St P Sea Defences

After all that excitement our departure was no less inspirational as we were able to see a huge civil engineering project. (Please bare in mind my background and inherent enthusiasm for such projects.)

 

In order to protect St P from potential flood surges from the Gulf of Finland a 25.4 km barrier has been built (completed in 2010) across Neva bay. There are two parts either side of Kotlin island. It comprises a 6.5 m high embankment interspersed with 6 sluices and two navigational channels.

 

This is sluice No 5. 

The sluices comprise between 10 - 12 steel radial gates, each 24 m wide (total 300 m wide for each sluice) and 2.5 to 5 m deep. They can slice through 600 mm of ice.

To the north of the island there is a bridge for local shipping. It is 110 m wide with a lift gate some 12 m deep and 9 m thick to close off the water. The bridge can also be raised from 16 m to 25 m so larger ships can go through.

However that will not do for the likes of QV. The channel for larger ships is just to the South of the island. The island is endowed with a range of old and abandoned naval defences which first have to be negotiated.

  They clearly do not form part of any defence system now.

On the gulf side of the island sits the new navigation channel. It is 200 m wide and 16 m deep with the gates 23.5 m high. Vehicular traffic travels underneath in a tunnel while on top the first visible structure is the control building.

Soon the massive gates appear. They comprise a 130 m 'A' frame which is 65 m wide and revolve around a 1.5 m steel ball encased in a bronze casing. They are made of steel with the curved gate section a steel box. When retracted they sit in their own dry dock.

To move them into the closed position, the dry dock is flooded and the gates then float and are pushed out by a tractor system. Once opened they are flooded and settle onto the floor of the channel. 

The whole operation takes 45 minutes. The reverse takes 2 hours and also has to be closely monitored as the river Neva could back up against the rear of the barrier and also cause flooding.

With ships as large as QV others traveling the opposite direction had to wait their turn.

The roadway system completes the barrier and runs along the bund and then in a huge roadway system down either side of Neva bay and around to the South of St P.  

All in all a massive project where the lead designer was my old outfit Halcrow. Here is a "mud map" thanks to a 2009 copy of the New Civil Engineer. Impressive eh?