Change in storage capacity at Amistad, Falcon reservoirs

By Sonny HInojosa
Water Advocate

Recently, the International Boundary & Water Commission (IBWC) met with representatives of the Lower Rio Grande Valley Water District Managers’ Association. The agenda for the meeting was to present the results of the 2014 Bathymetric Survey. Every 10 years a study is performed by the IBWC or their Mexican counterpart — Comisión Internacional de Limites y Aguas (CILA) to determine and quantify the sedimentation occurring at both international reservoirs. The CILA performed the 2014 Survey. In 2024, the IBWC will perform the Survey.

The result of the survey includes gains and losses in the Amistad and Falcon reservoirs.

At Amistad International Reservoir, the Survey indicates a total loss of storage capacity of 48,828 acre feet. The Unites States’ share of the reservoir capacity is 56.2% and that equated to a loss of 27,442 acre feet of storage capacity for the US. At Falcon International Reservoir, the Survey indicated a gain in storage capacity of 19,386 acre feet. The United States’ share of the reservoir capacity is 58.6% and that equated to a gain of 11,361 acre feet of storage capacity for the US.

The total conservation capacity for both reservoirs was 5,922,348 acre feet. The new conservation capacity is 5,892,907 acre feet which reflects the loss of 29,441 acre feet of storage.

The new conservation capacity for the U.S. at both international reservoirs is now 3,375,802 acre feet reflecting the loss of 16,081 acre feet of storage capacity. Previous conservation capacity was 3,391,883 acre feet.

As of Oct. 14, the U.S. had 718,538 acre feet in storage which is 21.28% of the U.S. conservation storage capacity. The all-time low was 19.06% which occurred in 1998.

Today, Oct. 25, 2023, will mark the end of the third year of the current five-year cycle of the 1944 Treaty with Mexico. Mexico is to deliver to the U.S. a minimum of 350,000 acre feet annually, as an average, over a five-year period from six named tributaries that flow into the Rio Grande above the international reservoirs. At the end of five years, Mexico should have delivered to the U.S. a minimum of 1,750,000 acre feet.

As of Oct. 14, 2023, Mexico’s target delivery was 1,040,411; however, Mexico has only delivered 372,401 acre feet (just a tad over one years’ requirement). Mexico is behind in their deliveries to the U.S. by 668,010 acre feet.