The Ems Barrage, Germany - the engineering feat of the century providing more than just coastal protection

The Ems Barrage, Germany - multi-purpose structure on the Lower Ems

The Ems Barrage, Germany - fascine mattresses stabilise barrage foundation in river course

HaTe E 1200 C reinforced nonwoven by HUESKER Synthetic is being used to secure the base of the Ems Barrage, Germany, in the course of the river. The present paper describes this technically fascinating exercise in hydraulic engineering.

A new barrage is being built on the Lower Ems, Germany, four kilometres from the Dollart region on the Dutch/German border. This engineering project of the century is an important element of the region's coastal protection strategy and will substantially improve storm-tide protection on the Ems all the way to the reach level above Herbrum. When closed, the barrage will hold back storm surges at levels of more than +3.70 metres above sea level, or about 2 metres above mean high tide. Volumes of water of this order of magnitude will now no longer be able to advance uncontrollably upstream. Damming the water at this point will also permit larger ships to pass from the docks at Papenburg to the North Sea, meaning that the barrage will also secure jobs in the region. Work on the barrage is scheduled for completion by mid-2002.

Stabilising the Foundation with Fascine Mattresses

The base of the barrage will be stabilised by fascine mattresses laid in the course of the River Ems. The mattresses comprise a 150mm thick layer of brushwood with a fascine willow grid at a spacing of 1 x 1 metres, and up to 135 x 30 metres in size.

HaTe E 1200 C, a marine-compatible reinforced nonwoven by HUESKER Synthetic, is being used as backing for the rafts. Loops have been woven into this robust geosynthetic material to simplify the work of joining the fascine mattresses to their fixing point on land.

This HaTe geotextile fulfils several functions. Firstly, it provides a good foundation on which to build the individual rafts. Then, in the course of installation, the geotextile and the brushwood layer together will prevent the construction stone from sinking through and into the silty riverbed. Once in place, the separation /filtration functions of the geotextile will prevent the erosion of fines from the riverbed.

The geotextile will also hold the layers of brushwood and willow in place. With dimensions of up to 135 x 30 metres, the fascine mattresses employed at the Ems Barrage site are unusually large. "We have the right conditions here for building the rafts on land and then floating them to the installation site," says Henning Dageförde, Technical Manager of Colcrete, the Essen-based company in charge of the construction work.

Installing fascine mattresses calls for a great deal of experience

Each of the thirty-six fascine rafts are towed individually to the site by tugs, then initially secured to appropriately positioned mooring pontoons. The actual work of installation depends on the tide, the best time being while it is on the turn or just before, when the river current is at its weakest.

The rafts are manoeuvred into position with the aid of GPS receivers on the mooring pontoons over the sinking position. The mattress is then gradually loaded with stone ballast. A total of 80,000 m² of fascine mattresses and about 120,000 tonnes of stone fill will be installed. The hydraulic stone is being additionally stabilised by colloidal cement at the more sensitive areas of the sill and the piers. Colloidal cement is a special-purpose, non-segregating material, which can be worked under water without dispersion.

Size of the Barrage

In the locality of the Ems Barrage, the distance between the main Moormerland dike's northern bank and that of the Rheid dike's southern bank is 1,040 metres. The 476 metre long barrage is being erected between the banks of the Ems. Connecting dikes will join the barrage to the main dikes on either side. To meet requirements, the cross-section of the barrage is designed to have little influence on discharge and tidal dynamics in the Ems. There will be seven openings in total. For nautical and hydraulic reasons, the main navigation span will still lie in the path of the previous navigation channel. There will be a 50 metre wide secondary span to the north, and an equally wide inland-waterways opening to the south. Four further secondary spans adjoin to the south.

Navigation Spans and Gates

The barrage is being built on the Ems, a Federal Navigable Water Course, so its channels must be correctly designed for shipping traffic. There will be no height limit for seagoing vessels passing through the main navigation span, a rotating-segment gate of the type tried and tested on the Thames Barrage in London. In normal operation, with the barrage open, the gate segment rests in a trough in the sill.

The inland-waterway opening will be closed by a segmented gate, which is raised in normal operation. The clear passage under the gate and operating bridge will 5.75 metres at mean high tide. This opening is intended only for navigation by barges on the Leer/Papenburg route. The navigator can tell from a water-level indicator downstream of the barrage if the available passage is high enough for his vessel. If not, especially at particularly high tides, a change of course will be required through the main navigation span instead. At 60 metres wide, the span is large enough for two-way traffic comprising both inland craft and coastal motor vessels.

The Environment and Management of Water Resources

The southern connecting dike is to be built over 4.2 hectares of Atlantic salt meadow on the Nendorp foreshore. Action taken to replace this site includes the acquisition of 10 hectares of intensively used foreshore in the region of the Leda estuary, which are now being made available for a bird sanctuary. Another 110 hectares of agricultural land have been bought as compensation on the Nendorp and Midlum foreshore, where a series of ponds and larger stretches of water are being provided for appropriate bird and fish species.

Twenty-six hectares of riverside woodland are being planted above Papenburg to compensate for the construction's effect on the landscape. These measures will redress the environmental impact of the Ems Barrage.

NEU: Video zum Projekt 'Emssperrwerk':
huesker_ems_en.asf (1,88 MB) - Streaming Format