The Harrier

Subtitle: The newsletter of Devon Birds

South Milton Ley Reserve – Horswell Ditch

Work on Phase 1 of a two year project to increase biodiversity and to create a viewable area of open water at South Milton Ley Nature Reserve has just been completed and what a result! Excavated and completely full in less than two weeks, a reservoir of open, fresh water has been created with just a bit of levelling and profiling left to do on the banks during Phase 2, next autumn, followed by planting and the installation of a viewing blind.

Creating open water at South Milton Ley has been tried before but previous attempts in the lower, more saline region of the reedbed, which was the only part Devon Birds owned at the time, were thwarted by the rapid recolonization of cleared areas by Common reed (Phragmites australis) and because variable water levels often prevented access for maintenance.

In 2015 Vic Tucker, the reserve manager, inspired by habitat seen during a holiday in Greece, proposed widening and deepening an existing shallow, narrow and overgrown ditch much further up the reedbed to create an area of fresh water, which would remain manageable from the adjacent banks irrespective of water levels in the lower reserve. The open water and gently sloping banks would benefit a variety of birds, fish, amphibians and invertebrates. From this point on the project was unofficially nicknamed “Vic’s Ditch”. Discussions followed and research indicated that it needed to be about 100m long and 4m wide to be effective and 1.5 to 2m deep to prevent Phragmites from growing in the centre. This would involve shifting a lot of soil!

Outline proposals were submitted to Devon Bird’s Council and, with their provisional approval, sent to Natural England. The whole of the reedbed at South Milton Ley is a Site of Special Scientific Interest, protected under law and nothing can be done to any of the watercourses there without the consent of Natural England. After dialogue with them, a site visit with one of their officers and consultation with the contractor, the proposals were refined, reviewed and refined again before a location on the southeast side of the reedbed was selected, close to the public footpath crossing the reserve. The stream here, known as Horswell Ditch, drains land to the south and this location could accommodate an area of open fresh water of sufficient size, avoiding damage to the existing reedbed and helping to raise the water table in a relatively dry part of the reserve.

Following appropriate planting, a bank on the northern side of the ditch, constructed from the excavated spoil, should benefit breeding Reed Bunting, Cetti’s and Sedge Warblers and the occasional passage Aquatic Warbler. These species have a well-documented preference for reedbed margins and ditches with scattered shrubs and other emergent vegetation. The sloping waterside margins should also prove attractive to Water Rail, Snipe, Common and Green Sandpipers and possibly passage Spotted Crake. Some sections of bank will be left vertical and others will be shallow and scalloped for diversity. With Phragmites kept at bay, a four metre wide ditch will enable both the banks and the open water to be viewed, something which is impossible elsewhere at SML. Devon Birds will install a blind at the western end of the widened ditch enabling members to observe birds without disturbing them or the habitat.

With all of these positive benefits Natural England approved the work with a few minor conditions and contributed significantly to the costs of excavation and the installation of the sluice. Thanks are due to all those involved in preparing, reviewing and submitting the proposal documents.

Work on Phase 1 of Horswell Ditch, has just finished. The sluice was installed first, before excavations commenced, to minimise the amount of sediment travelling down the watercourse. This proved highly effective as can be seen in the picture below, with turbid water upstream of the sluice and clear water downstream.

This year’s works were completed in less than ten days and the water level had risen by 30 to 40cm to the top of the sluice by the end of this period. Flow rates downstream of the sluice are unaffected. The northern bank is currently too soft and wet to take the weight of an excavator so Phase 2, the final profiling and scalloping, will take place in the autumn of 2018, allowing the spoil plenty of time to drain and consolidate. Colonisation of the new habitats by plants and animals will be monitored and, if successful the project could be extended or repeated elsewhere in the reserve.

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