GIS for Coastal Zone Management - Chapter 4

CHAPTER FOUR Monitoring Coastal Environments Using Remote Sensing and GIS Paul S.Y. Pan 4.1 INTRODUCTION This paper concerns the monitoring of the marine and coastal environment in South Wales using state-of-the-art survey techniques and a geographic information system (GIS). One of the most important natural resources in South Wales is its marine aggregate. This resource is vital to the regional economy in that it provides the building industry with that most essential of raw materials, sand and gravel. However there are growing concerns as to the possible effects of the commercial extraction of aggregate on the coastal and marine environment, and a number of environmental monitoring procedures are in place to detect changes. These range from traditional beach profile surveys to state-of-the-art airborne remote sensing techniques. The National Assembly for Wales has pioneered the use of airborne LiDAR (Light Detection and Ranging) for the acquisition of highly detailed topographical data on beaches, and CASI (Compact Airborne Spectrographic Imager), for the determination of the state of the vegetation along part of the coastline. LiDAR is capable of accurately detecting changes in beach levels. The procedure began in 1998 and will continue until at least 2003, giving an unprecedented insight into coastal changes over time. Another remote sensing technique has also been deployed. Close-range photogrammetry has been used to determine the degree of retreat of unstable sea-cliffs. All the data collected is used to populate a GIS. Data acquired in this way is compared with that from various monitoring procedures carried out previously (aerial photography and beach profiles). A number of advanced techniques have been developed in parallel to the GIS for the interpretation, analysis and visualization of the data. A number of invaluable lessons have been learned. Apart from the site-specific monitoring procedures, other strategic data sets such as the macro-fauna community distribution, modelled parameters, etc., have also been acquired from a number of sources. Amongst these parameters, the most important of all is the sediment environment. It defines the fuzzy geographical boundaries in which distinctive hydrodynamic regimes operate. A summary on the resources and constraints is generated for each of the sediment environments. These resources and constraints summaries together with the GIS form the basis of a decision-support system for assisting the formation of policy for the management © 2005 by CRC Press LLC of the marine resource. The findings will shape future decisions about the sustainable use of the marine resource in South Wales. 4.2 BACKGROUND The marine and coastal environment is important to Wales. About 75% of the length of the country is coastal, allowing the waters of the Irish Sea and the Bristol Channel to lap its shores (Figure 4.1 and the colour insert following page 164). South Wales lies adjacent to the Bristol Channel, a body of water largely unaltered in its current dimensions since its beginnings as a marine transgression in the early Holocene. (The Holocene, or post-glacial epoch, covers the period for the end of the Pleistocene about 10,000 years ago to the present day). Here the coastal areas are not only characterized by a number of urban and industrial centres, such as Newport, the capital city Cardiff, Bridgend, Port Talbot and Swansea, but also by many cherished areas of special landscape and nature conservation interest, such as: the Gwent Levels; the Kenfig National Nature Reserve and candidate Special Area of Conservation (cSAC) designated under the European Habitats Directive; the Gower Area of Outstanding Natural Beauty (AONB) – the first to be designated in the United Kingdom; and the Glamorgan Heritage Coast (Figure 4.2 and colour insert). Together, and for different reasons, these coastal areas attract thousands of visitors every year, providing employment opportunities for some of the local population. One of the unseen resources of the Bristol Channel, however, contributes to the local economy in a different way – by yielding high quality building sand for local industry, an essential prerequisite for many forms of economic activity. Whilst this economic activity brings undoubted prosperity to South Wales and neighbouring regions in mid Wales and South-West England, many people perceive changes to their familiar coastlines, and in particular, to the sandy beaches. There are growing concerns as to the possible effects of the extraction of marine sand from the Bristol Channel, and not everyone thinks the removal of this resource is acceptable or sustainable. Generally, in Welsh waters, the extraction of sand from the marine environment by dredging is licensed by the Crown Estate. (The Crown Estate Commission is the representative of the Crown, which, in the UK, constitutes the owner of the seabed out to a 12-mile territorial limit). However, the decision on whether a production license should be granted essentially rests with the Environment Minister at the National Assembly for Wales – a devolved and autonomous arm of central Government that came into being in 1999. With its inception has come a desire to increase outside involvement in policy-making and administration, and to increase transparency and accountability in deciding major issues. The challenge for the Assembly’s civil servants is to continue to provide objective advice to Ministers in an ever-evolving social, economic, environmental, cultural and political context. This advice must be based on facts and scientific evidence, together with the specialist and professional judgement of the officers involved. All of the dredging licenses granted in recent years have stringent environmental monitoring conditions attached. It is the scientific data from these monitoring procedures that form the basis of sound advice. © 2005 by CRC Press LLC This paper discusses the introduction of a Geographic Information System (GIS) into part of the National Assembly for Wales for the analyses of the monitoring data. It highlights the technique’s influence on the monitoring procedures and the way it has helped reshape the environmental monitoring requirements in relation to dredging licenses. By way of illustration, a number of the state-of-the-art procedures currently deployed are examined. Figure 4.1 Wales and its surrounding areas. 4.3 DATA ANALYSES USING GEOGRAPHIC INFORMATION SYSTEMS The benefits of modern computerized GIS have been well documented by others, for example, Clark et al., 1991 and Maguire, 1991. GIS was first introduced to the former Welsh Office (now the National Assembly for Wales) in early 1997 for analysis of the monitoring data acquired in respect of the dredging license at Nash Bank. A prototype was developed using ESRI’s (Environmental Systems Research Institute Inc.) ArcView GIS. The benefits of the technique over the traditional paper-based reporting were immediately apparent. It: x provided a stable platform for the integration of disparate data from different sources; x allowed a large quantity of data to be stored and processed; x provided a seamless geographical database overcoming the restrictions of traditional map/chart boundaries; © 2005 by CRC Press LLC x provided facilities for sophisticated analysis and cross-examination of data; and x provided advanced facilities for the display and visualization of data to a wider audience. After a period of evaluation, the technology was adopted for operational use. It would play a key role in re-shaping the environmental monitoring procedures. GIS highlighted the weaknesses of some of the established procedures in terms of both the quality and coverage of the data. The capability of GIS in handling spatial data, in particular, has also presented new opportunities for the introduction and subsequent adaptation of more efficient and cost-effective procedures. The following sections discuss some of these new and innovative environmental monitoring techniques. They are: the assessment of cliff instability using close-range photogrammetry; repeated topographical surveys using Light Detection and Ranging (LiDAR); and habitat mapping of sensitive sites of nature conservation interest using Compact Airborne Spectrographic Imager (CASI). Figure 4.2 South Wales and the Bristol Channel 4.3.1 Assessment of Cliff Instability Using Close-Range Photogrammetry The Nash Bank lies in the Bristol Channel very close to part of the Glamorgan Heritage Coast. The sandbank contains about 200 million tonnes of material and is a relic feature of the last (or “Devensian”) glaciation. The bank is formed ostensibly from pre-existing glacial and glacio-fluvial deposits subsequently © 2005 by CRC Press LLC moulded by advancing seas. At low water its eastern end is often exposed above the surface of the sea, and it resides, at its nearest point, only 300 metres from the shore. Its physical orientation and proximity to this area of sensitive coastline means that it acts as a “barrier” to incoming waves, and is therefore an important structure in terms of coast protection. Physical processes such as the movement of sediment in, on and around the feature, as well as human activities, are altering the shape of this sandbank. One way of measuring the “vulnerability” of the nearby coastline to such changes is by careful scientific examination of instability in the highly unstable Blue Lias cliffs that predominate. Extremely accurate measurements of the geometry of a representative 800-metre section of this geologically special part of the Glamorgan Heritage Coast, and including part of the Southerndown Coast Site of Special Scientific Interest (SSSI), have been undertaken since 1997 using close-range photogrammetry. Its application in this context is unique in the United Kingdom. Annual surveys have been undertaken in August of each year between 1997 and 2000. A further one took place in February 2001. 4.3.1.1 Close-Range Photogrammetry: The Technique Close-range photogrammetry operates on the same principle as aerial photography. It produces highly detailed geometric data of three-dimensional structures. Data capture involves the use of a specialist metric camera oriented horizontally on a tripod, and usually mounted on top of a theodolite. The lenses are calibrated and their distortion characteristics considered for subsequent data processing. The technique is also known as terrestrial photogrammetry. Both aerial and close-range photogrammetry have been described in detail in Wolf (1985). Close-range photogrammetry involves photographing the features or structures being surveyed using the metric camera in a known orientation from two positions. The camera positions and their orientation can be established by “traditional” surveying methods, such as using visual intersection combined with theodolite measured distances from known control points. Alternatively, a number of control points can be set up in the area being surveyed and subsequently included in the photogrammetric survey. These control points are used to compute the position and orientation of the two camera positions. Data is derived from the photographic images by simulating the relative orientation of the two camera positions, and processing involves the generation of a three-dimensional stereo model representing the geometry of the structure. It is relatively labour-intensive because the orientation of the two camera positions is not always parallel, and this means additional computational requirements. However, the generation of the 3D geometric model has been helped by advances in automatic image matching techniques in the past decade. Close-range photogrammetry has been used widely for surveying architectural structures worldwide. Its main advantage is that it can survey the physical dimension of any structure that does not lend itself readily to traditional surveying techniques. It has also been used extensively by traffic accident investigators for collecting data from the scenes of accidents where a very limited period is available for data capture. It is therefore a technique which is characterized by a short set up time, data capture by relatively straightforward © 2005 by CRC Press LLC ... - tailieumienphi.vn