International Conference on Rain Water Cistern Systems
St Thomas, Virgin
Islands - June, 1984
C: Some Cistern Cystems
A Rainwater Catchment
System For Agricultural Water Supply
Rakocy, John A. Hargreaves, Ayyappan Nair
College of the Virgin Islands, USA
A rainwater catchment system was established to demonstrate the Feasibility
of using rainwater catchment to supply high quality water for agricultural use.
The catchment consists of a nylon-reinforced polyvinyl Chloride (PVC) tarpaulin
that is 24 mils thick, 60.8 m long and 30.4 m wide. The tarpaulin is situated
on leveled ground lengthwise along a 3% slope. The edge of the lower quarter of
the tarpaulin covers an earthen dike with a maximum height of 0.6 m. All of the
edges are buried in the ground to secure the tarpaulin.
Rainwater flows off the tarpaulin by gravity through two outlets at the base
of the dike and collects in a 12.5-m3 sump where it is then pumped to a 65-m3
above-ground storage tank equipped with a floating cover to prevent evaporative
loss. When the storage tank is full, the sump and catchment Provide 75 m3 of additional
The catchment system, including the storage tank, cost $19,800 to construct
in 1983. Based on mean rainfall of 1120 mm, the system should Collect 1,673 m3
of rainwater annually, valued at $13,260. The payback period for the system will
be approximately 1.5 years. The tarpaulin, which cost $9,600, has an 8-year guarantee.
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