Storage Of A New Water Resource For The Arizona Desert: The development of large surface water-spreading facilities

Mario R. Lluria

Hydrosystems, Inc., Phoenix, Arizona, U.S.A.

For decades agriculture, industry and the urban areas of southern Arizona relied principally on groundwater for its sustenance, development and growth. Although Phoenix had a limited supply of surface water from the Salt River Project  surface reservoirs on the Salt and Verde Rivers this source is subjected to extreme weather changes typical of this semi-arid region of North America. The considerable overdraft of the aquifers limited their continued use as the main water supply. Import of surface water, water re-use, water conservation and strict control of groundwater abstraction were implemented. In 1993 the Central Arizona Project Aqueduct, which conveys all of Arizona’s Colorado River  (CAP) water entitlement, was completed. To store and manage this new water resource large storage facilities were needed but none existed. One small surface reservoir was built by enlarging an existing one. However, many more were needed especially adequately distributed regionally to serve the numerous and widely spread agriculture and urban centers. Since the available volumes of CAP water were large the storage facilities needed to be of considerable capacity. Surface water-spreading facilities were the most adequate for that purpose. Given the necessary hydrogeologic conditions, they are the more cost-effective and rapid construction and operation alternative. The Salt River Project in partnership with six Phoenix area municipalities constructed and started the operation of the Granite Reef Underground Storage Project (GRUSP) in May, 1994. This facility consisting of seven recharge basins constructed in the dry channel of the Salt River has stored to date ( 12/2009) approximately 1230 million cubic meters of CAP water and smaller volumes of reclaimed water. Its operation has notably contributed to replenish the aquifer, improved the groundwater quality and improved the management of the water resources of  several of its users. The GRUSP  has an annual capacity under favorable conditions of 120 million cubic meters. This pioneer project was followed by several other large water-spreading facilities in Phoenix and in the city of Tucson.  Today there are nine other large facilities with a total annual aquifer storage capacity of  approximately 800 million cubic meters of water. Most store CAP water except GRUSP and SRP’s NAUSP  facility which also store reclaimed water and Salt and Verde Rivers water. These facilities with  minor contributions from  many small (less than  10 million cubic meters/year) facilities which predominantly store reclaimed water,  have made the use of MAR a very appropriate and successful technology for the management of the limited water resources of  this fast growing desert area of  the southwestern U.S.A.