C+S June 2022 Vol. 8 Issue 6 (web)

of The District’s coastline in 2005 and again in 2011. At The District, riprap has been placed on top of the sand as a rock armor or rock revet - ment to dissipate wave energy and protect coastal homes from storm inundation. Riprap is flexible, versatile, and when embedded in the sand, may be the most robust temporary countermeasure observed at The District. Although, cheaper than an engineered solution, importing riprap is relatively expensive and requires large equipment to place the boulders. As scour begins to affect the toe of the riprap revetment, boulders eventually roll and topple seaward, and need to be maintained by restacking and redistributing the boulders.

Figure 4: Permeation grouting and riprap

Figure 5: Two 4-foot-tall interlocked Muscle Wall barrier pieces

action and erosion. They perform best when installed partially buried, to protect the toe of the wall from scour, and set in a tiered-wall con - figuration (Figure 6). The Muscle Wall barriers can be disassembled after the storm passes, or left in place for multiple seasons. Property owners within The District also employ Muscle Wall barriers as tempo - rary flood protection along decks and patios to divert water away from the home. The system may be rapidly deployed by the homeowner and taken down and stored after the storm surge subsides.

Permeation grouting exposed

Riprap revetment at individual properties

Figure 6: Single and two-tiered Muscle Wall barriers at The District

While pressure grouting and riprap are robust solutions, both systems are still considered short-term and come with a relatively high cost. Permeation grouting resists further scour in front of the property, but does very little to stop wave action from hitting property behind the improved ground. Riprap reflects and dissipates only some of the wave energy, and must be maintained regularly. In addition, both the City of Dana Point and the California Coastal Commission discourage further use of riprap. Muscle Wall Barriers Muscle Wall is a linear low-density polyethylene (LDPE) portable barrier product used for flood control, sediment control, stormwater control, coastal erosion, and material containment (Figure 5). The ap - proximately 6-foot-long barrier pieces are interlocked, secured to each other using ratchet tie down straps and filled with readily available water to produce a stable barrier system. When testing the Muscle Wall product as a flood barrier, the United States Army Corps of Engineers (USACE) found it remained stable under various loading conditions, stating, “The barrier was undamaged by waves, overtopping, debris impact, or riverine current.” In addition, the USACE concluded that compared to a typical sandbag barrier of the same height, the Muscle Wall barrier took 27 times fewer person-hours to construct, had 4 times less seepage, and withstood all tests without damage. For reference, one 4-foot-tall Muscle Wall bar - rier is equivalent to approximately 468 typical sand bags. In 2016, the first Muscle Wall barriers were installed at individual residential properties within The District as a temporary revetment to protect beach sand and property structures/improvements from wave

Single Muscle Wall Barrier

Four-year old, two-tiered Muscle Wall Barrier

Numerous Muscle Wall barrier applications have been deployed at The District to preserve beach sand behind the wall, while coarse gravel and cobble collected in front of the wall. Several of the walls had be - come buried due to the natural, dynamic action of the beach. While permeation grouting and gabion baskets present a potential beach haz - ard when partially or completely buried, the polyethylene Muscle Wall barriers, with their contoured corners and relatively soft shells, did not appear to present the same hazard when buried (Figure 7). In contrast to the observed degradation of sandbags and gabion bas - kets, we did not observe evidence of damage or degradation of the Muscle Wall product deployments, either in adjacent beach reaches or in ocean waters. Discussion During our site visit, we observed that unprotected properties adjacent to a property utilizing one of the mitigation measures discussed above, often exhibited greater effects of scour than properties adjacent to other



June 2022

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