[ANALYSIS] The flood from our drainpipes

The sight of manhole covers being lifted up - even carried away by water - is just one of the consequences of our unwise practice to have rainwater flow straight off our rooftops and into the main sewers.

Heavy storms are now the prelude to rainwater contaminated by sewage, overflowing from the sewers and forcing manholes open. The result? Contaminated run-off flowing down streets, and then ultimately discharged into our valleys or even the sea.

Even though illegal and punishable by law - houses cannot have storm-water drains from roofs and yards connected to the public sewer - the Water Services Corporation has admitted it is unable to enforce this basic rule. Last year, the corporation's spokesperson wrote in to the Sunday Times admitting the WSC had "no control over this sorry situation".

"The corporation can only appeal to the public to refrain from the practices mentioned above and carry out remedial action whenever possible."

The WSC knows its waste-water system is not designed to act as a combined sewer to take in a huge volume of rainwater during heavy downpours. So if storm water is instead allowed to flow along the streets, the sewers can carry on functioning as normal.

But this system still gets disrupted during storm because of the hundreds - if not thousands - of buildings which today have storm water pipes connected to the public sewer system. To many of us, it is a given state of affairs.

To counter the effects of overflowing sewers, the WSC inspect and clean the mains on a regular basis, replacing and upgrading defective and undersized mains as soon as possible.

Philip Grech, who led the drainage department between 1989 and 1996, and today is part of the Malta Water Association, has described this problem as a dramatic one. The scale of the problem was already identified in a sewage master plan in 1992, which included initiatives to prevent manholes from overflowing. Grech however blames the overflowing sewers on a lack of planning, especially in the way road levels were set.

"As long as rainwater ends up in the sewage system, the greater the risk will be that storm water gets contaminated with sewage from over flowing manholes," Grech told this newspaper in 2011, expressing scepticism at plans to contain flooding by channelling storm water to outfall pipes emerging in the bays at Ta' Xbiex and Xghajra.

The scale of the problem

Since more than 30% of Malta's surface area is built up, with most of this development happening in the last 30-40 years, flooding has become more frequent and this comes at a considerable cost: insurance claims arising from the September 2003 storm in Malta exceeded €10 million.

One possible solution would be to construct storm water reservoirs to collect and re-use the runoff. But space in urban areas for reservoirs is limited, competing for space with basements, garages and car parks and other modern amenities.

Indeed, economic and financial studies carried out in preparation of Malta's Storm Water Master Plan in 2006 concluded that the "the possibility of creating large reservoirs was considered unfeasible" and close to impossible for cisterns to be built beneath existing buildings.

In itself, the absence of cisterns from most of today's buildings built over the past half a century has aggravated matters. A legal requirement since the times of the Knights of Order of St John, the requirement to store rainwater in a cistern was largely unenforced for the past half a century. This requirement is mandatory for the certification of the energy performance of new buildings through a legal notice which only came in to force in 2009 and which was not still not fully enforced a year later.

Government's slow response

Ever since Malta was ravished by the great floods of September 2003, plans for a national flood relief project have been in the offing. But when will these plans become reality?

In August 2007, resources and infrastructure minster Ninu Zammit announced a project involving the excavation of a vast network of underground tunnels aimed at hitting two birds with one stone: solving the flooding problems in problematic areas while recovering a substantial amount of water which presently ends up wasted. But the project was scaled down, following the results of a feasibility study conducted by Isreali consultancy firm Tahal.

The Israeli experts concluded it would cost €80.31 to produce just one cubic metre of water - even more expensive than the €49 required to produce the same amount through desalinisation (Malta produces potable water using reverse osmosis) - even if this amount did not take in consideration capital and depreciation costs.

Resources minister George Pullicino's €56 million, EU-financed project, will now see storm water diverted to an outfall in Ta' Xbiex and Ta' Barkat in Xghajra, having been green-lit by MEPA earlier this year. The National Flood Relief Programme is expected to protect Malta from massive floods which normally occur every five years, and to ensure that in the event of flooding, the water depth on Maltese roads is always under the 10cm level - above which, the flood would start producing damages.

According to government plans, storm water will be separated from oils and grit along the roads before it enters the underground tunnel network.

And since at present storm water is discharged into the sea without any form of prior treatment, the Ta' Xbiex discharge will be equipped with a monitoring station to monitor the quality of the water before it is discharged into the sea. Ta' Xbiex was chosen as the site of the outfall because water circulation in this area is much better than in other localities like Msida or Pietà.

The NFRP - scaled down since Ninu Zammit's project - will still harvest 680,000 cubic metres of storm water, which can be made available for irrigation through a reservoir in Wied Ghollieq, beneath the University in Msida.

But the government's decision to focus exclusively on flood relief was slammed by the consultants who conducted the strategic environmental impact assessment on the NRFP's storm water master plan of 2006, arguing that storm water should be stored to alleviate pressure on the groundwater aquifers.

"The revised Storm Water Master Plan does not put forward an adequate plan for an effective infrastructure which conserves the groundwater aquifers while solving the problems associated with flood relief."

According to the study, the original proposal to harvest water in tunnels would have saved between 5.5 and 8 million cubic metres of water that could provide irrigation for 65% of agricultural demands.

But the NRFP's director Carmelo Mifsud Borg, speaking to MaltaToday in 2010, said that once the water ends up in the road, it gets contaminated. "It could get mixed with sewage, oils and other dangerous materials. To be reused, it has to be re-polished."

And to capture and store storm water, and then polish it for irrigation purposes, a costly infrastructural investment is required. "Economically, it does not make sense to let this water drain into the roads and then spend a lot of money to capture, store it and polish it to make it good for consumption and than to deliver it."

Mifsud Borg has suggested that the solution lies in enforcing the law requiring all houses to store rainwater in a well, rather than spending money to recollect the run-off from the roads. "Since the time of the Knights, households were required to store storm water in a cistern and this avoided the dispersal of water in the roads. Unfortunately, since the 1960s this law was not enforced," Mifsud Borg said.

Thinking out of the box

Hydrologist Marco Cremona, supported by the Malta Council for Science and Technology, has come with a technological fix for the problem posed by rainwater flooding our streets: a borehole to direct water into the aquifer rather than pumping water out of it.

The MCST project is carrying out research on the innovative idea to develop a product known as the GEO-INF system, that will meet the dual objectives of flood mitigation and groundwater recharge, while taking up minimum space and set-up costs. The system has no moving parts and is powered by gravity.

"GEO-INF is an idea I came up with around two years ago as a retrofit solution for buildings that do not have a rainwater cistern," Cremona said.

Although having an underground rainwater cistern remains a legal obligation for all residences, GEO-INF offers a practical solution through which water falling on these buildings will be recharged in the aquifer after being filtered, instead of drifting into the streets and creating problems. At the same time, if this water is recharged into the aquifer, it will help the country solve its other problem: that of the depletion of the aquifers.

"The process is quite straightforward," Cremona says. "Runoff from roofs is directed into a buffer tank, which overflows into a filter and then is injected by gravity into a borehole, which is drilled to a particular depth.

"The filtered water dissipates into the geology and eventually makes its way to the aquifer, recharging the water table with chloride-free, nitrate-free rainwater and at the same time alleviating flooding."

But although full of potential, the infiltration borehole idea cannot be put into practice in Malta before extensive research is carried out on a number of parameters that would determine its efficiency and efficacy, and potential pollution risk to the integrity of the aquifer. Malta is still fertile ground for Cremona's revolutionary idea, but a combination of legal enforcement and a national flood relief infrastructure will need to be in place for the island to escape the ravages of flooding.