Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Over the last few decades, wave run up prediction has gained the interest of numerous researchers and
every newly-published paper has aimed to predict wave run up with greater accuracy. Wave run up is
defined as the vertical elevation reached by a wave's, front water edge as it runs up a beach, measured
relative to the still water line. Wave run up is dependent on the incidental wave height, the wave
period, the beach slope and the wave steepness. The majority of publications incorporate all of these
factors, but some do not, which has led to numerous debates.
The goal of this study is to do a re-assessment of previously published wave run up formulae, to
obtain a more informed understanding about wave run up and the available predictive empirical
formulae. The study also seeks to evaluate the Mather, Stretch & Garland (2011) formula. The
method for undertaking this objective comprised a physical model test series with 10 regular wave
conditions on a constant slope, being 1/24, performed with an impermeable floor. Also, a beach study
in the field was done on Long Beach, Noordhoek, where run up measurements were taken for 30
minute intervals, resulting in five test conditions.
A numerical model was employed in conjunction with the beach study to determine the local offshore
wave parameters transformed from a deep water wave rider. This information was used to correlate
the run up measurements with known wave parameters.
Firstly, the physical model assessment was performed to provide a proper foundation for run up
understanding. Plotting empirical normalised run up values (R2/H0 ) versus the Iribarren number for
different formulae, a grouping was achieved with upper and lower boundaries. The physical model
results plotted on the lower end of this grouping, resulted in prediction differences of more than 10%.
These differences may have been caused by the unevenness of the physical model slope or the fact
that only one slope had been tested. Despite this, the results fell within a band of wave run up
formulae located on the lower end of this grouping.
An assessment of the beach measurements in the field gave a better correlation than the physical
model results when compared to normalised predicted wave run up formulae. These measurements
also plotted on the lower end of the grouping, resulting in prediction differences of less than 10% for
some empirical formulae.
When comparing these empirical predictions to one another, the results demonstrate that the formulae
comparing best with the beach measurements were Holman (1986) and Stockdon, Holman, Howd, &
Sallenger Jr. (2006). Extreme over predictions were found by Mase & Iwagaki (1984), Hedges &
Mase (2004) and Douglass (1992). Nielsen & Hanslow (1991) only compared best with the beach measurements and De la Pena, Sanchez Gonzalez, Diaz-Sanchez, & Martin Huescar (2012) only
compared best to the physical model results.
This study supports the formula proposed by Mather, Stretch, & Garland (2011). Applying their
formula to the measured results presented a C constant of 3.3 for the physical model and 8.6 for the
beach results. Both values are within the range prescribed by the authors.
Further reasearch minimized the array of possible „C‟ values by correlating this coefficient to
Iribarren numbers. „C‟ values between 3.0~5.0 is prescribed for low Iribarren conditions (0.25-0.4)
and values between 7.0~10 for higher Iribarren conditions are 0.75-0.8. However, this formula is still
open for operator erros whereby the „C‟ value has a big influence in the final result. The best
formulae to use, from results within this thesis, is proposed by Holman (1986) and Stockdon et.al
(2006). These formulae are not open to operator erros and uses the significant wave height, deep
water wave length and the beach face slope to calculate the wave run up. / AFRIKAANSE OPSOMMING: Gedurende die afgelope paar dekades, het golf-oploop voorspellings die aandag van talle navorsers
gelok en elke nuwe geskrewe voorlegging het gepoog om meer akkurate golf-oploop voorspellings te
verwesenlik. golf-oploop kan definieer word as die vertikale elevasie bereik deur 'n golf se
voorwaterkant soos dit op die strand uitrol, gemeet relatief vanaf die stilwaterlyn. golf-oploop is
afhanklik van die invals-golfhoogte, die golfperiode, die strandhelling en die golfsteilheid. Die
oorgrote mederheid publikasies uit die literaturr inkorporeer al hierdie faktore, maar sommige nie, wat
groot debatvoering tot gevolg het.
Die doel met hierdie studie is om vorige gepubliseerde golf- oploop formules te re-evalueer, om 'n
meer ingeligte begrip van golf- oploop en beskikbare voorspellende formules te verkry. Die studie
poog terselfdertyd ook om golf-opvolg tendense, uniek aan Suid Afrikaanse strande te evalueer deur
die huidige formule wat tans hier gebruik word, te assesseer. Om hierdie doelwit te bereik, is gebruik
gemaak van 'n fisiese model toets reeks bestaande uit 10 reëlmatige golfstoestande op 'n konstante
ondeurlaatbaare strandhelling van 1/24. 'n Veldstudie was ook uitgevoer op Langstrand, Noordhoek,
waar golf-oploopmetings met 30 minute tussenposes uitgevoer is, vir vyf toets-toestande.
Tesame met die veldstudie, is 'n numeriese model aangewend om die gemete diepsee data nader ann
die strand wat bestudeer is te transformeer. Hierdie inligting is benodig om 'n verband tussen tussen
oploop-metings en bekende golf parameters te bepaal.
Eerstens is die fisiese model assessering uitgevoer om 'n behoorlike basis vir die begrip van golfoploop
in die veld te verkry. Deur die emperiese, genormaliseerde oploop waardes (R₂/H₀) vir verkeie
formules teenoor die Iribarren getal te plot, is 'n groepering met hoër en laer grense gevind. Daar is
gevind dat die fisiese modelwaardes op die laer grens plot, en het verskille met die emperiese waardes
van meer as 10% getoon. Hierdie verskille is moontlik veroorsaak as gevolg van 'n oneweredige
fisiese model strandhelling of deur die feit dat slegs een helling getoets is. Ten spyte hiervan, het die
model oploop waardes binne die bestek van golf- oploop formules geval.
Assessering van die veldmetings het 'n beter korrelasie as die fisiese modelresultate getoon, tydens
vergelykings met genormaliseerde golf-oploop formules van die emperiese formules. Die oploop
waardes van hierdie metings het ook geplot aan die laer grens van die groepering, met verskille van
minder as 10% vir die meeste gevalle van die emperiese formules.
Wanneer hierdie emperiese voorspellings vergelyk word, is gevind dat die formules wat die beste
ooreenstem met die fisiese model, die van Holman (1986) en Stockdon, Howd, & Sallenger Jr. (2006) is. Die emperiese formules van Mase & Iwagake (1984), Hedges & Mase (2004) en Douglas (1992)
het die golf-oploop oorvoorspel. Nielsen & Hanslow (1991) het slegs die beste met die strandmetings
vergelyk, terwyl De la Pena, Sanchez Gonzalez, Diaz-Sanchez & Martin Huescar (2012) slegs die
beste vergelyk het met die fisiese-model resultaat.
Hierdie studie ondersteun die formule voorgestel deur Mather, Stretch, & Garland (2011). Deur hul
formules op die gemete bevindings toe te pas, is 'n C konstante van 3.3 vir die fisiese model resultate,
en 8.0 vir die stranduitlslae bepaal. Beide waardes lê binne die grense wat deur die outeurs voorgestel
is.
Verdere navorsing het getoon dat moontlike waardes vir die „C‟ konstante tussen 3.0 en 5.0 moet
wees vir Iribarren waardes van tussen 0.25 en 0.4. Vir hoër Iribarren waardes, 0.75-0.8, moet die „C‟
kosntante tussen 7.0 en 10 wees; dog is die formule steeds oop vir operateur foute. Die
hoofbevindinge van die tesis is gevind dat die beste golf-oploop formules, om tans te gebruik, die van
Holman (1986) en Stockdon et.al (2006) is. Hierdie formules kan glad nie beinvloed word deur
operateurs foute nie en maak gebruik van die invals golfhoogte, die golfperiode en die strandhelling
om die golf-oploop te bepaal.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96562 |
| Date | 03 1900 |
| Creators | Roux, Abraham Pierre |
| Contributors | Toms, Geoff, Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 103 pages : illustrations |
| Rights | Stellenbosch University |
Page generated in 0.0031 seconds