CORONA, Calif. – About three dozen Green River residents attended a meeting here July 25 to learn about the progress of the ongoing flood risk management project adjacent to their homes and to ask questions about construction methods and their impacts on the local community.
Chadi Wahby, a civil engineer who is one of the design engineers for the project, told residents the project is part of an overall effort to protect the banks of the subdivision and the 91 Freeway along the Santa Ana River in anticipation of possible increased future flows there due to water releases from Prado Dam.
“This is part of a much larger project for flood risk reduction,” Wahby said. “We need to be better prepared for the expected increases in release capacity from Prado in order to protect the homes downstream.”
Green River is the first housing development downstream from Prado Dam. When all elements of the Santa Ana River Mainstem project are in place, Prado Dam’s release capacity will increase from 10,000 cubic feet per second to 30,000 cubic feet per second. Without fortification to the river banks and other improvements, the increased flows could potentially damage homes, businesses and infrastructure.
The segment, officially known as the Santa Ana River Mainstem Lower Santa Ana River Channel, Reach 9 Phase 2A, is part of a 30-year, $2 billion project to reduce the risk of flood damage along the river’s 96-mile journey from Seven Oaks Dam near San Bernardino to Huntington Beach where it flows into the Pacific Ocean.
Wahby told the residents that design engineers had to consider varying conditions when analyzing design options for bank protection. Because of the proximity of the work to the river and the homes, environmental aspects, topographic conditions, scour analysis, soil conditions, bedrock elevations and condition, and right-or-way limitations, one solution could not be applied to the entire length of the project, he said.
“Some areas will have grouted stone, while others will have sheet pile, for example,” Wahby said.
Daniel Duarte, representing the contractor CJW Construction, Inc., told residents that placement of the rocks should be complete in about three months. Installation of approximately 500 sheet pilings, that are 40 to 60 feet long, is expected to take several months.
“The upcoming noise was an issue,” said Eileen Takata, the Corps’ Watershed Program Manager, “but overall it seemed they realized that it’s temporary, and the long-term benefits of flood protection would be worth it.”
Duarte said vibration monitors will record measurements during rock placement and pile driving, and noise monitors will ensure the contractor is in compliance with noise restrictions.
"It’ll be noisy,” Green River board member Roy Kojac told the residents, “but it has to be done."
Derek Walker, a landscape architect with the Corps, told residents about the re-vegetation strategy that will result in both riparian and upland habitats being restored.
“The vegetation should come back pretty easily,” Walker said. “It will germinate at different rates, so there will be a variety in height and maturity. We’ll also plant grasses. They’ll be annuals, so it will come back each year.”
The meeting was the third held by the Corps so far to inform residents about the project and to address their concerns.