Management Implications of Flood/Ebb tidal dominance: its influence on saltmarsh and intertidal habitat stability in Poole Harbour

Abstract

Saltmarshes are important habitats and have historically declined in the south of the UK and as sea-level rise is predicted to accelerate these losses are expected to increase. In order to explore estuary morphodynamics with relation to accretional and erosional trends at an estuary and sub-estuary scale, historic aerial photography were analysed with saltmarsh changes from 1947 and 2005 quantified. Using the Telemac model developed by HR Wallingford, tidal asymmetry of peak tides and slack duration was mapped and correlations between tidal asymmetry and saltmarsh change examined. Results indicate that there is a significant relationship between areas of flood dominance and the historic accretion of saltmarsh. However, there is no statistical correlation between areas that had experienced erosion and ebb dominance, indicating other dominant drivers of erosion processes. Results using hypsometric calculations suggest that the whole harbour behaves as an ebb dominant system and therefore tends towards erosion. However, when split into a sub-estuary scale, different creek systems show varying morphology and the hypsometry changes. This may have serious management implications where estuaries are manipulated through dredging and development, leading to significant effects on the surrounding intertidal habitats. However, managed realignment planning could also exploit the potential for enhancing flood dominance and hence accretion wherever possible.