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TRM triumphs in California water-harvesting project

June 1st, 2006 / By: / Feature, Reinforcement

Turf reinforcement mat to the rescue in Riverside County.

Master Drainage Plan, Line E, San Jacinto Basin

This project had been planned to capture stormwater and excess agricultural flows during the Southern California rainy season, then reuse this water to replenish the area’s groundwater basin during times of drought.

The 50-ft.-wide x 8,000-ft.-long, 12-ft.-deep channel was constructed under the guidance of the owner, the Riverside County Flood Control and Water Conservation District (RCFCWCD). The initial design used the available sandy soil, reinforced with a hydroseeded native grass and plant mix on the slopes and floor of the channel.

In November 2004, a superintendent for the general contractor was in the process of closing out the contract on the project, when a single torrential storm severely eroded many of the 2:1 slopes (particularly the radii) and scoured the floor of the channel, leaving the functionality of the channel in question.

Concrete, rock, and grout were the initial methods considered to repair the damaged channel. But time and budget constraints forced the lead engineer, Clyde Johnson of the RCFCWCD, to search for other protection options for the Line E channel.

Concrete, rock, and grout were the initial methods considered to repair the damaged channel. But time and budget constraints forced the lead engineer, Clyde Johnson of the RCFCWCD, to search for other protection options for the Line E channel.

The first delivery of the matting, 50,000 yd.2, arrived on the job site the first week of December 2004, just prior to the record-setting Southern California rainfall that would soon be on the way. Because of the sandy, non-cohesive soil composition, extra long 12-in., 9-gauge staples were used to anchor the mat to both the side slopes as well as the channel floor.

The slopes were hydroseeded with a drought-tolerant native grass and flower mix, and then the TRM installation commenced. After approximately 20,000 yd.2 of installation, the record-breaking storms of December 2004/January 2005 sloshed Southern California. The weather would momentarily clear, the crews would rush out and continue installation of the matting, only to have the job site subsequently at a standstill for days at a time because of the torrents of rain.

Although designed as a low- to medium-flow channel (1,350 cfs), the MDP-Line E channel was often subjected to amounts of water far beyond its designed hydraulic capacity due to the relentless rainfall and reservoir breaches throughout the entire San Jacinto Basin.

The unvegetated installation area was closely monitored for failures by RCFCWCD, KEC Engineering, and Triumph Geo-Synthetics during this period. Much to the satisfaction (and relief!) of all concerned, there were no slope or channel-bottom failures where the matting had been installed; however, the areas that did not have any TRM protection did sustain damage.

The final installation segments were slated for completion by March 15, 2005, and by that time, much of the channel already had a strong stand of vegetation. The seed mix was kept in place despite months of unusually heavy rainfall.

Having overcome all of these obstacles—a major change order, a redesign, poor soils, and extremely inclement weather—the reinforced matting for this project performed far beyond expectations.

“Incredibly, much better than I ever thought it would,” said Mike Luna of the RCFCWCD.

Forrest Pharaoh, regional manager with Triumph Geo-Synthetics Inc. in Fullerton, Calif., and Ron Bygness, editor of Geosynthetics (formerly GFR), contributed to this article.

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