Undergraduate Thesis - Feasibility of Rainwater Harvesting in Paarden Island

An introduction to the history of rainwater harvesting

Rainwater harvesting has a very long history. According to Gould and Nissen-Petersen (1999, p. 7) clay pots dating back to 4000 BC were found in Gansu Province in China where they were believed to have been used to collect rainwater runoff from roofs. Gould and Nissen-Petersen also mentioned evidence of rainwater being used in India around 2000 BC. Mediterranean archaeologists (Gould & Nissen-Petersen, 1999) have also found evidence of rainwater harvesting in Roman, Phoenician and Carthaginian civilisations from around 2000 BC. Rainwater harvesting has been used by human civilisations for many millennia and is still being used in some parts of the world where water supply is scarce such as on coral and volcanic islands as well as in arid regions (Gould & Nissen-Petersen, 1999).

 

The decline in rainwater use has been mainly due to dam building, ground water utilisation and piped water schemes which occurred in the middle of the twentieth century (Gould & Nissen-Petersen, 1999). Strictly speaking these techniques are still a form of rainwater harvesting, just at a much larger scale than what was previously done. Most of the large dams that have been built have underperformed and had negative impacts on the environment and the people that were displaced (World Commission on Dams, 2000). In the last few years the trend has moved back to small scale rainwater harvesting techniques. In Europe and other first world countries the trend has been driven by a need to be more “green” and sustainable, in other parts of the world rainwater harvesting is used as a sole supply of freshwater due to a lack of infrastructure. 

 

The definition of rainwater harvesting

There are many different definitions for rainwater harvesting in use today, most of which are slight variations of the same idea but modified to suit the article that was written. In a World Bank report on Water Harvesting for Plant Production (Begemann, et al., 1988, p. 4) the idea was conceptualised as follows “rainwater harvesting is usually employed as an umbrella term describing a whole range of methods of collecting and concentrating various forms of runoff (rooftop runoff, overland flow, stream flow, etc.) from various sources (precipitation, dew, etc.) and for various purposes (agricultural, livestock, domestic and other purposes)”. 

 

More recent versions of the definition refer to rainwater harvesting as “a technology used for collecting and storing rainwater for human use from rooftops, land surfaces or rock catchments using simple techniques such as jars and pots as well as engineered techniques” (UN-HABITAT, 2005, p. 1). Other authors (Khoury-Nolde, 2008) and (Vishwanath, 2008) also refer to rainwater harvesting as a technology that is used to collect and store water to be used later. In a South African paper, rainwater harvesting was described by Kahinda et al. (2008) as “the collection, storage and use of rainwater for small-scale productive purposes”

 

Using the first two definitions of rainwater harvesting it is possible to justify conventional piped systems as a very large rainwater harvesting system. The surrounding countryside is used a catchment area and the dams are considered to be the storage medium of the rainwater to be used at a later date. Treatment plants are used to treat the rainwater on a very large scale whilst the distribution networks of municipal pipes are the conveyance system used to transport the rainwater to the end user. All these components of a conventional piped system are present in a rainwater harvesting system. The only difference is the scale at which the rainwater is collected and the distance the water must travel to get to the end user. 

 

To avoid confusion in this document I will be referring to conventional pipe systems as the water supply that the end users in the City of Cape Town are accustomed to and are charged for by the City of Cape Town. Rainwater harvesting will be referred to as what Kahinda et al (2008) used to describe rainwater harvesting. The rainwater harvesting systems that will be used in Paarden Island will all be small scale in comparison to the conventional systems. The main idea is to represent rainwater harvesting as a water supply that is utilised at the same location as where it is collected. 

 

Rainwater harvesting is defined as ‘the collection, storage and use of rainwater on site’.

 

Rainwater harvesting in South Africa

In South Africa the Department of Water Affairs supports rainwater harvesting but has mainly focused this support on rural households for food gardens and other productive water uses (RSA GCIS, 2012, p. 654). Rainwater harvesting has allowed people who live in areas that do not have access to water reticulation systems some access to water. The Department of Water Affairs considers the implementation of rainwater harvesting systems to be an option that can be implemented within a short time frame (RSA GCIS, 2012, p. 654). 

 

The eThekwini Municipality has implemented the use of rainwater harvesting systems in 500 poor households and were able to save up to 10% on bulk demand. The Department of Water Affairs intends to distribute around 8000 rainwater harvesting tanks in 2012/2013 to help improve access to water and food production (RSA GCIS, 2012, p. 664).