Thesis (PhD (Civil Engineering))--University of Stellenbosch, 1989. / ENGLISH ABSTRACT: Several aspects related to the estimation and selection of design wave conditions were investigated. An analysis program which includes strict quality control routines was developed for digital Waverider data. All available Waverider data from deepsea records were analysed with this program. A remarkable similarity in simultaneously recorded wave heights between Cape Town and Port Elizabeth was found. This similarity was used to compile a near continuous wave record over an eight year period for the Southern Cape coast. The 10537 values of significant wave height (Hmo) which made up the record for the Southern Cape were found to give a good visual fit to the Extreme I and Log-normal distributions over the entire range of Hmo values. Design wave heights derived from the Extreme I distribution were found to be insensitive to assumptions regarding the independence and identical distribution of the wave height samples and the method used for parameter estimation. Design wave heights for the coastline between Oranjemund and Port Elizabeth were found to be strongly correlated to the latitude of the recording site. High waves along these coasts are invariably caused by the passage of cold fronts past the southern tip of the continent. Wave heights reduce as the distance from the west to east route of these cold fronts increase, thus the reason for the abovementioned correlation. No deepwater wave records are available east of Port Elizabeth. Shallow water records indicate that a reduction in wave height can be expected between Port Elizabeth and East London.