David Gilvear

Quantification of channel bed morphology in gravel-bed rivers using airborne multispectral imagery and aerial photography

The potential for mapping in-channel morphology within shallow gravel-bed rivers using airborne multispectral imagery and aerial photography is illustrated using a case study from the River Tummel, Scotland. The technique described relies on a good correlation between observed light reflectance levels from a water body and water depth. Measured water depths are regressed against reflectance levels derived from airborne multispectral imagery and black-and-white aerial photographs, to obtain equations that can be used for mapping channel bathymetry. The technique has a great deal of potential for wide-ranging applications, including detailed morphological surveys, assessing in-channel changes and mapping riverine habitats.© 1997 John Wiley & Sons, Ltd.

Mapping intertidal estuarine sediment grain size distributions through airborne remote sensing

Abstract The intertidal environments of estuaries represent critical exchange environments of sediment and sediment bound contaminants. Ecological and sedimentological related investigations of these environments require monitoring methods that provide rapid spatially representative data on sediment grain size distribution. Remote sensing has the potential to provide synoptic information of intertidal environments. Previous in situ and laboratory-based reflectance investigations have demonstrated that for effective quantification of sediment grain size distributions, remote sensing platforms must include measurements within the short-wave infrared (SWIR). In addition, the timing of image acquisition, in relation to tidal cycles and sediment moisture content, is critical in optimising the spectral differences between the coarser sand and finer ‘mud’ fraction of sediments. Daedalus 1268 Airborne Thematic Mapper (ATM) has been identified as an appropriate platform and sensor for providing accurate synoptic maps of estuarine sediment distributions. This paper presents the results from the application of ATM 1.75 m resolution data to the mapping of surface sediment grain-size distributions across intertidal areas of Ribble Estuary, Lancashire, UK. ATM imagery was acquired after the intertidal area was exposed to strong summer drying conditions. Pre-processing and linear unmixing of the imagery collected of the intertidal zone following a period of drying allowed accurate sub-pixel determinations (1.75 m resolution) of sediment clay (r2=0.79) but less accurate for sand (r2=0.60). The results also demonstrate deterioration in the image calibration with increasing sediment moisture content and microphytobenthos cover. However, recombining the subpixel end member abundances through multivariate regression analysis improved the image calibration significantly for both sediment clay and sand content (r2>0.8) for imagery collected in both dryer and wetter conditions. These results demonstrate that ATM data, or similar, can be used to gain quantitative information on intertidal sediment distributions and such data has application to a wide variety of estuarine research.

Fluvial geomorphology and river engineering: future roles utilizing a fluvial hydrosystems framework

Abstract River engineering is coming under increasing public scrutiny given failures to prevent flood hazards and economic and environmental concerns. This paper reviews the contribution that fluvial geomorphology can make in the future to river engineering. In particular, it highlights the need for fluvial geomorphology to be an integral part in engineering projects, that is, to be integral to the planning, implementation, and post-project appraisal stages of engineering projects. It should be proactive rather than reactive. Areas in which geomorphologists will increasingly be able to complement engineers in river management include risk and environmental impact assessment, floodplain planning, river audits, determination of instream flow needs, river restoration, and design of ecologically acceptable channels and structures. There are four key contributions that fluvial geomorphology can make to the engineering profession with regard to river and floodplain management: 1. to promote recognition of lateral, vertical, and downstream connectivity in the fluvial system and the inter-relationships between river planform, profile, and cross-section; 2. to stress the importance of understanding fluvial history and chronology over a range of time scales, and recognizing the significance of both palaeo and active landforms and deposits as indicators of levels of landscape stability; 3. to highlight the sensitivity of geomorphic systems to environmental disturbances and change, especially when close to geomorphic thresholds, and the dynamics of the natural systems; and 4. to demonstrate the importance of landforms and processes in controlling and defining fluvial biotopes and to thus promote ecologically acceptable engineering. Challenges facing fluvial geomorphology include: gaining full acceptance by the engineering profession; widespread utilization of new technologies including GPS, GIS, image analysis of satellite and airborne remote sensing data, computer-based hydraulic modeling and geophysical techniques; dovetailing engineering approaches to the study of river channels which emphasize reach-scale flow resistance, shear stresses, and material strength with catchment scale geomorphic approaches, empirical predictions, bed and bank processes, landform evolution, and magnitude–frequency concepts; producing accepted river channel typologies; fundamental research aimed at producing more reliable deterministic equations for prediction of bed and bank stability and bedload transport; and collaboration with aquatic biologists to determine the role and importance of geomorphologically and hydraulically defined habitats.

Quantifying geomorphic and riparian land cover changes either side of a large flood event using airborne remote sensing: River Tay, Scotland

The potential of high resolution multi-spectral airborne remote sensing to detect and quantify changes in channel morphology and riparian land cover are illustrated. The River Tay is a partially embanked wandering gravel bed river, and Airborne Thematic Mapper data, which collect reflectance in the visible, near, mid and thermal infrared, were acquired in 1992 and 1994 either side of a 1:65 recurrence-interval flood event. Imagery was radiometrically, atmospherically and geometrically corrected in order to minimise atmospheric and geometric changes between the 1992 and 1994 scenes. A maximum likelihood classifier was then used on each image and change was quantitatively mapped using a classification comparison approach. Bathymetric mapping was undertaken by applying a Lyzenga algorithm to ATM bands 5, 6 and 8 to account for an exponential decrease in electromagnetic radiation penetration through the water column with depth. Despite the magnitude of the flood event, no major changes in channel position or form occurred but the change detection algorithms revealed subtle changes not observed in the field. Bar head accretion, bar tail formation and extension, bar dissection, localised bank erosion and the overriding of low level vegetated islands by gravel lobes were the main forms of change. On the floodplain, flood embankment failures resulted in fans of sands and gravels on agricultural land. More generally, the study reveals the potential for using airborne remote sensing to detect change in fluvial systems and as a mutually complementary tool to field survey.

Hydrology and the ecological quality of Scottish river ecosystems

Hydrology is a primary control on the ecological quality of river systems, through its influence on flow, channel geomorphology, water quality and habitat availability. Scottish rivers are widely perceived to be of high ecological quality, with abundant flow volumes and high water quality. However, historical and current river flow regulations, and land use change have altered the physical and chemical characteristics of Scottish rivers, with adverse consequences for aquatic biota. Baseline hydrological, geomorphological and water quality conditions in Scottish rivers are thus summarised. The impacts of river regulation and land use change on the hydrology, geomorphology and water quality of Scottish rivers are then discussed. Consequences of these changes for aquatic habitat are examined, with particular reference to the economically significant salmonid species (Salmo salar and Salmo trutta). Policy and management issues relating to the future ecological quality of Scottish rivers are reviewed. These include the impacts of climate change on ecological quality, the calculation and implementation of ecologically acceptable flows, and river restoration and best management practices within integrated catchment planning.

Character of channel planform change and meander development: Luangwa River, Zambia

Air photo interpretation and field survey were used to examine rates and patterns of planform change over the last 40 years on an 80 km reach of the Luangwa River, Zambia. The river, a tributary of the Zambezi, is a 100–200 m wide, medium sinuosity sand-bed river (sinuosity index 1·84). High rates of channel migration (<33 m a−1) and cutoffs on meandering sections are frequent. Some meandering reaches, however, have remained relatively stable. A form of anastomosing with anabranches up to 14 km in length is also a characteristic. Patterns of meander development vary between bends but all can be described in relation to traditional geomorphic models; change occurs by translation, rotation, double-heading, concave bank bench formation and cutoff causing river realignment. At the local scale spatial variability in bank resistance, induced by floodplain sedimentology, controls rate of bank erosion, and valley-side channel ‘deflection’ is also apparent. Copyright

Quantification of the water balance and hydrogeological processes in the vicinity of a small groundwater-fed wetland, East Anglia, UK

Abstract Badley Moor Fen exists in a region of the UK where potential evapotranspiration exceeds annual rainfall. The wetland is maintained by an input of Chalk groundwater in an area where the groundwater aquifer is regionally confined below boulder clay. The large groundwater contribution to the water balance arises from a unique local geological situation on the margin of the valley floor that allows the vertical movement of groundwater to the surface under a strong upward head gradient. The groundwater contribution is the dominant water input and maintains saturation within the immediate vicinity of the source of groundwater. Surface water outflow, via adjacent drainage channels, is the major output. The groundwater component is also important in that, as a result of hydrochemical change in the groundwaters with flow towards the surface, tufa has been precipitated. The calcium bicarbonate rich groundwater and tufa accumulation have given the site a unique character, with an exceptionally rich calcareous fen community.

The influence of surface and interstitial moisture on the spectral characteristics of intertidal sediments: Implications for airborne image acquisition and processing

Intertidal sediment distribution is an important factor in the understanding of estuarine ecological, morphological and pollution processes. Airborne remote sensing is identified as a cost-effective tool that may be used to provide accurate synoptic maps of estuarine sediment distributions. However, prior to the collection and analysis of airborne imagery, spectral characterization of intertidal sediments is fundamental. Through a series of in situ

A GIS-based approach to mapping probabilities of river bank erosion: regulated River Tummel, Scotland

This study explores the use of Geographic Information Systems (GIS) techniques for mapping river channel planform change and bank erosion probability. The method used is primarily based on an approach developed by Graf (Graf, W.L. 1984. ‘A probabilistic approach to the spatial assessment of river channel instability’, Water Resour. Res., 20(7), 953–962), which proposed that bank erosion probability could be determined for any given cell on a floodplain by taking into account (i) its distance laterally and in the upstream direction to the active river channel, and (ii) a value representing flood magnitudes for the given period. In this study, Grafs method is refined by using a GIS approach and by incorporating the influence of geomorphic variables, such as river bank morphology, sediment type and floodplain vegetation, on bank erosion rates. In addition, the technique is applied to a wandering gravel-bed river of roughly 80 m width, representing a different type and size of river to that used in Grafs study. Thus, the wider applicability of the technique is tested. In addition, the analysis here covers only a short time scale (1988–1994) compared with that used by Graf. The high temporal resolution of this study is enabled by the use of aerial photography and also by the substantial channel changes that occurred within this time period as a result of several high magnitude flood events. The results of the study indicate the usefulness and validity of the approach, particularly with regard to floodplain erosion hazard mapping and the assessment of the effects of altered flood regimes and land use. Copyright

A preliminary investigation into the spectral characteristics of inter-tidal estuarine sediments

Abstract In the Ribble Estuary, Lancashire, U.K., systematic associations between discharge of radionuclides from the British Nuclear Fuels plc (BNFL) plants at Sellafield and Springfields and sediment size-fractions exist. The ability to map these associations through in situ spectroscopy (0·4-2·5 μm) of sediments at low tide was investigated. Laboratory spectra of inter-tidal sediment samples collected from the Ribble show a strong negative correlation (–0·7 to –0·8) between their radionuclide-associated clay content and reflectance within the 0·4-2·5 μm range. Field spectra of the same samples showed a less distinct relationship as a result of the presence of surface moisture, cyanobacteria, and halite within the intertidal zone. Methods are proposed to account for these problems.