River Management Techniques. Upper Wharfedale Best Practice Project (Information Series No 6)

2.0. Managing the retreat of the river

2.1. Heber floodbank scheme

BACKGROUND INFORMATION

In the 1980s a river engineering scheme was undertaken, following which the river has gradually re-adjusted itself. In the process of doing this areas of river bank erosion have developed.

DESCRIPTION

The site at Heber, on the left bank of the river, had become severely eroded and the existing floodbank was in danger of being breached causing flooding of meadowland critical to current farming practice, economy, and conservation value. The eroded banking mainly comprised fine soils which had formed a vertical cliff face and had been colonised by sand martins. A large shoal of gravel, ecologically important to retain on the right bank of the river, was acting to direct river erosive forces against the left bank in high flow conditions.

2.1

LOCATION:
Buckden, SD 939766

LENGTH: 215m

DATE UNDERTAKEN:
Autumn 2001

COST: £31,288

This scheme used the river management principles developed by the project to:
  • Carry out emergency repairs to banks where the river poses an imminent threat to the conservation and economic value of the whole farm, prior to the implementation of longer term solutions;
  • Improve riverside and floodplain habitat to create an irregular wide buffer zone and;
  • Maintain the physical and ecological dynamics of the river, enabling it to dynamically form wetlands in areas where the most environmental benefit can be obtained at least economic cost.

DESIGN

A managed retreat solution was adopted by re-aligning the existing floodbank and setting it further back from the river. This rationale allowed for the loss of some meadowland that would be compensated for by the development of a wider wildlife buffer zone, and moved towards the long-term vision of enabling a wetland area to develop further into the field supporting rushy pasture.

SPECIFICATION

The plan opposite shows the new floodbank and its location. The site length is 215m. The bank is set back about 10m from the original bank and has a comparable height of 1.3m with a flattopped profile. Its river face slope is 1:2 and the landward face is 1:4 to facilitate a mowing option. The total bank width is 9m. An Emorsgate EM19 Yorkshire Dales SSSI grass seed mix was specified.

Trees and shrubs

Tree planting was limited to a total of 15 trees, randomly planted in clumps along the riverside slope of the new bank, with tree guard protection around individual trees. Native species were used and included: alder Alnus glutinosa of Phytophora disease-free stock, ash Fraxinus excelsior, oak Quercus robur, silver birch Betula pendula, blackthorn Prunus spinosa, and goat willow Salix caprea. The height was between 0.9m and 1.20m and the root collar diameter 35mm-50mm.

Fencing

A livestock fence has been erected along the new floodbank to link in with adjacent existing fence lines in accordance with BS1722, using galvanised wire to comply with BS4102. HT 8/80/15 netting was used. The fence height was not less than 1.05m high with at least one top row of barbed wire. Straining posts were a minimum diameter of 150mm, and 2.15m long at a spacing not exceeding 100m. Struts were not less than 80mm diameter and 1.9m long, notched into straining posts at an angle no greater than 45 degrees.  Intermediate posts were 65mm diameter and 1.7m long at a spacing not exceeding 3.5m.

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