Laserfiche WebLink
Chapter 13:Hazard Analysis—Coastal Erosion <br /> Coastal erosion occurs when the beach migrates toward the land in order to compensate for <br /> beach erosion as it tries to maintain a constant supply of sand(see the right side of the <br /> photo). If sand is not available to a beach, such as when a wall is built to protect the land,the <br /> land is stabilized,however beach erosion will occur(see left side of photo). <br /> � i <br /> Unstabilized - <br /> Stabilized - land lost <br /> beach lost beach preserved <br /> land preserved <br /> Figure 13-2. Effects of beach stabilization <br /> Photo courtesy of Charles Fletcher <br /> Installing a seawall or revetment(i.e.,hardening a shoreline) interferes with the natural cycle <br /> of beach erosion. Rather than pulling sand from a landward supply in order to promote waves <br /> breaking further off-shore during the seasonal high wave period, the seawall or revetment <br /> prevents this natural phenomena from occurring. Thus,the land itself begins to erode. <br /> Therefore, it is tragically ironic seawalls or revetments have been installed to prevent coastal <br /> erosion, but their very presence exacerbates the very problem they were supposed to resolve. <br /> (Source: Fletcher, Charles, Eric Grossman, Bruce Richmond. Atlas of Natural Hazards in the <br /> Hawaiian Coastal Zone. 2000.) <br /> 13.2 Significant Historical Events <br /> Due to the youthful geographic age of Hawaii Island, sandy beaches are fairly uncommon; <br /> instead rocks or cliffs line most shores. <br /> 13.3 Probability of Occurrence <br /> Sandy beaches are dynamic sedimentary systems that naturally experience phases of erosion <br /> and accretion that operate over a range of time intervals. Frequent short-term changes are <br /> seasonal - erosion mostly occurs in seasons when storms that generate erosional wave <br /> regimes are more frequent. Rapid erosional episodes may also be produced by high- <br /> magnitude storms, such as tropical cyclones or intense low pressure systems. The degree of <br /> erosion that occurs within a particular erosional phase can be highly variable, and this <br /> 13-2 Hawaii County Multi-Hazard Mitigation Plan <br />