Port of Falmouth development initiative: habitat removal and relay as mitigation for dredging - a proposed approach
Type:
Presented during:
CEDA Dredging Days 2015 - Innovative Dredging Solutions for Ports, Rotterdam
Authors:
Adnitt CS - Royal Haskoning DHV, United Kingdom; Sheehan EV and Attrill MJ - Plymouth Marine Institute, United Kingdom; Sansom M - Falmouth Harbour Commissioners, United Kingdom
Abstract: The Falmouth Harbour Commissioners and Falmouth Docks and Engineering Company Ltd have put forward a proposal to improve the port facilities and approach channel at Falmouth, Cornwall. The project is known as the Port of Falmouth Development Initiative (PFDI) and lies within the Fal and Helford Estuaries Special Area of Conservation (SAC) and proposed Falmouth Bay to St. Austell Bay Special Protection Area (SPA). The proposed PFDI comprises dredging works, seabed mitigation and berth construction and has the potential to result in an adverse effect associated with the dredging works to deepen the channel. Potential impacts that could arise as a result of the proposed project have been identified during an Environmental Impact Assessment (EIA) phase and include potential for the direct loss of dead maerl habitat during dredging works. Maerl is a calcified seaweed (a red seaweed that deposits calcium carbonate within its cell walls, forming a brittle skeleton) that lives unattached on the seabed in specific areas (Hall-Spencer 1998). The structure provides branched nodules which provide a valuable habitat for a high diversity of species (Barbera et al. 2003, Pena et al. 2014). Once the maerl dies it generally fragments and loses its colour. Dead maerl also provides a habitat although not supporting such diverse communities as live maerl habitat. As a measure to mitigate dead maerl habitat loss it is proposed to remove the dead maerl, deepen the proposed dredge area and re-lay the dead maerl habitat following deepening. A trial dredge has been conducted and has shown that species recolonisation occurs within 44 weeks showing no significant effect on species abundance and number of taxa. This paper summarises the proposed mitigation works and the results of a trial dredge to determine the potential success of the mitigation measures.
Key words: Mitigation, Maerl, Habitat.