DESIGN WAVES FOR THE SOUTH AFRICAN COASTLINE
byJAN ROSSOUW
DISSERTATION APPROVED FOR THE DEGREE
DOCTOR OF PHILOSOPHY
AT THE UNIVERSITY OF STELLENBOSCH
Promotors
Declaration
I the undersigned declare that the work contained in thesis is my own original work and has not previously in its entirety or in part been submitted at any university for a degree.
DESIGN WAVE· CONDITIONS FOR THE SOUTH AFRICAN COASTLINE
SYNOPSIS
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 remarkabl e s imil ari ty in simultaneousl y 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.
Des ign wave hei ghts deri ved from the Extreme I di stri but i on were found to be
insensitive to assumptions regarding the independence and identical
di stri but i on of the wave hei ght sampl es and the method used for parameter estimation.
Design wave heights for the coastline between Dranjemund and Port Elizabeth were found to be strongly correlated to the 1at i tude of the recordi ng site. High waves along these coasts are i nvari ably caused by the passage of col d
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.
Cyclones affect the extreme wave heights along the Natal North coast and standard methods of design wave height estimation are not applicable in this area.
Wave peri od di stri buti ons between Oranjemund and Port E1 i zabeth are vi rtua11y i dent i ca1 with an 80 percent range of peak energy peri od (Tp) of 9s to 16s
.and a median Tp of 12,5s. East of Port E1 izabeth wave periods reduce
gradually all the way up to Richards Bay.
DESIGN WAVE CONDITIONS FOR THE SOUTH AFRICAN COASTLINE
Synopsis
List of Tables
List of Figures
Li st of Symbols
Acronyms
TAB L E
o
F
CON T E N T S
Page No.
(i )T-l
F-l
S-l
A-I
1.
INTRODUCTION
1
2.
WAVE INFORMATION REOUIRED BY THE DESIGN ENGINEER
4
2.1
GENERAL.
4
2.2
WAVE HEIGHT PARAMETERS
4
2.2.1
Design Significant Wave Height
4
2.2.2
Maximum Individual Wave Height
5
2.2.3
Occurrence of Groups of High Waves
,
5
2.3
WAVE PERIOD PARAMETERS
5
2.3.1
Energy Density Spectrum Associated
wi th the Des ign Storm ...•...• 5
2.3.2.
Peak Energy Period (Tpl and Zero Crossing
Period tTzl Associated with the Design Storm
6
•
2.3.3.
Period associated with the Maximum Individual
Wave and Groups of High Waves ...•.•... 6
3.
WAVE RECORDING
7
3.1 GENERAL ...•••...•...•...••.•.•..•...7
