Thesis (MScEng (Civil Engineering)--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: A study of the state of reservoir sedimentation in South Africa based on reservoir
sediment deposit data, has shown that a considerable number of reservoirs have
serious sedimentation problems. The analysis of the reservoir sediment deposit data
showed that almost 25% of the total number of reservoirs have lost between 10 to
30% of their original storage capacity. The average storage loss due to sedimentation
in South African reservoirs is approximately 0.3% per year while the average annual
storage loss for all the reservoirs in the world is 0.8%.
The aim of this research was to develop sediment yield prediction methods based on
analytical approaches and mathematical modelling. The sediment yield prediction
methods can be used in planning and management of water resources particularly in
reservoir sedimentation control. The catchment erosion and sediment yield modelling
methods can be applied in temporal and spatial analysis of sediment yields which
results are essential for detailed design of water resources, particularly in the
identification of critical erosion areas, sediment sources and formulation of catchment
management strategies.
Current analytical methods for the prediction of sediment yield have been reviewed.
Nine sediment yield regions have been demarcated based on the observed sediment
yields and catchment characteristics. Empirical and probabilistic approaches were
investigated. The probabilistic approach is based on analysis of the observed
sediment yields that were calculated from reservoir sediment deposit, river suspended
sediment sampling data and soil erodibility data. The empirical equations have been
derived from regression analysis of the variables that were envisaged to have a
significant effect on erosion and sediment yields in South Africa. Empirical equations
have been developed and shown to have accurate and reliable predictive capability in
six of the nine regions.
The probabilistic approach has been recommended for the prediction of sediment
yields in the remaining three regions where reliable regression equations could not be
derived. The predictive accuracy of both the probabilistic and empirical approaches was
checked and verified using the discrepancy ratio and graphs of the observed and
calculated data.
While the analytical methods are needed to predict the sediment yield for the whole
catchment, mathematical modelling to predict sediment yields is applied for more
detailed analysis of sediment yield within the catchment. An evaluation of available
catchment sediment yield mathematical modelling systems was carried out. The main
criteria for the choice of a numerical model to be adopted for detailed evaluation was
based on the following considerations: the model’s capabilities, user requirements
and its application. The SHETRAN model (Ewen et al., 2000) was therefore
specifically chosen because of its ability to simulate relatively larger catchment areas
(it can handle catchment scales from less than 1km2 to 2500km2), its ability to
simulate erosion in channels, gullies and landslides, its applicability to a wide range
of land-use types and ability to simulate land use changes. Another model, ACRU
(Smithers et al., 2002) was also reviewed.
The aim of the model evaluation was to provide a conceptual understanding of
catchment sediment yield modelling processes comprising model set up, calibration,
validation and simulation. The detailed evaluation of the SHETRAN model was done
through a case study of Glenmaggie Dam in Australia. The flow was calibrated and
validated using data from 1975 to 1984, and 1996 to 2006 respectively. The results
for both the calibration and validation were reasonable and reliable. The sediment
load was validated against turbidity derived sediment load data from 1996 to 2006.
The model was used to identify sources of sediment and areas of higher sediment
yield. The land use of a selected sub-catchment was altered to analyse the impact of
land use and vegetative cover on the sediment yield. Based on the results, the
SHETRAN model was confirmed to be a reliable model for catchment sediment yield
modelling including simulation of different land uses. / AFRIKAANSE OPSOMMING: ‘n Studie van die stand van damtoeslikking in Suid-Afrika toon dat daar ernstige
toeslikkingsprobleme by baie reservoirs bestaan. ’n Ontleding van die
toeslikkingsyfers gegrond op damkomopmetings toon dat omtrent 25% van die totale
getal reservoirs tussen 10 en 30% van hulle oorspronklike opgaarvermoë verloor het.
Die gemiddelde tempo van damtoeslikking in Suid-Afrika is 0.3%/jaar, wat laer is as
die wêreld gemiddeld van 0.8%/jaar.
Die oogmerk met hierdie navorsing was om sedimentlewering voorspellingsmetodes
te ontwikkel deur gebruik te maak van analitiese metodes en wiskundige modellering.
Die sedimentlewering voorspellingsmetodes kan gebruik word vir die beplanning en
bestuur van waterbronne en veral vir damtoeslikking beheer. Die opvangsgebied
erosie en die sedimentlewering modelleringsmetodes kan toegepas word in
tydveranderlike en ruimtelike ontleding van sedimentlewering. Hierdie inligting
word benodig vir die detail ontwerp van waterhulpbronne en veral vir die
identifisering van kritiese erosiegebiede, bronne van sediment en die formulering van
opvangsgebied-bestuur strategië.
‘n Literatuuroorsig oor die huidige metodes vir die voorspelling van erosie en
sedimentlewering is gedoen.
Nege sedimentasie streke is afgebaken in Suid-Afrika, gegrond op waargenome
damtoeslikkingsdata en opvangsgebied-eienskappe. Proefondervindelike en
waarskynlikheidsbenaderinge is ondersoek. Die waarskynlikheidsbenadering is
gegrond op die ontleding van waargenome damtoeslikking wat bereken is uit
reservoir opmeting data en rivier gesuspendeerde sediment data, asook data oor
gronderosie.
Die proefondervindelike metode se vergelykings is afgelei vanuit regressie ontleding
van die veranderlikes wat ‘n belangrike invloed het op die erosie en sedimentlewering
in Suid-Afrika. Daar is bevestig dat die ontwikkelde proefondervindelike (empiriese)
vergelykings ‘n akkurate en betroubare voorspellingsvermoë in ses van die nege
streke het. Die waarskynlikheidsbenadering is aanbeveel vir die voorspelling van sedimentlewering in die ander drie streke, waar betroubare regressie vergelykings nie
afgelei kon word nie. Die voorspellingsakkuraatheid van albei metodes is nagegaan
en bevestig deur gebruik te maak van die teenstrydigheidsverhouding en grafieke van
die waargenome en berekende data.
Analitiese metodes van sedimentleweringsvoorspelling is nodig vir ‘n volle
opvangsgebied, terwyl wiskundige modellering om sedimentlewerings te voorspel
gebruik kan word om ‘n meer in diepte ontleding van die sedimentlewering binne ‘n
opvanggebied te doen. ‘n Evaluasie van beskikbare wiskundige modelle wat
opvangsgebied sedimentlewering kan voorspel, is gedoen. Die hoofkriteria vir die
keuse van ‘n model vir gebruik by gedetailleerde ontleding is gegrond op die
volgende: die vermoëns van die model, wat verbruikers benodig en die aanwending
van die model. Die SHETRAN model (Ewen et al., 2000) is spesifiek gekies weens
sy vermoë om relatief groter opvangsgebiede te simuleer (dit kan opvangsgebiede
van 1km2 tot 2500km2 wees) asook om erosie in kanale, dongas en grondverskuiwing
simuleer. Dit kan toegepas word op ‘n wye reeks grondtipes en kan ook die gevolge
simuleer as die gebruik van die grond verander. ‘n Ander model, ACRU (Smithers
et al., 2002) is ook ondersoek.
Die doel van die modelevaluering was om ‘n konseptuele begrip te kry van
sedimentlewering modelleringsprosesse wat die opstelling, kalibrasie, toetsing en
simulasies insluit. Die volledige evaluasie van SHETRAN is gedoen deur middel van
‘n gevalle-studie van die Glenmaggiedam in Australia. Die riviervloei is gekalibreer
en getoets deur gebruik te maak van data wat strek van 1975 tot 1984, en van 1996 tot
2006 onderskeidelik. Die resultate van beide die kalibrasie en die toetswas redelik en
betroubaar. Die sedimentlading is gekalibreer teen velddata van 1996 tot 2006. Die
model is gebruik om bronne van sediment te identifiseer, asook gebiede met ‘n hoër
sedimentlewering. Die gebruik van die grond op ‘n gekose sub-opvangsgebied is
verander om die impak van grondgebruik en plantbedekking op sedimentlewering te
ontleed. Die resultate bewys dat die SHETRAN model ‘n betroubare model is vir groot
opvangsgebied sedimentlewering modellering, asook vir die simulasie van
verskillende grondgebruike.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2863 |
| Date | 12 1900 |
| Creators | Msadala, V. P. |
| Contributors | Basson, G. R., 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 |
| Rights | University of Stellenbosch |
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