Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The investigation of the interrelationship of the fluvial morphology and the salinity of the Great Fish River
Estuary was performed by the combination of a two-dimensional morphological model and a one dimensional
advection dispersion module. Two scenarios were defined for investigation, namely Scenarios A and B. Model
bathymetry and grid/network for each model and scenario was compiled from topographical information
obtained from aerial photos, SRTM data, LIDAR and 24 measured river cross sections of the area from the river
mouth up to 27km upstream of the river mouth. Model boundary conditions were developed from empirical
formulas and measured data from the Department of Water and Sanitation (DWS). Both models were calibrated
with results obtained during field measurement conducted from 5 – 7 May 2012.
Scenario A consisted of a long term 5 year morphological simulation (1 May 2007 to 30 May 2012) with
manual mouth closure events for identified river low flow periods. Water levels upstream of the river mouth
were extracted from the two-dimensional morphological module and used as the downstream boundary
condition of the one-dimensional advection dispersion (salinity) model. For scenario B floods with return
periods between 1:2 and 1:100 years were simulated in the morphological model. The resultant bathymetries
were then used to compile the network and bathymetry of the one dimensional advection dispersion (salinity)
model. The different flood resultant bathymetries were then used with equal boundary conditions (representative
of the average flow in the river) in the one dimensional salinity model. The predicted salinity was compared for
each bathymetry used.
From model results distinct trends were observed. During low flow conditions the estuary basin fills with
sediments and during floods the sediments are flushed out of the estuary. Large magnitude floods greatly erode
the estuary especially in the middle reach, during floods the tidal inlet experiences overtopping and subsequent
erosion, the constriction at the tidal inlet is completely destroyed during larger floods. The estuary mouth in its
closed state experiences slight overtopping and the mouth is breached during periods of high river flows.
The magnitude of salt intrusion depends mainly on the size (the constriction) of the river mouth (tidal inlet).
During periods of mouth closure the average salinity in the estuary decreases, average salinity increases if the
tidal inlet area is increased. The extent of salt intrusion is approximately 10 km upstream of the river mouth
when the mouth is open and the intrusion length increases during spring tides. / AFRIKAANSE OPSOMMING: Die verwantskap tussen die Groot Vis Rivier Estuarium morfologie en sout toestand is ondersoek deur die
kombinasie van ‘n twee dimensionele morfologiese model en ‘n een dimensionele sout model. Twee toestande
is gedefinieer vir ondersoek naamlik Scenario A en Scenario B. Die area vanaf die rivier mond tot 27 km
stroomop van die rivier mond is deur die modelle gesimuleer. Die gemodeleerde area stem ooreen met die area
waar gemete rivier-snit diepte metings beskikbaar was, onbrekende data is aangevul met behulp van lugfotos,
LIDAR- en SRTM- data. Die model grens toestande is bepaal met empiriese vereglykings asook gemete data
vanaf die Departement Waterwese. Beide numeriese modelle was gekalibreer met veld data verkry vanaf 5 tot 7
Mei 2012.
Scenario A het behels ‘n langtermyn 5 jaar morfologiese modellering (1 Mei 2007 tot 30 Mei 2012) met toemond
toestande gedurende gedefinieerde rivier vloei toestande. Die watervlakke van die twee dimensionele
morfologiese model stroomop van die mond is gebruik as die stroomaf grenstoestand van die een dimnesionele
model om die effek van die morfologiese veranderinge te inkorporeer in die sout model. Scenario B het behels
die simulering van rivier vloede met herhaal periodes tussen 1:2 en 1:100 jaar in die morfologiese model. Die
rivier-bodem vlakke verkry van laasgenoemde simulasiesis toe gebruik in die een dimensionele sout model met
dieselfde grenstoestande wat ooreenstem met die gemiddelde toestande in die Groot Vis Rivier. Aangesien die
grenstoestande dieselfde was en net die rivier-bodem vlakke gevarieer is, kon die effek van vloede op die
souttoestand in die estuarium bepaal word.
Uit die model resultate kon duidelike tendense waargeneem word. Gedurende lae rivier vloei toestande is die
estuarium gevul met sediment en tydens vloede het die sediment weer ge-erodeer en gedeponeer in die oseaan.
Groot vloede veroorsaak baie erosie in die estuarium veral in die middel bereik en by die riviermonding. Indien
die vloed groot genoeg is word die riviermond vernouing totaal uitgespoel. Die riviermonding in die geslote
staat ondervind effense oorstroming en word oopgespoel indien die rivier vloei groot genoeg is.
Die graad van die sout indringing in die estuarium hang hoofsaaklik af van die grootte (die vernouing) van die
rivier mond. Gedurende toe mond toestande is die gemiddelde sout vlakke in die estuarium laer, wanner die
rivier monding groter raak, word die gemiddelde sout vlakke in die estuarium meer. Die omvang van die sout
indringing strek tot ongeveer 10 km stroomop van die rivier mond wanneer die mond oop is en die indringing
afstand neem toe gedurende spring getye.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96952 |
| Date | 03 1900 |
| Creators | Julyan, Enrique Edward |
| Contributors | Basson, Gerrit 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 | 214 pages : illustrations |
| Rights | Stellenbosch University |
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