use of water within IID. As one might expect, however, certain factors were central to Reclamation’s arriving at the conclusion that IID’s beneficial uses of water would be less than its requested water deliveries. In particular, Reclamation relied on its discussion of operating efficiencies, focusing on the generation of tailwater and the need of water for soil leaching.

Reclamation begins its discussion of operating efficiency by discussing IID’s operating efficiency over time. Because much data on on-farm deliveries, tailwater and water for leaching are not available, Reclamation used data on district-wide inflows and outflows to attempt to compare operating efficiencies over time. Although there has been annual variation, gross net use of water within IID has typically varied from 1.5 million acre-feet/year to a little more that 2 million acre-feet/year. Gross net use has varied from about 700,000 acre-feet/year to a little over a million acre- feet/year. Gross efficiency, however, which is gross net use divided by gross inflow, peaked at about 72 or 73 percent in the mid-1980’s and is currently about 67 percent. Reclamation concludes that: “IID has historically been able to achieve higher levels of efficiency than has occurred recently. If the efficiencies of the 1985-87 period had been applied to the 2002 calendar year, the 2002 diversions would have been reduced by approximately 256,000 acre-feet.

Reclamation then continues by analyzing the key components of irrigation efficiency: crop evapotranspiration, leaching and tailwater. After comparing the estimates of the various experts in the case, Reclamation determined that there was “technical consensus” on the need for water for crops grown in IID. The various expert estimates ranged from 1.72 million acre-feet/year to 1.76 million acre-feet/ year; because the highest estimate had been made by Reclamation’s own expert, Reclamation relied upon that estimated crop water use in its determination.

Perhaps the most contentious portion of Reclamation’s analysis concerned the quantity of water required for crop leaching for “on-farm soil salinity control.” Estimates provided by the parties — in sharp contrast to the estimates of crop evapotranspiration — varied greatly. IID’s experts estimated that there was a need for 338,000 acre-feet of water for leaching. The experts for Coachella Valley Water District (an adjacent water district in California) estimated the leaching requirement at 292,000 acre-feet. By contrast, the experts for the Metropolitan Water District of Southern California (Metropolitan) and for Reclamation differed in their estimates by only 6,000 acre- feet, with the experts for Metropolitan estimated leaching water at 193,000 acre-feet while the experts for Reclamation estimated leaching water at 187,000 acre-feet.

IID’s estimate was divided into two components: deep percolation leaching, where water flows vertically through the soil and so flushes salts from the soils to be used by crops, and horizontal leaching, where water flows horizontally across the soil surface in order to flush salts from the soil. Reclamation rejected the component of leaching associated with horizontal leaching on the grounds that this practice “is not utilized at any other known locations in the western United States” and that a study a half-century ago showed that “surface flushing will not often be a justifiable procedure in the reclamation of saline soil.” Reclamation concluded that “[h]orizontal leaching is not recognized as a credible scientific concept for salinity control in any other irrigated areas with similar soil conditions.” Reclamation’s analysis then turned to the water required for deep percolation. Reclamation rejected IID’s estimate as being based on 1997 and older data and because that estimate “appeared to be influenced by the estimated amount of tile water (flowing from drains).” Instead Reclamation pointed out that its study and the study performed by Metropolitan “were based upon the most recent data available.” These studies “used different methods, yet arrived at essentially the same answer. Therefore, their independent efforts served to verify each other.” The net result of this analysis was to reduce Reclamation’s estimate of IID’s need for water by about 150,000 acre-feet.

The other major area of disagreement among the experts’ submittals concerned the appropriate level of tailwater from IID’s facilities. Reclamation stated that Metropolitan’s expert provided an estimate that tailwater should, in the long term, be no more than 5 percent. Reclamation characterized this estimate as “particularly credible evidence, given the extensive and science-based analysis, as cited above.” Reclamation’s own experts estimated that it was feasible to reduce tailwater to 11 to 12 percent. IID’s regulations prescribe monetary penalties for tailwater over 15 percent but ID estimated that historical tailwater was 17 percent. Other estimates of historical tailwater ranged up to 27 percent. Given these data, Reclamation determined that an acceptable level of tailwater for the 2003 water year is 15 percent of on-farm deliveries, or about 334,000 acre-feet. This level is about 92,000 acre-feet less than quantity of tailwater generated in IID historically. Over a longer period of time, Reclamation estimated that IID should be able to reduce tailwater to the range of between 5 and 12 percent. The California story on the Colorado River seems to unfold daily — and the developments will have important ramifications throughout the West.