2007 Ground Water Summit

Tuesday, May 1, 2007 : 1:10 p.m.

Cessation of Transboundary Seepage from the All-American Canal: Consideration of Impacts to the Mexicali Aquifer Given Changing Watershed Conditions

Deborah L. Hathaway, PE, SS Papadopulos & Associates Inc.

Water seeping from the All-American Canal in the United States provides recharge to the Mexicali  Valley aquifer in Mexico.  This water has benefited agricultural users, wetlands and in part, has replaced channel infiltration that occurred historically via a predecessor canal and natural deltaic processes. As part of conservation measures in the United States, a replacement canal is to be constructed that minimizes the infiltration losses; thus, increasing the water supply available from water diverted into this canal for United States users.  Absent this source of fresh water recharge, declines of groundwater levels and degradation of quality is projected in Mexico, along with loss of wetlands.  With drought and increased upstream development in the past decade, the Colorado River basin is undergoing significant hydrologic change that, in turn, is impacting the hydrologic environment of the delta region in Mexico.   The impacts from the loss of canal seepage to the Mexicali Valley aquifer will be of increased severity in the context of the future hydrologic regime, as compared to that anticipated 15 years ago when the United States prepared an Environmental Impact Statement at the end of an unusually wet period that resulted in high “surplus” flows to the delta.    Furthermore, proposed mitigation measures that might have appeared promising during earlier, wetter, periods, are likely to be infeasible under projected future conditions.    Aside from cultural or legal perspectives that may argue towards the irrelevance of transboundary impacts in this case,  a watershed perspective would caution planners to carefully evaluate the impacts of this change in the context of  watershed conditions on both sides of the border, and in the context of today’s hydrologic regime.  

The 2007 Ground Water Summit