Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: This study sets out to describe the incipient motion process in cobble/boulder bed rivers in terms of the unit applied power approach. This objective has been met through the collection of data on stone movement from a total of thirteen flood events observed in two undisturbed rivers in the Western Cape, namely the Molenaars and Berg Rivers. The data were plotted on the original modified Liu diagram for incipient motion and it was found that the threshold of movement for the smaller stones did not conform with the portion of the Liu diagram which represents fully turbulent flow (i.e. where ~ gDs tv: = 0.12 for Re. >13). It was concluded that the only reason that could explain this deviation is the fact that the original modified Liu diagram had been derived for uniform particle size beds while the data of the Molenaars and Berg Rivers represent non-uniform particle size beds. This was proved through re-deriving the y-axis function of the original modified Liu diagram to include a factor that makes provision for the roughness of a non-uniform particle size bed. It was found that the average absolute roughness of the non-uniform particle size beds in the Molenaars and Berg Rivers is reasonably well approximated by a value of k=da. Design curves (in terms of the original modified Liu diagram parameters) for intensity of motion were also produced. Although it is not possible to read off accurate percentages of movement values directly from these curves, it should be possible to deduce reasonably accurate values in practical situations. / AFRIKAANSE OPSOMMING: Die studie poog om die begin van beweging proses in klip/rotsbed riviere te beskryf in terme van die eenheids aangewende drywing metode. Hierdie doel is bereik deur die insameling van klipbewegingdata in 'n totaal van dertien vloedgebeurtenisse in twee ongerepte riviere in die Wes-Kaap, naamlik die Molenaars en Bergriviere. Die data was geplot op die oorspronklike aangepaste Liu diagram vir begin van beweging en dit was gevind dat die grens van beweging vir die kleiner klippe nie ooreenstem met die gedeelte van die Liu diagram wat volle turbulente vloei verteenwoordig nie (waar ~ gDs tv; = 0.12 vir Re. >13). Daar was tot die gevolgtrekking gekom dat die enigste rede wat die afwyking kan beskryf is die feit dat die oorspronklike aangepaste Liu diagram afgelei was vir uniforme partikelgrootte beddens terwyl die data van die Molenaars and Bergriviere nie-uniforme partikelgrootte beddens verteenwoordig. Dit was bewys deur die heratleiding van die y-as funksie van die oorspronklike aangepaste Liu diagram om 'n faktor in te sluit wat voorsiening maak vir die ruheid van 'n nie-uniforme partikelgrootte bed. Dit was gevind dat die gemiddelde absolute ruheid van die nieuniforme partikelgrootte beddens in die Molenaars en Bergriviere word redelik goed benaderd met 'n waarde van k=ds4• Ontwerpkurwes (in terme van die oorspronklike aangepaste Liu diagram parameters) vir intensiteit van beweging was ook ontwikkel. Alhoewel dit nie moontlik is om baie akkurate persentasies van beweging af te lees van die kurwes nie, is dit moontlik om akkuraat genoeg waardes te verkry in praktiese situasies.

Channel instability has occurred in the Bell river, north eastern Cape, in the form of meander cutoffs, incipient meander cutoffs, channel straightening and general channel instability. Recent cutoffs occurred in 1974 and 1988. The study examines the spatial and temporal controls of channel form and pattern in the Bell river in order to assess the causes of channel instability. From the 17 km surveyed stretch, it was found that the main spatial controls of channel form were riparian vegetation density and channel bed material. Discharge as estimated in the field was not the main controlling variable of channel form. Two distinct groups of stream beds were identified from the survey; an upper gravel-bed stream and a lower sand-bed stream. These sites displayed distinct form ratios, channel gradients and bed material characteristics. The incidences of major channel instability were identified as being the transitional zone between the two reaches. Examination of temporal controls of channel form included climatic trend analysis and catchment sediment production analysis. Rainfall analysis indicated that no long term progressive trends in the annual or seasonal data existed. Distinct wet and dry cycles occur with peaks every 16 to 19 years. Wet cycles are the result of an increase in the frequency of daily events rather than in the magnitude of events. Flow record analysis demonstrated the relationship between regional discharge and upper catchment rainfall. Coincidence of peak flows and channel straightening were also noted. Soil erosion surveys showed that erosion had increased in the catchment and that accelerated erosion were probably the result of overstocking and poor veld management. It was concluded that channel changes in the Bell river are possibly the result of anthropogenic influence in catchment and channel processes. Increased sediment production to the channel resulted in channel aggradation with attendant instability. The plantation of riparian vegetation led to perimeter stability in the short term at flows less than bankfull discharge, but served to reduce cross-sectional area in the long term, thereby increasing the potential for flooding, meander cutoffs and channel change

The Klein Berg River catchment is intensely cultivated with orchards, vineyards and wheat, while also ensuring a water supply to the main urban center, Tulbagh, and the two conservation areas (Waterval and Groot Winterhoek). The primary objective of this thesis is to determine channel change over a long and short time period, and to relate these changes to landuse change within the catchment. <br /> <br /> Assessing stability of a selected reach within the catchment was done on a short term basis with the use of erosion pins and cross<br /> profiles, while aerial photographs of over 55 years (acquired during 1942, 1967, 1987 and 1997) which were analysed using Geographic Informations Systems. Rainfall and discharge data, which were available for a period of 49-years were statistically analysed and used to determine trends. Vegetation characteristics were assessed by means of transects within the study reach. The results over the short time period (18 months) indicate noticeable channel change in the form of erosion and deposition within the channel. Bank material composition and riparian invasive alien vegetation play an important role in bank stability. Sand was the dominant grain size of the bank material, and fluvial entrainment occurred during periods of high flow. Woody alien trees prevent the growth of protective ground vegetation, and thus the soil is prone to erosion. Undercutting was also observed with the invasive woody trees, resulting in treefall. Debris dams were also common in the channel and depending on their position in the channel, either cause or prevent bank erosion. Landuse change over the 55-year period illustrated its effects on channel stability. Shrublands within the catchment has been replaced with invasive alien vegetation along the riparian zone, while shrublands along the Obiekwa Mountains, were replaced with cultivated lands. The patterns (shape and size) of lateral and point bars within the study area changed significantly within the 55-year period, which indicates a change in the discharge and sediment dynamics within the catchment. The change in sediment dynamics may be due to agricultural activities and urbanization. The increased trend in rainfall, especially during the winter season within the catchment is also an important catchment control. The study has revealed the integrated nature of variables within the catchment. It is thus recommended that a holistic and integrated approach at a catchment scale is required in the assessment of channel change of a river.

The Klein Berg River catchment is intensely cultivated with orchards, vineyards and wheat, while also ensuring a water supply to the main urban center, Tulbagh, and the two conservation areas (Waterval and Groot Winterhoek). The primary objective of this thesis is to determine channel change over a long and short time period, and to relate these changes to landuse change within the catchment. <br /> <br /> Assessing stability of a selected reach within the catchment was done on a short term basis with the use of erosion pins and cross<br /> profiles, while aerial photographs of over 55 years (acquired during 1942, 1967, 1987 and 1997) which were analysed using Geographic Informations Systems. Rainfall and discharge data, which were available for a period of 49-years were statistically analysed and used to determine trends. Vegetation characteristics were assessed by means of transects within the study reach. The results over the short time period (18 months) indicate noticeable channel change in the form of erosion and deposition within the channel. Bank material composition and riparian invasive alien vegetation play an important role in bank stability. Sand was the dominant grain size of the bank material, and fluvial entrainment occurred during periods of high flow. Woody alien trees prevent the growth of protective ground vegetation, and thus the soil is prone to erosion. Undercutting was also observed with the invasive woody trees, resulting in treefall. Debris dams were also common in the channel and depending on their position in the channel, either cause or prevent bank erosion. Landuse change over the 55-year period illustrated its effects on channel stability. Shrublands within the catchment has been replaced with invasive alien vegetation along the riparian zone, while shrublands along the Obiekwa Mountains, were replaced with cultivated lands. The patterns (shape and size) of lateral and point bars within the study area changed significantly within the 55-year period, which indicates a change in the discharge and sediment dynamics within the catchment. The change in sediment dynamics may be due to agricultural activities and urbanization. The increased trend in rainfall, especially during the winter season within the catchment is also an important catchment control. The study has revealed the integrated nature of variables within the catchment. It is thus recommended that a holistic and integrated approach at a catchment scale is required in the assessment of channel change of a river.

Information regarding the ecological wellbeing of the Natalspruit and its adjoining wetlands is essential if the river is being managed using sound ecological management principles. Despite this, little is known about this river, with little documentation at the regional or municipal level. This study partially addresses this knowledge gap by evaluating the impacts of human activity on a section of the Natalspruit and its adjoining wetlands. It reports on pollution concentrations found at selected sample sites and compares the results to Rand Water data and the National Standards and Guidelines of South Africa for physicochemical parameters and contaminated soils. Water samples were collected at five chosen sample sites during May and July 2018. Soil samples were taken during July 2018. The study found that water at all five sample sites is not suitable for drinking, the health of livestock and recreational use due to the present and high Total Coliform levels (ranging from 450 CFU/100ml to 100 000 CFU/100ml), as well as Turbidity, Total Hardness, TDS, Mg, NO2, SO4, and BOD which also exceeded the guidelines. Only site SS1 (May) exceeded the CaCO3 concentrations regarding livestock health. No guidelines were available for DO levels on the health of livestock. Cl levels in the Natalspruit was suitable for drinking. PO4 concentration at all the sites were all within the guidelines of acceptable levels for aquatic ecosystems. In terms of heavy metals, Cr levels significantly exceeded the guidelines at all five sample sites with the exception of ecosystem health. This is of great concern due to the toxicity of Cr. Cu concentrations exceeded the guidelines for both all land-uses protective of water resources and ecosystem health, at SS1, SS2, SS3 and SS5. Ni concentrations exceeded the guidelines for all land-uses protective of the water resources at SS5. Pb and Zn concentrations exceeded the guidelines for the land-uses protective of the water resources at all the sites with the exception of SS4 for Pb and SS2 and SS4. SS1 and SS5 reported Zn concentrations higher than the guideline for the protection of ecosystem health. SASS 5, PES and EIS assessments indicated moderate to severe modifications of the river. Thus, mining, industrial activities, surface runoff from densely populated informal settlements and wastewater treatment plants have negatively impacted upon the river. Decades of environmental neglect and effluent discharge have degraded the ecosystem, thus necessitating rehabilitation. However, as the study was limited in both time and scope, so additional research should be undertaken. / Environmental Sciences / M. Sc. (Environmental Management)