| Coastal engineers have long recognized the need for a storm classification system that combines wave conditions, storm surge, and the length of time for the storm event. A new classification system has been developed that is based on the conservation of total horizontal momentum. This research concentrated on developing the theory and then applying that theory for a 10-year period of data from the Army Corps of Engineers Field Research Facility (FRF) in Duck, North Carolina. When fully developed, the Coastal Storm Impulse scale (COSI) may be applied to all previous Hurricane and Northeaster storm events along a coast and can be calculated during future events as the storm moves in space and time.;Newton's second law of motion relates the forces, F, needed to cause an acceleration, a (dV/dt), of a given mass, m. A lesser-known form relates the impulse, I (F*dt), required to cause a change in the momentum (m*dV) of the mass. Radiation stress theory (Longuet-Higgins and Stewart, 1964) can be used to calculate the depthintegrated and time-averaged horizontal momentum flux of the waves. Hughes (2004) refined the theory and introduced the maximum wave momentum flux that needs only the wave height, period, and water depth in the computation. Uniform, open-channel flow theory can be used to calculate the depth-integrated horizontal pressure and flow-induced momentum of the current. The still-water depth (hydrostatic) component can be removed to leave only the storm surge momentum. Wave-induced momentum and surge-induced horizontal momentum are simply added together to produce the total storm momentum in units of force per unit crest width. When integrated over the storm duration, the storm impulse, Is, is the result for a particular location at the coast.;Both a synthetic Hurricane and synthetic Northeaster were developed. These are similar to the scales used for the calibration of the Army Corps of Engineers Storm-Induced Beach Change (SBEACH) software (Larson, Kraus, and Byrnes, 1990). These synthetic storms were used to calculate the Storm Impulse Standard Event, ISE of 4.8 x 106 N-m-hr. The COSI scale is then defined as: COSI=ISISE to present a relative scale or indicator of the magnitude of the coastal storm compared with the standard. Over twenty-five years of "normal" and "storm" conditions for waves and water levels are available from the U.S. Army Corps of Engineers Field Research Facility (FRF) at Duck, NC. The definition of a storm is based on wave heights of 1.6m in deep water (Dolan, et.al 1988). The ten-year period from 1994 to 2003 was studied, resulting in 160 storm events. COSI events ranging from a value less than 1 to greater than 10 were observed during this period.;It was determined that using conservation of storm momentum to combine wave conditions and storm surge over the duration of the storm is a satisfactory means to categorize storm events. Further research into application of the concept is required to extend to the entire length of shoreline affected by the storm event, applicability outside Duck, North Carolina, and application to historic storm events. |
