Are beaches eroding and losing sand because of seawalls? Assemblymember Hanna-Beth Jackson has sponsored a new bill, AB947, proposing the removal of all seawalls by “a date-certain.” Additionally, this bill will prohibit property owners from making any repairs to these seawalls, which they now own. AB947 seems to be attempting to primarily blame the loss of sand causing beach erosion on seawall and other hard protection devices used by private property owners. Government-installed seawalls or hard protection devices used for public highways, public beaches, public buildings, and other public structures may not be included in AB947.
The AB947 bill is designed to fix a symptom of beach erosion by elimination of the private seawall or hard protection devices, when in fact, beach erosion is caused by other major factors such as less sediment/sand flow to replenish the beaches. The choking of sediment/sand flow to the ocean is caused by constructed watershed and flood control systems. These devices include the covering of land areas with hard surfaces, dams, debris basins, channeling rivers and streams, which inadvertently halt the natural flow of sediments which are the basic building blocks of the California beaches.
All beaches throughout the world are in constant movement with sand seemingly leaving and also being deposited. The sand along the California coastal region basically flows from the west to the east. A large portion of California beaches in recent years seems to have less sand, and because of this fact, the opinion is that there is beach erosion. Waves typically break at an angle relative to the shoreline, but retract straight back. The grains of sand traverse in a zigzag pattern along the shoreline. Depending on currents and wind, sand can be pulled off shore or deposited on shore. The substantial restriction of the natural sediment flow to the ocean is restricting the sediment/sand flow necessary to replenish the beaches. It is partially true that seawalls can contribute to the flow of sand, but devices such as piers, groins, highway hard protection systems, ports, harbor channels, wetlands, revetments, and breakwaters will also contribute to the natural flow of sand. All hard devices have an effect of “catching” sand on the upstream side of the device, but at the expense of the downstream side of the device. The downstream side of the device experiences erosion or sand depletion at a much higher rate than normal. It is possible to construct seawalls with frontage baffling, which can disperse and deposit sand at a higher rate.
AB947 is a bad bill because coastal erosion is a complex issue, which will never be solved using the elimination of the seawall as a single solution. AB947 is attempting to revise the California Coastal Act by elimination of the private seawall protection device. It appears that AB947 is attempting to eventually re-claim private property for public use, without paying for it.
AB947 could also eventually negatively affect Malibu landside private and commercial property owners by causing increased costs of bank loans, higher costs of insurance and lower appraisal values, because Malibu will be generally considered as a higher risk.
Alan V. Ruzicka, Consulting Engineer