Over pumping is the temporary diversion of water or wastewater around a section of a pipeline, drainage system or pumping station using pumps and temporary pipework. Also called bypass pumping, it is used when flow needs to continue while the normal route is isolated for repair, maintenance, replacement or connection works.

For contractors, engineers and project managers, the key question is whether the affected system can safely stop operating for the entire work period. If it cannot, a temporary flow-management arrangement needs to be planned before isolation begins.

This guide explains where over pumping fits, how it differs from groundwater dewatering, and what to prepare before requesting support for a UAE infrastructure project.

When is over pumping required?

Over pumping is needed when the normal flow route becomes unavailable and the project cannot accommodate the incoming flow through an approved shutdown, storage or alternative gravity route. The decision depends on the network, the work duration and the consequences of interruption.

Sewer repairs and rehabilitation

Relining, replacing or repairing a live sewer can require a section to remain isolated while wastewater continues arriving upstream. A temporary bypass transfers that flow to an agreed receiving point beyond the work area.

Pumping station maintenance or replacement

Temporary pumping may be needed while permanent pumps, controls or associated pipework are unavailable. The temporary system must suit the operating period and expected flow variation, including periods when the construction team is not on site.

Manhole works and new connections

Modifying a manhole or connecting new pipework can interrupt an existing flow path. Early assessment helps establish whether the works can use a controlled shutdown or require a bypass.

Stormwater network works and emergency repairs

A drainage diversion may be needed where works obstruct an active flow route. For stormwater systems, the assessment should consider the conditions expected during the work period. Damaged sewers or drainage assets may also require temporary diversion while repairs are organized. Industry guidance identifies peak flow, fluid characteristics and contingency planning as important inputs to sewage bypass planning.

How does over pumping differ from dewatering?

Over pumping manages flow through an existing network. Groundwater dewatering controls water in the ground around an excavation. A project can need both, but one does not automatically perform the other’s function.

Illustrative example: a contractor replacing a sewer may need a bypass to carry wastewater around the isolated pipe and a separate dewatering arrangement to control groundwater entering the trench. The wastewater diversion does not, by itself, lower the surrounding groundwater table.

Arabian Equipment’s dewatering services include groundwater-control methods and over pumping. Selecting the correct combination starts with identifying where the water originates and where it must go.

What determines the temporary pumping arrangement?

A suitable arrangement depends on the required flow, the resistance of the complete system, the fluid being handled and the installation constraints. A pump’s connection diameter or maximum advertised flow is not enough to select it.

Flow and total dynamic head

Record normal and anticipated peak flow in liters per second (L/s) or cubic metres per hour (m³/h), together with the source of those figures. Total dynamic head, expressed in metres, represents the energy per unit weight the pump must add, including elevation and pressure differences and losses through the pipework and fittings.

The designer checks the required duty against the pump curve and operating limits. Total-head calculations and performance-curve reviews support design-point searches. Actual selection still needs the project's system data and engineering assessment.

Fluid, suction conditions and pipe route

Identify whether the fluid is wastewater, stormwater or another liquid, and describe known solids or debris. Confirm water levels, equipment positions and access for installation and maintenance. Map the route to the receiving point, including changes in level, bends, valves and road crossings.

For procurement, request the proposed operating duty and arrangement alongside the equipment list. This makes the basis of the quotation easier to review. AER’s article on factors affecting pump selection provides further groundwater-dewatering context.

Standby capacity and monitoring

Discuss what happens if a pump stops, power is lost or incoming flow increases. Agree the standby arrangement, alarm response and responsibilities for checking the system. A spare pump alone does not explain how service will be maintained during a fault.

Monitoring should be matched to the risk and duration of the work. The operating plan should identify who receives alarms, who can respond and what action is taken when an agreed limit is reached. See AER’s explanation of continuous pump monitoring.

What should UAE project teams confirm before starting?

For works in Dubai, Abu Dhabi or elsewhere in the UAE, identify the asset owner and the project-specific approval route early. Ask the responsible parties to confirm the proposed isolation, temporary pipe route, receiving connection, access arrangements and any discharge conditions that apply. Do not assume that agreement on the pump selection also approves these other elements.

Prepare a site-specific method statement and risk assessment covering the work and temporary installation. Work around sewer infrastructure can involve confined space hazards; diverting flow does not make a manhole safe to enter. The UK Health and Safety Executive’s confined-space guidance is a useful general hazard reference, while the applicable UAE and project requirements must be confirmed separately.

Before isolation, agree how the temporary system will be commissioned, monitored and handed over. The responsible engineer and asset owner should determine the acceptance criteria and the conditions for restoring the permanent route.

What information should accompany an over pumping enquiry?

Use this checklist to make the initial discussion more useful:

• Project location, asset owner and planned activity.

• Required start date, expected duration and permitted work windows.

• Available drawings, pipe sizes and proposed connection points.

• Normal and peak flow estimates, units and supporting records.

• Fluid type and known solids or debris.

• Suction and receiving levels, route length and site-access constraints.

• Available electrical supply or proposed fuel arrangements.

• Required standby, attendance, monitoring and emergency-response scope.

• Approval status and any conditions already issued by the responsible parties.

Mark missing information as unknown so it can be assessed. Comparing quotations against the same scope helps reveal whether installation, pipework, controls, operation and removal are included.

Frequently asked questions

Does every pipeline repair need over pumping?

No. Some works can use an agreed shutdown or another suitable flow-management method. The asset owner and project engineer should assess whether that arrangement can accommodate incoming flow for the full work period.

Can the same pump be used for groundwater and sewage?

Do not assume it can. Suitability depends on the specific pump, fluid, solids-handling characteristics, operating duty and manufacturer limitations. Ask for the proposed model and duty to be checked for the actual application.

What affects the cost of an over pumping system?

The scope can include pumps, temporary pipework, installation, power or fuel, standby equipment, monitoring, operating support and removal. Duration, access and the required duty also affect the quotation. Provide the checklist information to obtain a project-specific assessment.

Discuss your project with Arabian Equipment

Arabian Equipment Rental LLC (AER) provides over pumping and bypassing of stormwater and sewerage manholes as part of its dewatering offering. If your project involves an existing flow route that will be interrupted, contact Arabian Equipment to discuss the project. Share the available drawings, flow information and programme so the required scope can be reviewed.