Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The primary aim of this study was to evaluate, calibrate and verify the SDF run-off
coefficients at a quaternary catchment level in the C5 secondary drainage region
(SDF basin 9) and other selected SDF basins in South Africa by establishing the
catchment parameters and SDF/probability distribution-ratios. The probability
distribution-ratios were based on the comparison between the flood peaks
estimated by the SDF method and statistical analyses of observed flow data.
These quaternary run-off coefficients were then compared with the existing
regional SDF run-off coefficients, whilst the run-off coefficient adjustment factors
as proposed by Van Bladeren (2005) were also evaluated.
It was evident from this study that the calibrated run-off coefficients obtained are
spread around those of Alexander (2003), but were generally lower in magnitude.
The adjusted run-off coefficients (Van Bladeren, 2005) had a tendency to
decrease in magnitude with increasing recurrence interval, whilst some of the
adjusted run-off coefficients exceeded unity.
The extent to which the original SDF method overestimated the magnitude and
frequency of flood peaks varied form basin to basin, with the SDF/probability
distribution-ratios the highest in the Highveld and southern coastal regions with
summer convective precipitation. In these regions the flood peak-ratios were
occasionally different by up to a factor of 3 or even more. The southern coastal
regions with winter orographic/frontal precipitation demonstrated the best flood
peak-ratios, varying from 0.78 to 1.63.
The adjusted SDF method results (Van Bladeren, 2005) were only better in 26%
of all the basins under consideration when compared to those estimated by the
original SDF method. On average, the adjusted SDF/probability distribution-ratios
varied between 0.30 and 6.58, which is unacceptable.
The calibrated version of the SDF method proved to be the most accurate in all
the basins under consideration. On average, the calibrated SDF/probability distribution-ratios varied between 0.85
and 1.15, whilst at some basins and individual return periods, less accurate
results were evident.
Verification tests were conducted in catchments not considered during the
calibration process with a view to establish whether the calibrated run-off
coefficients are predictable and to confirm that the method is reliable. The
verification results showed that the calibrated/verified SDF method is the most
accurate and similar trends were evident in all the basins under consideration. On
average, the verified SDF/probability distribution-ratios varied between 0.82 and
1.19, except in SDF basins 6 and 21 where the 5 to 20-year return period flood
peaks were overestimated by 41% and 56% respectively, which is still
conservative.
The secondary aim of this study was to develop a customised, user-friendly
Design Flood Estimation Tool (DFET) in a Microsoft Office Excel/Visual Basic
for Applications environment in order to assess the use and applicability of the
various design flood estimation methods.
The developed DFET will provide designers with a software tool for the rapid
investigation and evaluation of alternative design flood estimation methods either
at a regional or site specific scale. The focus user group of the application will
comprises of engineering technicians, engineering technologist and engineers
employed at civil engineering consultants, not necessarily specialists in the field of
flood hydrology. The DFET processed all the catchment, meteorological
(precipitation) and hydrological (observed flows) data used as input for the various
design flood estimation methods. / AFRIKAANSE OPSOMMING: Die primêre doelwit van die studie was om die SDF-afloopkoëffisiënte op ‘n
kwartinêre opvangsgebiedvlak in die C5-sekondêre dreineringsgebied (SDFopvangsgebied
9) en ander gekose SDF-opvangsgebiede in Suid-Afrika te
evalueer, te kalibreer en te verifieer deur die opvangsgebiedparameters en
SDF/waarskynlikheidsverspreiding-verhoudings vas te stel. Dié
waarskynlikheidsverspreiding-verhoudings was gebaseer op die vergelyking
tussen die vloedpieke soos beraam deur die SDF-metode en statistiese analises
van waargenome vloeidata. Dié kwartinêre afloopkoëffisiënte is met die
bestaande streeksgebonde SDF-afloopkoëffisiënte vergelyk, terwyl die
afloopkoëffisiënt-aanpassingsfaktore soos voorgestel deur Van Bladeren (2005)
ook geëvalueer is.
Dit het duidelik uit die studie geblyk dat die gekalibreerde afloopkoëffisiënte
verspreid rondom die van Alexander (2003) is, maar in die algemeen laer in
omvang. Die aangepaste afloopkoëffisiënte (Van Bladeren, 2005) was geneig om
af te neem in grootte met ‘n toename in die herhalingsperiode, terwyl sommige
afloopkoëffisiënte ‘n waarde van 1 oorskry het.
Die omvang waartoe die oorspronklike SDF metode die grootte en herhaalperiode
van vloedpieke oorskat het, wissel van opvangsgebied tot opvangsgebied, met die
SDF/waarskynlikheidsverspreiding-verhoudings die hoogste in die Hoëveld en
suidelike kusstreke gekenmerk deur konveksie-somerreënval. In hierdie streke het
die vloedpiekverhoudings gereeld verskil tot en met ‘n faktor van 3 of selfs meer.
Die suidelike kusstreke met kenmerkende ortografiese/frontale winterreënval het
oor die beste vloedpiekverhoudings beskik wat gewissel het tussen 0.78 en 1.63.
Die resultate van die aangepaste SDF-metode (Van Bladeren, 2005) was slegs in
26% van al die opvangsgebiede beter as die beramings van die oorspronklike
SDF-metode. Die aangepaste SDF/waarskynlikheidsverspreiding-verhoudings
het, met verwysing na gemiddeldes, tussen 0.30 en 6.58 gewissel, wat
onaanvaarbaar is. Die gekalibreerde weergawe van die SDF-metode was die mees akkurate metode
in al die opvangsgebiede van belang. Die gekalibreerde
SDF/waarskynlikheidsverspreiding-verhoudings het, met verwysing na
gemiddeldes, tussen 0.85 en 1.15 gewissel, terwyl die resultate van sommige
opvangsgebiede en individuele herhalingsperiodes minder akkuraat was.
Verifikasietoetse is uitgevoer in die opvangsgebiede wat nie tydens die
kalibrasieproses gebruik was nie om vas te stel of die gekalibreerde
afloopkoëffisiënte voorspelbaar is en om te bevestig dat die metode betroubaar is.
Die verifikasieresultate het getoon dat die gekalibreerde/geverifieerde SDFmetode
die mees akkurate metode is en dat soortgelyke tendense duidelik was in
al die relevante opvangsgebiede. Die geverifieerde
SDF/waarskynlikheidsverspreiding-verhoudings het, met verwysing na
gemiddeldes, tussen 0.82 en 1.19 gewissel, behalwe in SDF-opvangsgebiede 6
en 21 waar die 5- en 20-jaar herhalingsperiode-vloedpieke onderskeidelik met
41% en 56% oorskat is, wat steeds konserwatief is.
Die sekondêre doelwit van die studie was om ‘n gebruikersvriendelike
“Design Flood Estimation Tool” (DFET) in ‘n Microsoft Office Excel/Visual Basic
for Applications omgewing te ontwikkel om die gebruik en toepaslikheid van die
verskeie ontwerpvloedberamingsmetodes te bepaal.
Die DFET sal ontwerpers voorsien van ‘n sagtewareprogram om alternatiewe
ontwerpvloedberamingsmetodes op streek- of plaaslike skaal te ondersoek en te
evalueer. Die fokus-gebruikersgroep vir die toepassing van die program sal
bestaan uit ingenieurstegnici, ingenieurstegnoloë en ingenieurs werksaam by
raadgewende siviele ingenieurs, nie noodwendig vakkundiges in die veld van
hidrologie nie. Die DFET was gebruik om al die opvangsgebied-,
meteorologiese (reënval) en hidrologiese (waargenome vloeie) data vir die
verskeie ontwerpvloedberamingsmetodes te verwerk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5340 |
| Date | 12 1900 |
| Creators | Gericke, Ockert Jacobus |
| Contributors | Du Plessis, J. A., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 1 v. (various foliations) : ill. |
| Rights | University of Stellenbosch |
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