Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The Zambezi River is the largest east-draining river in Africa. It captures runoff from 8
different countries before draining into the Indian Ocean in Mozambique through the
Zambezi Delta which is recognised as a (Ramsar) Wetland of international importance. The
Zambezi River flows are currently regulated by four large hydropower dams within its
catchment. Much attention has been given in recent literature to the detrimental effects of the
altered flow regime as a result of dams on the Zambezi River and the Delta in particular.
Existing research relating to these negative effects includes many detailed ecological,
hydrological and qualitative morphological studies but to date no detailed morphological
modelling studies have been conducted in this regard.
In this thesis a two-dimensional coupled hydrodynamic and morphological numerical model
of the Zambezi Delta is created using topographical information obtained from a navigational
study (Rio Tinto, 2011). The model hydrodynamics are calibrated using recorded water levels
and flows at two gauging stations within the model domain. The bed load sediment transport
is calibrated using field measurements (ASP, 2012b). The effects of dams on the Zambezi Delta are investigated by performing two 10 year
simulations, one representing the current (post-dam) scenario and the other representing a
pre-dam scenario. These simulation results show a significant decrease in flooded areas and
sediment movement on the floodplains as a result of dams. Additional effects on channel
widths and depth, on bed gradings, and on tidal water level variations are analysed.
The model is then used to simulate a proposed environmental flood release scenario. Such
releases have been recommended as a means to partially mitigate the negative impacts of
dams on the Zambezi River. In this case an annual flood release supplying a peak flow of
8500 m3/s (slightly less than the pre-dam mean annual flood of 10 000 m3/s) was found to cause slightly more flooding of the close floodplains and to have small effects on the river
channel width.
The model predicts hydrodynamics and bed sediment transport of non-cohesive sediments
with suitable accuracy but an issue with the suspended transport of cohesive sediments was
identified. Recommendations are made for addressing the suspended sediment transport
inaccuracy. The model, in its current form, can provide quantitative information regarding the
hydrodynamics and course sediment transport of the general delta region on a coarse scale.
With additional computational resources and accurate topographical information the model
can be refined to give accurate predictions for localised areas within the delta. Such
information would be valuable to specialist studies addressing the environmental effects of
various proposed flooding scenarios or future dams. / AFRIKAANSE OPSOMMING: Die Zambezirivier is die grootste oos-dreineerende rivier in Afrika. Dit ontvang afloop van ag
verskillende lande voor dit in die Indiese Oseaan in Mozambiek uitmond. Die Zambezidelta
work erken as 'n RAMSAR vleiland van internasionale belang. Die vloei in die rivier word
tans gereguleer deur vier groot hidro-elektriese damme binne sy opvangsgebied. Baie aandag
is in die onlangse literatuur gegee aan die nadelige gevolge van die veranderde vloei as
gevolg van damme op die Zambezi Rivier en spesifiek op die Delta. Bestaande navorsing
met betrekking tot hierdie negatiewe effekte sluit in detail ekologiese, hidrologiese en
kwalitatiewe morfologiese studies, maar tot op datum is geen gedetailleerde morfologiese
modelleringstudies gedoen nie.
In hierdie tesis is 'n twee-dimensionele gekoppelde hidrodinamiese en morfologiese
numeriese model van die Zambezi Delta geskep met behulp van topografiese inligting wat
verkry is uit 'n navigasiestudie (Rio Tinto, 2011). Die model hidrodinamika is gekalibreer
deur teen watervlakke en vloei by twee meetstasies in die model domein. Die bedvrag
sedimentvervoer is gekalibreer met behulp van veldmetings (ASP, 2012b). Die ȉnvloed van die damme op die Zambezi Delta is ondersoek deur twee 10-jarige
simulasies, een wat die huidige ( na-dam ) scenario en die ander wat 'n voor-dam scenario
ondersoek. Hierdie simulasie resultate toon 'n beduidende afname in die oorstroomde gebiede
en sedimentbeweging op die vloedvlaktes as gevolg van damme. Bykomende effekte op
kanaalbreedtes en -diepte, op die bedgraderings , en op getywatervlak variasies is ontleed.
Die model is vervolgens gebruik om 'n voorgestelde omgewingings vloedloslaating te
ondersoek. Sodanige loslaatings is aanbeveel om die negatiewe impak van damme op die
rivier gedeeltelik te verminder. In hierdie geval gee 'n jaarlikse vloedloslaating met 'n
piekvloei van 8500 m3/s (effens minder as die voor-dam gemiddelde jaarlikse vloed van 10 000 m3/s) effens meer oorstromings van die vloedvlaktes en het 'n klein uitwerking op die
rivierkanaalbreedte.
Die model voorspel die hidrodinamika en bedsedimentvervoer van nie-kohesiewe sedimente
met betroubaarheid, maar 'n probleem met die vervoer van kohesiewe sedimente is
geïdentifiseer. Aanbevelings word gemaak vir die aanspreek van die kohesiewe
sedimentvervoer onakkuraatheid. Die model, in sy huidige vorm, kan kwantitatiewe inligting
oor die hidrodinamika en natuurlik sedimentvervoer van die algemene delta streek by
benadering verskaf. Met bykomende rekenaar hulpbronne en akkurate topografiese inligting
kan die model verfyn word om akkurate voorspellings vir plaaslike gebiede binne die delta te
gee. Sulke inligting kan waardevol wees vir spesialis-studies van die omgewingsimpakte van
verskillende voorgestelde vloedloslaatings of toekomstige damme.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86402 |
| Date | 04 1900 |
| Creators | Kime, Robyn Laura |
| Contributors | Basson, G. R., 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 | xix, 115 p. : ill. |
| Rights | Stellenbosch University |
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