The United States Section of the International Boundary and Water Commission (USIBWC) continues to monitor the effects of Hurricane Alex on the Rio Grande Basin and is moving into flood operations in the coming days due to the expected impact of flow from Mexican tributaries downstream of Falcon Dam.  The USIBWC is closely coordinating this event with the National Weather Service and the Mexican Section of the Commission.

The Commission continues to analyze the potential effects of precipitation on two Mexican reservoirs on the San Juan River, a tributary that flows into the Rio Grande at Rio Grande City, Texas and Ciudad Camargo, Tamaulipas.  The Mexican Section of the Commission has indicated that it expects the downstream reservoir on the San Juan River, Marte R. Gomez Dam, to spill floodwaters beginning Sunday, which would increase flow in the Rio Grande.  The timing and extent of any impact on the Rio Grande is still being analyzed but based on the current reports from the Mexican Section, diversion of water into the internal floodways in the United States and Mexico appears likely.   Residents in the Lower Rio Grande Valley should monitor National Weather Service warnings and forecasts for any updated information about conditions in the Rio Grande Basin into next week.

The USIBWC operates a system of Rio Grande flood control levees, dams, and floodways in the Lower Rio Grande Valley in Hidalgo, Cameron, and Willacy Counties.   To prepare for flood conditions, on Saturday, July 3, USIBWC crews will begin closing all drainage and irrigation structures that pass through USIBWC levees in order to prevent floodwaters from the Rio Grande, Banker Floodway, Main Floodway, North Floodway, and Arroyo Colorado from flowing into adjacent communities.  Once the structures are closed, drainage from the land side of the levee that would normally flow into the river or floodways will be blocked so any local storm water flows will need to be pumped over the levee by the community or drainage district responsible for local storm water management.  As conditions warrant, USIBWC staff will move into Flood Fight Operations.  During this phase of response, crews work 24 hours per day to patrol flood control levees to identify and respond to any problems that could arise such as erosion along the levees, freeboard encroachment, or seepage on the land side of the levees.  Sand bagging operations will be established if needed.  Crews also take more frequent flow measurements to track and document the flood.

As part of its flood operations, the USIBWC exchanges information with the Mexican Section of the Commission regarding flood conditions.  The USIBWC provides data about Mexico’s Rio Grande tributaries to the National Weather Service, which uses this and U.S. data to formulate flood forecasts.  The two Sections of the Commission jointly operate the Retamal and Anzalduas Diversion Dams as necessary to divert Rio Grande floodwaters into each country’s floodway or to make flood releases from Amistad and Falcon International Storage Reservoirs located upstream on the Rio Grande.   In May, the U.S. and Mexican Sections of the Commission conducted their annual flood workshop in preparation for the hurricane season.

Information about Rio Grande flow as well as storage and release data from U.S. and Mexican reservoirs in the Rio Grande basin is available on the USIBWC web page at:  http://www.ibwc.gov/Water_Data/Reports/RG_Flow_data.html