Although Qatar is a desert environment, at least twice a year heavy rainfall results in massive disruption to urban areas and flood damage to infrastructure, retail outlets and private homes.
The vision behind the Musaimeer Pumping Station and Outfall Tunnel in Qatar is to protect the southern Doha area from flooding and future climate risks that could hold back urban development, while minimising the environmental impact during construction and operation.
This has been achieved by pumping rainwater and stormwater along a 10.2km-long outfall tunnel and discharging the water offshore on the seabed, where the impact on the marine environment is reduced. The outfall tunnel is the longest tunnel worldwide used for discharging ground and surface water offshore.
Working as project manager on behalf of Ashghal, the Public Works Authority of Qatar, we ensured that the project’s complex engineering elements were completed on time and on budget. This included a reinforced concrete underground pump station with two wet wells, each with 2,500m³ storage capacity. It also has ten submersible pumps with a capacity of up to 19.7m³ per second and can empty an Olympic swimming pool in two minutes.
We prioritised sustainability throughout the project, which ran from November 2017 to September 2022. This included effective resource allocation; a sustainable, innovative and durable design; the use of local goods and service providers and meeting future capacity needs.
Innovative techniques
The 10km outfall tunnel lies 15m beneath the seabed under the Persian Gulf and was constructed through challenging ground and marine conditions. The tunnel connects with a 19,600m2 diffuser field structure, which releases the rainwater at the seabed and is designed and constructed in line with stringent environmental standards to protect marine life.
The project used prefabricated construction elements, following design for manufacture and assembly (DfMA) principles, to deliver substantial programme savings and efficiencies. This also helped to overcome some of the challenges of working at a compact 16ha site, where 90% of the asset is located below ground.
Precast roof slabs and beams were used in the pump station and prestressed roof slabs were used for all above ground buildings. Precast segments were also used in the outfall tunnel.
We used state-of-the-art building information modelling (BIM) to monitor project progress and cost with precision and to identify potential problems early in the design phase – reducing waste, rework and volume of resources.
Around 335,912 tons of tunnel spoil from the project tunnelling works were reused for coastal reclamation with a cost saving of QAR8.4M (US$2.3M). The project also implemented measures to minimise CO2 emissions – for example, transporting the spoil from the project tunnelling works directly to the Al Khor municipality without any intermediate stockpiling.
Project efficiency
Tight programme management ensured the project was completed on time and on budget. Project data was digitally captured, recorded and shared with the client using the international construction operations building information exchange (COBie) standard.
This provided detailed monitoring of project progress down to the level of employee shifts and quick analysis of any deviations from the schedule. The early identification of potential problems meant that recovery or mitigation measures could be undertaken to keep the project on schedule and eliminate any unnecessary costs.
The overall project was completed 56 days ahead of schedule. Meanwhile, an additional remotely located pump station (capacity of 7m³ per second), which was a variation on the main project, took only 219 days to complete from start to operation.
Environmental achievements
To future-proof Qatar’s infrastructure and protect the environment, 22 design alternatives were assessed for disposing of storm and ground water to ensure the optimal solution was chosen in terms of engineering viability, cost effectiveness, operational efficiency, environmental impact and climate-resilience.
The project is designed to withstand climate change effects up to 2060 and to minimise the environmental impact during operation. All potential flooding hazards that could affect equipment, buildings and other assets were evaluated. The final design integrated measures to reduce surface water run-off and mitigate flood risks from a one in 50-year storm event.
The project has received environmental awards including the Ashghal Green Award in 2020 and the 2022 CEEQUAL (Very Good), the highest score ever in Qatar.
By draining rainwater and alleviating flooding in a 270km2 catchment area, the Musaimeer pump and outfall tunnel removes a barrier to sustainable urban development in southern Doha. The new hydraulic infrastructure is designed to keep ground water below –3m, which will reduce the need for expensive foundation works and lower the cost of urbanisation.
Project successes
- The critical portion (Outfall Tunnel) was completed on budget and 56 days ahead of schedule.
- 9.2M hours were worked with no lost time injuries (LTI) in 2022.
- In 2020, 2021 and 2022, the project received Gold Awards from The Royal Society for the Prevention of Accidents (RoSPA).
- The project has received environmental awards including the Ashghal Green Award in 2020 and the 2022 CEEQUAL (Very Good), the highest score ever in Qatar.
- In 2022 the project received further industry excellence awards from ICE Qatar and MEED.