Guidelines for rainwater harvesting system design and assessment for the city of Johannesburg, South Africa

Abstract

Abstract. As water demand increases rainwater harvesting (RWH) systems are increasingly being installed for water supply but comprehensive hydrologic design guidelines for RWH do not exist in many parts of the world. The objective of this study was to develop guidelines for the hydrologic design and assessment of rainwater harvesting (RWH) systems in the City of Johannesburg, South Africa. The data for developing the guidelines were mainly obtained from multiple daily simulations of potential RWH systems in the city. The simulations used daily rainfall from 8 stations and demands based on the probable non-potable uses of RWH systems – toilet flushing, air conditioning and irrigation. The guidelines were confined to systems that would typically fill up in the wet season and empty towards the end of the dry season of the same year. Therefore, supply-to-demand ratios ranging from 0.1 to 0.9 were applied. Two generalized design charts of dimensionless relationships were developed. One relates the yield ratio with supply-to-demand ratio and reliability while the other relates the yield ratio with the storage-to-demand ratio and reliability. Reliability was defined as the probability of exceedance of annual yield in order to incorporate the large inter-annual variability of rainfall experienced in the region. The analyses and design of an example RWH system is used to illustrate the application of the design charts.

Potential Water Balance using Rainwater: An Analysis of Delhi, Megacity in India

“…Comparing the present study with another similar study, it was observed that a 4,000 L concrete tank installed with a roof area of 40 m 2 was adequate to take care of the water demands of a household consisting of four members [34,35]. Similarly, a study conducted by Woltersdorf et al in [36,37]. According to Imteaz et al, a tank size of 7,000 L is required to achieve 100% reliability for toilet flushing and laundry [38].…”

Journal of Water and Land Development

“…The average functionality status of the RWH schemes is 22.94% which is below the average functionality standard of RWH, which is 50% [NDIRITU et al 2018]. As per the result of the study shown in Figure 6 most of the schemes are non-functional.…”