Water demand of selected residential properties with access to groundwater in serviced areas of the Cape Peninsula

Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: This study focuses on the water demand of selected residential properties with access to groundwater in serviced areas of the Cape Peninsula. This winter rainfall region is typified by hot and dry summer months, corresponding to peak garden water demand. Water restrictions in the area are relatively common and primarily target outdoor use. Groundwater serves as an alternative source of water to some consumers in the area, but little is known about the extent of such use and the impact thereof on potable water demand. A major part of the area is underlain by a primary, unconfined aquifer that has been reported to have high exploitation potential. Its unconsolidated sand and shallow water table provides ideal conditions for small scale groundwater abstraction. Several owners of properties situated above the aquifer unit have capitalised on this and utilise groundwater as an alternative to potable water, mostly for garden irrigation purposes. The main objective of this research was to investigate the average extent of the expected reduction in average annual municipal water demand due to private groundwater use at the selected properties in the study area. The methodology involved abstracting data from the City of Cape Town’s registration process for the private use of non-potable water. The data was recorded between 2000 and 2006 and was available only in hard copy format. The registration data was used to identify residential properties with access to private groundwater sources, based on the physical addresses recorded on the registration forms. The rate of groundwater abstraction was not recorded during the registration process, nor was any of the properties spatially referenced. The data set contained information for 4 487 properties, of which 3 764 could ultimately be used in the analysis. Data from a recent hydro-census in Hermanus (which was done by others prior to this study) was used to test the intended research method first. This trial investigation involved only 114 properties and was used to streamline the proposed methodology for application on the full-scale analysis of the City of Cape Town data. Each address was captured electronically, verified manually and filtered to extract only those representing residential properties for which groundwater use was registered. In order to identify the properties spatially, the addresses had to be converted to coordinates through a procedure called geocoding, so as to plot each spatially and obtain the attributes such as stand size, position and the unique Surveyor General’s code. This was necessary in order to link the addresses to the municipal treasury system and obtain their latest available water consumption records using a commercial software package that incorporates consumer information. Next the actual annual water consumption figures were compared with recently published water demand guidelines based on stand size as single explanatory variable. The selected residential stands were divided into pre-defined stand size categories. The average water consumption of all the stands in each size category was calculated and compared with the suggested water demand as per the guidelines used, based on the centre value of the size range of each category. The results of the comparative analysis confirm findings from two earlier studies where lower municipal water use was reported for residential properties with access to groundwater in a summer rainfall region. The results further showed that the mean average annual potable water demand of consumers in the study area with access to groundwater was on average 31.4% lower than those considered without such access in the same region. This represents an average reduction of 333 l/stand/day (about 10 kl/stand/month) in the potable water demand of the selected residential stands. This study therefore confirms that serviced residential stands with access to private groundwater sources in the Cape Peninsula have lower average metered water consumption from the municipal supply system.AFRIKAANSE OPSOMMING: Hierdie studie fokus op die water anvraag van geselekteerde residensiële erwe met toegang tot grondwater in gedienste woongebiede van die Kaapse Skiereiland. Die gebied is ‘n winterreënvalstreek, met warm, droë somermaande wat saamval met piek water aanvraag vir tuinbou. Waterbeperkings in die area is relatief algemeen, veral op die buitegebruik van water. Grondwater dien as alternatiewe bron vir sommige verbruikers, maar kennis oor die omvang van sulke gebruik, sowel as die impak wat dit het op die aanvraag na drinkbare water is beperk. Die grootste deel van die gebied ter sprake is geleë bo ‘n onbegrensde hoof waterdraer, met berigte hoë ontginningspotensiaal. Die ongekonsolideerde sand en hoë watertafel is ideal vir kleinskaalse grondwateronttrekking. Heelwat van die eienaars van grond wat bo hierdie akwafeer geleë is het die situasie uitgebuit en gebruik grondwater as alternatief vir drinkwater, veral vir tuinbesproeiïng. Die hoofdoel van hierdie navorsing was om die gemiddelde omvang van die verwagte vermindering in gemiddelde jaarlikse munisipale wateraanvraag weens die privaat gebruik van grondwater by die geselekteerde erwe in die studiegebied te ondersoek. Die metodiek het die onttrekking van data uit die Stad Kaapstad se registrasieproses vir die privaat gebruik van nie-drinkbare water behels. Hierdie data, wat tussen 2000 en 2006 vasgelê is, was slegs in harde kopie formaat beskikbaar. Die registrasie data is gebruik om woonerwe te identifiseer met toegang tot privaat grondwater bronne, volgens die fisiese adres verskaf op die registrasie vorms. Die tempo van grondwater onttrekking was nie opgeneem gedurende die registrasie proses nie, so ook nie ruimtelike aanwysings na die ligging van die eiendomme nie. Die datastel het inligting bevat oor 4 487 eiendomme, waarvan 3 764 uiteindelik bruikbaar was in die analise. Data van ‘n onlangse hidro-sensus in Hermanus (wat deur ander gedoen is voor die aanvang van hierdie studie) is gebruik om die beoogde navorsingsmetodiek eers te toets. Die toetsondersoek het slegs 114 eiendomme behels, en is gebruik om die voorgestelde metodologie meer vaartbelyn te maak voor toepassing op die volskaalse analise van die Stad Kaapstad data. Elke adres is elektronies vasgevang, met die hand geverifiëer, en dan gefilter om slegs die residensiele eiendomme waarvoor grondwater gebruik geregistreer is, te behou. Om die ruimtelike verwysing van die eiendomme verder te kon indentifiseer, moes die adresse omskep word in koördinate om sodoende die erwe te kon posisioneer en die erfgrootte, posisie en die unieke Landmeter Generaal kode van elke erf te verkry. Dit was nodig sodat die adresse aan die munisipale stelsel gekoppel kon word om sodoende die jongste beskikbare waterverbruik rekords te verkry deur gebruik te maak van ‘n kommersiële sagteware pakket wat verbruikers-inligting inkorporeer. Hierna is die werklike jaarlikse waterverbruik syfers vergelyk met onlangs gepubliseerde wateraanvraag riglyne, gebaseer op erfgrootte as enkel verklarende veranderlike. Die geselekteerde woonerwe is toe in voorafgekose kategorië verdeel volgens erfgrootte. Die gemiddelde waterverbruik van al die erwe binne elke grootte-kategorie is bereken en vergelyk met die voorgestelde wateraanvraag volgens die riglyne, gebaseer op die middelpuntwaarde van die grootte strekking van elke kategorie. Die resultate van die vergelykende analise staaf die bevindinge van twee vroeër studies wat laer munisipale watervebruik rapporteer vir residensiële eiendomme met toegang tot grondwater in ‘n somerreënvalgebied. Die resultate wys ook dat die gemiddelde jaarlikse drinkbare water aanvraag van verbruikers in die studiegebied wie toegang het tot grondwater, gemiddeld 31.4% laer is as dit van verbruikers wie beskou word sonder sulke toegang in dieselfde streek. Dit verteenwoordig ‘n gemiddelde vermindering van 333 l/erf/dag (rondom 10 kl/erf/maand) in die aanvraag na drinkbare water van die geselekteerde woonerwe. Hierdie studie bevestig dus dat gedienste residensiële erwe met toegang tot privaat grondwater bronne in die Kaapse Skiereiland laer gemiddelde gemeette waterverbruik vanuit die munisipale toevoerstelsel het