Integrated Water Resources Management (Proceedings oi'a symposium held at Davis. California. April 2000). IAHS Publ. no. 272. 2001. 139

Water resource policies in the Imperial and Mexicali Valleys

MARIA DE LA PAZ CARPIO-OBESO University of California Cooperative Extension, Desert Research and Extension Center, 1050 E. Hoi ton Road, Holtville, California 92250, USA e-mail: [email protected]

THALIA GAONA-ARREDONDO Facultadde Arquitectitra, Universidad Antonoma de Baja California, Mexicali, Baja California, CP 21280, Mexico

Abstract The Imperial and Mexicali Valleys are located on the international border between Mexico and the United States, covering an area of 410 465 ha. Both valleys are in the Sonoran Desert, with high summer temperatures (42- 48°C). Water quantity is limited and the soil very dry; however the valleys are very productive. The main source of water for this region is the Lower Colorado River. Historically, the main economic activity has been agriculture. Imperial County is one of the top ten agricultural counties in the United States, worth more than 1 billion US$ in annual crop production. The Mexicali Valley is one of the most productive valleys in Mexico, with approximately US$ 145.75 million (9.50 pesos per US$) in crop production. The main user of water is agriculture, but the cities on the border are growing and the demand for water is increasing. Water transfers occur from the Imperial Valley to San Diego on the United States side, and from the Mexicali Valley to Tijuana, Mexico. The challenge facing the valleys is the maintenance of high agric­ ultural productivity in the long-term, without producing adverse impacts to humans and to ecosystem health. This paper provides some alternatives to enhance water management in the valleys.

Key words Colorado River, USA; desertification; irrigation; multi-state water law

INTRODUCTION

The Colorado River basin is the major river basin in the southwestern United States (Fig. 1). It runs from the Rocky Mountains to the Gulf of California, draining 637 140 Ion2 from seven states: Colorado, Wyoming, Utah, New Mexico, Nevada, Arizona and California. It also runs through two Mexican states: Baja California and Sonora. The Colorado River conveys water some 2044 km from the western slopes of the Rocky Mountains before forming the international boundary between the United States and Mexico between Yuma and San Luis, in Arizona. The international reach of the river covers a distance of 39 km. The Colorado River subsequent flows for 160 km in Mexico before emptying into the Gulf of California. The Colorado River Law allocates 9251 Mm3 year"1 to the upper and lower basins (Table 1), and an additional of 1850 Mm3 year"1 to Mexico. This is the permanent and secure volume for Mexico; however, when the river has excess water, Mexico may receive 2096 Mm3 year"1. In drought years, the reduction of water to Mexico is in the same proportion as that in the United States (IBWC-CILA, 1944). 140 Maria de La Paz Carpio-Obeso & Thalia Gaona-Arredondo

Fig. 1 Map of the Colorado River basin showing the division between the upper and lower basin, as well as the states.

Table 1 Lower Colorado River basin allocation.

Distribution Amount (Mm3) Percentage Nevada 370 4 Arizona 3453 46 California 5427 50 Mexico 1850

California's water use has historically exceeded its basic apportionment, because it has been allowed to divert the unused apportionment of Arizona and Nevada, plus to divert surplus water. The major local agencies in California using Colorado River water are: Palo Verde Irrigation District (PVID); Bard Water District (BWD), Cochella Valley Water District (CVWD) and Imperial Irrigation District (HD). Water from the Colorado River is also diverted to the Metropolitan Water District (MWD) for use in southern California urban areas and to other agriculture and urban interests along its course. Reduction of California's Colorado River use from the current level of 6414 Mm3 to 5427 Mm3 annually has had a strong impact for the South Coast region. In 1994, the MWD provided Los Angeles with about 20% of its total water supply. In 1996, almost 90% of San Diego County Water Authority's total water supply was purchased from MWD (DWR, 1998). Water resource policies in the Imperial and Mexicali Valleys 141

IMPERIAL VALLEY

The IID is the largest irrigation district in the United States. The amount of water it receives annually from the Lower Colorado River averages 3823 Mm3. Ninety eight percent of IID water is used for agriculture. The remaining 2% is delivered to nine Imperial Valley cities, which treat it to safe drinking water standards and sell it to their residents. There is no "top soil" in the usual sense in the valley, which is a large bowl filled with a conglomerate of elements transported by Colorado River flood waters. The land area irrigated in the valley is approximately 202 500 ha. IID also maintains 2341.4 km of drainage ditches, which ultimately discharge water into either the Alamo or New rivers. These rivers are the main tributaries to the Salton Sea. The availability of Colorado River water and a favourable climate make the Imperial Valley one of the most productive agricultural regions in the United States. The Imperial Valley has an agriculturally based economy, annually producing approximately 1 billion US$ in crops (Fig. 2). The major crops are alfalfa, lettuce, carrots, sugar beet, broccoli, cantaloupes, onions, wheat, and sudan grass hay. Alfalfa is the principal field crop (Table 2), requiring 0.7995 mJ ha"1 (6.5 acre-ft) annually to maintain yields. To sustain the high productivity, the farm community is required to use agrochemical products (pesticides and fertilizers; Table 3). These products may impact beneficial water use of the downstream users. The main drainage water discharge of the valley ends in the Salton Sea.

500 ,•1995 « 400 : • 1996 5 300 rrffc ! • 1997 ]• 1998 200

3 100

0J « .0331 1/1 •H o M O â S N i 2 u <« Sjj -a > ru i > [A. Fig. 2 Imperial Valley gross value of agricultural production, 1995-1998. Information based on the Imperial County Agricultural Crop and Livestock Report.

Table 2 Alfalfa productivity in the Imperial Valley 1994-1998.

Year Hectares (ha) Gross value in US$ 1994 77463.54 165 352 000 1995 73872.40 126 517 000 1996 65252.00 124 101 000 1997 68170.41 149 037 000 1998 72299.38 127 880 000 Based on the annual Imperial County reports. 142 Maria de La Paz Carpio-Obeso & Thalia Gaona-Arredondo

Table 3 Imperial Valley agrochemical use, 1994-1998.

Year Agrochemical use (kg) 1994 2727059.76 1995 3850288.96 1996 3794951.66 1997 3851890.02 1998 4250209.19 Based on the annual Pesticide Use Report.

MEXICALI VALLEY

The Colorado River delta in Mexico includes the Mexicali and San Luis Rio Colorado valleys. They form Colorado River Irrigation District no. 14 (82% of the water is used for agriculture, 12% for urban use, and 6% for industrial use). Irrigation is by gravity flow from the Lower Colorado River, or from federal and private wells. Recently, District no. 14 gave the water rights to the local farmers; however the administration of the source is still controlled by the federal government. During the recent past, the cultivated land area in the valley has decreased. Currently 207 965 ha are irrigated, with water rights for 250 000 ha. The valley represents 95% of the agricultural activity in the state of Baja California; the other 5% is on the coast (BC State Government, 1997). The main crops in the valley are cotton, wheat, horticultural crops, and alfalfa, representing about 75% of the cultivated area. In 1998, horticultural crops represented 23% of the total valley production; in 1981 it was only 2%. In 1991, the gross value of horticultural crop production was 15 million US$, on 15 700 ha. In 1998, the same area provided a gross value of 92 million US$. Desertification plays a major role in the valley. FAO, in 1980, divided desertification in to primary and secondary processes. This paper considers only the primary processes in desertification, which have a strong impact on the population and on the ecosystem. The primary aspects include degradation of the vegetation cover, water erosion, aeolian (wind) erosion, and soil salinity. Aeolian erosion and soil salinity are the most adverse impacts (National Commission of Arid Zones, 1994). The rate of aeolian erosion in the valley is one of the highest in the nation >200 t ha"1 year"'. Colorado River Irrigation District no. 14 has severe soil salinity problems, occurring on 45%o of the total land area of the district. Salinity problems in this area have several sources; one of them is the quality of the water that Mexico receives from the Lower Colorado River, at the Morelos Dam. The Colorado River is a salty river. The seven- state Colorado River Basin Salinity Control Forum has recommended numeric salinity criteria for three lower main stream stations: 723 mg l"1 below Hoover Dam; 747 mg l"1 below Parker Dam and 879 mg l"1 at Imperial Dam. These mean salinity levels do not apply to the water quality that flows into Mexico. Water delivered to Mexico has to have an average salinity of no more than 115 + 30 mg 1"' higher than the annual average salinity of water at the Imperial Dam (IBWC-CILA, 1973). The average salinity of water delivered to Mexico is approximately 1100 mg l"1. Other soil salinity sources are soil texture, shallow water tables, tile drainage, tillage, brackish well water, subsoil stratification, and open drainage maintenance. Water resource policies in the Imperial and Mexicali Valleys 143

CONTRASTS BETWEEN THE IMPERIAL AND MEXICALI VALLEYS

- Irrigated land: Imperial Valley 202 500 ha and Mexicali Valley 207 965 ha. - Water use for agriculture in the Imperial Valley (3823 Mm3) represents more than twice the water allocated to Mexico (1850 Mm3). - Mexicali Valley represents about 95% of the state of Baja California agricultural production (SAGAR, 1997); Imperial Valley represented 4% of California's agricultural production in 1998 (Agriculture Commissioners' Report, 1999). - Imperial Valley transfers water to the South Coast (San Diego and Los Angeles); Mexicali Valley transfers water to Tijuana, Tecate, and Ensenada by the Mexicali- Tijuana aqueduct. - Imperial County had approximately 142 100 inhabitants in 1999. Mexicali has approximately 700 000 (INEGI, 1995). - The principal crops are very similar in both valleys. - In Imperial Valley, to reduce the impacts of soil salinity, growers apply more water than the crop requires to leach salts out of the soil and into a subsurface system of porous tile drains that collects some of the salts. Agricultural water use efficiency for Imperial Valley is 77% (IID, 1998). In Mexicali Valley the agricultural water use efficiency is 56% (COSAE, 1998). - The federal government in Mexico subsidizes more than half of the real price of water. The cost varies based on the delivery system. For gravity flow and federal wells, the cost is 0.23 US$ per 1 s"1 day"1, which is equivalent to 2.68 US$ per thousand m3. If the source is from private wells, the cost varies according to the depth of the well, pump capacity, pump operation conditions, and energy. An average cost is 0.70 US$ per 1 s"1 day"1. Agriculture water cost in Imperial Valley is 14.00 US$ per acre-ft or 0.97 US$ per 1 s"1 day"1 (COSAE, 1998).

WATER MANAGEMENT ALTERNATIVES

The following alternatives are suggested to enhance water management in the Imperial-Mexicali valleys: (a) Infrastructure rehabilitation of the Colorado River Irrigation District no. 14 (CNA, 1995). (b) Establishment of the real cost of water, in order to penalize users that are not making good use of the resource. The real value of the cost of water will allow conservation and will maintain the infrastructure, (c) Inclusion of water management programmes to evaluate environmental impacts, through environmental indicators, such as salinity, erosion, wetland loss, biodiversity reduction, desertification increase, reduction in irrigated land area, human health, flooding, and drought, (d) Use of a legal framework that ensures the sustainability of the valleys. Rational use of water, (e) Co-participation and co-responsibility between government and water users for construction, conservation, operation, and main­ tenance of the infrastructure, (f) Desert education defined as the understanding of the fragile ecosystem that we have, without the water. Implementation of water conservation educational programmes at all levels: farmers, kindergarten, elementary and high school, college, and the public in general, through field days, radio programmes, seminars, workshops, and formal courses, (g) Promotion of the re-use of wastewater for agricultural use in crops (such as alfalfa, forage sorghum, bermuda 144 Maria de La Paz Carpio-Obeso & Thalia Gaona-Arredondo grass, rye grass, barley, and cotton) and for landscape use in parks, gardens, and golf courses (Tanji et al., 1993). (h) Implementation of "best management practices", such as improvement of irrigation scheduling, furrow dykes, sediment basins, cut-back irrigation, land-levelling, slope adjustment, drip irrigation, and tail water recoveiy systems.

REFERENCES

Agricultural Commissioners' Report (1999) Summary of County Agricultural Commissioners, California, USA. COSAE (Comision de Servicios de Agua del Estado) (1998) Futuro del Agua en Baja California 1995-2020, 4-29. Gobierno del Eslado de Baja California, Mexico. Comision Nacional de Zonas Aridas (1994) Plan de Acciôn para comhatir la Deserlijicacion en Mexico (PACD- MEXICO), 73-94. Secretaria de Desarrollo Social, Mexico. CNA (Comision Nacional del Agua) ( 1995) Programa Estatal Hidraulico. Gerencia Estatal del Estado de Baja California, Mexico. BC State Government (Comité de Planeacion del Desarrollo del Estado de Baia California) (1997) Plan Estatal de Desarrollo 1996-2001, 11-12. Gobierno del Estado de Baja California, Mexico. Department of Water Resources (1998) California Water Plan Update Bulletin 160-98, vol. 1 and 11. California!! Department of Water Resources, USA. [ID (Imperial Irrigation District) ( 1998) Annual Report. Imperial Irrigation District, California, USA. INEG1 (Institulo Nacional de Estadistica Geografia e lnformatica) (1995) Encuesta Nacional de Poblacion y Vivienda. INEGI, Mexico. IBWC-C1LA (Internacional Boundary Water Commision-Comision Internacional de Limites de Agua) (1973) Minute 242. Delegaciôn de Asuntos Agrarios y Colonizacion. Seccion de Fomento Agricola y Ejidal. IBWC-C1LA (International Boundary Water Commission-Comision Internacional de Limites de Agua) (1944) Tralado de Agitas Internacionales celebrado el 3 de febrero de 1944. Delegaciôn de Asuntos Agrarios y Colonizacion. Seccion de Fomento Agricola y Ejidal. SAGAR (Secretaria de Agricultura Ganaderia y Desarrollo Rural) (1997). Produccion Agricola de Baja California, pp. 27-35. Centro de Estadisticas Agropecuarias, Mexico. Tanji, K., Ramos-Galvan, M. & Carpio-Obeso, M. P. (1993) Initial Assessment on Opportunities for Re-use of Wastewaters in Mexicali Valley, Mexico. UCD-UABC, Mexico.