Combating Coastal Bluff Erosion

Coastal Bluff ErosionLiving near the ocean is a dream for many, but the reality can be anything but. Property damage or loss caused by coastal bluff erosion can destroy the reward of a lifetime of hard work. First, what is a coastal bluff and what can happen to a property when erosion occurs? Coastal bluffs consist of the entire slope that lies between a marine terrace and the sea. They are formed when there’s a rapid uplift of the shore relative to sea level. Erosion is a natural process that occurs to bluffs over time and through various mechanisms, leading to instability.

Coastal bluffs are subject to erosion via several mechanisms, including creep, sheetwash, rilling and gullying and sudden collapses. Creep refers to the slow, downslope movement of a mass of sediment. A large factor in the promotion of creep is groundwater seepage, and engineering solutions include irrigation restriction and the installation of horizontal drains, or hydroaugers, and pumping wells.

Sheetwash is the process by which material is carried by a film of water flowing over the surface of the bluff. Gullying and rilling occur when water flows over the bluff into gullies or distinct drainage systems. Sheetwash, rilling and gullying are caused by surface runoff. Mechanisms to control surface runoff include water redirection, bluff regrading, and drainage culverts.

Sudden collapses may also pose a threat to bluff integrity, with types of incidents including landslides and rockfalls. Marine erosion, or wave attack, can also oversteepen the seacliff and facilitate slides and falls. Beaches and offshore bars/reefs can serve as protection against marine erosion, as they can absorb wave energy.

Slope erosion is a common problem in coastal areas. Over time, coastal bluff erosion has caused severe damage to Palisades Park in Santa Monica. Nearly 100 years ago, John Percival Jones, a U.S. Senator and co-founder of Santa Monica, liked to sit on the bluffs and watch the sunset. Today, he couldn’t get near them. Access to the park has been restricted and a chain-link fence now prevents folks from enjoying the views and sea breezes that Senator Jones was so fond of. In fact, the precipice of the park is in danger of crumbling and falling down to the Pacific Coast Highway below. Damage caused by water itself is the enemy here, and the park has suffered over 30 landsides since 1930.

The factors described above make building on coastal bluff areas a risky prospect and cause trouble for current property owners. Many communities, such as Santa Monica and Malibu, are considering “managed retreats”. That means that many houses will be abandoned to the eroding geology, and owners and builders will need to begin considering moving upland, away from the beaches and bluffs.

The team at Helfrich-Associates interfaces with coastal commissions, building departments and property owners. We work together with all involved parties to ensure that properties affected by such erosion are stabilized and made safe for residences or commercial properties. Helfrich-Associates specializes in remedial measures to control surface runoff, manage groundwater, and protect the base and upper portions of the bluff itself.

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