Design of stormwater ponds towards the reduction of metal toxins in surface waters that are utilised for South African primary food production

Brink, Isobel Christine (2016-03)

Thesis (DEng)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT: This research originated from a need for civil engineering practice to address metal pollution in stormwater runoff. Specific emphasis was placed on metals that could affect the quality of crops, livestock and fish in South Africa. Detention and retention ponds are commonly used for surface water quality control, and these types of structures were therefore investigated. No prominent pond design methods were found, however, that directly incorporate consideration of metal pollution in the context of food security. In addition, there was a lack of information on how methods could be adapted to address metal pollution specifically. It was argued that focussing on relationships between pond efficiency and design could generate information towards augmenting design philosophies and methodologies. This became the project thesis. The methodology used for the investigation into relationships between pond efficiency and design was constrained by the available data. Statistics and probability theory were the main tools used. Data was obtained from an international database and therefore little was known about possible sources of error. Although a large variety of data on a number of metal toxins and solids was found, individual data sets were often small. These factors meant that data trends (rather than specifics) between ponds were used as the basis for conclusions. Modelling was employed to theoretically test the validity of trends indicated by statistical analysis. These included identification of pond efficiency predictors with logistic regression, curve fitting of a time polynomial to outflow mass data to indicate the class of particulate settling, and hypothetical sedimentation modelling with MIKE 11 software. Results indicated certain pond parameters that were influential in removal processes, but many of these were not explicitly included in prominent design methods. These methods were therefore found to be inadequate for efficient pond design. Data trends indicated a number of processes of importance in metals removals. This information was used to create conceptual models of pond functioning, which were used to augment established engineering theory for application in pond metals removal. The project thesis was therefore accepted. A design philosophy of high levels of control on pond hydraulics and metal loads was recommended. Detention and retention pond functioning for metals removal was illustrated to be highly complex, making detailed modelling enterprises difficult, time consuming and costly. Control over hydraulics and in/out boundaries can simplify pond design.

AFRIKAANS OPSOMMING: Hierdie navorsing spruit uit ‘n behoefte vir die siviele inginieurswese praktyk om metaalbesoedeling in stormwater aan te spreek. Spesifieke klem was gelê op metale wat die voedingskwaliteit van landbou, veeteel- en visteelprodukte kan bëinvloed. Detensie en retensie damme word algemeen gebruik vir vars water kwaliteitskontrole en hierdie tipe strukture was dus ondersoek. Geen prominente dam ontwerpsmetodes was gevind, wat direk oorweging van metaalbesoedeling in die konteks van voedsel sekuriteit geinkorporeer het, nie. Daar was ook ‘n tekort aan inligting oor hoe metodes aangepas kan word om spesifiek op metaalbesoedeling te fokus. Die argument het ontstaan dat ‘n fokus op verhoudings tussen damdoeltreffendheid en ontwerp inligting kan genereer wat gebruik kan word om waarde toe te voeg aan ontwerpsmetodes en filosofieë. Hierdie het die projek tesis geword. Die metodologie wat gebruik was, was beperk deur die beskikbare data. Statistiek en waarskynlikheidsteorie was meestal gebruik. Data was van ‘n internasionale databasis verkry en dus was daar min inligting oor moontlike bronne van waarnemingsfoute. ‘n Wye verskeidenheid data was beskikbaar, maar die individuele datastelle was meestal klein. Hierdie faktore het daartoe gelei dat data tendense (eerder as spesifieke hoedanighede) gebruik was vir gevolgtrekkinge. Modellering was gebruik om die geldigheid van data neigings te toets en te staaf (of teen te staan). Dit het statistiese, wiskundige en rekenaar modellering met MIKE 11 sagteware ingesluit. Resultate het sekere dam parameters aangedui as invloedryk in verwyderings prosesse, maar baie daarvan was nie eksplisiet ingesluit in prominente ontwerps metodes nie. Hierdie metodes was dus bevind om onbevoeg te wees vir doeltreffende dam ontwerp. Data neigings het ‘n aantal prosess aangedui wat belangrik was in metaal verwydering. Hierdie inligting is gebruik om konseptuele modelle vir dam funktionering te skep wat verder gebruik is om waarde toe te voeg aan bestaande ingenieursteorie vir gebruik in metaal verwydering in damme. Die projek tesis was dus aanvaar. n Ontwerpsfilosofie van hoë vlakke van kontrole oor dam hidroulika en metaalladings was aanbeveel. Detensie en retensie dam funkstionering was gewys om hoogs kompleks te wees, wat gedetaileerde modelering moeilik, tydrowend en duur kan maak. Kontrole oor dam hidroulika en in/uit grense kan dam ontwerp vereenvoudig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98370
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