Resolutions to U S Mexico Groundwater Disputes in the Colorado River Basin Melissa Nichole Brandt Environmental Sciences University of California at Berkeley Abstract Water use has been disputed for years in the Colorado River Basin which extends from Wyoming United States to the Gulf of California Mexico Over allocation of water has caused conflicts between the U S and Mexico which have led to the formation of several international treaties and agreements However none of the legislation has specifically addressed groundwater issues Since the intentions behind groundwater distribution are not delineated clearly in the letter of the law it may be interpreted in several ways The lack of clarity has perpetuated the disputes leaving both countries unsure of how to proceed in claiming their own rights to water usage The U S being the wealthier upstream country has been in a position of greater power in determining the distribution of rights In search of a more equitable solution however both parties are discussing the general issue of water rights in the U S Mexico border region specifically in terms of the Colorado River While the doctrine of equitable apportionment has worked in the U S to solve interstate water conflicts it has not yet proved itself in the international arena due to the lack of an ability to enforce international law Also groundwater in the lower Colorado River basin is already over drafted meaning that some parties would have to give up water they currently use California has proposed lining the All American canal which would preserve more water for the state but would also result in a net groundwater loss across the border in Mexico In order to reach a specific solution the U S and Mexico need to negotiate a new treaty to specifically address groundwater rights in the Colorado River Basin However before they can proceed both countries first need to agree upon a protocol for establishing groundwater rights Introduction In arid regions disputes over water have existed throughout time and are predicted to be one of the major sources of international conflicts in the future Elmusa 1995 Groundwater is particularly essential to the livelihood of communities in arid regions where underground aquifers provide storage of water which can be accessed seasonally or during drought years The Colorado River supports more than 23 million people 21 5 million in the U S and 1 5 million in Baja California and Sonora Mexico Furthermore it is used to irrigate an agricultural zone of 250 000 ha in Mexico representing 95 of the agricultural activities of Baja California Vald s Casillas et al 1998 According to theorists such as Albert Utton 1983 groundwater should be treated the same as surface water However the systems of groundwater flow and the groundwater problems that exist are drastically different from surface flow water Unlike groundwater surface water can easily be diverted and it usually originates from precipitation Davidson 1979 Groundwater on the other hand accumulates in underground aquifers for thousands of years and only a small percentage can be recharged through precipitation Continuous overdraft can cause the land to sink and aquifers to collapse resulting in a loss of valuable water storage space to be drawn upon in times of drought Furthermore groundwater pollution can be more devastating than surface water pollution since natural surface water cleaning mechanisms such as sediments are not available to serve the same function in the aquifers which hold millions of acre feet of water Groundwater Hydrology in the Lower Colorado River Basin The Lower Colorado River Basin extends from Nevada Utah New Mexico Arizona and California to Mexico at which point the water exits the Delta region at the Gulf of California see Figures 1 2 The total area of the Colorado River basin is 651 100 km2 with 10 400km2 or 1 6 of this in Mexico International Water Law Project 2000 Groundwater is a vitally important component of the hydrological system used to sustain the ecosystem and human actions including development and agriculture which take place in this arid region Davidson 1979 Groundwater is formed when water from precipitation irrigation or stream river seepage is absorbed into the ground and then collects in aquifers Wilson 1982 The formation of groundwater is a continuous process which has been taking place for thousands of years Aquifers which consist of porous underground soils that allow for water flow can be stacked Figure 1 Map of the Colorado River Basin Source Morrison et al 1996 Figure 2 Map of the Lower Colorado River at the U S Mexico Border Source Morrison et al 1996 on top of each other horizontally and separated by layers of more dense soil called aquitards see Figure 3 Water can then be accessed by either pumping wells or by artesian wells the latter of which bring water to the surface by making use of natural land slope and physical properties to force water out of the ground Aquifers are an extremely important source of underground storage for water supplies that can be utilized in arid regions at all times and most significantly during drought years A very small percentage of precipitation annually contributes to the groundwater levels most recharged groundwater comes from contributory upstream aquifers and seepage from canals and streams Throughout most of the Colorado River region ground water is pumped from storage in excess of replacement This causes a directly proportional increase between the pumping depth to water and to the volume of Figure 3 Groundwater Aquifer Source Wilson 1982 water pumped and the physical character of the aquifer Since aquifers tend to be more firmly cemented and less porous and permeable with depth when water levels decline the rate of decline commonly increases even though the pumping rate is held constant The cost of pumping increases at a geometric rather than arithmetic rate with the combination of water level lowering caused by removal of water from storage and the increase in rate of lowering per unit of production Davidson 1979 Over drafting of groundwater can have serious consequences because when water is depleted at a non sustainable level water tables can drop causing need for deeper wells and thus more expensive equipment McCarthy 1995 Furthermore the aquifer can collapse reducing valuable water storage capacity and causing flooding and the land surface can sink or crack costing large amounts of money to fix
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