FY 2015

A Tsunami Forecast Model for Arena Cove, California

Spillane, M.C.

NOAA OAR Special Report, PMEL Tsunami Forecast Series: Vol. 10, 140 pp, doi: 10.7289/V5000020 (2015)

Operational tsunami forecasting by NOAA’s Tsunami Warning Centers relies on the detection of tsunami wave trains in the open ocean, inversion of these data (telemetered via satellite) to quantify their source characteristics, and real-time modeling of the impact on threatened coastal communities. The latter phase of the process involves, for each such community, a pre-tested forecast model capable of predicting the impact, in terms of inundation and dangerous inshore currents, with sufficient resolution and within the time constraints appropriate to an emergency response. To achieve this goal, considerable advance effort is required to tune each forecast model to the specific bathymetry and topography, both natural and manmade, of the impact area, and to validate the model’s performance with a broad set of tsunami sources. Where possible, the validation runs should replicate observed responses to historical events, but the sparse instrumental record of these rare but occasionally devastating occurrences dictates that comprehensive testing also include a suite of scenarios that represent potential future events.

During the forecast model design phase, and in research mode outside the pressures of an emergency situation, more detailed and slower-running models can be investigated. These models, referred to as reference models, represent the most credible numerical representation of tsunami response for a study region, using the most detailed bathymetry available and without the run-time constraint of operational use. Once a reference model has been developed, the process of forecast model design is to determine where efficiencies can be gained, through reducing the grid resolution and increasing the model time step, while still adequately representing the salient features of the full solution.

This report documents the reference and forecast model development for Arena Cove, a small inlet south of the rocky Arena Point headland in southern Mendocino County, California. Both the cove and the headland serve as reference points in coastal reports and are tourist venues but, while several tsunami have been detected by the tide gauge there, no injury or infrastructure damage have been reported to date. The Manchester Beach area north of Point Arena is low-lying and subject to inundation and has been included in the model domain.