Objective: create or restore coastal habitat by reinstating or managing the tidal regime
Definitions
● Benthic invertebrates = invertebrates living at the bottom of the water column
(macro: >1 mm; meio: < 1 mm; micro: < 0.1 mm).
● Ebb = period from high water to low water, i.e. when the tidal waterline is retreating.
● Intertidal zone = area between high and low tide.
● Managed realignment = a technique where coastal defences (e.g. sea walls) are
breached or removed to reinstate tidal exchange, allowing an area previously protected to become flooded. Also known as ‘managed retreat’.
● Regulated tidal exchange = allowing regulated flow of tidal water through existing
coastal defences. Sometimes referred to as ‘controlled reduced tide’.
● Spring tide = Extreme tides occurring when the Sun, Moon and Earth are aligned
leading to strong gravitational pull. These produce the highest and lowest tides that
regularly occur. Spring tides occur twice each month.
1. Description
Tidal exchange permits the periodic inundation with sea water that is a defining feature of tidal flats and salt marshes. Tidal exchange can be facilitated by breaching or removing the existing coastal defences, as in managed realignment, or controlling tidal flow through existing coastal defences, as in regulated tidal exchange (Ausden, 2007; Scott et al. , 2012). Often, the aim is to restore tidal exchange to impounded salt marshes, where roads or bridges, for example, restrict tidal flow (Ausden, 2007). New defences typically need to be built further inland to protect human infrastructure and farmland from flooding. This intervention has been used extensively in Europe, namely the UK, Germany and the Netherlands (Wolters et al. , 2005; Rupp-Armstrong & Nicholls, 2007; Scott et al. , 2012). One of the major benefits of replacing hard coastal defences, such as sea walls, with salt marshes and tidal flats is that the natural defences provide protection from flooding with reduced maintenance costs. As such, economic benefits of intervention can exceed the costs, making funding decisions clear.
2. Evidence for effects on biodiversity
Effect on birds : Sites with restored tidal exchange are known to support shorebirds, with bird numbers beginning to increase within one to three years (Slavin & Shisler, 1983; Brawley et al. , 1998; Atkinson et al. , 2004; Natuhara et al ., 2005; Badley & Allcorn, 2006; Armitage et al. ,
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