BANK SPOIL REMOVAL:

UPPER MIDDLE REACH MEADOW

Some 700-1,000 tonnes of spoil were removed along a meadow width about 122m. with a tracked digger and two 2.5t tracked dumper trucks, as described in the Logistics section above. The work revealed the sinuous character of this stretch of river, the frontage of the river bank itself extending to some 130m.  The re-profiled bank was taken to about 18” above the water line, and 2 m further back it was stepped up another 229mm or so to bring the profile to the level of the meadow as a whole.

The spoil had been piled to the highest level close to the river and it fell away gradually to meadow level. When all was cleared it showed that in the main the buried area stretched back some 9-11 metres from the river. However where the river swung away in two bends the area of coverage with spoil had extended to 14 metres immediately downstream of tree 2, and similarly to 19 metres at tree 1, the old alder.

The restoration of the site not only re-connects the river with the floodplain meadow, but completely transforms the visual impact. One can now see the whole stretch of the river on this meadow, instead of peering down a high bank to see just a few yards to left and right.

The spoil was principally a good rather peaty soil, probably coming from river widening in the past with some bank removal over a much wider area of river frontage. Within this were some areas of sandy soil containing stone and gravel. Presumably this came from dredging of the river bed. It was these spots, where we had cut two of the three sampling sections with a digger, that had lead us to believe that it would be worth riddling the spoil to recover stone and gravel.

The spoil was covered with dense nettle growth, with some other vascular plants present. The vegetation was stripped off to make a separate heap on the arable field, where it would be allowed to rot down. The major part of the spoil removed was heaped on the field and later spread over about 2,500 square metres to a depth of

150 mm or so. Some 10t of larger stone was recovered by hand from both ends of the operation, the river bank and heaping and then spreading on the arable field. The stone recovered at the river end was used to create two areas of larger stone on the river bed there.

As described above in Logistics and Materials, the 130 m of bank required protection with a hazel buffer structure to protect the bank from higher and stronger flow levels. Areas of sharp turn would be the most vulnerable. The same technique was used as described under bank narrowing. In addition coir matting was used to give additional protection. The matting came in rolls 2 metres wide and some 30 metres long. This was spread over the top of the revetment and the first level of bank, and additional pegs were fixed to hold the bank edge of the matting in place.

For the final 28 m the matting was put down first before the hazel revetment work was done. This is not expected to make any difference to the final result as regards how well the bank is stabilised and the regeneration of vegetation, but this will be monitored. The plant species that grow from the bare soil, and the succession stages, will be an important part of the follow through studies on the whole bank of the upper middle reach meadow.

The removal off-site of the spoil to the field was carried out under a waste disposal exemption licence. This necessitated the analysis of soil samples taken from the spoil bank and the arable field for which it was destined. A wide range trace metals and other elements were measured. In all cases there was a lesser amount of trace constituents in the spoil bank material than there was in the arable field. This could reflect a generally “cleaner” environment dating from the 60s or 70’s; or more likely the fact that the rivers and meadows have not borne an application of agrichemicals that can compare with arable land over the past decades. It would have taken a third analysis, that of the meadow itself as well as the spoil on it, to be sure on this point.

For larger photographs of the thumbnails on this page together with a brief description and [day/month]

For larger photographs of the thumbnails of spoil removal, side-channel repair work  with a brief description and [day/month]