Biomedical subjects

Graham J L Leeks

Publications and source records attributed to Graham J L Leeks.

7 recordsLinked to original sources

PubMed2005

River flow and associated transport of sediments and solutes through a highly urbanised catchment, Bradford, West Yorkshire.

The hydrological characteristics of catchments become drastically modified in response to urbanisation. The total contributions and dynamics of runoff, suspended sediment and solutes may change significantly and have important implications downstream where they may affect flooding, instream ecological habitat, water quality and siltation of river channels and lakes. Although an appreciation of the likely hydrological changes is crucial for effective catchment management they are still poorly understood. In this paper we present data from a network of river monitoring stations throughout the heavily urbanised Bradford catchment, West Yorkshire. Sites are upstream, within and downstream of the highly urbanised central part of the catchment. Flow, turbidity (calibrated to suspended sediment concentration) and specific conductance (surrogate for solute concentration), logged at 15-min intervals, are presented for a 12-month period (June 2000 to June 2001). The total amounts and dynamics of flow, solute and suspended sediment transport were investigated. Estimated total flow and suspended sediment transport for the monitoring period were found to be high in response to the high total rainfall. Flow and sediment transport regimes were extremely 'flashy' throughout the catchment and became increasingly flashy in a downstream direction. Suspended sediment discharged from the Bradford subcatchment makes an important contribution to downstream sediment transport on the river Aire at Beal. Data suggest that the urbanised part of the Bradford catchment is extremely important in contributing solutes to the Beck (river). Although flow and sediment are also contributed to the Bradford Beck in the urbanised part of the catchment the data suggest that significant amounts may enter the combined sewer system and bypass the river. Understanding the spatial and temporal variations of flow and the transport of suspended sediment and solutes in rivers in urbanized subcatchments is crucial to their effective management and monitoring. Furthermore, this knowledge may be extremely important to the management and monitoring of downstream rivers in large scale mixed catchments.

Cities↗

PubMed2003

PCB congener dynamics in a heavily industrialized river catchment.

PCB congener concentrations in the water column of a highly industrialized river catchment, the Aire/Calder, in N.E. England were determined weekly on a routine basis, and 2 hourly through selected high flow (flood) events. Bed, suspended and floodplain sediment PCB congener concentrations were also determined along transects of the rivers investigated. Weekly monitoring revealed that the sum of 11 quantified (Sigma11) PCBs rose in concentration by two orders of magnitude during late summer compared to their winter minimum values. This rise was concurrent with sustained periods of low flow. SigmaPCB concentrations were rapidly diluted during high flow (flood) events. Suspended sediment was, on average, 13 times more contaminated with PCBs than bed sediment, with means of 4.0 and 53.8 ng/g, respectively, while floodplain samples had an intermediate concentration of 29.8 ng/g. Principle components analysis (PCA) of congener profiles showed that all three sediment types were similar, but that congener profiles differed considerably between sediment and whole-water samples. There was no change in the percentage contribution of individual PCB congeners apparent from weekly whole-water monitoring. However, the congener pattern in whole-waters changed systematically during high flow events. PCA showed that whole-water samples collected during high flow events had progressively more sediment characteristics, and then returned to whole-water characteristics on cessation of the event. The PCA evidence, dilution of PCB concentrations during events, and suspended sediments more contaminated than bed sediments, indicate that the major sources of PCBs in this catchment are current inputs from sewage treatment works, rather than remobilization of bed sediments.

Journal Article↗

PubMed2003

The temporal and spatial variability of sediment transport and yields within the Bradford Beck catchment, West Yorkshire.

Recent EU directives have emphasised the need to understand and limit potential water quality problems within urban river systems. Under certain conditions sediments and contaminants derived from industrial and domestic waste and the urban surface may be expelled into urban rivers via the sewer and drainage system. These discharges may lead to water quality problems within urban catchments. One aspect of water quality is the suspended sediment. This can be directly detrimental to water quality by affecting the habitat for fish and other biota but it is also closely associated with pollutants, such as heavy metals, which may be adsorbed onto the sediments surface. This paper presents a comparative analysis of sediment yields for a small mixed rural/urban catchment, the Bradford Beck in West Yorkshire, over a number of precipitation events. Flow and water quality parameters were monitored at a high temporal resolution at strategic sites within the urban watercourse over a 2-year period. Rainfall was measured at six locations within the catchment. Analysis of discrete rainfall events allowed an understanding of the temporal and spatial variability of sediment transport within the catchment to be developed. The results demonstrated that for individual storms the sediment yields from the urban sub-catchment were generally higher than those from the rural system although the annual yields were comparable. Sediment transport within the urban area, for large events, was dominated by the impact of the Combined Sewer Overflows discharging. Within these events peak suspended sediment concentration, SSC, were generally higher than the rural system. Within smaller events the main sediment source within the urban area was the surface runoff discharging directly to the urban river. Analysis of SSC and discharge relationships illustrated the different sources of sediment for contrasting events. Within the rural system clockwise hysteresis, indicating exhaustion of sediment supply, was noted for larger storms. The high temporal resolution monitoring has enabled a better understanding of sediment dynamics within the Bradford Beck system to be developed. The general conclusions drawn can provide guidance for addressing sediment related water quality issued in other urban systems.

Journal Article↗

PubMed2003

The impact of a convectional summer rainfall event on river flow and fine sediment transport in a highly urbanised catchment: Bradford, West Yorkshire.

Urban watercourses are important assets to cities, but they often have extremely 'flashy' hydraulic regimes and poor water quality, making them potential hazards. Current knowledge of the impact of intense rainfall events on urban river water discharge and, in particular, fine sediment transport is limited. Continuous monitoring of flow and turbidity (subsequently calibrated to suspended sediment concentration) was undertaken at a network of four sites throughout the highly urbanised Bradford catchment in West Yorkshire, NE England. An intense convectional rainfall event, which occurred over central Bradford in June 2001, generated extreme flow and fine sediment transport responses at the most downstream site, Shipley Weir. In just 15 min, discharge increased from 0.45 to 34.6 m(3) s(-1) (median annual peak instantaneous discharge of 27.5 m(3) s(-1), 1983-2001) and suspended sediment concentration increased from 14 to 1,360 mg l(-1). A peak sediment flux of 47.2 kg s(-1) was recorded. It is demonstrated that this extremely large and urban flux of fine sediment is likely to have a major downstream impact on water quality in the River Aire.

Journal Article↗

PubMed2003

Fingerprinting suspended sediment sources in a large urban river system.

Very few studies have attempted to quantify the sources of suspended sediment transported in urban river systems. In this study, statistically verified composite fingerprints and a multivariate mixing model have been used to identify the main sources of the suspended sediment transported by the River Aire and its main tributary, the River Calder. Because of the polluted nature of the Aire/Calder catchment and its effect on fingerprint property concentrations, source tracing was undertaken separately for the upper and lower reaches. The mean contributions from individual source types (i.e. surface materials from woodland, uncultivated and cultivated areas, channel bank material, road dust and solids from sewage treatment works) varied between the upper and lower reaches of the rivers, reflecting the change in land use from primarily pasture and moorland in the upper reaches to mainly urban areas (with some cultivated land) in the lower reaches. The suspended sediment in the upper reaches of the River Aire originates largely from channel bank sources (43-84%) and from uncultivated topsoil (16-57%). In the lower reaches of the Aire/Calder system, local sources of cultivated topsoil contribute 20-45% of the suspended sediment load and there is a significant contribution from urban sources, such as road dust (19-22%) and solids from sewage treatment works (14-18%). In the upper reaches, the proportion of sediment derived from each of the two main geological areas corresponds broadly to the proportion of the catchment occupied by each geological area. The relative contribution from the Rivers Aire and Calder to the suspended sediment load transported below the confluence demonstrates that most of the sediment is derived from the River Calder.

Journal Article↗

PubMed2003

Land Ocean Interaction: processes, functioning and environmental management: a UK perspective.

The hydrochemical and physical functioning of UK river basins, estuaries and coastal waters through to the open sea are outlined in relation to British environmental research over the last ten or more years. An overview of a considerable body of published work is presented in the context of current findings and future research challenges. This is linked to this special issue of Science of the Total Environment 'Land Ocean Interaction: processes, functioning and environmental management: a UK perspective' for which this contribution provides a conclusion.

Ecosystem↗

PubMed2003

Land-ocean interaction: processes, functioning and environmental management from a UK perspective: an introduction.

This paper provides a foreword to a special edition of Science of the Total Environment concerned with land-ocean interaction from a UK perspective as linked to processes, functioning and environmental management. The volume structure is presented together with an outline of the nature of the individual papers. The areas covered are: (1) freshwater chemistry, (2) riverine sedimentology, (3) tidal river, estuarine and coastal chemistry, (4) estuarine and coastal sediments and (5) shelf-sea-ocean linkages. The foreword provides as an introductory link to the broader perspectives of contemporary UK research in this area, which comes in a conclusions paper at the end of the volume.

Conservation of Natural Resources↗