A Wave CI imatology for U.S. Coastal Waters

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Abstract
Over the past 20 years, the Coastal Engineering Research Center has operated wave gages along the Atlantic, Pacific, and Gulf coasts of the U. S. Cumulative wave height distribution functions for ten gage locations have been studied in the format of the exponential distribution. One complete year of data, at six observations per day, appears to give a reliable wave height distribution up to the 1% level of occurrence. Wave data from shipboard weather reports have been compared to wave gage data and found to be of some use in describing long term summaries of coastal wave height conditions. INTRODUCTION Ocean wave sensors, operating in the harsh environment of coastal waters, record a complex phenomenon which is not easily interpreted. The simplest analysis approach is to characterize wave conditions from each record by a single wave height and wave period. The Coastal Engineering Research Center (CERC) has accumulated a body of wave data of this type determined from pen and ink records. These data, despite their limitations, contain useful wave climatology information. Reports from shipboard observers provide a body of less precise wave information for offshore waters. WAVE GAGE DATA Since 1948, CERC has been operating wave gages at various locations along the coasts of the United States (Figure 1). Gages have been placed and maintained in water of depths from 3 meters (10 feet) to 30 meters (100 feet) below Mean Sea Level, but most data have been taken in water from 3 meters to 8 meters (25 feet) deep. For each gage location, data have been recorded over a period of time ranging from a few months to over 15 years. Most wave data were obtained with the step resistance type gage (a staff gage) described by Williams (1969). For many years the step resistance gage was the only type of surface wave gage which operated with consistency in the ocean environment. Recently other reliable surface gages have become available. One type, which interferes less than the step gage with the waves, is the continuous wire gage. A comparison of objective wave height estimates (Esteva and Harris, 1970) based on simultaneous records from these two gage types has shown that estimates of significant wave height from the step gage records are on the order of a foot or 20% higher than the estimates obtained from the continuous wire gage records (Figure 2, from Harris, 1972). Wave height estimates from pressure gage records reported by Esteva and Harris, corrected to surface conditions, agree well with height estimates from the continuous wire gage. Pen and ink wave records, usually 7 minutes long, were recorded every 4 hours at gage sites until May, 1966; since then, data from some gages have been transmitted directly to CERC via telephone line. These data are recorded at the CERC laboratory in the form of pen and ink records and, in digital form, on magnetic tape. In July, 1971, most gage stations were modified to obtain pen and ink records every 6 hours, to coincide with synoptic weather charts.

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