Levee project to start this summer, for sure
The U.S. Corps of Engineers will break ground on the first phase of a long-awaited river levee project this summer, according to project manager Jerry Nieto.
The entire flood protection project will rebuild 43 miles of riverbank on the west side of the Rio Grande between San Acacia and the south end of the Bosque del Apache National Wildlife Refuge.
Funding has been secured to build Phase I, a three-mile section of engineered levee between Otero Ave. and the Socorro Diversion Channel. A request for proposals can be issued now that objections by the U.S. Fish and Wildlife Service and other entities over impacts to water quality, habitat and sensitive species have been settled. The current Final Supplemental Environmental Impact Statement details these discussions. Nieto said public comments on the FSEIS will be accepted until Feb. 24.
The existing “spoil” bank — the pile of dirt between the low-flow channel and the river — does not meet the Federal Emergency Management Agency’s engineering specifications for a flood protection structure, Nieto said. The project will replace it with an engineered levee designed to withstand a hundred-year flood, approximately 29,900 cubic feet per second flow rate at San Acacia dam, according to the FSEIS.
The San Acacia gauge showed about 9,000 cfs flow during the September 2013 deluge. Then river broke through a bank north of the dam, flooding a low-lying section of the Sevilleta National Wildlife Refuge, but not in the reach the Corps has targeted for levee reconstruction.
An engineered river levee coupled with the existing Corps-built Socorro Diversion Structure looping around the west and north of town will improve FEMA’s flood risk designation for area residents, he said. Property flood insurance rates are based on FEMA’s risk assessments.
The U.S. Corps of Engineers will completely remove the current spoil bank and the “jetty jacks” flanking it in one-mile increments, he said, and then construct an engineered levee along the river and west 1,000 feet along the diversion channel southeast of Escondida. The new levee will be about the same size as the existing spoil bank. The jetty jacks will be replaced, and, in some places, rock rip-rap will be installed on the river side of the levee.
Jetty jacks are large metal x-shaped structures connected with cables the Corps installed in the 1950s to protect the bank from erosion from flood water, he said. Their impact on the river has been criticized in recent years, according to a University of New Mexico Water Resources Program report.
Once the public comment period ends, the final report will be forwarded to the Corps’ headquarters in Washington, D. C., he said. The contractor will be chosen in March, and construction will start by this summer. Since work will undoubtedly begin during the monsoon season, the contractor will be required to take measures to prevent flooding while the bank is breached for reconstruction.
Funding for the first phase has been secured, including matches to federal funding from the N.M. Interstate Stream Commission and the Middle Rio Grande Conservancy District, said N.M. Interstate Stream Commission spokesperson Lela Hunt. The City of Socorro contributed about $50,000, said MRGCD chief engineer Subhas Shah. Funding for the next phase depends upon the fate of state water infrastructure bills currently under consideration during this year’s legislative session, Hunt said.
The final SEIS can be viewed at www.spa.usace.army.mil/Missions/Environmental/.EnvironmentalComplianceDocuments/EnvironmentalImpactStatementsROD.aspx.