Sediment budget analysis for coastal management, west Dorset

Abstract

BackgroundThe identification and characterization of geomorphological units or systems is particularly important in the coastal zone. Indeed, the consequences of failure to appreciate the physical environment can be more acute on the coast, as rapid, major changes are a reality for land use planning and development. On the coast, it is often more useful to map the landscape in terms of sediment ‘cells’ (i.e. process units) rather than terrain units (i.e. landform units) as an understanding of the supply and transport of sediment (e.g. sand and shingle) is fundamental to dealing with many shoreline problems. Sediment is circulated in what often can be regarded, for practical purposes, as almost closed cells that are separated by boundaries across which little beach material is transferred. Each cell can be characterized in terms of the inputs, outputs, stores and sinks of sediment.For example, to understand the development of a beach it is useful to consider it as a store of shingle or sand supplied from source areas on the adjacent coastline or offshore (Fig. 1). Beach building material might be supplied from the seabed, moved onshore by wave energy, or from rivers and eroding cliffs. This material is then redistributed along the shoreline by waves (‘longshore drift’), unless prevented by barriers such as headlands or breakwaters. Although longshore drift might be prevented by these barriers, some of the material can still be ‘lost’ to the system around the seaward end of the barriers or offshore, particularly during large storms.Sediment inputs

A Simple GIS-Based Tool for the Detection of Landslide-Prone Zones on a Coastal Slope in Scotland

“…However, it must be worth noting that our tool can effectively capture two key drivers of slope instability-i.e., surface water accumulation and slope gradient, constituting a simple but robust approach that links both slope topography and hydrology. The proposed tool can thus serve as a basis to gain spatial knowledge about the interaction of different environmental and natural processes, and how those combine to create instability for slopes in a wider area (e.g., watershed) to inform and support workflows for the mitigation and restoration of landslides [20]. A systematic approach like the one suggested by [20], which underpins this tool, will ultimately allow the identification of instability drivers, which, in turn, can allow identification of the most suitable mitigation or protection methods to interrupt the key driving process rather than attempting smaller, potentially more numerous, solutions for providing local remediation.…”

“…In cases where there is no legal owner of the site at risk, such as the case study site presented here, the relevant stakeholders (residents at and on adjacent sites, recreational users, interest groups and similar) can define the strategy and also provide insight into the history of instability on the site (Table 1), which can form the basis of a more detailed instability inventory [43]; Figure 9). The detailed investigations should target not only the drivers of instability but also the other elements of the system [20], including the soil, vegetation, flora/fauna, and their interactions. The mitigation measures can be targeting the high-risk areas identified by the GIS-based tool and can be instrumented to provide an insight into their behaviour and effect on the surrounding environment and areas of lower risk.…”

“…However, while these attributes constitute some of the major underlying slope instability factors (e.g., steep and convex slopes are more prone to failure, same as slopes with aspects which do not favour growth of vegetation reinforcing and stabilising slopes; [18]), they still need to be linked to the main driver of landslides-i.e., the precipitation-derived water accumulating and saturating the slope forming materials [19]. Simple but robust approaches linking both slope topography and hydrology should be very interesting to support workflows for the mitigation and restoration of landslides [20].…”

“…The problems with landslides and soil mass wasting have traditionally been solved in a similar way for both potential slope instability and mitigation of instability which has already occurred. Whilst the techniques and methodologies applied towards the solution of these problems are similar, the types and use of data differ significantly [20]. Typical workflow activities include gathering desk study information (e.g., aerial photos, geological information, hydrological mapping, historical records, etc.…”

Applications of remote sensing for geohazard mapping in coastal and riverine environments

“…Archive aerial photography has been used extensively in the UK to map and quantify changes in riverine and coastal landforms (e.g. Winterbottom & Gilvear 1997;Lee & Brunsden 2001;Brasington et al 2003). Repeated close-range terrestrial photogrammetric surveys have been used to map spatio-temporal changes along gravel-bed river banks and channels, allowing the identification of locations where individual clasts had been removed (Pyle et al 1997;Butler et al 1998).…”