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Saudi Arabia's water transformation

One of the two holiest cities in the world of Islam is about to undergo a radical long-term transformation - and water is at the heart of it.

An oasis city for millennia, Madinah in Saudi Arabia sits on a network of wadis, shallow river channels that only occasionally carry flowing water. These days the city relies mainly on desalinated seawater for its potable water supplies, and in common with many cities in the Middle East, has a rising groundwater problem.

With rapid urban expansion now underway, however, the most critical concerns the city authorities are addressing are the flood risks the wadis currently represent.

Most attention is focussed on the 55km of the Wadi Al Aqeeq, which is referred to as the “Blessed Valley” in the Quran. This has a catchment area of around 5,500km2 and runs approximately south to north to the west of the city centre. In 2013, BuroHappold Engineering together with Moriyama and Teshima Planners were commissioned by the Madinah Development Authority to produce a masterplan for the wadi, one that would be implemented over the next 20 years.

Wadi

Wadi: Prone to flash flooding during intense rainfall

It would cover not just the wadi but also the land surrounding it. The rehabilitation of the wadi was seen as an opportunity to transform this area within the city and outside it.

BuroHappold partner Alan Travers says it was soon obvious that any flood mitigation scheme could have significant beneficial effects on the local environment and ecology as part of the wider masterplan. And that would not be all.

“There are enormous opportunities in the social, economic and cultural fields as well,” he says. “Land next to the rehabilitated wadi could be developed, in some areas at a higher density than the current norm, fostering urban regeneration. It was a win-win situation.”

“Average annual rainfall figures don’t give much of a clue, and the so-called ‘rainy season’ between November and March is a slight misnomer,” Travers says. “Most of the 100mm or so of annual rainfall comes in the form of very intense, short duration storms, which can lead to destructive flash flooding.”

Alan Travers, BuroHappold

BuroHappold’s original 86 week, six phase contract is due to finish soon, but may well be extended. The first phase, the basic hydrological analysis, was challenging.

“Average annual rainfall figures don’t give much of a clue, and the so-called ‘rainy season’ between November and March is a slight misnomer,” Travers says. “Most of the 100mm or so of annual rainfall comes in the form of very intense, short duration storms, which can lead to destructive flash flooding.”

Flash floods caused chaos in the Red Sea port of Jeddah in 2010, when more than 100 people drowned. Ten more lives were lost in more floods the following year, and 13 more died in 2013. In Madinah, however, there has been no major flood event in living memory.

Over the years, the shallow wadis became neglected and ignored. As rapid urban development began to encroach, the wadis increasingly became convenient utilities corridors leading to contamination and loss of environmental diversity. Much of this degradation has led to a worrying reduction in flood capacity.

It soon became apparent that the most critical section of the 55km of the wadi was the 14km that runs close to the historic centre of Madinah, the stretch between the Miquat Mosque and the confluence with the Wadi Quanat to the north. Working with the limited hydrological data available, the BuroHappold team came up with some alarming predictions, as Travers reports.

“A 1 in 200 year event would see in the order of 2,000m3/sec flowing down the wadi. This would cause significant flooding in parts of the city centre, with the Mosque of the Prophet under threat.

wadi

For reprofiling: The wadi will be redesigned to create a green public amenity

“Out of bank flow would occur with an event somewhere between 1 in 5 and 1 in 10 years. These could be life threatening events.”

It was also estimated that peak velocity could be as high as 8m/second, where scour and erosion would be a serious problem. Flood risk mitigation was obviously to be the team’s top priority - but there was no appetite for the barren concrete lined channels that scar the urban landscapes of many flood-prone cities around the world.

Travers says: “We had a different vision - of shaded walkways and picnic sites, with new plantings and flowing water. Rehabilitating the wadi would help restore cultural vitality as well as making it easier to protect it against further encroachment.

“There were still some areas of environmental and ecological value, with high and rising groundwater levels. We had lots to work with.”

“Land next to the rehabilitated wadi could be developed, in some areas at a higher density than the current norm”

Alan Travers, Buro Happold

One challenge was to deal sensitively with sections of the wadi that had already been lined with concrete. At 150m wide with vertical walls up to 10m high this section hardly fitted into the project team’s vision of a lush green corridor winding through the city.

With no realistic prospect of demolishing this construction, BuroHappold’s response has been to create stepped, accessible terracing. The walls will be faced with locally sourced stone and screened with native planting to provide habitat and corridors for environmentally rich public realm.

BuroHappold associate director David Palmer says that there were other hydrological challenges inherent in working in Madinah, in common with other parts of the Middle East. “The scarcity of historical rainfall and flood data can be a challenge, and complex analysis involving extrapolation and interpolation is required in order to make best use of the 40 years of data.”

Wadi

Dry: Low rainfall means that wadis are dry for much of the year.

“The links between environment and development tend to be less well publicised in Saudi Arabia than they might be here,” adds BuroHappold associate Henry Fletcher.

“We’ve been trying to raise the level of consultation, and also to improve the limited local understanding of the wadi’s importance to the city.”

Critical section

Design of this critical section was given top priority. The wadi will be reprofiled over most of the 14km and formed into a “landscaped, stepped” configuration, its actual geometry derived from a range of return period flows. Each step will be planted with native vegetation, to minimise scour and erosion. During the time the team has been on the project only once has there been water flowing down the wadi – but this will change under the current plans.

“Groundwater will be pumped into a landscaped dry weather flow channel so that there will always be flowing water in the wadi,” Travers explains. “There’s no real shortage of groundwater at the moment, and its use in this way will help manage the rising groundwater problem.”

A channel will be carved through the apron of the existing concrete lined section to facilitate the flow. Generous native planting along the banks of the wadi will help realise BuroHappold’s original vision. Irrigation with groundwater and treated sewage will keep the corridor green.

At the moment, urban run-off is not seen as a major problem locally, although the rapid recent expansion of low-density development adjacent to the wadi could increase the lack of permeability in the area.

“Groundwater will be pumped into a landscaped dry weather flow channel so that there will always be flowing water in the wadi”

Alan Travers, BuroHappold

BuroHappold’s masterplan adopts the water-sensitive urban design (WSUD) approach, along with Sustainable Urban Drainage Systems (SUDS). The proposed scheme will promote higher-density development with increased green spaces in some wadi-side locations, which should help reduce the loss of permeability and infiltration of stormwater. This priority section alone required the production of five packages of documentation, which also highlighted another Middle Eastern challenge. “It’s very difficult to get highly technical English translated effectively into Arabic,” Travers says. “As the masterplan will be the catalyst for the entire 20 year rehabilitation programme, it was important to get the documents right.”

Well advanced

Work to produce design packages for the 12 km2 of land inside the wadi corridor is well advanced. Production of development guidelines for the approximately 450 km2 of land lying on either side is also underway.

This will result in an integrated implementation plan for the authority. Currently it is estimated that rehabilitating just 10km of this section will cost upwards of £400M.

Two other key locations identified in the masterplan are a bioremediation plant and, further downstream, the Al-Ghaba Dam, where there is open water. “Treated waste water will be ‘polished’ in the bioremediation plant before being discharged into the Wadi,” Palmer says.

“And at the Al-Ghaba Dam there will be additional picnic sites. Such sites are very popular with the local population, as there is a long tradition of eating outdoors.”

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