Water and Energy Feasibility of a Coastal Resort in the Dry Zone
A 40-room resort is proposed on a 1.8 ha coastal site 55 m from the mean high water line near Trincomalee, in the dry zone. There is no mains water. The existing borehole yields 2,500 L per day in the dry season. At the client's target of 300 L per room per day, plus kitchens, laundry and irrigation, demand is about 16,000 L per day. Mean annual rainfall is 1,200 mm, falling mainly from November to January; the dry season can run 90 days with almost no rain. The roof area available for rainwater collection is 1,800 m². The client proposes a 30 kWp rooftop PV array and standard split air-conditioning in every room. The plot falls 2.5 m from the road to the beach, and a neighbour's well 90 m away shows salt intrusion at 12 m depth.
1. Carry out a water balance. Can the site support the project as proposed, and what would you change?
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Do the arithmetic in the order that actually controls the answer: demand first, then supply, then storage.
Demand reduction. 300 L per room per day is a choice, not a constraint. Low-flow fixtures, aerators, dual-flush WCs, waterless urinals and a linen-reuse policy bring it to about 150 L, so 40 rooms use 6,000 L per day. Add kitchen and laundry 2,000 L, and irrigation 500 L if planting is native and there is no turf. Total about 8,500 L per day.
Supply. Borehole 2,500 L per day. Rainwater: 1,800 m² × 1,200 mm × 0.85 runoff coefficient is about 1,836 m³ per year, or roughly 5,000 L per day averaged across the year - but almost none of it falls in the dry season.
Storage. To carry 8,500 L per day through a 90-day dry spell needs about 765 m³ of storage, which is not buildable at a sane cost. A realistic 150 m³ tank carries about 18 days.
Conclusion. On annual average, supply is about 7,500 L against 8,500 L demand, and in the dry season it collapses. The site cannot support 40 rooms at the briefed standard. Add greywater treatment and reuse from showers and basins, roughly 2,000 L per day recovered, and harvest air-conditioning condensate; that closes the annual gap but not the seasonal one. Then reduce the room count to about 30, or accept a documented seasonal water restriction. Do not increase borehole abstraction: the nearby salt intrusion at 12 m means over-pumping risks pulling seawater into the aquifer and destroying the resource permanently.
2. Propose the energy and comfort strategy, and test whether 30 kWp of PV is the right place to start.
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Start with load, not supply. In this climate the cooling load is dominated by solar gain through glazing and the roof, and every kilowatt of gain removed is cheaper than a kilowatt of PV installed.
Passive first: orient rooms to catch the south-west monsoon and cross-ventilate; deep verandahs and shaded openings on east and west; light-coloured or ventilated roof with insulation; limit and shade glazing; ceiling fans to allow a 26 °C setpoint. Then efficient inverter air-conditioning, solar thermal for hot water, and LED lighting throughout.
Estimate the residual load. Forty rooms at about 2 kWh per day each is 80 kWh, plus 40 kWh for common areas and kitchen, giving roughly 120 kWh per day. A 30 kWp array in the dry zone at about 4.5 kWh per kWp per day produces around 135 kWh per day - enough on annual average, but it generates in daylight while the peak load is at night. That means either grid connection, a battery, or accepting a lower solar fraction, and the capital cost of storage has to be weighed against the passive measures it would displace.
The honest recommendation is to fund shading, roof insulation and efficient equipment before increasing the array. 30 kWp is a reasonable target, but it should be the residual after load reduction, not a design starting point.
3. Identify the approvals required and explain how they should be sequenced against the design process.
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The approvals are not a single gate at the end; two of them can end the project, so they must come first.
- Coastal Conservation Department. The site is inside the coastal zone, 55 m from the mean high water line, so a permit is required before development. The setback, the erosion history and the storm-surge level will determine what can be built and where. Plant rooms, electrical equipment and the water tank must be sited above the surge line, not at 2.5 m above the road on a falling site.
- Central Environmental Authority. A resort of this scale is a prescribed project; confirm whether an Initial Environmental Examination or a full EIA is required, and expect the water balance and effluent disposal to be central issues.
- Water Resources Board. Groundwater abstraction needs a permit, and the salt-intrusion evidence will weigh against a high abstraction rate.
- Local authority building approval for the design as developed.
- Sri Lanka Tourism Development Authority classification, which imposes its own facility standards.
Sequencing: resource and hazard studies come before design freeze. The water balance and geotechnical and salinity work should inform the brief, not be retrofitted to it. Submitting for approval before those studies is how projects get consent for a scheme the site cannot actually support, which leaves the architect defending an undeliverable design.