Reliability analysis of rainwater tanks using daily water balance model: Variations within a large city

Abstract

A daily water balance model is used for the performance analysis and design optimisation of rainwater tanks at four different regions of Melbourne; North, Central, SouthEast and SouthWest. These four different regions of Melbourne are characterised by notable different topography and rainfall characteristics. From historical rainfall data, three representative years (dry, average and wet) are selected. Reliability is defined as percentage of days in a year when rainwater tank is able to supply the intended partial demand for a particular condition. For the three climatic conditions, a number of reliability charts are produced for domestic rainwater tanks in relation to tank volume, roof area and number of people in a house (i.e. water demand). It is found that for a relatively small roof size (100 m2), 100% reliability cannot be achieved even with a very large tank (10,000 L). Reliability becomes independent of tank size for tank sizes larger than 4000-7000 L depending on the location. This is defined as threshold tank size, relationships with threshold tank sizes and annual rainfall amounts are then established for all the locations. A new factor named 'Rainwater Accumulation Potential (RAP)' has been introduced and maximum achievable reliabilities for different reasonable RAPs under different climatic conditions are presented for all the locations selected in this study. From these findings, for the design of rainwater tank size it is recommended to have a RAP value of 0.8-0.9 for greater Melbourne.

Generalized Storage–Yield–Reliability Relationships for Analysing Shopping Centre Rainwater Harvesting Systems

“…The storage fraction has been specified as storage capacity divided by annual rainfall volume [26,28] or as this ratio multiplied by the ratio of rain days to dry days [27]. For RWH analysis, reliability has been commonly defined as volumetric reliability (volume supplied to that demanded over the simulation period) [6,[28][29][30][31] or as the ratio of days of full supply to the total days of simulation [26]. However, volumetric reliability does not capture inter-annual variability of rainfall, and statistical analyses of the yield (or volumetric reliabilities) obtained in each year of simulation have been used to incorporate this variability [25,27].…”

“…However, volumetric reliability does not capture inter-annual variability of rainfall, and statistical analyses of the yield (or volumetric reliabilities) obtained in each year of simulation have been used to incorporate this variability [25,27]. The effect of inter-annual rainfall variability has also been assessed by analysing RWH performance for dry, normal and wet years [29] or for a typical dry year [32]. Since South Africa experiences large inter-annual variability of rainfall [3], the RWH guidelines to be developed in the current study needed to incorporate inter-annual rainfall variability and to also fully integrate reliability (the quantifier of variability) into the regression equations of the model.…”

Estimating the Rainwater Potential per Household in an Urban Area: Case Study in Central Mexico

“…These authors designed a methodology to determine the size of tanks of rainwater storage at the household level, considering that the distribution of rainfall can vary from one point to another of the city. Concerning their storage capacity, Imteaz et al [8,9] and Rahman et al [10] indicated that daily rainfall analysis is expected to produce more realistic rainwater tank sizing than using monthly rainfall data.…”

Designing Rainwater Harvesting Systems Cost-Effectively in a Urban Water-Energy Saving Scheme by Using a GIS-Simulation Based Design System

“…The best known storage sizing for RWHSs is the water balance model. A review of the literature revealed that the water balance equation has been accepted and adopted by researchers to simulate the behavior of RWHSs, and to predict their performance [16,18,[20][21][22][23][24][25][26][27]. RWHSs in dense urban areas appear to be economically advantageous [28][29][30].…”