Round Britain's CatchmentsAuthor(s): Bruce WebbSource: Area, Vol. 14, No. 2 (1982), pp. 132-133Published by: The Royal Geographical Society (with the Institute of British Geographers)Stable URL: http://www.jstor.org/stable/20001798 .

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Round Britain's catchments

Report on the UK meeting of the IGU Commission on Field Experiments in Geomorphology, 16-24 August 1981.

Two days of paper sessions at Exeter University, four days of field visits to sites in Devon, Avon, Powys, Dyfed, Yorkshire and Derbyshire, and a final day of presentations at Huddersfield Polytechnic comprised the busy schedule for the 1981 Meeting of the Commission, which took as its theme 'Catchment Experiments in Fluvial Geomorphology'.

Papers presented on the subject of runoff and erosion dynamics emphasised the varying importance of different runoff production mechanisms in contrasting environments. Results from detailed studies undertaken on steep and gentle slopes in the Bristol area by M. G. Anderson et al. indicated the importance of overland flow but also suggested that controls of its generation varied with hillslope morphology and plot scale. In contrast, J. A. A. Jones and F. G. Crane demonstrated that flow from subsurface pipes accounted for 46% of the runoff generated in the small upland Maesnant catchment of Mid-Wales, and M. P. Mosely showed that subsurface flows through macropores at velocities of up to 2cm-' were of considerable importance in forested catchments in South Island, New Zealand. The key role of soil properties in determining runoff was emphasised by many papers at this meeting, and a useful method of experimentally characterising spatial variability of soil hydrodynamic properties was presented by B. Ambroise. Spatial contrasts at other scales of resolution, such as the difference between slope and flood plain hydrology in a small Amazonas tributary, were shown by S. Nortcliff and J. B. Thornes to strongly influence streamflow response. A logical development in studying runoff dynamics involves investigation of the relationship between zones of runoff production and areas of erosion in catchments, and interesting preliminary work in this direction was introduced by M. McCaig for the pattern of wash erosion around an upland stream head, and by

T. P. Burt et al., for the spatial distribution of solutional denudation in a hillslope hollow and spur system.

Sediment sources and yields were a specific focus of several papers, and some spectacular yields of up to 25 tha-'. a-' were reported from small catchments in Romania's Hilly Regions by D. Balteanu and I. Taloescu. In the case of some sources, such as road-bank gulleying studies by M. J. Haigh in central Oklahoma, the mechanisms and magnitude of sediment supply are relatively easy to isolate and to quantify. In other circumstances, sediment sources may be

multiple or not immediately obvious, and A. Imeson and R. Vis have identified at least four types of contributing area in forested drainage basins of the Keuper region of Luxembourg. The advantages of combining plot studies and catchment experiments in investigations of sediment sources were apparent from the work of W. Froehlich and J. Slupik in the Homerka catchment, Poland, whereas the value of studying suspended sediment properties to an understanding of mobilisation and conveyance processes was demonstrated by D. E. Walling and P. Kane from results on sediment quality of several Devon rivers.

Considerable attention was also given to the topic of solute processes and yields, and several presentations highlighted the need to study interactions between the lithosphere, hydrosphere and biosphere in order to gain an understanding of solute dynamics. W. Swank, reporting results of the classic investigations at Coweeta Experimental Forest, clearly demonstrated the influence of different tree covers on water chemistry, whereas I. D. L. Foster and I. C. Grieve presented the chemical budget of a single forested ecosystem in north Warwickshire. T. M. Gallie and

0. Slaymaker have identified five major vegetation-soil groups in a coastal subalpine environ ment of Canada which are associated with different hydrological properties and distinctive water compositions, and the link between hydrological pathways and solute levels was also stressed by A. G. Williams and J. L. Ternan in their comprehensive study of chemical weathering on the Dartmoor granite. A. C. Armstrong also reported close links between runoff and N03-N levels in clay soils affected by drainage of different types.

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Round Britain's catchments 133

Further paper sessions considered field experiments concerned with slope processes and river channels, and E. W. Anderson and N. J. Cox demonstrated how variables controlling soil creep rate may be successfully isolated. The relationship between hillslope form and process was discussed by I. Ichim and V. Surdeanu, and the wide variety of field techniques being used by the Institute of Hydrology to investigate erosion in several rivers of mid-Wales was colourfully illustrated by G. J. L. Leeks. Vegetation was shown by A. M. Gurnell and K. J. Gregory to influence stream channel processes at hillslope, small subcatchment and reach scales, whereas

M. Klein linked channel and near-channel erosion to the occurrence of hysteretic relationships between suspended sediment concentration and water discharge. Channel adjustments over longer periods of time were discussed by I. Ichim and M. Radoane and by A. Werrity, the latter having recorded complex channel changes triggered by flash floods on Dorback Burn, Inverness-shire.

In the context of denudation studies, A. P. Schick and J. Lekach showed sediment conveyance in small arid catchments to be highly sporadic, very short-lived and strongly influenced by preparation time preceding the event. The role of extreme events is generally less pronounced in humid temperate environments, but a detailed study of sediment and solute transport in Devon rivers led B. W. Webb and D. E. Walling to stress inter- and intra-catchment contrasts in

magnitude and frequency characteristics of fluvial denudation. 0. Slaymaker underlined the difficulties involved in denudation budgeting and advocated the use of multiple field experiments and the method of strong inference to achieve sound estimates of erosion rates.

The meeting also considered studies of mud and debris flows. The spectacular geomorphic effects associated with rapid mass movements generated by the Mount St. Helens eruption were described by M. Brunengo, and innovative experimental and field measurements being employed to study and to model the fluid dynamics of mudflows generated by this event were presented by L. Fairchild and T. Dunne. A contrasting analysis of debris flow motion, based on the concepts of solid mechanics, was applied by S. Okuda and H. Suwa to the intensively monitored Kamikamihori Fan of the North Japan Alps, and use of microforms and fabric for predicting mudflow tracks on alluvial cones in the same region was discussed by H. Hirano and T. Ishii.

In conjunction with the field programme, a number of papers were devoted to field experi ments in the Pennines. In this session T. P. Burt and A. T. Gardiner analysed runoff and sediment production in a small peat-covered catchment suffering from considerable erosion, and S. T. Trudgill, A. M. Pickles, K. R. J. Smettem and R. W. Crabtree individually presented findings from the work of the Whitwell Wood Project. These included the formulation of initial hypotheses of hydrology and solute uptake in hillslope soils on Magnesian Limestone, the application of laboratory solution experiments and field studies of soil water residence time and soil water movement in relation to soil structure, and some conclusions regarding solute sources and solutional denudation.

The application of a definite experimental methodology to field studies in geomorphology was much discussed at the meeting, and in concluding the paper sessions M. Church suggested that few existing or past programmes of field observation have met the criteria of a classical scientific experiment. Visits were held to field sites in the Exe Valley, at Abbots Leigh near Bristol (D. Bosworth and P. Kneale), on the River Severn (C. R. Thorne, R. D. Hey and J. Lewin), in the

Maesnant catchment, at the Institute of Hydrology, Plynlimon (M. Newson), in the Southern Pennines, and at Whitwell Wood. These gave participants the opportunity to further quiz British geomorphologists about their experimental designs and other general topics such as scale dependent controls in fluvial systems and the value of process measurements to understanding landform development. Although one delegate was heard to complain about 'too much hydrology and too little geomorphology', this meeting, organised by Tim Burt and Des Walling and sponsored by the US Army European Research Office, was generally much enjoyed by participants from home and overseas, and confirms the healthy status of fluvial studies in the UK. Proceedings from the meeting are to be published by Geo Books in 1982.

Bruce Webb University of Exeter

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