Near the coast, a basement dig meets groundwater within a few metres. The three dewatering methods, how to choose the pumps, and what to plan for discharge.
On coastal plots in Dubai, Abu Dhabi and Sharjah, groundwater often sits only a few metres below the surface. Dig a basement or a deep foundation and the excavation starts to fill. Dewatering lowers the water level so the work can be done in the dry, and the pumps have to keep running, reliably, until the structure is ready for the water to come back.
Three ways to dewater
| Method | How it works | Suits |
|---|---|---|
| Sump pumping | Water collects in sumps inside the excavation and submersible drainage pumps lift it out. | Shallow digs, modest inflow, soils that don't wash out easily |
| Wellpoints | A ring of small wells around the dig, joined to a header and drawn by a wellpoint pump under vacuum. | Sandy soils and shallow excavations, roughly 5 to 6 m per stage |
| Deep wells | Larger wells around the site, each with its own submersible pump. | Deeper excavations and higher inflows |
The method comes from the geotechnical report: the soil, the water level, the excavation depth, and how fast water will flow in. The pumps come after.
Choosing the pumps
- Flow. Size from the predicted inflow in the geotechnical report or a pumping test, with margin for the first days, when the pumps remove stored water as well as inflow.
- Head. The lift out of the excavation plus the friction in the discharge line, which on a large site can be long.
- Solids. Groundwater in sandy ground carries fines. Drainage pumps with hardened, wear-resistant impellers, or an agitator for sludge, last far longer than clean-water pumps.
- Standby. A single pump failure can flood a pit overnight. Plan a standby pump for every duty pump, or at least for the critical ones.
- Power. Most sites run on generators. An automatic changeover to a standby generator protects the dig if one fails.
Discharge and approvals
Pumped groundwater usually carries silt and is often saline, so it cannot simply be run into the nearest drain. Settlement tanks let the silt drop out before discharge. Discharging groundwater generally needs approval from the relevant authority in each emirate, so check the permit requirements for the site before pumping starts and build their monitoring into the plan.
Monitoring while it runs
- Observation wells to confirm the water level stays below the formation level.
- A flow meter on the discharge, which is often a permit condition as well as a useful check.
- Daily checks on pumps, fuel and settlement tanks, and a clear call-out plan for nights and weekends.
Stopping at the right time
Dewatering cannot simply be switched off when the basement slab is poured. Rising groundwater pushes up on the slab, and until the structure above is heavy enough to resist it, that uplift can crack or lift the slab. The structural engineer sets when pumping can stop, and the pumps stay on until then.
What to send for a quote
Send the geotechnical report, the excavation plan and depth, the programme, and the power available on site. We supply submersible dewatering pumps for construction sites in Dubai, Abu Dhabi, Sharjah and across the UAE. See the submersible range on our water pumps page, or send the details.
