If you are new to Florida’s coast, you might not know what a seawall is or what it does. However, if you own beach-front property, a seawall is sometimes the only thing protecting your home from serious damage. Here are five facts about seawalls and seawall repair:
What is a seawall?
A seawall is a barrier between the home and the ocean. Contrary to popular belief, the seawall is usually behind the beach. That is, the beach and the ocean are in front of the seawall and any buildings are behind the seawall. This helps guarantee your home is getting the best protection from the tides.
Seawalls may take three forms:
- Vertical: A flat concrete wall oriented perpendicular to the ground and parallel to the coastline.
- Curved: A concrete wall that is curved rather than flat. A curved seawall is concave as viewed from the beach and ocean.
- Mound: An earthen embankment that runs parallel to the coastline. Unlike vertical and curved seawalls, mound seawalls are made from loose material, such as rock, rubble, and concrete chunks instead of poured concrete.
What do seawalls do?
Although seawalls can serve a variety of purposes, their primary purpose is to prevent erosion. Erosion prevention takes two forms.
- Seawalls prevent passive erosion by blocking sand and soil from naturally flowing downhill due to water flows, wind, and gravity. In this respect, seawalls are analogous to retaining walls built on terraces.
- Seawalls prevent active erosion by absorbing, deflecting, or dissipating ocean wave energy to prevent erosion. Without a seawall, the ocean tides, waves, and currents will carry soil and sand away from the coastline.
Additionally, seawalls act as a barrier against flooding during ocean surges caused by storms, hurricanes, and tsunamis. Although seawalls are only infrequently needed for this purpose, seawalls can work in combination with natural barriers such as reefs and trees to reduce the risk of ocean flooding.
What is seawall erosion?
Seawall erosion is a natural and expected process that seawalls undergo. That is, no seawall is intended or expected to last forever. There are several processes at work that cause seawall erosion.
- Wave reflection: Waves striking the seawall are reflected. This causes water pressure to increase in front of the seawall and redirects and drives waves down toward the base of the seawall. These downward waves scour sand and soil at the base of the seawall, causing seawall erosion.
- Longshore drift: Similar to wave reflection, longshore drift occurs when waves striking the seawall are redirected sideways. It is important to note that wave reflection and longshore drift always occur to some extent when waves strike the seawall. Longshore drift causes sand and soil supporting the base of the seawall to be pushed sideways, causing seawall erosion. Seawall erosion due to longshore drift can be particularly severe at the ends of seawalls.
- Hydrostatic water pressure: Hydrostatic pressure occurs on the opposite side of the seawall. Because the seawall is intended to block waves on the ocean side, it often does not drain water from the land side. Water can saturate the soil behind the seawall, pushing the seawall or eroding the soil around the base of the seawall, thereby causing seawall erosion.
How are seawalls repaired?
Seawalls can be repaired by compacting the soil and filling the voids and cracks created by seawall erosion. Typically, this involves injecting chemical grout, like structural polyurethane foam, behind the seawall. Structural polyurethane foam expands to fill cracks and voids and compact soil. Structural polyurethane foam not only eliminates voids that may cause seawall failure, it also stabilizes the ground so that it better supports the seawall.
If subsidence due to seawall erosion has affected a home, foundation repair may also be needed. A slab foundation is a solid slab of concrete that is poured as a single piece. It is typically four to six inches thick at the center and up to twenty-four inches thick at the edges to strengthen the perimeter. Pre-stressed concrete foundations include cables or steel rebar to compress the slab, providing additional strength.
Voids under foundations can cause severe damage to the home. Foundations can also be repaired by injecting structural polyurethane foam into voids that may form under the foundation.
Seawalls are important for preventing erosion and subsidence. When seawalls themselves are undermined, they can be stabilized by injecting structural polyurethane foam. When you have more questions about how to protect your home’s foundation, rely on Foundation Tech for help.