Battling Mother Nature Environment Maintenance

Engineering Solutions to Coastal Erosion

BY DAVID LAGER

With hurricane season soon beginning, many community association boards and managers know to hope for the best but prepare for the worst.

That said, the desirability of waterfront property will never completely wane despite growing threats from storms and rising sea levels, leaving real estate investors, managers and owners to question the most effective approach – environmentally and cost-wise – to erosion control.

A number of options exist under the categories of “hard” and “soft” engineering solutions.

Rock structures, concrete retaining walls, steel sheet pile walls and similar breakwaters constitute the traditional “hard” approach to shoreline and coastal protection. Sheet pile walls and geo tubes also provide a high degree of protection against severe storm conditions. While these methods offer a means of protecting the shoreline from storm-driven waves and surf, there is growing concern among coastal engineering experts that they may be accelerating erosion as they increase wave reflection and alter natural shoreline processes. Other disadvantages to hard solutions include beach deficit, the negative impact on adjacent beaches and likely loss of a recreational resource. Moreover, hard erosion solutions are historically expensive to initially install and require periodic maintenance.

There is a growing tendency toward “soft” engineering methods. These approaches are designed to allow natural coastal erosion processes to continue while still providing some protection of property. Most common among soft solutions is the use of biodegradable materials like jute and coir products. Mats are made from coir, which is a natural fiber extracted from the husk of coconut, and placed into large envelopes and bags. The enclosures are then filled with locally compatible beach sand and erected into terraces extending up the face of the coastal bank. Unlike their hard solution counterparts, these soft measures absorb wave and surf effects, helps sand to build up naturally and also thwarts wave reflection.

Coir envelopes have key advantages in terms of the environment. They can be “planted” with locally indigenous vegetation to restore coastal banks. Since those materials are in their original vegetated condition, they provide benefits for birds and other wildlife.

Stabilization programs that utilize coir envelopes have been documented to slow the rate the erosion at coastal property. Placing beach-compatible sand in these envelopes at the same volume that would be eroded by wave and surf action over the course of a year can result in a protection program with proven results to absorb rather than reflect energy. Furthermore, this practice is more compatible with existing shoreline dunes and coastal banks that so often dot coastal properties.

So, what’s the downside of soft solutions? The not-so-good news is that they tend to be more temporary in nature than hard methods. Also, while the initial cost is on the low side, ongoing replenishments can drive up the expense over the years.

An advance in soft erosion solutions is a protection system from Australia called ELCOROCK, a pioneering method that was used for the first large scale application in this country earlier this year at a condominium community in Plymouth, Mass. This shoreline protection system use five- to seven-ton geotextile bags filled with sand. The containers are then placed at the toe of the coastal bank to form a stable, durable protection system. It is presently being used in Massachusetts to stabilize and rebuild a 300-foot long area of shoreline bank that is eroding. The bank is located below a group of condominiums and the 18th tee box of the association’s golf course.

Although new to this country, this system has been used in Australia for more than 20 years. Its use of relatively small geo tube containers is considered in most applications to be superior to large geotextile bags since they are installed in a terrace pattern, which reduces the potential for wave reflection, dissipates wave energy by allowing the wave to run up the face of the terraces and also moderates the cost of repairs.

It’s inaugural use at the Massachusetts community is in the form of a four level terrace installation (12 feet of vertical elevation). The installation is designed to withstand erosion from ocean waves and against rain and run off. These geo-bag containers are heavy enough to withstand hurricane and particularly nor’easter storm forces that are common in New England.

While Floridian condominium dwellers typically face a fuller brunt from hurricane fallout, the use of soft engineering method systems can have positive effects and reduce the impact of wave reflection. Climate change, rising sea levels and buildout all contribute to coastal erosion, but heightened concern elicits improved technology, making a larger number of solutions available to help quell some of the ravages of nature and time.

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David Lager is CEO of NETCO, a coast erosion/project management firm.
To contact Mr. Lager, please e-mail  dlager@netcomanage.com or call 781-863-6270.

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