A design team involving cbec and Salix was engaged by Groundwork North East to undertake the development of detailed designs for five sites on the rivers Blyth, Wear and Esk, where previous investigations indicated that local site conditions were favourable for the development of a salt marsh habitat
Upon undertaking the site visits, it was deemed that the Bridge Dock site on the River Wear, Sunderland, was not viable for further design development, as the existing bed level of the river was too low to raise to a viable level for a salt marsh habitat.
The optimal elevation for salt marsh species is between 1.48 metres above ordnance datum (mAoD) (mean high water neaps) and 2.52 mAoD (mean high water springs). The observed salinity at high tide for the Blyth site was 33.5 parts per thousand at high tide, considered to be saline but still appropriate for salt marsh species, and 10.03 at low tide, considered to be brackish water and well suited for salt marsh species. The dominant salt marsh species present among the rocks and cobbles along the upper margin of the bank was marsh samphire (Salicornia europaea). Below the rocky intertidal area, mudflats were reinforced with car tyres, and the area was predominantly being used as a feeding ground for wading birds. Favourable conditions for salt marsh species were in accretional zones situated in the top quarter of the tidal range, i.e., between mean high water neaps and mean high water springs.