Lining irrigation reservoirs: what it saves a UAE farm

Farms across Al Ain, the Al Dhafra region and the inland areas of the northern emirates depend on stored water. The reservoir is filled from a well or a tanker and drawn down over days or weeks — and on the gravelly, permeable ground typical of these areas, an unlined basin quietly returns a large share of that water to the ground.

Is it seepage or evaporation?

Both make the level drop, and they need completely different responses. A simple field test separates them:

1. Stop all abstraction and inflow for three or four still days.
2. Mark the water level against a fixed staff and record the drop each day.
3. Float a container of water in the reservoir, filled to the same level as the basin, and measure its drop too. The floating container loses water only to evaporation.
4. The difference between the two drops is seepage.

Evaporation alone in a UAE summer is substantial. If your basin is dropping at three or four times the container rate, the majority of the loss is going into the ground and lining is the answer.

What gauge a farm reservoir needs

For an exposed reservoir with a few metres of head, 1.0 mm HDPE is the practical minimum and 1.5 mm is the sensible default. The reasons to go to 1.5 mm are exposure and abuse rather than water pressure: a farm reservoir gets cleaned, gets pumps dropped into it, occasionally gets a tractor near it, and sits under full sun whenever it is drawn down.

On gravelly Al Ain-type subgrades, budget for a 300–400 g/m² cushion geotextile beneath the sheet. It is a small line item and it is what stops slow puncture from the material below.

Building it so it lasts

• Anchor trench around the full perimeter. Non-negotiable on an exposed basin.
• A protected access ramp, so a pump or a cleaning crew never drives on bare membrane.
• Boot details at every pipe. Fill line, draw-off, scour — each one extrusion-welded and clamped. Pipes pushed through slits and taped are the standard cause of farm reservoir leaks.
• Freeboard and an overflow. A reservoir filled to the crest will overtop eventually, and water running over the crest scours the anchor trench out.
• Keep it full where you can. Water is the best protection a liner has; an empty basin baking through July is working harder than a full one.

Doing something about evaporation

Lining does nothing for evaporation, and on an open basin in this climate that loss is significant. Three approaches, in descending order of both effectiveness and cost:

• Floating cover — a welded membrane floating on the surface, with rainwater removal and proper edge detailing. The most effective option and an engineered system in its own right.
• Shade structure over the basin — no contact with the water, easier maintenance, a more modest reduction.
• Floating elements — balls or panels. Quick to deploy, moderate effect, and they have to be retrieved before the basin is cleaned.

Which makes sense depends on how the reservoir is operated and what the water costs you. If the basin is drawn down and refilled constantly, a cover is harder to justify than on one that sits full for weeks.

The economics

Lining a farm reservoir is one of the few agricultural investments with an arithmetic that is genuinely simple. Take the measured seepage rate, multiply by the hours the basin holds water each year, and multiply by what a cubic metre costs you — pumping energy, tanker deliveries, or the value of what that water grows. Compare with the lining cost across a design life measured in decades.

On permeable ground the answer usually comes back in a small number of seasons, and after that the saving is permanent and needs no operating spend. That is a rare shape of return on a farm.

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