Paul Farres - Academia.edu (original) (raw)

Papers by Paul Farres

Catena, Apr 1, 1988

Techniques of digital image processing are now common place in remote sensing research. This pape... more Techniques of digital image processing are now common place in remote sensing research. This paper considers the potential use of some of these procedures on 'frame grabbed' video images. The example taken is that of the evolution of stone pavements and their implication for interrill erosion processes. The resuits indicate a relationship between the total erosion loss and the rate of stone pavement areal cover. In addition the paper shows how the technique could be of great assistance in the monitoring of many different types of environmental processes.

Earth Surface Processes and Landforms, Jul 1, 1985

The stability of individual soil aggregates to impacting water drops is now regarded as a fundame... more The stability of individual soil aggregates to impacting water drops is now regarded as a fundamental parameter required in any soil erodibility assessment. This stability has been measured by the use of single drop rainfall simulators, the characteristics and operation of which have, in the past, shown considerable variation. The drop sizes, impact frequency, drop fall height, chemistry of drop-forming liquid, aggregate pretreatment, and definition of breakdown affect the way in which the apparatus can be used to define stability. Within this paper each one of these characteristics is considered and a piece of apparatus proposed which is believed to give results with increased consistency and replicability. The described apparatus can be readily reproduced in any laboratory situation, and has the added advantage of being not only appropriate for the measurement of indices of stability, but also of providing an environment in which the mechanisms of aggregate breakdown can be investigated.

Catena, 1984

Abstract Aggregate stability to drop impact is of fundamental importance to many aspects of the s... more Abstract Aggregate stability to drop impact is of fundamental importance to many aspects of the soil system, in particular rainsplash erosion. The role of moisture content is considered by the use of a single drop simulator on soil aggregates of known moisture content selected from the Hamble series. Results indicate a negative logarithmic relationship between time to breakdown and specific moisture content. In addition the variability of the results drastically declines with increasing moisture content. The results are explained in terms of distribution of moisture within the aggregates prior to experimentation.

Catena, Feb 1, 1987

The work of a number of authors is integrated to reveal a sequence of events occurring during rai... more The work of a number of authors is integrated to reveal a sequence of events occurring during rainsplash erosion. The implication of this sequence is that aggregate stability plays a central regulatory role. Using 20 iron rich soils from Mozambique it is shown that their temporal dynamics as regards splash loss is consistent with this proposed sequence, and that in addition aggregate stability does directly relate to total splash loss over a 50 minute period of rain. By now considering the soil properties a statistical model is formulated. A model which seems to imply that the central regulatory role of aggregate breakdown is only a partial answer to erodibility, as important are the characteristics of the breakdown bi-products.

The Photogrammetric Record, 1998

The importance of soil surface microrelief has been identified in the literature of soil erosion.... more The importance of soil surface microrelief has been identified in the literature of soil erosion. However, studies of soil microrelief have often ignored photogrammetry as a means of obtaining soil surface data. This paper recognizes the validity of analytical photogrammetry to quantify height changes at the experimental plot scale (Յ 1 m 2). Additionally, however, analytical photogrammetry enables the recording of non-morphological information (including soil aggregates and rock fragments) so that the impact of such features upon the evolution of soil surfaces may be considered. The two forms of information may then be integrated within a geographical information system to relate the effects of such features upon soil surface height changes.

CATENA, 1990

MUCHER 1986). Conventional wisdom recognises that the downslope movement Reported here is an unus... more MUCHER 1986). Conventional wisdom recognises that the downslope movement Reported here is an unusual type of and accumulation of soil material can colluvial deposit whose associated transresult from soil creep (KIRKBY 1967), port pathway involves a substantial subinterrill contribution by pluvial erosion surface component. The deposit repre-(DE PLOEY 1977)or more dramatically sents the downslope transfer of nitrogen-as fan-type forms emerging from rill and enriched agricultural soil into a semigully systems (POESEN 1987). Colluvial natural woodland soil, creating signif-accumulations are typically found in Euicant localised eutrophication. The rope associated with slopes with a long amount of material involved was c. human landuse history (KWAAD 1977). 65 kg, and covered an area of c. 7.7 m 2. The colluvial deposits themselves are to It appears that the deposition was rapid, be recognised in the landscape either as and the outcome of a single transport valley infills, or as unusually thick soil event. The absence of more general obunits behind natural/semi-natural barriservations prevent the calculation of an ers such as hedgerows and field boundaerally-representative long-term rate of aries with old woodlands. Deposits may operation. The status of this process also be seen as discrete steps in the midin the general modification of temperate die of slope units in which the whole hillslopes is still a matter for conjecture, slope unit is now completely under agricultural use with the previous barriers

CATENA, 1980

The paper sets out to investigate how the characteristics of drop impacts control when soil aggre... more The paper sets out to investigate how the characteristics of drop impacts control when soil aggregate breakdown takes place, and what might be the most important mechanisms involved in this breakdown process. A single drop rainfall simulator is used which enables the formation of drops of very different characteristics to impact onto a single soil aggregate. By the use of Principle Components analysis these variations in drop impact characteristics are synthesised into three orthogonal components. Component scores are then regresses against time to aggregate breakdown, the analysis achieves 92 % explanation of variation in this dependent variable. The interpretation of the results shows slaking to be of prime importance in aggregate breakdown, it does not preclude physio-chemical mechanisms from this process and therefore provides a base from which these mechanisms can be studied in a new series of controlled experiments.

Earth Surface Processes, 1978

One of the fundamental mechanisms operative during pre-overland flow soil erosion is crusting. Th... more One of the fundamental mechanisms operative during pre-overland flow soil erosion is crusting. The form of the crust, its relationship to infiltration, have been described by earlier workers. But the way in which a crust forms and develops through a single storm has not been considered. A set of controlled laboratory experiments were undertaken to look at this. In these experiments a constant rainfall intensity was used, and supplied by a rainfall simulator, the soil was held constant throughout the experiments. The areal development through a single storm event was looked at by means of time sequence air photographs, and the vertical development by the study of time sequence thin sections. The results show how crust formation may be regarded as a discrete rapid event with respect to time. The rapid development moves towards an equilibrium state prior to the initiation of overland flow. A model of the mechanisms of crust development is also formulated.

QRA Annual Discussion Meeting 2018, 2018

International audienc

Earth Surface Processes and Landforms, 2015

In recent years there has been a growing body of literature on depositional signatures associated... more In recent years there has been a growing body of literature on depositional signatures associated with historic extreme waves on rocky coasts. Here, in the context of the Maltese islands, we place an innovative focus on evidence of erosional forms. The field evidence is concentrated along the NE flank of the islands at a topographically varied range of sites and up to an altitude of 13 m. A range of forms is broadly classified in terms of their morphologies and the forces responsible for their formation. Sockets, eroded scarps, scoured terrains, clifftop erosion scars, swept terrains and spillways are interpreted as consequences of overwashing of the landscape by an extreme wave or waves. These forms are shown to be controlled by flow intensity, topography and lithology, and especially rock bedding and jointing. They comprise the source areas for associated depositional evidence allowing transport paths to be estimated, and may significantly enhance the reconstruction of extreme wave events. It is likely that similar (and additional) erosional forms are present elsewhere in the Mediterranean domain, where comparable lithological and topographic situations are exposed to extreme waves.

Zeitschrift für Geomorphologie, 2014

Field evidence from the Maltese Islands is presented of extreme wave activity in the central Medi... more Field evidence from the Maltese Islands is presented of extreme wave activity in the central Mediterranean Sea. An extensive range of extreme wave signatures, both erosional and depositional, is here presented for the first time and indicates a wave attack from the NE. Existing models of runup and boulder detachment imply that the extreme wave signatures lie beyond the capabilities of storm waves. These considerations, taken together with the range of evidence available, point toward tsunami as the agency responsible, which is consistent with the evidence from Mediterranean marginal coasts opposed to the Maltese Islands. Evidence from existing boulder detachment, tsunami runup and wave velocity models suggests that tsunami with shoreline wave height of up to ~4 m, and with local velocities of >10 ms-1 would have been required in order to form the signatures observed.

Environmental Conservation, 2005

Earth Surface Processes and Landforms, 2003

Traditionally, landforms have been measured using a combination of field survey techniques and an... more Traditionally, landforms have been measured using a combination of field survey techniques and analogue and analytical photogrammetry. With advances in computing power digital photogrammetric solutions are now seen as offering an affordable and cost effective way of mapping topographic features. This paper looks at the relative merits of each of these photogrammetric techniques, in terms of the practical considerations involved in data extraction and accuracies that can be achieved for a case study. The site investigated is Maiden Castle, situated southwest of Dorchester in Dorset, UK. This paper examines the relative accuracies of both digital and analytical photogrammetric techniques in relation to ground control points recorded using a global positioning system (GPS). Colour stereoscopic aerial photographs were taken of Maiden Castle, Dorset, in November 1999 at a scale of approximately 1 : 4000. Stereo models were constructed using pre-marked ground control points positioned using post-processed differential GPS. Subsequent analysis involved the calculation of residual values produced by comparing the computer-generated surface with a set of test points measured using differential GPS. This research demonstrates that the optimal digital system matched the performance of analytical photogrammetry for the collection of geomorphological data.

Geological Society, London, Special Publications, 2010

The historic cart ruts of Malta are incised into the underlying bedrock topography. Anomalous rel... more The historic cart ruts of Malta are incised into the underlying bedrock topography. Anomalous relationships between their routeways and the uneven terrain beneath suggest that they originated on a land surface different from that of today. An exposure close to a cart-rut location near Naxxar reveals evidence of limestone terrain development and its role in the evolution of the cart-rut patterns. Specifically, it reveals that cart trackways were most probably superimposed from a soil cover onto an underlying bedrock surface topographically different from the former soil surface. A model is developed demonstrating likely relationships between human activity, soil erosion and trackway evolution leading to the incision of the trackways into the bedrock.

World Geomorphological Landscapes, 2019

Most people will be familiar with wheel ruts caused by the passage of farm vehicles in the muddy ... more Most people will be familiar with wheel ruts caused by the passage of farm vehicles in the muddy fields of soil-covered farming landscapes. However, significantly fewer will have observed ruts of similar dimensions in solid rock. Such features are an enigmatic part of the Maltese landscape. Archaeologists have understandably focused on such issues as the date, purpose and cultural context of the features. However, to the geomorphologist, their field characteristics as described here at four key sites provide a range of evidence for their mode of formation and indeed their role as indicators of environmental change. An experimental geomorphological approach has established that two-wheeled carts could readily have inadvertently formed the ruts in the local limestones of low to medium mechanical strength. Once created, they are indicative of a very effective means of transporting significant loads around Malta. The cart-ruts are discussed in the contexts of both archaeological history...

This study considers changes occurring on a soil surface after exposure to simulated rainfall. Th... more This study considers changes occurring on a soil surface after exposure to simulated rainfall. The soil surface in question has a crop cover of artificial maize, and interest focuses specifically on the surface features produced by leaf drips. An analytical photogrammetric approach is used to examine surface morphological change at a small scale (1 mm). These topographical changes are then related to sub-surface crust development as observed by the use of impregnated polished blocks. For the first time therefore soil surface and soil sub-surface changes are integrated together in one study. The results reveal a `cut and fill' type process in which aggregate welding and breakdown operate in parallel.