Education city is a prestigious 850ha development on the outskirts of Doha, the capital of Qatar. Promoted by the not-for-profit Qatar Foundation, the futuristic city’s aim is to provide a world-class education to the people of the Emirate.
The landmark, architect-designed conurbation contains international education and research facilities, including branches of Cornell University and Texas A&M, residential housing, sports facilities, state-of-the-art equestrian and medical research centres, a museum and convention centres.
Global engineering consultancy Atkins was commissioned in 2005 by the Foundation to design the primary site infrastructure - drainage, water, electrical, telecoms, IT, security, roads, a light rail system, central plant facilities, three multi-storey car parks, a solid waste facility and three integrated transport hubs as well as landscaping.
Atkins Design Manager Will Broad explains: “The city is intended as a flagship exemplar for Qatar, showing the way forward both for education and facilities.”
InfoWorks CS is being used to optimize the design of the stormwater drainage network, a complex system comprising sewers, soakaways, storage lagoons and pumping stations that need to cope with the demands of the area’s infrequent but often intense, short-lived winter storms.
Mr Broad notes: “We began work using a different software solution, but InfoWorks was more suited to the larger scale catchment area, and is able to represents rainfall runoff more realistically. This enables greater confidence in the sizing of the network.”
The gravity-based stormwater system discharges into a 2.4m diameter microtunnel that discharges to the Persian Gulf, but the capacity of this is limited, and hence discharge from the Education City site must be restricted. Attenuation is therefore a key element of the surface water management strategy.
Mr Broad explains: “The overall water strategy for the Education City site involves groundwater use for non-potable applications such as irrigation and District Cooling - a reverse osmosis system treats the saline groundwater and rainfall forms a major part of the recharge of the aquifer. Allowing infiltration of storm water back into the aquifer is therefore an integral part of the surface water management as well as the water strategy for the site.”
Attenuation design
Design of attenuation systems was complicated by ground conditions, which predominantly comprise limestone combined with a high water table level. Soakaways have been stipulated for buildings on the site’s higher ground, and at lower levels underground attenuation systems will be used. The surface water system will act as a combined land drainage and surface water system - this will allow some control over water table levels in addition to providing a rainwater collection system. All flows collected are directed via the RO plant, with flow in excess of the plant capacity being discharged to the microtunnel.
The design criteria for flooding frequency comply with the requirements of the Qatar Highway Design Manual and Qatar Sewerage and Drainage Design Manual Volume 3. The system had to cope with a variety of design return periods for flood protection depending on the type and prestige of the development, up to the one in 25 year event for prestige or ceremonial developments.
InfoWorks CS was used to size the stormwater network to ensure that the array of systems (including a proposed golf course which will also provide attenuation and storage) work together to ensure an optimum delivery of stormwater for aquifer recharge.
The design storm hydrographs were developed using government-approved Qatar University work by A.S. Bazaraa and S. Ahmed* which is relevant to local conditions and rainfall characteristics.
Data acquisition
Data on the landscape itself was obtained from a number of sources. Mr Broad explains that as-built drawings and records of the existing network were used for parts of the campus that are already constructed, including a 10,000m3 storage tank and pumps that return flows to the network. These records were input into the model, along with information from the site survey, known road levels, the site grading plan and the overall master plan.
InfoWorks CS was used as a design tool to size the un-built elements of the system to prevent flooding at the design storm return period. There was little information that could be used to calibrate the model. Rainfall occurs typically once per year - this timing is incompatible with the project programme, and hence a typical flow monitoring and model verification exercise could not be accommodated within the design timescales. However, historic rainfall records were obtained from Qatar’s Public Works Authority and simulated within the model, to ensure that the system could absorb the type of flows that were known to occur locally.
In lieu of calibration, sensitivity assessments were undertaken and siltation assessed to ensure the design was adequately conservative to account for typical maintenance factors such as sand within the network. ..
Although the InfoWorks CS2D model was not available when the initial calculations were made, Mr Broad says: “It’s a tool we’re aware of. If we were to start again it would be key to designing the surface water strategy.”
Results
The results of the modeling showed that InfoWorks was a suitable tool to refine and optimize the stormwater system for the city, and that the solution has direct applications for issues in the region. Mr Broad adds: “The Public Works Authority is also using InfoWorks CS, hence our model can be imported seamlessly into the wider Doha network model, and simulations undertaken to ensure the proposed design achieves the objective of preventing local flooding without detrimental effect to the downstream system.”
He adds: “Stability was also extremely important - the site has a lot of attenuation, and a lot of dynamic flows, surges and backflows. We use flow control devices to limit discharge from the system and modeling all of this can be achieved in InfoWorks. The system is very user friendly - it is possible to overlay elements in the background, such as maps, and it is easy to show the client the results of the modeling.”
Mr Broad concludes: “InfoWorks CS is already an industry standard in various parts of the world. It is a very useful design tool, and you can do a lot of things with it that other solutions do not achieve. There were various challenges on the site and it handled all of the issues well, without the need for added modules - everything was in one place and very easy to use.”
*’Rainfall characterization in an arid area’