In January 2005, a surge of water overwhelmed the retention basin of the Santa Clara River in St. George, Utah. Originally built to protect the nearby highway, the expansion was gradually surrounded by residential and commercial structures. The retaining wall was categorized as a high-risk dam due to the construction of homes and businesses below it.
Excessive rains and melting of large snow packs in the mountains overlooking the Santa Clara and Rio Virgin Rivers caused water to rise to levels unseen since the winter of 1862. Due to the flooding, 28 homes were destroyed, condemned or damaged. There was an estimated $85 million in private property loss and an additional $140 million in damage to local infrastructure.
Maccaferri gabion mattresses were installed in phases and were used to protect the banks of the Santa Clara River. The stone confinement within the units allowed for higher shear stress resistance than riprap. These structures, made of PVC-coated galvanized wire, were divided into compartments and filled with stones at the project site. After installation, the gabion mattresses formed flexible, permeable, monolithic structures. These devices offer long-term performance against aggressive flow conditions and do not rely on vegetation for their hydraulic performance.
In 2010, similar heavy rains fell on the community, but this time the results were different. Even though water flows exceeded the 2005 levels, only minor flooding was reported and the riverbanks remained intact. The only additional work that was needed was the use of heavy equipment to remove debris buildup at bridges.