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• Impacts of Climate and Sea-Level Change on Coastal Gullies

There is a considerable body of research into the effects of climate change on river flows (see Arnell et al.,2001, for a review), but little is known about associated morphological responses. This is because channel changes are often too small to be observable over short timescales(Kirkby, 1996), whereas longer term(sedimentary) records are often fragmentary (Sear & Arnell, 2006). Our empirical understanding of river channel responses at the spatial (reach) and temporal (decadal) time scales most relevant to river management (Hooke, 1994; Warner, 1995; Inman and Jenkins, 1999; Sear and Arnell 2006) therefore remains poor. An alternative approach is simulation, and established models are available to predict catchment (Willgoose et al., 1991; Tucker and Slingerland, 1997; Tucker et al., 2001; Coulthard et al., 2000, 2002, 2005) and reach-scale channel/gully dynamics (see ASCE, 1998; Darby & Van de Wiel, 2003, for reviews). In these models, channel morphology evolves in response to the (time-varying) influxes of runoff and sediment load supplied from the catchment upstream. However, for predictive (as opposed to hindcasting) applications these fluxes must be estimated in some way. In principle, and so long as appropriate climate data is available (e.g. from Global or Regional Climate Models), landscape evolution models (LEMs; Willgoose et al., 1991; Tucker and Slingerland, 1997; Tucker et al., 2001; Coulthard et al., 2000, 2002, 2005) can be used to simulate water & sediment delivery, and the impacts on channel morphology in reaches downstream. However, in practice some modifications are required to ensure appropriate process representation for their use within the context of gullies (Leyland and Darby, 2008) and to ensure that the models are applied at a sufficiently high spatial resolution that issues of scale do not preclude their use for predicting morphology and substrate.

This project is concerned with the coastal gullies (known locally as ‘Chines’) that are common along the cliffed, southwest, coast of the Isle of Wight. An ability to predict the morphology of these gully systems is important because the diversity of features and processes (deeply incised channels offer shelter and variable aspects, eroding cliffs provide new substrate for colonizing vegetation and invertebrates)sustains important habitat diversity – indeed, coastal gullies are recognized as having particular habitat significance. Previous research (Leyland and Darby, 2008) has identified the key factors influencing coastal gully morphology as being related to two competing processes that interact to control in-gully erosion rates (active erosion sustaining the key habitat) and gully length (directly determining the amount of available habitat). These factors are (i) the rate of sea-cliff erosion, which acts to reduce gully length while simultaneously generating knickpoints, and (ii) the rate of knickpoint migration upstream, the latter being controlled by the erodibilityof the substrate and the forces exerted on gully beds by storm runoff.

A key driver of morphological change in river systems in general – and coastal gully systems in particular - is, therefore, climate change (Brown, 2003; Knox, 2003; Conlan et al., 2007). However, at present there have been no studies which have linked climate with runoff-driven morphological changes over the time and spatial scales (decadal, reach) that are meaningful to management. The importance of this topic justifies an effort to tackle this gap. This project will address this issue, in the specific context of coastal gullies encountered along the southwest coast of the Isle of Wight, through the novel combination of realistic climate, coastal erosion, hydrological and morphological models. A key innovative aspect will be the application of these models to look at the impacts of climate-induced changes in coastal erosion and storm runoff on the morphology of coastal gullies, on the basis that it is preservation of morphological process that is essential to sustaining habitat diversity within the gullies.

The project will employ the University of Southampton's supercomputer (Iridis3) to ensure that the uncertainties associated with a wide range of RCM model inputs are fully accounted for in the work

Categories

Life sciences simulation: Environmental hazards

Physical Systems and Engineering simulation: Climate, Earth surface dynamics, Landscape evolution, Sediment transport