The River Glaven is set in most attractive countryside, and the closer the examination the more we realise how valuable it is as a wildlife habitat and the range of species dependent on it; including a number of protected or featuring in national and local  Biodiversity Action Plans.

 

Nevertheless for a variety of reasons the river as a whole has suffered over past decades through changes in farming and land management practices, and policies for flood risk management; a principal reason for the existence of the RGCG to work with those concerned to make changes which are beneficial to the river and the wider catchment.

 

Even within the relatively short stretch of river concerning this project, there are considerable differences in the river landscape and wildlife habitat. There are broadly four reaches along “our” stretch.

 

The upper reach is thickly wooded on both sides, with mature alder and some fine ash, with a fair amount of ivy on many trees. The river here is on a steep gradient and fast flowing, and retains natural bank formations. There are variations in the river course, with bends and deep pools, and areas where it races over the gravel bed.  These characteristics make it good for brown trout, invertebrates in the river, and for the wildlife chain as a whole. The trees add some leaves and light woody debris to the river, which add to the value by nurturing insect life. We planned to do no work here other than in a short section where we would clear a few sycamore trees which would  permit sunlight on the river beside footbridge 2 (map 1 summarises our work proposals); the rest of this reach would remain heavily shaded.

 

The upper-middle reach is similar in most respects but almost all the trees are confined to the west bank. Again this is a “good” stretch of river for trout, a marker species for much wildlife; and with the additional light the appearance of water-crowfoot in the river bed. It is also a part of the river frequented by the kingfisher.

 

It suffers however from the 70s and 80s legacy of widening of the river and dredging with a subsequent lowering of the river bed. These operations left a high bank of spoil on the open side facing a meadow, and where there are just two trees. Thus the natural progression of the degree of wetness between the river and meadow, and the characteristic species of plants and insects which depend on this, is lost to a high and dry spoil bank.

 

We have been keen to select a place such as this where the spoil bank could be removed and the natural regeneration that follows could be studied by the RGCG. The Environment Agency was supportive in principle for another reason. They favour, where appropriate, the re-connection of river and natural flood plain. In severe rain events flood water may be “held-up” in areas where there are no houses which could be affected. So spoil bank removal, and the formation of a more natural profile, was introduced into our programme. Our plan for this would involve the removal of hundreds of tonnes of spoil off-site, and recovery of the gravel and flint in the spoil, and disposal of the separated soil on arable land.

 

The lower-middle reach of the river runs diagonally across the meadow, with high spoil banks on each side and no trees. The gradient of the river remains quite steep, so that the flow is fast over a generally good gravel bed. It is however rather uniform in nature, and the plan is to introduce some flow deflector measures, to be created by “large woody debris”; a good “natural” example, a tree which had fallen across, was shown in the article “Let Sleeping Logs Lie” in our April 2006 Newsletter.

 

The lower reach of the stretch runs from footbridge 1 (see map 1) down to the Ford. Here the river profile has flattened. The flow is slower, and a sand silt deposit over the gravel dominates. The flow is also slowed by the river being too wide in places. The emphasis here is to carry out some narrowing in places, and also to introduce some gravel riffles. The riffles are beneficial to trout and invertebrates as noted above; and we would hope that they extend the amount of habitat available to four species all recorded in the vicinity of the Ford; bullhead, stone loach, brook lamprey and white-clawed crayfish.

 

So while the stretch of river has a great deal to offer in terms of its wildlife, the RGCG project aims to make improvements to the river habitat as a whole, and to the micro-habitats so important to the wide range of wildlife that the river supports.

 

We looked to close some circles in how we would implement the works. The felled sycamore trees would supply the trunk sections required for the large woody debris. But also we estimated a need for some 120 faggots for river narrowing works, and some 200 wood stakes; a portion of this would come from these trees, and much of the remainder from hazel and alder growing close by.

 

The plan for the spoil from the river bank was to sieve off-site on an arable field nearby, using a grading machine to give two “cuts” of stone material. These were to be a spawn gravel in the size range 10-50mm, and larger stone, to be used in the construction of the riffles. The recovered soil will be spread over arable land.

 

Finally we would have the potential for flood risk reduction in the removal of the spoil bank as well as the conservation (and landscape) benefits where we make a re-connection between river and flood plain.

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