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The Harnham Water Meadows Framework Management Plan - Annexes

Annex VIII. Managing ditches for water voles and other wildlife

By Beth Nightingale, formerly Water Vole Recovery Project Officer Wiltshire Wildlife Trust

Background

Ditches are important habitats and refuges for water voles as they often maintain more stable water levels and offer relative safe escape areas off main rivers during flood. Ditches are also important for a host of aquatic and emergent wetland plants, as well as invertebrates such as diving beetles, snails and dragonflies and damselflies and operate as wildlife corridors linking together rivers and streams, ponds and wetlands.

Dredging and De-Silting

Dredging ditches halts succession and maintains open water. This activity is potentially very damaging to water voles and their habitat. In order to minimise this potential impact the following best practice guidelines should be followed:

De-silting should be phased with a minimum of one third of any ditch remaining untouched. Ideally

ditches should be managed on rotation to ensure a diversity of successional stages with the

greatest variety of plant and animal communities. The length of the rotational cycle depends on

a number of site-specific factors. The longer this is, the better for wildlife but a 3-5 year cycle

usually meets the management needs of the site and the wildlife needs.

Timing of works should be between November and January to avoid water vole breeding season

and disturbance to other wildlife.

Access to the channel should be from one bank only. If possible, a long reach excavator should be

used with the machine should be 5m back from the bank top to avoid compaction and

potential damage to the burrows.

Work should be carried out from the downstream end working upstream to allow plant seeds and

invertebrates to be washed downstream. Ideally materials should be taken from the centre of

the channel leaving a wet berm, fringe of wetland vegetation on the edges.

Spoil should be disposed at least 2m away from the bank top. If the site is within the floodplain,

spoil cannot normally be disposed. If left for 24 hours invertebrates that have been removed have

a chance to return to the ditch.

Vegetation Management

Water voles are herbivorous and require a wide range of plants. The ideal bank is one that grades from open water with aquatic plants through to emergent and marsh vegetation to herbs and a hedgerow. Most banks are usually quite restricted in width and tend to only hold one of these habitats. Quite often the bank is either left open and overgrazed and poached by livestock or it is mown, leaving the water voles no cover to hide from predators in or with not enough to eat. At the other extreme ditches are fenced off and not managed at all. Scrub usually encroaches or if a hedgerow exists on one bank it tends to spread and the ditch will eventually dry out. In order to maintain a variety of vegetation types management is required through cutting or grazing. Grazing should be at a low stocking density in the early spring and autumn ideally with cattle. Vegetation cutting, as with de-silting, needs to be carried out in sections on a rotational basis.

The best practice guidelines are to:

Cut vegetation on one bank only; maintain a fringe of vegetation along the waters edge.

Divide the bank into 20m length compartments and cut non-adjacent sections on a 2-4 year

rotation.

A rotational bank cut.

Remove the cuttings from the bank, if good enough grass quality use for hay, if not compost away

from the watercourse.

Cutting aquatic plants that are floating or submerged should be carried out in a similar rotational

basis, ideally leaving two thirds of the channel uncut.

Relevant agencies should be consulted in planning operations. The first task on Seven Acres drain with water voles is to remove three of four isolated clumps of vegetation that impede flow during high discharge, and dispose the dredgings 2m from the water’s edge, but only on the south west side. In subsequent years, the above rotational bank cut should be adopted. There is no immediacy to cut the main carriage between the Town Path and Lower Seven Acres which will be kept under review.

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