Recharging of Harvested Rooftop Rainwater – Gaza Case Study

Abstract

High water demand from the coastal groundwater aquifer, which is currently the main and only source of fresh water in Gaza Strip, has led us to think about new non-conventional water resources. One of these resources is the rainwater harvesting which has to be taken into consideration in the present time. A pilot project for rainwater harvesting from houses rooftops has been implemented in Deir Al Balah – Gaza in 2012. The main purpose of this pilot project was to collect the rainwater coming from roofs of twenty seven houses and then to allow that water to percolate freely into the soil through an open end soakaway unit proceeded by treatment unit (Grease/Sand Trap) . This research presents the study of the applicability of this project in Deir Al Balah - Gaza, and that is conducted using four main points: social acceptance, harvested rainwater quantity and quality and finally the mathematical modeling. The social acceptance was achieved by a questionnaire, a public meeting and household interviews. The results of the social survey showed a wide acceptance and satisfaction about the harvesting project itself and in general its idea. The harvested rainwater quantities was calculated depending on the annual rainfall intensity, runoff coefficient and the area of each home’s roof. The harvested rainwater quality was tested for different parameters such as TDS, TSS, CL, NO3, pH, EC and F.C for two monitoring years and then analyzing the results, after that a comparison was made with the WHO and Palestinian Standards for drinking water. The results of water quality tests showed that the parameters were much lower than the WHO and Palestinian Standard values of drinking water. Finally, The mathematical modeling depended mainly on constructing four models; one was an ideal sand column and considering three different soil profiles in different locations at the study area. The three models in that area gave good results for the arrival time of the rainwater to the groundwater aquifer and these results were very close to the ideal sand column which means that the study area was very suitable for the recharge of the harvested rooftop rainwater.