Reprint from the Progress Times - August 17, 2007
©Progress Times 2007 - All Rights Reserved

Commission releases dam inspection results

The International Boundary and Water Commission, United States and Mexico (IBWC), jointly with its technical advisors from the U.S. Army Corps of Engineers, Mexico’s National Water Commission, and Mexico’s Federal Electricity Commission, have released the results of the recent Five-Year Safety of Dams Inspection for four international dams located in the Rio Grande Basin.

The inspectors determined that all four dams are generally well maintained and are currently capable of operating under normal conditions. The dams are also capable of operating under flood conditions, with the exception of Retamal Dam where modifications of flood operating procedures is recommended.

In evaluating the dams, the inspectors considered risk-based Dam Safety Action Classes as follows: DSAC I – Urgent and Compelling (Unsafe, DSAC II – Urgent (potentially unsafe), DSAC III – High Priority (conditionally unsafe), DSAC IV – Priority (Marginally unsafe), and DSAC V – Normal (safe).

Based on the inspection, the experts have placed the IBWC dams in the following class:

– Amistad Dam (DSAC II) – Located near Del Rio, TX-Ciudad Acuña, Coahuila, the dam is used for water storage, flood control, and hydroelectric power. The classification is based largely on naturally-occurring sinkholes, which have existed since the dam was constructed, potentially affecting dam stability. The report recommends that a panel of geotechnical consultants be convened to further evaluate and study the stability of the dam foundation.

– Falcon Dam (DSAC III) – Located near Roma, TX-Nueva Ciudad Guerrero, Tamaulipas, the dam is used for water storage, flood control, and hydroelectric power. The classification is based on a past history of seepage during higher water levels. The report recommends using current analytical methods to update the seepage stability analyses so that IBWC can confirm or change the DSAC and undertake any repairs that may be needed.

– Anzalduas Dam (DSAC IV) – This diversion dam is located near McAllen, TX-Reynosa, Tamaulipas is used for flood control and to effect releases for downstream water users in both countries. The inspectors made various recommendations for maintenance and electrical upgrades, which are already underway. Additionally, sediment and sandbars near the dam should be removed.

– Retamal Dam (DSAC III) – this diversion dam located near Donna, TX-Rio Bravo, Tamaulipas is used for flood control. The classification is based on center gate oscillation during flood events, which has caused problems in regulation flow and has the potential to damage the gate and/or hoist components. The inspectors recommend that the gate lifting system be replaced with a different type of system. Until that work is accomplished, they recommend that flood operating procedures be modified to minimize use of the center gate. They further recommend that a sandbar downstream of the dam be removed.

The complete text of the Safety of Dams inspection reports is available online at: http://www.ibwc.state.gov/PAO/CURPRESS/2005/Dams.pdf.