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|Title:||Interaction of seawalls and beaches : eight years of field monitoring, Monterey Bay, California|
|Authors:||Griggs, Gary B.|
Tait, James F.
Moore, Laura J.
|Publisher:||Coastal and Hydraulics Laboratory (U.S.)|
|Series/Report no.:||Contract Report;CHL-97-1|
|Abstract:||Abstract: Coastal protection structures have historically been the most common approach. to dealing with the problem of shoreline erosion in the United States. Three potential impacts of these structures have been identified, and include: (A.) impoundment or placement loss, (B.) passive erosion, and (C.) active erosion. The first two are relatively straightforward and predictable. The third has been the subject of considerable discussion and debate, but until recently, has not been systematically investigated in the field. This report presents the results of 7 years of biweekly to monthly monitoring of beaches adjacent to seawalls along the central California coast. These surveys have allowed evaluation of both the seasonal beach changes due to the presence of seawalls as well as any longer tenn effects. Although active erosion during winter months has been documented at seawalls in this study, erosion has been seasonal and temporary in nature. A comparison of summer and winter beach profiles on beaches with seawalls and on adjacent control beaches reveals no significant long-term effects or impacts of seawalls in this location during this 7-year period. After 7 years of surveying, however, the question of how the seawall-backed beach would behave compared with the control beaches during a period of severe winter storms had still not been answered. During the eighth, and final, year of surveying an opportunity to answer this question was presented. In January and March of 1995, two winter storms struck the central coast causing extensive flooding and beach erosion. This report includes the results of surveys from January to September 1995, and reveals that the behavior of the seawall beach during these storms was consistent with the conclusions reached after the previous 7 years of surveying this site.|
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