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1st International Conference on Rain Water Cistern Systems
Honolulu, Hawaii, USA - June 1982

Section 3: Design, Cost, And Policy

Page 184

Rain Water as a Water Supply Source in Bermuda

D.H. Waller
Technical University of Nova Scotia, Canada

Introduction

Any description of rain water supply systems in Bermuda must take into account the geography and history of this small mid-Atlantic country.

The island of Bermuda is located at 32° north latitude, 65° west longitude, 917 km east of the North American coast. The "island" is actually a . series of seven small islands, joined by bridges, that are the unsubmerged portion of limestone deposits, approximately 100 m from the sea floor. The aeolean limestones, laid down during glacial advances and retreats of the Pleistocene era, are loosely cemented and extremely permeable. The rock is covered by a soil layer approximately 15 cm thick.

The island is 30 km long, with a mean width of approximately 1.5 km and.a maximum width of 3 km. The total area is 53.1 km2. The elevation of most of the land mass is less than 30 m above sea level, rising to a maximum of less than 100 m.

The climate is semitropical and frost free. Mean monthly temperatures approximate 20°C in winter and 30°C in summer. The average annual rainfall, based on records since 1886, is 146.8 cm (Vatcher 1974); minimum and maximum 12-month rainfalls are respectively 77.0 and 227.6 cm. Rainfall is fairly uniform during the year, but onlthly average values for April through July are lower than the annual mean.

One result of the high permeability of soil and rocks is the absence of freshwater streams and lakes. Groundwater underlies 20% of the land area, in five lens. The largest lens, with a mean thickness of 7.6 m, represents two thirds of the total area. Brackish water (1-10% sea water) underlies another 23% of the island (Vatcher 1974).

Bermuda today is a self-governing British colony.

The island was uninhabited until its discover in 1503. It has been continuously occupied since 1609, when it was settled by English colonists who also colonized Massachusetts and Virginia in the United States.

The first Bermuda houses were similar to those in England, but construction quickly adapted to indigenous materials of cedar and limestone. Native cedar was in short supply as early as 1620, and stone buildings were encouraged, using cedar for framing and trim. The native limestone, which can be cut with a saw and which hardens on exposure to the atmosphere, was cut into blocks for walls. Roofs, supported on cedar framing, were formed of overlapping limestone slates, 30.5 cm x 45.7 cm x approximately 3.8 cm. Limestone, burned in kilns, also provided the mortar used to assemble both walls and roofs. This form of construction is basically the same as that used today, except that concrete block walls have replaced limestone in recent construction: in 1980, 95% of households lived in houses with outer walls of limestone ("Bermuda stone") or cement block (Statistical Department 1980).

A unique feature of Bermuda roofs has been their role in water supply. Until the 1930s, rain water provided the only source of potable water. Water was collected on roofs, where wedge-shaped limestone "glides" were laid to form sloping gutters on the roof surface, diverting rain water into vertical leaders and thence into storage tanks.

Early storage tanks were rum puncheons or cisterns made of cedar. Others were formed by excavation into rock and made tight with mortar. Prior to the 20th century, tanks were located at the outside rear of dwellings, partly or entirely above ground. Water was removed from tanks by bucket or hand pump and carried indoors. In some later systems, hand pumps transferred water to elevated indoor storage tanks. Current systems include storage tanks under buildings with electric pumps and pneumatic tanks. Today, 96% of households are provided with piped indoor water supplies (Statistical Department 1980).

Rain water was also collected from "artificial catches" created by removing thin hillside soil and sealing the rock surface with mortar. Water from large artificial catches continues to provide significant quantities of water, e.g., an estimated 13.6 million l/yr from a catchment developed for a British military installation, and 45.5 million l/yr from a catchment serving a major hotel (Thomas 1980).

Roof water systems with adequate storage were not systematically encouraged until the 20th century. Prior to adoption of current public health regulations in 1951, storage capacities of 1400 to 22,000 l were common (previous public health regulations required up to 6800 l per occupant, although 13,000 litres per occupant were recommended), compared with typical storage today of 68,000.l.

Water was imported from North America during a five-year period from 1938 to 1968.

In 1932 a private company, Watlington Waterworks, began development of the largest of the groundwater lenses, providing up to 3.5 million k/day of brackish water for non-potable uses (primarily flushing) through a distribution system serving the central part of the island. Part of this water fed a desalination plant that provided potable water to several major tourist facilities. In 1979, the Bermuda Public Works Department and Watlington Waterworks commenced a joint venture aimed at rational development of the groundwater resource, involving new wells in the central lens and delivery of potable water through. the Watlington system.

By the 1960s, desalination plants had been installed by several major hotels, industry, and government. At present (June 1981) a government sea water distillation plant is reaching the end of its useful life, and a brackish water reverse osmosis plant is being brought on-line, by the Public Works Department.

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