Abstract
Coastal saltmarshes provide a range of ecosystem services, such as flood protection and carbon sequestration, but face rapid global losses. Managed realignment (MR) is an increasingly popular method to artificially recreate these habitats by reinstating tidal regimes to reclaimed land. However, to improve MR design, better knowledge of the processes that control morphological evolution in natural saltmarshes is needed. In this paper, we develop tools to assist in the monitoring of creek network evolution towards dynamic morphological equilibrium, a state of landform stability under current physical forcings. Using lidar (Light Detection and Ranging) datasets, we combined a semi-automated creek extraction algorithm, based on elevation and slope thresholds, with a novel algorithm for morphometric creek analysis. A comprehensive suite of morphological creek characteristics was extracted for 13 natural British saltmarshes, including: amplitude, length, sinuosity ratio, junction angle, width, depth, cross-sectional area, creek order, bifurcation ratio, drainage density, and drainage efficiency. Results closely matched with field-validated manual digitization results, and were significantly faster and less subjective to produce. Morphological equilibrium relationships from the literature were found to be applicable to the new dataset, despite yielding high prediction errors due to the inherent variety of creek network shapes in saltmarshes. New equilibrium relationships were also defined relating the creek network drainage efficiency to the mouth cross-sectional area and the marsh elevation. To improve future scheme designs, these tools will be used in further studies to monitor rates of evolution towards equilibrium in MR sites depending on their initial conditions.
Highlights
Coastal wetlands such as saltmarshes are valuable habitats that provide a wide range of ecosystem services (Luisetti et al, 2014)
The aim of this paper is to develop tools that will assist in the monitoring of creek network evolution towards morphological equilibrium using lidar data
We test the accuracy of creek parameters detected from freely available lidar Digital Surface Model (DSM) that have undergone minimal preprocessing, as is likely to be the case for most of the managed realignment (MR) monitoring work performed by the Environment Agency (EA) and consulting companies due to time constraints
Summary
Coastal wetlands such as saltmarshes are valuable habitats that provide a wide range of ecosystem services (Luisetti et al, 2014) They play important roles as biodiversity hotspots (Zedler and Kercher, 2005; Mossman et al, 2012), carbon sinks (Erwin, 2009; Ahn and Jones, 2013; Tempest et al, 2014), natural defences against coastal erosion and flooding (Möller and Spencer, 2002; Van Der Wal et al, 2002; Gedan et al, 2011), nurseries for juvenile fish (Luisetti et al, 2014), pollutant filters (Mudd, 2011), and sites for recreational activities (Luisetti et al, 2014). The implementation rate of MR in the UK still needs to increase fivefold to comply with Shoreline Management Plans that aim to realign 550 km of coastline by 2030 (Committee on Climate Change, 2017)
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