Marshlands and Sea Defences

One effect of global warning, we are warned, is an increase in severe weather systems. When these storms coincide with high spring tides, as they did recently, the result is flooding in low lying areas, and destruction of sea walls.

One of the reason for this, as marine biologist Andrew Syvret pointed out, is the land reclamation. How does this work? I would imagine that by extending St Aubin's bay outward, one result is that the inflow of water is contained, and funnelled. Before reclamation, there might have still been a funnelling effect, but only so far as the shore extended outwards, and the effect of reclaiming land has increased this considerably. We tend to think of the reclaimed land as the new area by the Marina, the Cineworld complex, the Radisson Hotel etc, but there is by far a much larger area of reclaimed land beyond the extent of the harbour, including a complex of industrial buildings (including the bus storage depot), but further out to sea even beyond that. I went out there yesterday to visit a friend who works in that area, and it is a huge area of landfill.

This also explains why Havre des Pas, while buffeted from the sea, did not have quite the same extent of damage. The reclamation site is only on the far side of Havre des Pas, while the rest of the coastline is relatively flat and curving round to Green Island. St Aubin's Bay, on the other hand, has the rocky coast going round to Noirmont on one side, and the reclamation on the other, making a vast pool of water, with nowhere for the water to escape when rushing in with spring tides, and southerly winds, hence the funnel effect.

There are three main troublespots in danger of flooding, and each was flooded.

St Aubin's Harbour, which is low lying, and in fact is in part an earlier experiment in land reclamation saw flooding. Hopefully, this will put paid to foolish notions about land reclamation for car parking, for unless the parking was raised, it would have been the first to be under water, with considerable damage to any cars parked.

Goose Green Marsh is another area (around Beaumont), and here the problem was compounded by the fact that rainwater and sewage systems use the same network, so that groundwater run-off (which was also floodwater run-off) overloads the sewage system, and led to the eruption of sewage into the marsh, when man-hole cover's blew, despite being bolted down. Firmer bolts - contrary to Guy De Faye's alleged ideas - are not the solution; the pressure will either blow them, or the water will back up and come out at the earliest weak points, probably inside people's houses.

St Helier is of course originally a reclaimed marshland, so it is not surprising that areas below sea level, such as Gloucester Street, became flooded, not for the first time. This, of course, is where the sunken road is due to surface as part of the Hopkins Masterplan. That enormously large document devotes just one mention to "risk of flooding" and directs the reader to the appendix, where there is a map of St Helier, the area by Gloucester Street where the road comes up, a grey oval over that site to indicate that is at risk (as if we didn't know), and a marginal note saying that Transport and Technical Services will come up with a solution. As a Masterplan goes, this is a fiasco! Instead of countless pictures of civic squares and the like from around the world - by way of illustration !!! - surely any plan should have had a whole section on the engineering aspects of the tunnel - pump systems, air filtration, running costs of maintenance - and of course prevention of flooding. It is painfully obvious that it has been prepared by architects who have little or know knowledge of civil engineering.

Of course, one option is to increase sea defences, and this is certainly necessary. But it would be foolish to assume that the tide cannot breach these, and the second line of reasoning should consider what defensive measures could be in place to prevent flooding if the tidal defences fail. Worst case scenarios have occurred recently; they may not be so uncommon in the future.