In the past, streams and other watercourses have had their banks straightened and reprofiled for various reasons including management of water flow, and to ease the cutting of bankside, marginal and aquatic vegetation. Artificial drainage channels were also normally constructed with straight edges and regular bank profiles. Where compatible with water management, banks can be altered and diversified to improve the habitat for wildlife, and soften their appearance. Reservoirs, dams and other water-impounding structures may need to retain an even profile and short vegetation to allow easy inspection of the structure, and to prevent any erosion.
On banks of natural watercourses and ponds, some bank erosion may be beneficial to promote habitat diversity. Eroding banks near mature trees provide particularly valuable habitat for mammals including otters. Willow, alder and other bankside trees allow the development of vertical and undercut banks, stabilised by the root system. Mature trees which fall into the water, without seriously impeding water flow, are also valuable. They create undercut banks, hollows and other niches, and sheltered, shady conditions at the water ’s edge, favoured by many creatures. On some created sites, dead trees have been dragged or winched into ‘fallen positions’ at the water ’s edge, to try and simulate these conditions.
Techniques for bank diversification include bank reprofiling by hand or machine, excavation of meanders and bays, and changes in vegetation management and dredging regimes.
Reprofiling
The following diagrams illustrate two examples of riverbank reprofiling. Vegetation can either be planted, or allowed to return naturally. Access and grazing of the bank may need to be controlled.
Meanders, backwaters and bays
In the past, river engineering works often involved the deepening and straightening of rivers, with the loss of valuable backwater habitats. Any opportunity to restore or create them should be used. Even small-scale features can be valuable. If possible, the design should utilise the flow of the river to scour the feature sufficiently to prevent it silting up.Two possible arrangements are shown below.
Outfall pipes present another opportunity to create a valuable backwater feature, and to allow the construction of a simple outfall, without the bank protection which would be needed if the outfall fed directly into the river.
For further details on this and other diversification features see The New Rivers and Wildlife Handbook (RSPB,NRA and RSNC, 1994).
