Estimation of Potential Wave Forces on Crystal Cove State Park Historical District
For this study, Coastal Environments (CE) estimated the horizontal and uplift forces on coastal structures under extreme events in order to properly design structures and foundations for 8 historic cottages fronted directly by the beach at Crystal Cove State Park.
In past studies in 2003 and 2013, CE established the risks of damage to all 17 historic cottages by coastal forces caused by storm waves, taking into consideration the likely acceleration in sea level rise.
The ground elevation of the cottages varies between approximately 12.5 ft, NGVD and 15.6 ft, NGVD. For level 1 risk cottages, the surge force was 943 lbs/ft and for level 2 risk cottages, the surge force was 350 lbs/ft.
Based on historical far field runup, it was determined that the risk of tsunami runup from far field sources at Crystal Cove is small. Using data from the USC Tsunami Research Center for local southern California sources with Catalina fault scenarios (Figure 1), an additional tsunami wave runup analysis for near field sources was performed using a deep water wave height of 1.4 meters and a tsunami period of 120 seconds. The calculated overtopping rate was ~14.5 ft3/s-ft.
CE recommended that the eight cottages be engineered, be re-founded on pilings, or renovated in a reasonably cost-effective way, such that if they are damaged, losses will be minimized. Coastal protection methods such as sand berming (soft protection) or reparation of existing seawalls (hard protection), was also recommended to provide some protection against 10- to 20-year wave storms; however, it was stated that they may not protect the cottages during a very extreme wave storm or events not considered in this study.