Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system
type: CreativeWork
description: ENGLISH ABSTRACT: Water users in the lower Vaal-Orange River system are subjected to chemicals and pathogens from sources over which they have little control. These sources include raw sewage from dysfunctional wastewater-treatment works, saline irrigation return flows and upstream discharges from the industrialised upper Vaal River region. For this thesis, water-quality impacts on users in the lower Vaal-Orange River system were examined. It was found that sewage, salt, sediments, and high-flow events are the main vectors of poor water quality. The main sources of water pollution were found to be untreated sewage discharges, irrigation return flows and the first flush of high flow from the Vaal River. A stressor assessment was performed using international water-quality guidelines and the water-quality database of the civil society organisation Gariep Watch. It showed microbial contamination of potable and irrigation water as the main risk to water users. This is caused by the deteriorating state and maladministration at municipal sewage-treatment works in the study area and in the Vaal River catchment area. Untreated sewage and irrigation return flows contribute to available plant nutrients in the lower Vaal-Orange River system. It was found that nitrogen, phosphate, and potassium levels in the irrigation water should be accounted for to prevent over-fertilisation of crops. Farmers may thus achieve substantial savings by lowering fertilisation rates. Moreover, plant-nutrient concentrations in irrigation return flows can be lowered, reducing eutrophication and other harmful effects on aquatic ecosystems. Raised salinity was pronounced in the study area. Over five years, 91.6% of the Vaal River’s salt (calculated salt load) going into the lower Orange River originated upstream of the study area. The salt is mainly conveyed downstream when flows are high. The sulphate-dominant salt load from the Vaal River dictates the chemical composition of the lower Orange River a…
abstract: ENGLISH ABSTRACT: Water users in the lower Vaal-Orange River system are subjected to chemicals and pathogens from sources over which they have little control. These sources include raw sewage from dysfunctional wastewater-treatment works, saline irrigation return flows and upstream discharges from the industrialised upper Vaal River region. For this thesis, water-quality impacts on users in the lower Vaal-Orange River system were examined. It was found that sewage, salt, sediments, and high-flow events are the main vectors of poor water quality. The main sources of water pollution were found to be untreated sewage discharges, irrigation return flows and the first flush of high flow from the Vaal River. A stressor assessment was performed using international water-quality guidelines and the water-quality database of the civil society organisation Gariep Watch. It showed microbial contamination of potable and irrigation water as the main risk to water users. This is caused by the deteriorating state and maladministration at municipal sewage-treatment works in the study area and in the Vaal River catchment area. Untreated sewage and irrigation return flows contribute to available plant nutrients in the lower Vaal-Orange River system. It was found that nitrogen, phosphate, and potassium levels in the irrigation water should be accounted for to prevent over-fertilisation of crops. Farmers may thus achieve substantial savings by lowering fertilisation rates. Moreover, plant-nutrient concentrations in irrigation return flows can be lowered, reducing eutrophication and other harmful effects on aquatic ecosystems. Raised salinity was pronounced in the study area. Over five years, 91.6% of the Vaal River’s salt (calculated salt load) going into the lower Orange River originated upstream of the study area. The salt is mainly conveyed downstream when flows are high. The sulphate-dominant salt load from the Vaal River dictates the chemical composition of the lower Orange River a…
author: Bekker, Frederik Jacobus
language: en
date published: 2025-12
date modified: 2026-07-24T04:40:06Z
provider: Stellenbosch University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Stellenbosch : Stellenbosch University