Modelling outdoor water use of homes in gated communities
Thesis (PhD)--Stellenbosch University, 2019.
ENGLISH ABSTRACT: Gated communities are commonly referred to as residential estates, or common interest housing developments. The homes in a particular gated community are often closed off to the general public by means of a boundary wall and security-controlled entrances. Landscaping and related outdoor water use is prescribed by governing documents of the gated communities. Outdoor water use is a major contributor to the total water use, as well as seasonal fluctuation of water use in gated communities. The accurate estimation of outdoor water use is therefore essential from a planning perspective, especially with water restrictions typically targeting outdoor water use. Earlier research notes living inside gated communities is different from living outside gated communities. It can thus be expected that water use within homes in gated communities would be different. Benefits and constraints in terms of cost, security, lifestyle, sense of place and exclusivity of gated communities are described in literature. Specific research has been published on the estimation of residential water use based on population, spatial scales, income levels and housing typology, while some studies focussed on end-use modelling. However, none of the earlier studies have addressed water use in gated communities and homes in gated communities per se. As part of this study monthly water use in gated communities was investigated. This study focussed on gated communities, because the unique development type has become increasingly popular and limited guidelines are available for estimating water use. Monthly water use of 2888 gated communities from three South African metropolitans was analysed in this study. The mean average water use per GC home was 0.64 kL/d, but varied between 0.49 kL/d and 0.66 kL/d in the three study samples. Some peculiarities of water use in gated communities are highlighted. Various outdoor water use components were mathematically defined and combined in this study to model outdoor water use. The model parameters were formulated and derived to describe conditions such as types of vegetation, irrigated area and size of pool. The parameters were stochastically populated to achieve parameter distributions that were used to simulate outdoor water use using the Monte Carlo method. Special attention was given to derive the parameter input for the garden footprint area by spatially analysing footprint areas of 1807 homes in gated communities. The results were compared with a knowledge review of architectural guidelines of existing gated communities. It is commonly accepted that total household water use is the summation of indoor water use, outdoor water use and real losses. If the total water use is known and the indoor water use and losses can be derived, outdoor water use can be estimated. One method used in this study to disaggregate water use components was to investigate wastewater flow from a gated community in order to estimate outdoor water use. The results showed outdoor water use contributed ~56% of total annual water use for the particular gated community under investigation. A second proxy method was derived to disaggregate indoor and outdoor components of the water use. The proxy method expresses the generally non-seasonal indoor water use as a function of lowest water use months. Based on the proxy approach analysis, indoor use was derived to be ~90% of the lowest month’s water use. Indoor water use estimated in this manner was then subtracted from the total monthly water use in order to obtain monthly outdoor water use data. The derived outdoor water use model was used to stochastically simulate outdoor water use. The simulated results were compared with actual data from three gated communities in the study group using the proxy approach of indoor use linked to the lowest month water use. The accuracy of the outdoor water use model ranged between 8% and 18%. From sensitivity analysis, it was derived that irrigation efficiency is a major influence in the accuracy of outdoor water use modelling and was also ascribed to the reason for over irrigation that occurred during transition seasons (autumn and spring). Applications of the outdoor water use model could include estimating the effect of outdoor water use restrictions, and designing the capacity of separated water distribution systems that would supply water of lower quality for outdoor water uses, specifically. This research contributed to the understanding of water use in gated communities, particularly by presenting novel methods for estimating outdoor use in gated community homes.
AFRIKAANSE OPSOMMING: Geen opsomming