Dartington Hall Estate – River and wetland restoration

The restoration (including a length of the Bidwell Brook) is proposed to enhance the biodiversity of the site

Project Brief

The Queens Marsh at Dartington is a 7.1 hectare diminished wetland created towards the end of the 16th century following installation of a weir on the main river Dart (downstream). Land drainage practices for agricultural improvement led to the deterioration of the wetland. The Dartington Hall Trust in partnership with the Environment Agency and Natural England would like to return the site to a functional floodplain wetland to create a mosaic of habitats to benefit a range of wildlife species. The restoration (including a length of the Bidwell Brook) is proposed to enhance the biodiversity of the site, which has deteriorated in recent decades due to agricultural improvements.

Cain Bio-Engineering were commissioned by the Dartington Hall Trust to a formalise design drawings and an ‘Assisted Recovery Plan’ detailing restoration options for assisted recovery of the Queens Marsh.

The Solution

A site meeting was convened with the Dartington Hall Trust to carry out:

  1. A site walkover and inspection of Queens Marsh and Bidwell Brook including a walkover of an upstream reach of river (reference reach);
  2. Discussions with Dartington Hall Trust regarding objectives of the restoration; and
  3. A site topographical survey by CBE including five topographical cross sections through the Queens Marsh field and Bidwell Brook to inform the proposed design and costing.

During the site walkover all site constraints were considered such as access roads to the site for hauliers and any weight limits or size restrictions on the surrounding roads.

A large section of the Bidwell brook upstream of Queens Marsh which was unaffected by the agricultural land drainage practices was viewed and acted as a reference reach for the proposed works to the Bidwell brook.

Natural features within the Bidwell brook that could inform us of the natural process that are taking place were also identified.

The topographical survey carried out informed us of the topography of the site including river bed depths, floodplain bund heights and low spots or depressions in the marsh. This informed the design and enabled us to view the disconnection between river and floodplain and identify the best locations to create a reconnection onto the marsh. The reference reach was compared to the downstream cross sectional profile of the degraded reach, this gave an indication of the natural channel profile which would form the basis for the river works. The topographical survey also identified low spots which would seasonally hold water and could be used as a base for ponds and wetland scrapes whilst enabling amounts of material for disposal to be calculated.

Once all the information had been collected and a site walkover and client meeting carried out, a design report was written. The report highlighted the objectives and aspirations of the restoration along with the feasibility of all the options discussed and cost implications for each option. Detailed plans and designs where drawn up to reflect each option including existing and proposed drawings. This design has now gone out to tender.