‘real’ geomorphology revisited

Some of the reasons are given for the editorial (Richards, 1990) now discussed by Rhoads (1994) and Bassett (1994). These include the lack of interest generally displayed by geomorphologists in matters of scientific philosophy and method, and the instrumentalist view of research often presented to postgraduate students given present funding imperatives. It is suggested that in a revision of views about the validity of a hypothesis-testing, critical rationalist methodology might have considerable implications for the practice of environmental sciences, and that accordingly the debate initiated by Rhoads and Bassett is worthy of continuation.     

Ergodicity and the ‘scale effect’

Solute plume spreading in an aquifer exhibits a ‘scale effect’ if the second spatial concentration moment of a plume has a non-constant time-derivative. Stochastic approaches to modeling this scale effect often rely on the critical assumption that ensemble averages can be equated to spatial averages measured in a single field experiment. This ergodicity assumption should properly be evaluated in a strictly dynamical context, and this is done in the present paper. For the important case of trace plume convection by steady groundwater flow in an isotropic, heterogeneous aquifer, ergodicity does not obtain because of the existence of an invariant function on stream surfaces that is not uniform throughout the aquifer. The implications of this result for stochastic models of solute transport are discussed. © 1997 Elsevier Science Ltd. All rights reserved     

On being a ‘real’ geomorphologist

In a recent editorial Richards (1990) advocated a realist perspective for geomorphology. Scientific realism, defined broadly, is the doctrine that science attempts to generate true knowledge of the observable and unobservable (i.e. non-empirical) aspects of an objective world. Various brands of realism exist; the particular version cited by Richards (1990) has not strongly influenced mainstream philosophy of science. Also, critical rationalism, which Richards (1990) contrasts with realism, fully adopts a realist perspective. In its broadest sense, realism encompasses the entire spectrum of geomorpho-logic research, thus providing a unifying philosophical framework for geomorphology.     

The Icelandic ‘rofabard’ soil erosion features

Soil erosion and desertification are severe problems in Iceland. Erosion processes are numerous, and more than one can occur at each site, resulting in many erosional forms. Erosion forms and an erosion severity scale are the basis for a recent national survey of erosion in Iceland. One of the most distinctive erosion forms in Iceland is an erosion escarpment, termed ‘rofabard’ in Icelandic. Rofabards are formed in thick but non‐cohesive Andosols that overlie more cohesive materials such as glacial till or lava. The relatively loose Andosols beneath the root mat are undermined, creating escarpments, or rofabards. The rofabards retreat as a unit, with a fully vegetated and rich ecosystem on top but leaving barren desert in their place. Rofabards are common within a 20 000 km² area. The Agricultural Research Institute and Soil Conservation Service erosion database suggests that erosion associated with rofabards has denuded 15 000 –30 000 km² of land that was previously fully vegetated and had fertile Andosols, but is now mostly desert. Erosion rates associated with rofabards are reported as the loss of vegetated land with Andosol mantle, measured as hectares per square kilometre per year. This measure of erosion has more meaning for Icelandic landscapes than the traditional tonnes per hectare per year. Estimated losses of Andosol cover in rofabard areas for the whole country are currently about 230 ha a⁻¹. This rate is about 10 times lower than the rate needed to cause estimated losses of Andosol mantle in rofabard areas since settlement, 1125 years ago. During peak years of soil erosion, losses were probably several thousand hectares per year, but the erosion rates slowed down as extensive Andosol areas have become barren deserts. Copyright © 2000 John Wiley & Sons, Ltd.     

‘Natural’ rivers, ‘hydromorphological quality’ and river restoration: a challenging new agenda for applied fluvial geomorphology

Fluvial geomorphology is rapidly becoming centrally involved in practical applications to support the agenda of sustainable river basin management. In the UK its principal contributions to date have primarily been in flood risk management and river restoration. There is a new impetus: the European Union's Water Framework and Habitats Directives require all rivers to be considered in terms of their ecological quality, defined partly in terms of ‘hydromorphology’. This paper focuses on the problematic definition of ‘natural’ hydromorphological quality for rivers, the assessment of departures from it, and the ecologically driven strategies for restoration that must be delivered by regulators under the EU Water Framework Directive (WFD). The Habitats Directive contains similar concepts under different labels. Currently available definitions of ‘natural’ or ‘reference’ conditions derive largely from a concept of ‘damage’, principally to channel morphology. Such definitions may, however, be too static to form sustainable strategies for management and regulation, but attract public support. Interdisciplinary knowledge remains scant; yet such knowledge is needed at a range of scales from catchment to microhabitat. The most important contribution of the interdisciplinary R&D effort needed to supply management tools to regulators of the WFD and Habitats regulations is to interpret the physical habitat contribution to biodiversity conservation, in terms of ‘good ecological quality’ in rivers, and the ‘hydromorphological’ component of this quality. Contributions from ‘indigenous knowledge’, through public participation, are important but often understated in this effort to drive the ‘fluvial hydrosystem’ back to spontaneous, affordable, sustainable self‐regulation. Copyright © 2006 John Wiley & Sons, Ltd.     

Observations of ‘freezing-induced redistribution’ in soil lysimeters

Data are presented of vertical profiles of soil water potential and soil temperature from a field lysimeter experiment with automatic water-table control at Silwood Park, Ascot, UK. The observed water-table fluxes confirm the analysis of profile response, which shows a diurnal pattern of upward water movement as a result of surface freezing, followed by reversed flow when soil thawing occurs. The results provide a clear, and relatively rare, illustration of the phenomenon of freezing-induced redistribution.     

Plastic pellets on Spain''s ‘Costa del Sol’ beaches

Plastic pellets, ranging in diameter from 2.7 to 4.5 mm, were collected from thirteen beaches on the Costa del Sol of Spain (Algeciras to Almeria). Although the pellets were common on most beaches surveyed, they were abundant on only four. Eighty-seven per cent of those collected were made of low density polyethylene (opaque, cream-yellow, and amber pellets), 8% were of high density polyethylene (solid white button-like pellets and orange-red conical pieces), and 4% were of ethylvinyl acetate (clear to translucent pellets). The absence of ‘crazing’ and encrusting biota on the pellets suggests their recent introduction to this marine environment.     

‘Bedload’ dynamics: Grain-grain interactions in water flows

Owing to experimental difficulties, the transport stage at which collisions between moving ‘bedload’ grains might become significant has never been investigated, yet the existence or otherwise of such collisions is of some importance in the understanding of the mechanics of sediment transport, in particular the theory developed by Bagnold. Application of the basic principles of gaseous kinetic theory to ‘bedload’ grains moving in saltant trajectories and the adoption of a ‘characteristic’ saltation path leads to the prediction that grain-grain collisions should dominate in the transport of coarse sands over plane beds in water flows above a transport stage of about 2, i.e. when the mean boundary fluid shear stress exceeds the critical boundary shear stress for grain motion by about 4 times. Above this stage interrupted saltations should always occur, with the ‘bedload’ grains held above the stationary bed by a combination of fluid and solid momentum transfer mechanisms. A classification of the types of grain motions is given and evidence is presented for the existence of an upward decrease in grain collision frequency and of grain concentration at the top of the ‘bedload’ zone.     

‘frost and salt’ weathering: Further experimental results

A laboratory experiment has been conducted to examine the effects of ‘frost and salt’ weathering (i.e. physical breakdown by the freezing of salt solutions) on a limestone. Results show that the presence of certain salts in solution can inhibit frost damage. These findings are in direct conflict with those presented by Goudie (1974) and, more recently, Williams and Robinson (1981). Comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed. If salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced-this is the case represented by the experiment of Williams and Robinson. Conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited-the case of the present experimental study. Caution is therefore advocated when attempting to extrapolate laboratory-derived results to infer on the behaviour of rocks under natural conditions. Several environmental situations in which ‘frost and salt’ weathering may be a possibility are dsiscussed, but it is concluded that further field data, especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions, would be necessary before more definite statements could be made about the efficacy of this process.     

Reservoir regulation by means of a ‘goal-oriented’ inflow predictor

A reservoir regulation scheme for the control of deficiency yields is described in the paper. According to such scheme, at the end of each decade (=ten days) the release in the following decade is established on the basis of current storage, downstream users' requirements and forecast of future inflows. Such forecast is supplied by a mathematical predictor, namely a recursive relationship, which points out the most likely values of future inflows on the basis of current and recent inflow measurements. It is a goal-oriented predictor, in the sense that its parameters are evaluated through a procedure, which takes into account the objective of reservoir regulation (=control of downstream deficits). The regulation scheme is applied to a real case and the resulting sequence of yearly deficits is evaluated. Such deficits are compared with the ones obtained by introducing a different (=non-goal-oriented) predictor into the scheme.     

Earthquake resistance of buildings with a ‘soft’ first storey

The dynamic, bi-linear response behaviour of a series of eight storey shear buildings subjected to simulated earthquake excitation is studied. The specific objective of the investigation is to determine under what conditions a yielding first storey can adequately protect the upper storeys from significant yielding. Two classes of buildings are considered: stiff (0.5 sec period) and flexible (2.0 sec period), and the basic parameters considered in the yielding first storey are the yield force level and the bi-linear stiffness. The results demonstrate that a very low yield force level and an essentially perfectly plastic yielding mechanism are required in the first storey to provide effective protection to the superstructure. Moreover, the required displacement capacity of such an effective first storey mechanism is found to be very large.     

Comments on richards: The problems of ‘real’ geomorphology

A number of comments are made as a response to the editorial “Real” geomorphology' (Richards, 1990). The call for more involvement by geomorphologists in current philosophical debate is welcomed and the adoption of a broadly realist scientific approach is supported. Some contentious issues arise from this debate and these are outlined and discussed.     

Evaluation of site effects in some localities of ‘Alta Val Tiberina Umbra’ (Italy) by numerical analysis

In the paper the application of a methodology for the evaluation of site effects in an area of Umbria Region (Italy) is shown. In the project 20 localities were analyzed. In this paper the results of some representative localities are presented. The objective of the project was to develop a methodology that may be easily repeated, in order to take into account site effects in urban planning. Therefore a series of geologic, geomorphologic (1:5.000 scale) and geotechnical analyses have been carried out, to identify the areas affected by site effects and to characterize the lithotechnical units. The expected seismic inputs have been calculated and the numerical analyses 1D and 2D have been done. The results, in terms of elastic pseudo-acceleration spectra and amplification coefficients, as a ratio between spectral intensity of output and input, give elements for urban planning, both for urban general choice and for buildings design.