Browsing by Author "Armitage, Neil"

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    An Experimental Study on the Infiltration Potential of Stormwater Ponds in Zeekoe Catchment, Cape Town, South Africa
    (2022) Mavundla, Kgomoangwato; Kalumba, Denis; Armitage, Neil; Okedi, John
    In early 2018, the city of Cape Town, with a population of approximately 3.8 million, was at risk of running out of water from the six large reservoirs to the east of the city. This was due to the worst drought in almost a century, which occurred between 2015 2017, causing the city to be declared a disaster area. Although alternative water resources had been identified, they had not been developed. This has now become imperative as droughts are expected to recur in the future. This study investigated the prospect of using existing stormwater ponds in the Zeekoe catchment area as infiltration cells transferring detained stormwater into the underlying aquifer storage zone to enhance the available groundwater resource. The Zeekoe catchment is a 89 km2 area within the 630 km2 Cape Flats Aquifer (CFA). Based on hydrogeological data and aquifer parameter interpretation, it is considered to have good storage characteristics that can support groundwater development for water supply. Bouwer (2002) highlights how infiltration tests in the field can be useful for estimating desired volumetric recharge rates within a certain area. The hydraulic conductivity of the unsaturated layer is an essential non-linear function of soil-water content and has been generally recognised as the most important transport property to describe the ability of soil to permit water movement. A series of in-situ infiltration experiments were conducted at three representative stormwater ponds using a Double Ring Infiltrometer (DRI) to determine the rate of water recharge. Infiltration data was interpreted using both the Green-Ampt and Horton methods to determine the hydraulic conductivity and infiltration decay constants. A total of 18 core samples retrieved from the in-situ infiltration test locations were analysed in the laboratory to determine the ed hydraulic conductivity through constant-head permeability (CHP) tests. The physical and hydraulic soil parameters gathered from field and laboratory tests were used as inputs for a finite element numerical modelling software (HYDRUS 2-D) to estimate the range of recharge rates for the study area. Based on field infiltration test results, the hydraulic conductivity was found to be 0.3 19.9 cm/hr; typical for silty sands to fine sands. Hydraulic conductivities estimated in the laboratory were greater than the field hydraulic conductivity by 103%. This could be attributed to entrapped air under field conditions which reduces the effective cross-sectional area available for water to flow. From the HYDRUS 2-D simulations, the period required for the wetting front movement from the pond surfaces to the water table ( 5.5 m below the surface) was 15 140 hours. Hydraulic conductivities estimated using the pedotransfer function (PTF) of the built-in software, Rosetta-Lite, were also greater than the field hydraulic conductivity values by 118%. For an actual test pond, the infiltration rates would be expected to be slower, and recharge times would be greater because the HYDRUS 2-D simulations did not consider layers of low permeability suggestion that the field saturated hydraulic conductivity could be taken as roughly 0.5 times the laboratory hydraulic conductivity was thus considered reasonable. This means that ponds in the central area of the catchment would be suitable for artificial recharge with an estimated infiltration rate of around 20.6 cm/hr which could provide a mean annual groundwater yield of 29 33 Mm3 . A more extensive survey would aid in assessing local conditions that may impede groundwater flow.
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    An investigation of the pollution contribution of catchments surrounding the Knysna Estuary, with implications for stormwater management
    (2019) Harvey, Alice Lindiwe; Armitage, Neil
    The Knysna Estuary is ranked highest in South Africa for conservation importance and is a haven for endemic marine species. The ecosystem services provided by the estuary include significant biodiversity value and amenity value for residents and tourists. The economy of Knysna is reliant on tourism, which in turn is dependent on ecosystem services. The health of the Knysna Estuary is currently threatened by poor water quality. If the water pollution can be addressed, ecosystems can be protected and significant social and economic costs of environmental degradation can be avoided. The pollution contribution of runoff from catchments to the estuary is imperfectly understood. Mitigation measures designed based on imperfect knowledge may be inappropriate or fail to address the pollution concerns. A poor understanding of the world views of stakeholders could lead to the design of socially unacceptable solutions. This study aimed to improve knowledge of the catchments surrounding the estuary, and stakeholders within these areas, to inform solutions. Surface water sampling and testing and analysis of national and municipal databases were used to assess the pollutant contribution of catchment runoff. High nutrient concentrations were conducive to eutrophic or hypertrophic conditions at most sites. Total Inorganic Nitrogen (TIN) concentrations exceeded 5 mg/â„“ at 60% of the sites. Ammonium concentrations made up a disproportionate fraction of the TIN readings, with most fractions exceeding 20%, and many exceeding 70%. Student t tests indicated that TIN concentrations at the Bongani River were significantly higher than historical data. Total Suspended Solid (TSS) concentrations at some sites were lower than historical data. E. coli spikes of over 30,000 CFU/100 mâ„“ were measured at nine sites in October 2018. The Bongani River catchment was identified as a significant source of elevated nutrients and E. coli. Elevated nutrients and TSS were also recorded in the effluent from the Knysna Waste Water Treatment Works (WWTW) with mean values of 36 and 24 mg/â„“ for Total Ammonia Nitrogen (TAN) and TSS respectively. A Kendall correlation analysis indicated significant positive trends in TIN and TAN, and negative trends in Soluble Reactive Phosphorus. A hydrological model was built for the Bongani Catchment. Data input to the model was obtained from site visits, literature, and a desktop study of available catchment information. The model was calibrated against observed data at two water level monitoring points. The model was used to estimate pollutant loads for large storms, and can be used to inform possible pollution mitigation strategies. Further water management challenges and pollution sources were identified through stakeholder interviews. A decision support tool was used to understand how stakeholder world views and values can inform the selection of socially acceptable solutions. Stakeholder interviews identified sewage leaks as a water management concern. This corresponds well with the elevated nutrient and E. coli concentrations measured in many catchments. Other identified pollutants were litter and TSS.
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    Century City as a case study for Sustainable Drainage Systems (SuDS) in South Africa
    (2011) Vice, Michael Alexander Pringle; Armitage, Neil
    South Africa's developing cities are experiencing rapid urbanisation, particularly in the major metropolises. Infrastructural development is a prominent component of the South African economy, and has been allocated hundreds of billions of Rands by the budgetary council in the present political term of office (2009-2014).
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    A computational fluid dynamics model for sediment movement based on the unit stream power approach
    (2001) McGahey, Caroline; Armitage, Neil
    This thesis introduces a three-dimensional numerical model based on the unit stream power approach for the prediction of scour profiles. The unit stream power approach is employed to define the incipient motion criteria for the sediment particles by comparing the available applied stream power with the individual particle power requirements for motion (Rooseboom 1992). The Movability Number (Lui 1957), which represents the shear velocity-settling velocity ratio, is related to the unit stream power and is applied as an alternative incipient motion criterion. The Movability Number, as adapted by Armitage (2001) to account for topography, is utilised for scour hole predictions.
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    Design flood peak determination in the rural catchments of the Eastern Cape, South Africa
    (2007) Hogan, K D; Armitage, Neil; Hughes, Dennis
    Rainfall is a natural occurring phenomenon, and is usually a welcome event, nourishing the earth and with it the fauna and flora. When the runoff is high, flooding occurs, leading to damage to the environment, property and even to loss of life. Flooding is becoming more common. The reasons for this are complex, and include social expansion, urbanization and may also result from global warming. These flooding events have significant implications to the engineering profession and the affected communities. The estimation of peak design floods is necessary for the planning and design of civil engineering projects. Over the past century standard methods for flood peak estimation have been developed for most countries, and are usually categorized in the literature as direct statistical analyses, regional statistical analyses, empirical methods and deterministic methods. Some of these methods are easy to apply, while others require an in-depth analysis of the catchment and other parameters. Each method has its limitations. In rural gauged catchments, design engineers in the workplace typically use statistical methods while in rural un-gauged catchments, they use empirical or deterministic methods, even although the reliability of these methods to estimate the design flood peak have never been verified in South Africa. The objective of this study was to identify the most reliable statistical, deterministic and empirical method(s) of flood peak determination in the rural catchments of the Eastern Cape, South Africa. In this investigation the recorded annual peak runoff from 18 river flow gauging stations in the Eastern Cape were statistically analysed using the statistical distributions commonly used in South Africa. These statistical analyses were used to establish a benchmark for evaluating the deterministic and empirical methods. The catchments of all the stations were then analysed using the deterministic and empirical methods. Finally, the empirical and deterministic methods were compared against the best-fit statistical method. This highlighted which empirical and deterministic method(s) under- and over-estimated peak floods when compared with the statistical analyses of recorded annual peak runoff. The finding from the statistical analyses was that the Log Pearson Type 3 (LP3) distribution performed the best, generally fitting the recorded data well. In the comparison of deterministic methods it was found that the Standard Design Flood (SDF) method was the most conservative deterministic method at the higher Recurrence Intervals (RIs) while the Rational Method-Alternative was the most conservative at the lower RIs. In the final comparison between the LP 3 distribution and the empirical and deterministic methods, it was found that in the higher RI range, the SDF estimated runoff values similar to that estimated by the LP3 distribution, while in the lower RI range, the Rational Method-Alternative variation proved to be the most consistent. The other deterministic methods generally under-estimated runoff values when compared to the LP3 distribution. Generally, the Regional Maximum Flood method appeared to have a RI about 1000 years, although it was as low as 1 :200 years in some of the smaller sized catchments. In rural catchments of all sizes in the Eastern Cape of SA, design engineers in the workplace should analyse a catchment using all of the statistical, deterministic and empirical methods available and then select the most conservative result.
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    Evaluating the potential for Blue-Green Infrastructure benefits using the case study of stormwater ponds in Cape Town, South Africa
    (2023) Fell, Jessica; Armitage, Neil
    A Water Sensitive City (WSC) is increasingly being pursued to deliver on various sustainability, resilience and liveability goals. Expanding Blue-Green Infrastructure (BGI) is a major step towards a WSC. BGI can provide multiple social and environmental benefits, from increased amenity to enhanced biodiversity to urban heat reduction. However, the expansion of BGI is not always feasible. This is particularly true in many Global South contexts with rapidly urbanising cities characterised by patterns of informality, inadequate infrastructure and service delivery provision, competition for space and increasing resource pressures. In such contexts, existing blue infrastructure (BI), i.e., natural or artificial water bodies such as rivers, canals, ponds, streams, wetlands and stormwater drainage provision, can be transformed to provide multiple benefits as BGI. This study presents a Multi-Criteria Analysis (MCA) methodology to evaluate the potential for existing BI to provide multiple benefits as BGI. The MCA methodology was developed through the case study of the City of Cape Town, South Africa. The multifunctional potential of the city's existing stormwater ponds, of which there are over 800, was evaluated. This was a contribution towards the city's 2020 Water Strategy commitment to ‘become a Water Sensitive City' by 2040 with multifunctional infrastructure. Using value-focused thinking, the MCA methodology incorporated seven benefits framed as WSC planning priorities: (1) ‘Enhancing cultural and heritage associations with water systems', (2) ‘Increasing water re- use', (3) ‘Reducing the Urban Heat Island (UHI) effect', (4) ‘Enhancing community services connections with water systems', (5) ‘Increasing access to blue-green space', (6) ‘Incorporating stormwater quality limitations', and (7) ‘Enhancing biodiversity'. A pilot MCA was conducted to assist the process. An associated criterion was selected for each WSC planning priority through semi-structured interviews with WSC experts in Cape Town. The criteria were scored, and stakeholder weights were obtained using three weighting methods: rating, ranking and pairwise comparison. A weighted additive model was used to combine the scores and weights. Ponds with a high potential to provide a combination of the seven benefits were identified. The relative prioritisation of the ponds for the individual and combined criteria were mapped in a Geographic Information System (GIS) to allow for the visualisation of the rankings. Synergies and trade-offs were assessed using Pearson correlation coefficients between criterion scores. In Cape Town, the ‘Enhancing community services connections with water systems' WSC planning priority had the largest number of high scoring ponds, with 36% within 290 m of a school, community centre or religious institution. Of the ponds, 12% had a high potential for Managed Aquifer Recharge for ‘Increasing water re-use'. This was largely because they overlie a shallow sandy primary aquifer in the city. For ‘Incorporating stormwater quality limitations', almost half of the ponds (46%) were within 200 m of a potentially contaminating activity (informal settlement, industrial, road, landfill, wastewater treatment works land cover). This indicated potential constraints to multifunctionality from poor stormwater quality. Synergies between ‘Increasing water re-use' and ‘Reducing the UHI', ‘Enhancing community services connections with water systems' and ‘Enhancing biodiversity' were indicated through statistically significant positive correlations. This helps to identify ponds for strategic prioritisation to leverage co-benefits. However, negative correlations revealed the trade-offs that prioritising ponds for ‘Increasing access to blue-green space' and ‘Increasing water re-use' may not be well suited to ‘Incorporate stormwater quality limitations'. Stakeholders regarded the benefits of ‘Increasing access to blue-green space' and ‘Increasing water re-use' as the most important across the weighting methods. The combined criteria using the different weighting methods indicated a hotspot of ponds with the highest relative multifunctional potential in the southern central part of the city. These ponds would be the highest priority for multifunctional transformation to maximise benefits as BGI for a WSC. The MCA methodology paired with GIS visual capabilities provides a strategic and participatory approach to evaluating the potential for existing BI to provide multiple benefits as BGI towards a WSC. Applying this methodology to Cape Town's existing stormwater ponds illuminated their multifunctional potential. The MCA methodology is transferrable as the WSC planning priorities are relevant to many urban Global South contexts. It is flexible, able to incorporate different benefits, and the steps could be customised for different types of BI.
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    Evaluating the Potential for Denitrification in PICP
    (2023) Brown, Luke; Armitage, Neil
    Urbanisation has led to an increase in impermeable surfaces that often act as waterways during rainfall events and aid in the transportation of pollutants to nearby water sources, such as dams or rivers. The nitrogen compounds are major pollutants, particularly nitrate (NO3 - ) and ammonia (NH3), which facilitate eutrophication and toxic algal growth. Many stormwater control measures (SCMs) successfully manage the stormwater runoff flows, however many are ineffective at removing the pollutants present within stormwater. This has led researchers to investigate how alternative systems, such as permeable pavements (PPs), can remove stormwater pollutants. Although studies have found PPs to be effective at removing NH3 and other pollutants, PPs are largely ineffective at removing NO3 - and in most cases have caused an increase in NO3 - concentration in PP effluent through the oxidation of NH3 compounds. Some studies on nitrogen removal in PPs have recommended the inclusion of a submerged zone to improve denitrification. Since permeable interlocking concrete pavements (PICPs) are the most widely used PP structure internationally, this study investigated the potential for denitrification in PICP through the incorporation of a submerged zone in its structure. It considered the three main factors controlling denitrification: (1) detention time, (2) inclusion of a carbon source (newspaper) and (3) submerged zone depth. The impact that these factors had on NH3 and phosphate (PO4 3- ) removal in a submerged zone were also investigated. This study used ten columns, each fully packed with 50-63 mm washed aggregate and included a 1.5 m deep submerged zone. The submerged zone of each column was fitted with taps (sample ports) spaced at 300 mm intervals from 0 to 1500 mm. Columns were paired according to detention time (1, 2, 5, 10 and ‘varied' days) with one set including newspaper as the carbon source, while the other set not. All columns were loaded with synthetic stormwater over a four-month period. Samples were taken from different submerged depths (0, 300, 600, 900, 1200 and 1500 mm) of each column and analysed for concentrations of NH3, NO3 - and PO4 3- . This study found that 10 (or more) days detention and providing a carbon source have the most significant impact on denitrification – providing an overall mean NO3 - and nitrogen removal of 41 and 59% respectively. Moreover, a submerged depth of 300 mm was sufficient to achieve a minimum NO3 - removal of 41% in columns which included a carbon source and had 10 days detention. An increase in detention time allowed for a decrease in both NH3 and PO4 3- concentration. The longest detention time of 10 days provided an overall mean NH3 and PO4 3- removal of 86% and 30%, respectively. However, the inclusion of a carbon source had no significant impact on NH3 and PO4 3- removal. In most cases an increase in submerged depth resulted in an increase in NH3 concentration from 600 to 1500 mm, and a decrease in PO4 3- concentration from 0 to 900 mm. This study concluded that PICP has the potential to significantly reduce NH3, NO3 - and PO4 3- compounds present in stormwater through the incorporation of a submerged zone, and thus ultimately improve the quality of water entering our water sources.
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    The evaluation and improvement of a sustainability index for intergrated urban water management in South African cities.
    (2009) Mureverwi, Charlene; Armitage, Neil
    Water is not only essential for maintaining life; it is a key component of sustainable social and economic development having links to, inter alia, health, 'sense of place', food production and industrial growth. Although progress has been made with regard to water supply, it is estimated that there are still 2.4 million people in South Africa without access to adequate water and sanitation services as defined by the United Nations (Statistics South Africa, 2008). It is possible that the failure in service provision can partly be attributed to a lack of an integrated approach with regard to the various aspects of urban water management. Stoeckigt (2006) and De Carvalho (2007) used a systems approach to develop a composite Sustainability Index (SI) which, by addressing five components of sustainability (environmental, social, economic, political and institutional), attempts to give a measure of the potential for sustainability in the context of integrated urban water management. This thesis describes an evaluation and modification of this Sustainability Index. The literature presented in this research examines Integrated Urban Water Management (IUWM) and sustainability indicators. A particular focus was given to service provision in South African cities and the various aspects of the urban water cycle. This thesis set out to explore the possibilities for the improvement of the SI to guide the efficient delivery of services and appropriate description of human impacts on the environment. From the literature reviewed, it was concluded that the success of IUWM requires an interdisciplinary approach with strong political and institutional backing. The evaluation and modification of the SI was guided by knowledge gained from a review of the literature and through experience gained from applying the SI to two case study areas. Two South African cities, East London and Port Elizabeth were selected as case studies to test the applicability and validity of the original and revised index. In the evaluation of the SI, data accessibility and transparency in the method were used to determine the effectiveness of the index. This was done with the objective of improving the SI and ultimately promoting sustainability performance in the management of urban water systems. East London and Port Elizabeth obtained overall SI scores of 56% and 60% respectively. East London and Port Elizabeth both performed best in the political component receiving scores of 83% and 93% respectively. On the other hand, both cities score lowest on the environmental component of the SI. This indicated a need for more stringent environmental monitoring. In applying the SI to the case study areas, a number of priority areas, which need to be addressed by the respective municipalities were highlighted. The overall SI performance for both cities shows relatively slow progress towards sustainability with both East London and Port Elizabeth needing to improve their urban water management. Results of the analysis demonstrated that the revised index can highlight areas for improvement and ultimately guide more appropriate policies for better service delivery and improved resource management.
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    Improving the design, construction, and maintenance of Permeable Interlocking Concrete Pavement (PICP) in South Africa
    (2023) Monyake, Motlatsi; Armitage, Neil
    Imperviousness caused by urbanisation leads to increased runoff volumes, flow rates, and contaminant loads. These may be mitigated by measures such as Sustainable Drainage Systems (SuDS) that seek to mimic the natural hydrology of a site. Permeable Pavement Systems (PPS) are a popular SuDS source control measure, with Permeable Interlocking Concrete Pavements (PICP) being the most common. PICP comprise specially designed concrete pavers, inter alia, with grooved and dentated sides forming ‘joints' to allow runoff to percolate into the underlying single-sized basecourse layers and potentially the subgrade. A geotextile may be fitted between the bedding and base layers and/or base layer and subgrade. However, many PICP installations in South Africa have prematurely failed through clogging. While some failures can be attributed to poor design, construction and site management, there is ongoing debate regarding the principal failure mechanisms, particularly in connection with the inclusion of a geotextile under the bedding layer. Field investigations were thus conducted at eleven sites in Cape Town and Gauteng to provide evidence-based data related to clogging. Additionally, accelerated laboratory tests that focused on the role that different pavers and upper geotextiles played in the clogging process were conducted at the University of Cape Town (UCT). The investigations identified four types of clogging mechanisms: i) Type I is when sediment fills up the top 30 mm of the joints, ii) Type II is when the sediment deposits on the bedding immediately below the joints, iii) Type III is when the sediment mixes with the bedding and clogs the geotextile, iv) Type IV is clogging of the underlying layers. The field observations indicated that rapid failure of PICP correlates with: high sediment loading from adjacent areas for example as a consequence of being linked to excessively large impervious surfaces, leaf and pollen drop from overhanging vegetation, abrupt braking at highly trafficked areas – in particular at intersections often widening joints, and lack of maintenance. The non-woven heat-bonded upper geotextiles that have been specially selected in the past owing to their ability to promote nutrient removal in PICP were found to be susceptible to puncturing in areas with considerable turning traffic. Maintenance trials demonstrated that air blowers could remove Type I clogging, but probably at the cost of accelerating Type II clogging. The presence of a geotextile was seldom a cause of clogging except in limited, specific circumstances. Accelerated laboratory tests showed that the smaller the paver joint opening ratio, the faster the joint was clogged by non-cohesive soils.
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    An investigation into the initiation of local scouring around rectangular """"long"""" contractions
    (2003) Lyons, Simone; Armitage, Neil
    Includes bibliography.
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    Managing nutrient flows into the Zandvlei Estuary, Cape Town using Sustainable Drainage Systems (SuDS)
    (2023) Ghoor, Zarmeen; Armitage, Neil; Okedi John
    The Zandvlei estuary is the only functional estuary on the False Bay coastline which forms part of the southeast boundary of the City of Cape Town (CCT) on the southwest coast of South Africa. It provides an important habitat for fledgling fish species in the area and is a popular recreational site for birdwatchers, sailors and conservation-enthusiasts. The estuary has experienced water quality problems for many years. It drains three upstream sub-catchments which are largely comprised of conventional drainage systems which carry stormwater pollutants into the watercourses that then drain into the estuary. Of the many pollutants that flow into the estuary, elevated nutrient levels (specifically phosphorus and nitrogen) are a major concern because they can lead to eutrophication and excessive plant growth. In recent years the estuary has experienced algal blooms resulting in adverse effects on local plants, and animal and human life. Sustainable Drainage Systems (SuDS) are holistic drainage practices that address, amongst other things, water quality issues like those experienced by the Zandvlei estuary by treating the stormwater. The aim of this study was to identify areas of raised nutrient concentrations and model various SuDS measures to improve the water quality of runoff. Surface water sampling in the catchment and a study of historical water quality data was undertaken to identify areas with higher nutrient concentrations. Phosphorus concentrations, in the form of SRP, was found to be above the eutrophic threshold in most samples, while nitrogen concentrations, in the form of TIN, were found to mostly be beneath the eutrophic threshold. The locations of higher nutrient concentrations coincided with suspected sources of raised nutrients based on a desktop study of the catchment that identified agricultural areas, golf courses that use treated effluent for irrigation, and commercial/industrial areas. Water level sensors were developed and placed in each sub-catchment to compare nutrient concentrations during storms to stream flow during storms. A hydrological and hydraulic model was built representing two of the river systems feeding into the Zandvlei estuary – the Keysers and Westlake River sub-catchments. The PCSWMM software package developed by CHI, which uses the SWMM engine developed by USEPA, was employed. Data regarding historical rainfall, land use, stream flow, surface cover, soil types, geology and historical temperatures were used to construct the model. The model was calibrated against historical stream flow data obtained from CCT. Various SuDS measures were modelled and grouped into three scenarios: Scenario 1 modelled local controls targeting the suspected source areas, Scenario 2 involved modelling large-scale regional controls, and Scenario 3 was a combination of the first two. The local controls modelled were swales and bioretention areas. The regional controls modelled were wetlands, primarily because the study area already contains wetland areas that are currently disconnected from the river systems. Wetlands were modelled with upper and lower limit treatment equations. The simulated wetlands were able to reduce the SRP and TIN concentrations to below the eutrophic threshold (below 0.25 mg/ℓ and 2.5 mg/ℓ respectively) for three years out of the 8-year simulation period. The various scenarios achieved pollutant reductions ranging from approximately 25-80%. The CCT requires a TP reduction of 45% and a TSS reduction 80%. For TP, this was achieved throughout the simulation period when wetlands are functioning efficiently (i.e. the upper treatment limit); while for TSS, this requirement was only achieved in some years when the wetlands are functioning efficiently. Scenario 1 showed the least pollutant removal overall, while Scenario 2 and 3 showed similar pollutant removal and flow reduction, suggesting that the effect of the proposed local controls is insignificant compared to that of the large-scale regional controls.
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    Managing the Water Quality of the Zandvlei Estuary using Sustainable Drainage Systems in the Diep Catchment
    (2022) Thewlis, Geordie; Armitage, Neil
    The Zandvlei Estuary is the only functioning estuary-wetland river system along the False Bay coastline and is therefore of extreme ecological importance. The estuary has and continues to face threats from excessive amounts of sediments and nutrients that can destroy its functionality. Historically, Zandvlei's most significant problems are eutrophication and siltation, which have occurred in the estuary due to elevated nutrient and sediment levels. Increased Total Inorganic Nitrogen (TIN) and Soluble Ready Phosphorus (SRP) are the primary causes of eutrophication in receiving water bodies. The excessive amounts of nutrients and sediments deposited into the estuary are a result of urbanisation and the subsequent change in anthropogenic activities in and around the Zandvlei's catchments. Additionally, the increased impervious surface area associated with urbanisation has caused a significant rise in runoff volumes and runoff rates in the stormwater drainage systems. In South Africa, stormwater drainage systems conventionally channel everything they collect into receiving water bodies without significant treatment or intervention to remove harmful substances. Sustainable Drainage Systems (SuDS) provide an alternative approach to managing stormwater runoff. Unlike the conventionally used stormwater systems designed with the singular goal of removing runoff, SuDS can provide both stormwater quantity and quality management while also allowing for the development of biodiversity and amenity. This project investigated the viability of improving Zandvlei Estuary's water quality by implementing SuDS in Zandvlei's Diep Catchment. PCSWMM, a modelling software developed by Computational Hydraulics International (CHI), was used to develop seven models. Included was an As-is model, developed, calibrated and verified to represent the Diep Catchment in its current state, a Pre-development model that provided an estimate of the Diep Catchment's runoff volumes and stormwater constituent loads before urban development altered the catchment, and five SuDS scenarios to test various treatment train designs. Pollutant indicators that were modelled included SRP, TIN, Total Phosphorus (TP) and Total Suspended Solids (TSS). SRP and TIN were included as they cause eutrophication, while TP and TSS were modelled as they are good measures of pollution. Scenario 1 utilised Source Control SuDS to capture and treat runoff as close to its source as possible. Scenario 2 reintroduced four wetlands and two retention ponds into the main river network. The stormwater network currently only uses these wetlands and ponds as attenuation storage during large rainfall events. Scenario 3 proposed a large, constructed wetland at the confluent of the two major stormwater systems in the Diep Catchment, Langevlei Canal and the Diep/Sand River. Scenarios 4 and 5 utilised combinations of SuDS controls from Scenarios 1, 2 and 3 to create more holistic treatment train systems. Scenario 4 employed the Source Controls from Scenario 1 and the large, developed wetland in Scenario 3. Scenario 5 utilised two wetlands and a retention pond from Scenario 2 and the large wetland from Scenario 3. The SuDS scenario results were compared to those obtained from the As-is Scenario to provide percentage reductions of indicator loads and runoff volumes. Additionally, the Pre-development results, which indicated the likely natural indicator loads and runoff volumes and thus probably best represented sustainable conditions, served as a benchmark against which all the modelling results could be compared. Scenario 5 provided the most significant mean reduction in indicator loads (57.3%), while Scenario 4 provided the largest drop in runoff volume, approximately 52%. As the primary goal of this project was the reduction in indicator loads, Scenario 5 would provide the most significant improvement in Zandvlei Estuary's water quality.
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    A measure of sustainability in the context of urban water management in South Africa
    (2013) Carden, Kirsty; Armitage, Neil
    The aim of this research was to develop an understanding of and measure the potential for sustainability in a South African urban water context. This was achieved through the use of a systems approach to develop and evaluate a composite index – the Sustainability Index for Integrated Urban Water Management (SIUWM) – based on a vision of what sustainable urban water management means to decision makers at selected local authorities around the country. The vision was expanded into a sustainability framework to identify suitable key indicators for the index, as well as those which link with existing regulatory measurement initiatives in the South African water sector. The hypothesis was that if a city improves its scores on all of its indicators over a period of time, there is potential for long-term sustainability in the specific urban water system. The SIUWM was applied as a ‘snapshot’ analysis to nine case study cities (using 2010 / 2011 figures) and the results highlighted the inherent strengths and weaknesses in the management of urban water in each city, and consequently across each dimension of sustainability. Regularly-updated and publicly-available quantitative data as well as qualitative information from interviews with municipal officials were used as input to the index. Key performance indicator scores from the Department of Water Affairs’ regulatory performance measurement systems were also used in the computation of the index scores. In this way the SIUWM was able to provide a detailed analysis which could be used over time to track changes in performance, establish goals and inform strategic processes to leverage support for improved water services. Through its visioning process, the SIUWM is also able to identify vulnerabilities in the water system and provide information that is potentially useful for mitigating the root causes of these vulnerabilities. Sustainability assessment in the urban water sector, by way of initiatives such as the SIUWM, is not only about taking stock of progress – it is also about identifying shortcomings and challenges so as to contribute to initiatives and policy-making aimed at achieving sustainability. By clarifying what sustainability constitutes in the context of urban water management in South Africa through the use of a multi-dimensional approach to sustainability assessment (as is achieved by way of the SIUWM), the mindsets of decision-makers can hopefully be successfully shifted to embracing a more integrated approach towards sustainable urban development and water sensitive cities.
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    The measurement and reduction of urban litter entering stormwater drainage systems
    (2003) Marais, Mark John; Armitage, Neil
    The purpose of this thesis is to describe the results of this monitoring programme and to set out generic guidelines for litter management in South African urban catchments.
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    Modelling local scour around bridge piers using TELEMAC
    (2005) Kabir, Alamgir; Armitage, Neil
    Scour at bridge crossings is a major cause of bridge failure. There are several different types of scour such as general scour, constriction scour and local scour. One of the most serious types is local scour which occurs as a result of vortex formation around bridge piers and abutments (Hoffmans & Verheij, 1997; Raudkivi, 1998; Melville & Coleman, 2000; Richardson & Davis, 2001; Armitage & McGahey, 2003). Local scour is also one of the most difficult to predict accurately. If not adequately designed for, local scour of a riverbed at a bridge pier may become deep enough to undermine the pier foundation and eventually cause the bridge to collapse. Complete protection against scour is expensive and therefore not a favourable design option. It is generally cheaper to ensure that the foundation lies below the maximum expected scour depth. Traditionally, the maximum scour depth is predicted from empirical equations derived from simple laboratory tests without much regard for local conditions. Alternatively, smaIlscale hydraulic models, which are laborious and time intensive, are widely used. In view of the above, increasing attention is being paid to the use of Computational Fluid Dynamics (CFD) based modelling for the prediction of local scour and its opposite, local deposition. The ever-improving capabilities of computers and the increasing availability of powerful and flexible CFD codes have further assisted in this process. This study is a contribution in this direction.
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    Numerical modelling of local scour in rivers using fluent 6.2
    (2005) Cunninghame, Margaret; Armitage, Neil
    Scour and deposition are natural processes which take place in a river as the stream profile adjusts to changing flow rates, sediment loads and other environmental conditions. Man-made obstacles to the stream flow such as bridge piers and abutments and other hydraulic structures alter flow patterns causing local scouring and deposition. Excessive scour undermines the foundations of bridges and other fluvial structures which may ultimately cause their collapse. Reliable methods are needed to model the complex flow features at bridge piers and abutments and hence predict the associated patterns of local scour. Empirical formulae are notoriously inconsistent in their predictions of local scour depth (Johnson, 1995) while physical modelling is time-consuming and therefore expensive.
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    Quantifying the potential for potable water savings in the Liesbeek River catchment
    (2014) Coulson, Daniel; Armitage, Neil
    The security of South Africa’s water resources has been identified as a major issue affecting the country’s potential for socio-economic expansion. With the realisation that current water management interventions require significant improvement, there has been growing interest in finding more effective approaches to water management. This dissertation aims to quantify the potential potable water savings that could be achieved through the implementation of selected sustainable water management interventions in the Liesbeek River catchment, Cape Town. The current water use model was constructed in the form of a water balance, using data collected from the catchment.
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    Quantifying the value of non-user benefits of improving water and sanitation in informal settlements
    (2013) Kobel, Dorothy; Del Mistro, Romano; Armitage, Neil
    This study investigated the value among society of the benefits of improving water and sanitation in informal settlements. The benefits of improving water supply and sanitation have been widely researched, both at a societal and at household level. Why then have the efforts to increase access to services over the last 30 years not achieved the desired results? The value of these benefits, measured through assessments of willingness to pay by the users, is commonly used in investment appraisals as indicators of project viability.
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    Reduction of pollution levels in the Chatty River through Sustainable Drainage Systems: A case study of the Bethelsdorp River sub-catchment
    (2023) Matalanga, Anabel; Armitage, Neil
    Chatty River, located in Gqeberha, South Africa, is the largest tributary feeding into the Swartkops Estuary and is among the three significant sources of pollution in the estuary, the other two being the Motherwell Canal and the Markman Canal. The Chatty River Catchment is mainly occupied by low-income residential areas resulting in pollution from stormwater runoff, litter, and raw sewage discharge. There are growing informal settlements and limited agriculture. In recent years, the high pollution level in the Swartkops estuary has led to the reduction and even halting of various social and cultural activities such as the Redhouse River Mile swimming event, cleansing ceremonies by traditional healers, and baptisms by the Zion Church. SuDS are appropriate for a range of contexts and purposes for example to minimise the impact of development on stormwater quality while maximising amenity and biodiversity through a suite of interventions designed to manage stormwater in a way that mimics nature. This study sought to understand the pollution contribution of the Chatty River and provide recommendations to improve its water quality through the possible inclusion of Sustainable Drainage Systems (SuDS). The Chatty River's physical, nutrient, and microbiological characteristics were assessed through water quality sampling and historical data review to identify pollutant hotspots. The high mean dissolved inorganic phosphorus (DIP) concentrations, in the form of orthophosphate, indicate eutrophic and hypertrophic conditions in most sections of the Chatty River. The mean nitrogen concentrations, in the form of dissolved inorganic nitrogen (DIN), on the other hand, were below the eutrophic threshold in most sections of the Chatty River. Microbiological pollutant analysis indicated high gastrointestinal health risks to any residents in the catchment who utilised the water for domestic and recreational use. Overall, no consistent relationship was established between pollutant concentrations and rainfall. This could possibly be because of point pollution for example, from overflowing manholes, which was observed to be intermittent. The extent of pollution highlighted by the water quality sampling indicated the need for mitigation measures. Hydraulic and hydrological models were constructed in PCSWMM, a stormwater management modelling software developed by Computational Hydraulics International (CHI) using the USEPA SWMM model as the ‘engine'. Both the Chatty River Catchment as a whole as well as the Bethelsdorp River sub-catchment, located within the Chatty River Catchment, were modelled to test the potential benefits of SuDS inclusion. Various scenarios were tested including: the current situation (‘As-is'); the likely Pre-Development situation representing the state before the influence of anthropogenic activities; and various retrofitted SuDS interventions. DIN, DIP and total suspended solids (TSS) were the pollutant indicators tracked in the model. DIN and DIP were used to assess the risk of eutrophication. TSS is a good measure of pollution as pollutants such as heavy metals that attach to suspended particles. The SuDS interventions included: a constructed wetland, a retention pond, and various infiltration practices. Six scenarios were explored, including various individual interventions, some regional controls and finally, the combination of all the interventions. Pollutant reduction from the different scenarios ranged from 13-80%. Rehabilitating the wetlands appeared to offer the most significant impact compared to the other regional SuDS interventions in Scenario 1 and 3, with a mean pollutant reduction of 30%. However, a combination of all the interventions had the highest pollutant removal when functioning efficiently of 72% and 80% for DIP and TSS, respectively. This is within the range of treatment required by the City of Cape Town (2009) Management of Urban Stormwater Impacts Policy which was used in the absence of a Gqeberha-specific guideline. Installing a treatment train of multiple SuDS interventions is seen as the most effective strategy to adequately improve water quality in the catchment to meet the standards presented by various guidelines.
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    Review and gap analysis of Water Sensitive Urban Design (WSUD) in Windhoek, Namibia
    (2019) Nambinga, Linekela Elias; Armitage, Neil
    With an ever-increasing population and global warming, fresh water resources are nearing depletion resulting in a global water crisis. As a consequence, cases of drought have been reported worldwide especially in sub-Saharan Africa. In addition to climate change, urbanisation adds strain to infrastructure as well as water supply and the management of water resources. As a result, most developing countries are faced with a water management challenge. There is thus a need for a paradigm shift towards an Integrated Water Management (IWM) approach. Worldwide, countries have responded to the Integrated Urban Water Management (IUWM) concept through the implementation of various management strategies; with Water Sensitive Urban Design (WSUD) emerging from Australia. Some closely allied management strategies in response to IUWM emerged in the USA as Low-Impact Development (LID), in the UK as Sustainable Drainage Systems (SuDS), and in New Zealand as Low-Impact Urban Design and Development (LIUDD). Namibia is situated along the south-west coast of Africa and is considered the driest country in sub-Saharan Africa. It is characterised by a semi-arid environment, with more than 80% covered by desert or semi-desert. The country is regularly afflicted by drought and has fluctuating and unreliable rainfall patterns, often accompanied by high evaporation rates. The City of Windhoek, as the capital city, the biggest municipality and also the largest densely populated town in Namibia, is faced with an ever-increasing shortage of water for its inhabitants. For close to 50 years, the water scarcity situation has led to direct waste water reclamation for potable re-use in Windhoek. Other measures implemented by the City of Windhoek (CoW) towards IUWM include Water Demand Management (WDM), Managed Aquifer Recharge (MAR) and Water Conservation (WC). In order for Windhoek to transform into a Water Sensitive City, the implementation of WSUD is imperative. Although the CoW has implemented measures towards IUWM, more options still need to be explored in order to contribute to IUWM processes and to ultimately become a Water Sensitive City. This research was aimed at conducting a comprehensive review of existing WSUD practices within the CoW and identifying gaps pertaining to WSUD implementation. The research confirmed, via a review of relevant literature, that the implementation of WSUD mainly flourishes when documented policies and regulations drive implementation. To review WSUD implementation in the CoW, this study followed a qualitative research approach by gathering data via online questionnaires using the SurveyMonkey platform. To validate the survey outcomes, structured interviews were conducted with selected survey participants to gain more insight into the outcomes. For the data collection, the study targeted a sample of managers and specialists from the three departments within the CoW that deal with urban infrastructure design and planning. A 72% response rate was achieved. The study revealed that there was a general understanding and knowledge of WSUD concepts among all the CoW stakeholders involved in water management, planning and design. This was mostly due to their academic knowledge and sometimes via exposure to existing WSUD practices within the city. Water Demand Management, Water Recycling, and Voluntary Green Roofs and Rainwater Harvesting were identified as existing WSUD options currently practised within the CoW. The study identified lack of capacity, lack of knowledge, lack of management support, a fragmented approach, the absence of policies and legislation, and no perceived financial benefits as barriers to WSUD implementation within the CoW. Based on the above findings, the study recommended that the City of Windhoek address existing barriers to WSUD implementation, increase awareness of WSUD within the city, secure government funding and apply for carbon credits to upscale the implementation of WSUD.