Search

Despite over a century of investigations into gullies and gully erosion, the characterization and categorization of gullies and the varied definitions, nomenclatures and terminology used has caused some confusion in understanding and communicating the relationships of gully forms and processes around the world. We firstly review the gully literature and highlight how a lack of consistency in gully definition and characterization prevents unifying theory from being developed within this important field of research, since it is often unclear whether different landscape features being discussed are comparable. We propose that conventionally employed qualitative planform and cross‐sectional characteristics of gullies alone are inadequate to define gully types, yet both these features remain central to most modern gully descriptions. We discuss the need to revise and augment these basic characteristics with clearly defined morphogenetic attributes such as landscape context, soil material characteristics, erosion processes, hydrological integrity, modes of development, and head/side‐wall morphology for an effective, practicable, generic gully classification scheme. Central to a gully classification scheme is the need for a clear definition of what a gully is – and is not – for which geomorphological criteria are proposed to differentiate a 'gully' from other 'incisional land surface forms'. This gully definition hinges largely on the identification of a retreating head scarp and the internal erosion by mass‐movement and other sidewall slope erosion processes, coupled with the transport of the soil materials from the gully void. By defining a gully and synthesizing descriptions of gully 'types' from the literature and our own experience, we propose key morphogenetic attributes of gullies necessary to form a framework for a systematic gully classification scheme. An initial, eclectic classification framework is presented as both a summation and a synthesis of the literature review, and as a progenitor to a dynamic generic classification scheme that is proposed in a follow‐up article. [ABSTRACT FROM AUTHOR]

The northeastern tip of the Arabian Plate and more precisely the Sultanate of Oman is proving to be an exceptional territory for understanding the geological and geomorphological questions facing scientists. Whether it is the problems of plate tectonics, orogenesis (lithology, structure, tectonics) or surface morphologies (fluvial, wind, coastal erosion, karstogenesis, etc.), routes in the mountains of Oman, its canyons or its deserts are very instructive. Among the main interests we will highlight the presence of the largest exposed ocean floor in the world (Sémail site), the incision in canyons of the raised terrain, an important little-known karst and exceptional deserts. These special circumstances have also made Oman a place of mineral deposits of rare metals and hydrocarbons, the basis of a very ancient human occupation and, with tourism, of its present wealth. [ABSTRACT FROM AUTHOR]

Abstract The 190 km2 Calhoun Critical Zone Observatory in the Piedmont region of South Carolina, USA lies in an ancient, highly weathered landscape transformed by historic agricultural erosion. Following the conversion of largely hardwood forests to cultivated fields and pastures for ~200 years, excess runoff from fields led to extreme sheet, rill, and gully erosion across the landscape. Roads, terraces, and a variety of other human disturbances have increased the landscape's surface roughness. By the 1950s, cultivation-based agriculture was largely abandoned across most of the Southern Piedmont due to soil erosion, declining agricultural productivity, and shifting agricultural markets. Secondary forests, dominated by loblolly and shortleaf pines, have since regrown on much of the landscape, including the 1500 km2 Sumter National Forest, which was purchased from farmers and private land owners in the 1930s. Although this landscape was intensively farmed for approximately 150 years, there are a few hardwood forest stands and even entire small watersheds that have never been plowed and degraded by farming. Such relatively old hardwood stands and watersheds comprise relic landforms whose soils, regoliths, and vegetation are of interest to hydrologists, environmental historians, biogeochemists, geomorphologists, geologists, pedologists, and others interested in understanding the legacy of land-use history in this severely altered environment. In this work we champion the need for high-resolution terrain mapping and demonstrate how Light Detection And Ranging (LiDAR) digital elevation model (DEM) data and microtopographic terrain roughness analyses (MTRA) can be used to infer land use history and management. This is accomplished by analyzing fine scale variation in terrain slope across the 1190 km2 CCZO using data derived from three independent and overlapping LiDAR datasets at varying spatial resolutions. Terrain slope variability MTRA is further compared to three other methods of capturing and quantifying fine-scale surface roughness. We lastly demonstrate how these analyses can be employed in concert with historic aerial photography from the 1930's, contemporary Landsat remote sensing data, and ecological field data to identify reference relic landforms: hardwood stands, hillslopes, and small watersheds that have experienced minimal anthropogenic erosion for study and conservation. Highlights • Human activities roughen the ground surface via enhanced erosion. • Minimally eroded areas can be extremely difficult to identify within large areas. • Remote sensing can be used distinguish highly vs. minimally impacted areas. • Minimally impacted areas have great value for research and conservation. • Our work increases researchers' ability to locate and utilize these areas. [ABSTRACT FROM AUTHOR]

Abstract Every year, gully erosion causes substantial damage to agricultural land, residential areas and infrastructure, such as roads. Gully erosion assessment and mapping can facilitate decision making in environmental management and soil conservation. Thus, this research aims to propose a new model by combining the geographically weighted regression (GWR) technique with the certainty factor (CF) and random forest (RF) models to produce gully erosion zonation mapping. The proposed model was implemented in the Mahabia watershed of Iran, which is highly sensitive to gully erosion. Firstly, dependent and independent variables, including a gully erosion inventory map (GEIM) and gully-related causal factors (GRCFs), were prepared using several data sources. Secondly, the GEIM was randomly divided into two groups: training (70%) and validation (30%) datasets. Thirdly, tolerance and variance inflation factor indicators were used for multicollinearity analysis. The results of the analysis corroborated that no collinearity exists amongst GRCFs. A total of 12 topographic, hydrologic, geologic, climatologic, environmental and soil-related GRCFs and 150 gully locations were used for modelling. The watershed was divided into eight homogeneous units because the importance level of the parameters in different parts of the watershed is not the same. For this purpose, coefficients of elevation, distance to stream and distance to road parameters were used. These coefficients were obtained by extracting bi-square kernel and AIC via the GWR method. Subsequently, the RF-CF integrated model was applied in each unit. Finally, with the units combined, the final gully erosion susceptibility map was obtained. On the basis of the RF model, distance to stream, distance to road and land use/land cover exhibited a high influence on gully formation. Validation results using area under curve indicated that new GWR CF RF approach has a higher predictive accuracy 0.967 (96.7%) than the individual models of CF 0.763 (76.3%) and RF 0.776 (77.6%) and the CF-RF integrated model 0.897 (89.7%). Thus, the results of this research can be used by local managers and planners for environmental management. Graphical abstract Image 1 Highlights • Three approaches ((a) CF and RF; (b) integrated CF-RF; and (c) combined GWR CF RF) used for GEZM. • A new methodological framework (GWR-RF-CF) was introduced for GEZM. • Geographically Weighted Regression was used to create several homogenous units. • GWR CF RF has higher prediction accuracy than other employed models. • GWR CF RF as a new approach can be used by decision makers for GEZM. [ABSTRACT FROM AUTHOR]

Abstract The objective of this research was to assess the effect of gullying on the erosive response at the basin scale by modeling. For this purpose, a distributed hydrological model, which includes erosion by raindrop, rilling and gullying, was configured and applied in a Mediterranean basin in southern Spain. The results show a range of parameters close to those provided by the literature and good agreement with field measurements. However, the simulations indicate that the rill erodibility parameter at the surface is overestimated by as much as 70% to compensate for gullying processes. Other parameters, such as the subsoil erodibility of the soil profile, play an important role in the erosive response of the basin. A geomorphological threshold for sediment yield that relates density of gullies and erodibility parameters was found. These responses are especially relevant in semiarid environments where the intense pulses of precipitation have important effects on landscape evolution. Highlights • Soil erodibility is overestimated to compensate gullying processes. • A geomorphological threshold relates gully density and erodibility. • Subsoil erodibility has a prominent role in erosive response. • Measuring gullying remains an important challenge at the basin scale. [ABSTRACT FROM AUTHOR]

The Bahluieţ catchment, located in the Moldavian Plateau, at the contact between the Jijia Rolling Plain, the Suceava Plateau and the Central Moldavian Plateau, has 54,866 hectares in size. The sculptural landforms are prevailing, described by elongated rolling hills, and are underlain by the Bessarabian layers laid in marine brackish facies. In turn, the typical plateau relief (Coasta Iasilor and the eastern border of the Suceava Plateau) is developed in coastal facies also Bessarabian in age.

Located in the Central Moldavian Plateau, the Stavnic catchment is associated to a left tributary of the upper Barlad River, and extends on 21,341 ha of which 39% is under forest.

Erosion rates in the hanging wall of the Alpine Fault are high, keeping pace with rock uplift over time frames of 104-106 years. On shorter time frames, prediction of temporal and spatial distribution of erosion is challenging and must account for local conditions and parameters including rock strength, topographic stresses and failure conditions. Constrained by field observations of rock strength, we use 3D mechanical models to predict where and by what mechanism slope failure and erosion are likely to take place along the Waikukupa section of the Alpine Fault. Shear failure is favoured along the base of slopes and where pore pressure is high. Tensile failure is favoured along ridges, higher on slopes and when pore pressure is moderate. A dry material with a high degree of rock strength heterogeneity promotes bedrock gully development, whereas distributed failure is more likely to occur when the material is saturated. [ABSTRACT FROM AUTHOR]

Hydric erosion is very active in the Upper Steppes area of Tunisia chiefly on the alluvial floodplains where it is largely controlled by suffusion. This erosive dynamic represents a threat for the agricultural lands. The erosive phenomena related to suffusion, causes gullying, banks undermining and enlargement of the section of wadis. A morphodynamic mapping based on field-observations, the exploitation of aerial photos multi-date data, and the study of some examples put moreover in evidence the sensibility of the area to erosion phenomena in relation with suffusion. The forms of gullying and a comparative study of orthorectified air photographs pose the problem of the factors of this accelerated evolution: rainfall aggressivity, soil erodibility, inclination of the slopes, weakness of the vegetal cover and inappropriate human activities.

An analysis is made of the manifestations of fluvial and aeolian processes in the southern, developed areas of Irkutsk oblast belonging to the upstream part of the Angara basin. We examine the formation probability and the recurrence frequency of disastrous geomorphological events. The study revealed their association with positive (fluvial processes) and negative (aeolian processes) extremes and anomalies of atmospheric moistening. It is shown that at the time of an extreme event the rate of the processes and the volumes of transported material increase abruptly (by an order of magnitude), and the affected areas show an increase. The criteria for an extreme fluvial event can be represented by a spasmodic buildup of gullies and appearance of new gullies, an abrupt increase in soil losses due to erosion of agricultural lands reaching 100−200 m/ha, death of crops, releases of mud flows, and destruction of roads, dams, bridges and other structures. The geomorphological consequences of the 1960 summer storm rains are considered to exemplify the disastrous fluvial events. The extremes of aeolian processes have the character of hurricanes encompassing most of the agricultural areas of Irkutsk oblast. The hurricanes are accompanied by a powerful removal of aeolian material from north-west to south-east to the water area of Baikal, to windward slopes and watershed divides of the mountain ranges along the eastern coast. The finest dust particles are transported to neighboring areas of Buryatia, Mongolia and China. The negative consequences of extreme aeolian events include agricultural crop destruction or damage, soil deflation, pollution of surface waters by deflation products, fires, damage to power transmission lines or even death of people. The findings were used in zoning the Upper Angara region according to the degree of geomorphological security of the territory. [ABSTRACT FROM AUTHOR]

• Dq suggests the degree of complexity of the multifractal pattern. • Low lacunarity value (Ʌg) indicates that the badlands are multifractal patterned. • Negative value of Δf (α) shows that gullying processes are active on a finer scale. Badlands are intensely gullied lands, undergoing heavy soil losses, bereft of sustainability and are degenerative to the verdant ecosystem. This paper aims at using multifractal and lacunarity analysis to badlands systems, with the objective of offering geomorphic correlation and interpretation of multifractal parameters to understand the nature of patterns and the operative processes in badlands. Interpretability of the parameters, namely generalised dimension (Dq) versus exponent (Q), multifractal function of the component (f(α)) versus Holder's exponent (α), (Δα), Δf (α) and lacunarity (Ʌ or λ), provides an efficient approach to comprehend and resolve the dynamic problem of badlands patterns. Four badlands sites were selected in the study area and the analysis was done using ImageJ software. The analysis showed that the sigmoidal curves of Dq versus Q decreasing towards higher values of Q (Q > 0) and the high values of Dq indicate that the badlands are typical multifractal patterns and have been densely dissected. The graphs of f(α) versus (α) are hump-shaped and are right-skewed with negative values of Δf (α), which suggests that erosion processes are active on a finer scale in the area. The greater values (Δα) show greater complexity in the study area, while the decrease in (Δα) may be indicative of adjustment of forms. The lacunarity values are very low, suggesting high intensity of dissection and homogeneity of the pattern of the system. This study may provide a basis for priority ranking for land conservation measures and in monitoring thereof in the badland areas. [ABSTRACT FROM AUTHOR]

The gullied systems from the Falciu Hills within the Chioara catchment (2997 ha) consist of both main types of gullies, discontinuous and large continuous ones along valley bottoms, and lots of ephemeral gullies. Several methods have been used to measure and estimate gully characteristics. Then, the gully development stages, the effect of the natural conditions, and especially the impact of land management on gullying in the Falciu Hills over the last two centuries have been defined. In addition, the role of gully erosion in triggering landslides has also been studied. Two main periods have been distinguished (until 1960 and 1961-2012) for assessing major characteristics of land degradation. The results show that total gully area in the Chioara catchment is 66.4 ha excepting for the ephemeral gullies, and areas occupied by gullies from the five study sub-catchments (2334 ha) account for two-thirds. Total length of the main gully network in the entire catchment is 33.2 km from which the five sub-catchments account for 71 %. The mean gully density of 1.11 km km supports the evidence that here gullying is the major environmental threat. Half of the gully areal growth and three-quarters of the new landslide area occurred over the 1961-2012 period. Delayed deforestation peaking during 1830-1930 and land conversion to arable use resulted in severe soil erosion, high aggradation along the non-gullied valley bottoms, and severe gullying. The average gully head retreat rate over the last two centuries from four trunk continuous gullies is 14 m year, and the sediment yield from gullying only accounted for 54-69 % of the sediment mass produced by water erosion. The evolution of gullies is linked to major land-use changes in the study area. Despite a decreasing tendency of gullying and catchment area over the last half century, gullying still remains problematically high in East Romania. [ABSTRACT FROM AUTHOR]

This article presents a field-based method to assess site- and rainfall-specific runoff coefficients to be expected for a given period of the year. The method is applied to recognize soil uses/covers leading to reduced runoff water supply of gullies in Kinshasa. The computation of the runoff coefficient needs an infiltration envelope, established on site during a period of interest, and a local pluviogram decomposed in pluviophases. Rainfall simulation is carried out in 35 representative urban sites located in gully runon areas to establish a site-specific infiltration envelope. The runoff coefficient of the 35 sites is calculated for 25 geomorphologically active rains recorded between 1975 and 2012. The results show that several site-specific characteristics control runoff coefficient. The first factor is the over-compaction of the soil. Earthen roads show a runoff coefficient of 96.0 %. The second factor is the presence of a lichen seal. Bare loose soil only colonized by a lichen seal shows a runoff coefficient of 40.7 %. For the other sites, the runoff coefficient is inversely proportional to the percentage of vegetation soil cover, a normally compacted bare soil having a runoff coefficient of up to 30 %, parcels with high grass or cultures providing complete coverage showing no runoff at all. However, mowed lawns develop an impervious root mat close to the surface and, therefore, do not follow this rule: They quickly produce runoff similar to the bare and compacted surfaces. Finally, the factor slope gradient is involved. The differences due to vegetation cover disappear gradually with decreasing slope. Below a slope gradient of 0.08 m m, the runoff coefficient is null on a bare surface. Currently, the critical rainfall for gullying in the high town of Kinshasa is 24.9 mm with a mean intensity of 21.8 mm h. Roads generate by far most runoff and, therefore, are considered as the primary reason for gullying. The other soil uses lead most of the time to much smaller runoff coefficients, but their relative contribution to the supply of gullies grows with rainfall increase in height and intensity. The results provide material for gully management and adaptation strategies and open perspectives for the development of an early warning system in the region of Kinshasa. The method shows potential for being applied in other urbanized environments. [ABSTRACT FROM AUTHOR]

Land degradation has been recognized as an important environmental threat in the Moldavian Plateau of eastern Romania. The cumulated action of natural factors, especially the coupling of the Kersonian sandy-clayey facies and the hilly fragmentation as well as anthropogenic ones resulted in triggering degradation processes, especially soil erosion, gullying and landslides. In addition, another issue of interest is the reservoir sedimentation. Land with slopes over 5% is subjected to soil erosion with different intensities and it represents the process with the highest extension. Landslides represent the most relevant geomorphological process, affecting particularly the cuesta fronts and amounting up to 34.6 % of the study area. Locally, where in the bedrock appear loose sandy and sandyloamy layers, numerous valley-bottom gullies and valley-side gullies have developed, some with an impressive growth. Even if through soil erosion, gullying and landslides are carrying significant quantities of solid material to the base of slopes, the average rate of sedimentation in reservoirs remains relatively low. [ABSTRACT FROM AUTHOR]

Abstract: Bardenas Reales badlands are located in the middle-western sector of the Ebro Depression, northern Spain. This consists of a big erosional depression with deeply dissected valley bounded by steep slopes. Labile argillaceous bedrock, scarce high intensity rainfall, and high temperatures, make erosion the dominant morphogenetic process. Several erosion processes operate in the Bardenas Reales: rilling, gullying, piping and mass movements. The relative role played by these processes on the morphogenesis is largely controlled by physico-chemical properties of the materials and climatic conditions. Precipitation distribution over the year controls the development of mass movements, whereas regolith physical–chemical properties favor piping, gullying and rilling during the rainfall maxima. Soil erodibility in this area is clearly controlled by the sodium content and the presence of swelling clays. These factors determine the distribution and appearance of piping processes. Cracking in Holocene clay deposits, devoid of swelling clays, is related to high sodium content that confers a dispersive character. Clay dispersion causes loss of cohesion favoring piping. In the rainfall maxima soil loss is significant and controlled by precipitation amount and maximum intensity. Conversely, during periods of cyclonic rain erosion is scarce and mass movements are the dominant process. In the slopes underlain by Tertiary mudstones, mud flows are frequent during the winter months. In winter time, when rains are of low intensity and evapotranspiration is limited, infiltration through cracks is high. Consequently water content in the regolith may increase until the plastic limit is reached. Under these conditions and due to the high gradient of the slopes (34°), shear strength is surpassed and the clay material is able to slide and flow. [Copyright &y& Elsevier]

Abstract: A strategy for use of vegetation to control soil erosion has been developed that is spatially targeted at hotspots and flow pathways in the landscape. It is based on the premise that most of the soil erosion in semi-arid areas is by water erosion along specific flow lines. Soil is removed from fields and transported downslope and into channels if the connectivity of flow and sediment pathways is high, causing offsite problems as well as loss of agricultural productivity. Vegetation can reduce that connectivity by decreasing erosion and increasing sedimentation. The research combines mapping and analysis of the connectivity pathways and erosion hotspots with analysis of the most effective indigenous plants to control erosion and suited to the particular landscape position and environment. The crucial innovative element is the combination of physical process understanding with plant ecology, and its spatial application. The scheme has been developed by research in the driest part of the European Mediterranean region, in SE Spain, and examples of application strategies are illustrated. It is particularly suited to upland rain-fed agricultural areas on soft rocks, which are highly vulnerable to land degradation. Recommendations are provided on locations for planting or encouraging vegetation growth and on suitable species. The spatially targeted strategies apply vegetation to the critical locations to intervene in the pathways and this minimal intervention approach still allows cultivation of fields. The methods proposed can form the basis for sustainable catchment management to combat soil erosion and desertification. [Copyright &y& Elsevier]

Abstract: Slope incision and subsequent development of rills, gullies and channels are responsible for significant soil losses and are often irreversible with very high restoration costs particularly in semiarid environments. The location of potential areas of erosion where these processes occur is vital to land management and conservation. The study of the relationship between the local slope (S) and the drainage area (A) through the geomorphological relationship S =αA b, combined with hydrologic simulation models, has proved to be appropriate for the identification and characterisation of potential areas of incision, especially when it takes into account the spatial distribution of soil properties and the evolution of hydrological processes. However, physical properties of soil, digital elevation models (DEMs) and flow algorithms used may affect the results. This study employs a distributed, physically-based hydrological model to evaluate the infiltration–runoff relationships and their influence on selecting critical area from three DEMs with different resolutions. The results show a significant scale effect on flow distribution and the location of threshold points on slopes. The results obtained from a 30-m DEM significantly differ from those obtained from 10 and 5-m DEMs because the former was unable to capture the spatial variability of geomorphic processes. The selected set of critical points shows high S–A correlations for different values of critical shear stress. The physical model confirmed the dominance of surface runoff in the study site and was validated from field identification of erosion risk areas, although for incision areas <2ha, an appreciable error remains in relation to the calculation algorithm used for the drainage network and DEM resolution. [Copyright &y& Elsevier]

Investigations of sediment transfer in upland catchments are rarely conducted over a sustained period of time, consequently a full understanding of the changing nature of sediment supply, storage and yield is often lacking. Three recent sediment budget studies from the Wet Swine Gill headwater catchment in the Lake District, Northern England, UK (a 0.65 km2, first-order tributary), provide evidence of changes in sediment transfer dynamics over the period 2002–2008. The first sediment budget in 2002 describes the impact of a hillslope debris slide and channelised debris flow event, where the former was the dominant budget component. The termination of the debris flow in the Wet Swine Gill channel meant that the vast majority of slide failure material was not transferred to the downstream fluvial system. However, subsequent modification of exposed hillslope sediment by post-event erosion processes and gully development resulted in ongoing erosion. A second sediment budget (June 2003–January 2004) demonstrated sediment yield downstream of the in-channel debris slide deposits far exceeds upstream fluvial sediment delivery by two orders of magnitude ( c. 4,000 kg and c. 20 kg, respectively). Erosion of sediment from the exposed hillslope failure scar ( c. 1300 kg) was less than channel erosion ( c. 3300 kg), and sediment transfers from both the hillslope and channel sediment sources are sensitive to high-magnitude, low-frequency trigger events including summer thunderstorms, and winter rainfall/ snow-melt events. However, linear regression analysis only demonstrates weak or insignificant relations between meteorological conditions and sediment yield. A final sediment budget in April 2008 shows the significance of both hillslope (inclusive of gullying) and channel erosion/ transfer processes over the six-year monitoring period. In this budget, like the first sediment budget, the hillslope system is marginally more dominant, and therefore demonstrates a further switch in the relative significance of hillslope and channel system components. When interpreting such findings the potential uncertainty in the budget components, particularly in the unmeasured residual components, should be considered, as the magnitude of the error can be large. These results suggest that contemporary event and post-event sediment flux in small headwater catchments are more complex than short-term investigations would initially suggest. Furthermore there is a clear need for continued, longer-term monitoring of sediment system dynamics and associated hydro-meteorological conditions, in order to develop understanding of how future climate change may impact upland sediment systems. [ABSTRACT FROM AUTHOR]

This paper deals with some human geomorphological aspects concerning the impact in the alpine area of the Southern Carpathians (Transylvanian Alps). After field investigations and taking into account the major effects of road building, military and mining activities, pasture and tourism activities in the geomorphological landscape we have the possibilities to present a distinct image of some relevant detailed situations. In our opinion the building of roads in the alpine area is by far the most dangerous way of intervention in the geomorphological landscape of the alpine area of the Southern Carpathians. The construction of these roads has altered the profile of the slope and new scarps have appeared. This situation associated with the vibrations induced by the traffic favours frost weathering, rock falling and rolling, coupled with the emergence of specific deposits and landforms (talus cones and scree) and, of course, with vertical and gully erosion, which is very typical of the area of soft rocks and soils. [ABSTRACT FROM AUTHOR]

A survey of valley fills in south-facing combes (headwater valleys) along the south side of the Exmoor massif revealed an anomalously deep infill in one valley. This infill of up to 5 m depth had been gullied revealing a complex stratigraphy. Studies of the stratigraphy, clast orientation and shape suggested several accumulation episodes under different environmental conditions commencing in a periglacial climatic regime. Later units included sandy silts which can be dated using optically stimulated luminescence (OSL) of quartz grains. The OSL dates, indicate that the inter-gravel silts accumulated in two periods, the Romano-British period and the 16th–17th centuries AD. A survey of the very small valley catchment revealed a linear trench of a type associated with early iron mining. Given the anomalously high volume of accumulated sediment from such a small catchment and evidence of mining on the slope above the site, the geomorphic mechanism is almost certainly the downslope transport of mining debris from the slope to the valley floor. This study suggests that the systematic survey of headwater valleys in metalliferous uplands may be one way of locating areas of early mining activity and that such deposits could provide a chronology of working and abandonment. [ABSTRACT FROM AUTHOR]

Abstract: In the Solway Firth — Morecambe Bay region of Great Britain there is evidence for heightened hillslope instability during the late Holocene (after 3000 cal. BP). Little or no hillslope geomorphic activity has been identified occurring during the early Holocene, but there is abundant evidence for late Holocene hillslope erosion (gullying) and associated alluvial fan and valley floor deposition. Interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500–2200, 1300–1000, 1000–800 and 500 cal. BP. Both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds: and palaeoecological data on climatic change (bog surface wetness) and human impact (pollen), together with archaeological and documentary evidence of landscape history, provide a context for addressing the causes of late Holocene geomorphic instability. High magnitude storm events are the primary agent responsible for gully incision, but neither such events nor cooler/wetter climatic episodes appear to have produced gully systems in the region before 3000 cal. BP. Increased gullying after 2500–2200 cal. BP coincides with population expansion during Iron Age and Romano-British times. The widespread and extensive gullying after 1300–1000 cal. BP and after 1000–800 cal. BP coincides with periods of population expansion and a growing rural economy identified during Norse times, 9–10th centuries AD, and during the Medieval Period, 12–13th centuries AD. These periods were separated by a downturn associated with the ‘harrying of the north’ AD 1069 to 1070. The gullying episode after 500 cal. BP also coincides with increased anthropogenic pressure on the uplands, with population growth and agricultural expansion after AD 1500 following 150 years of malaise caused by livestock and human (the Black Death) plagues, poor harvests and conflicts on the Scottish/English border. The increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late Holocene, and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events. In particular, the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion, and the hillslope gullying record in the region, therefore, contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape. [Copyright &y& Elsevier]

Abstract: Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to define the process-based gully development by providing quantitative information from long-term field measurements in small catchments. Three main areas of monitoring gullies were explored: aerial photographs of flights in 1960 and 1970, classical leveling and repeated survey through a particular close stakes grid after 1980. The Caesium-137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development. Most of the discontinuous gullies exhibit both proper gullying, mainly if not exclusively by gully head advance, and aggradation of the gully basin floor. Results indicated that the mean gully head retreat was 0.92 m year−1 and the mean areal gully growth was 17.0 m2 year−1. Both values indicate a slow erosion rate for this area. The average annual regime of gullying is pulsatory, one that is best described by great fluctuations. Conventional measurements on sedimentation over the period 1987–1997 indicate a higher rate of aggradation in the upper half of the gully floor. Information on the Caesium-137 depth profile was used to provide estimates of a mean sedimentation rate of 4.4 cm year−1 over the period 1963–1996 and 2.5 cm year−1 after 1986 for the short successive discontinuous gullies. A new classification of the discontinuous gullies based on two criteria, respectively, the field patterns and the rate of aggradation within the gully basin floor was established. For continuous gullies, linear gully head retreat, areal gully growth and eroded material rates were quantified for three periods (1961–1970, 1971–1980 and 1981–1990). Results indicate that gully erosion has decreased since 1960. This gullying decline is due to the rainfall distribution, and the increased influence of soil conservation practices. The mean gully head retreat of 12.5 m year−1 between 1961–1990 was accompanied by a mean areal gully growth of 366.8 m2 year−1 and a mean erosion rate of 4168 t year−1. As with discontinuous gullies, continuous gullies showed pulsatory development. The critical period for gullying over 1981–1996 covers 4 months from Mid March to Mid July in an area with mean annual precipitation around 500 mm. Another main finding of this 16-year stationary monitoring was that 57% of the total gullying occurred during the cold season, with the remainder during the warm season. Of the total gully growth, 66% results from only four years (1981, 1988, 1991 and 1996), when a greater amount of precipitation fell. [Copyright &y& Elsevier]

Abstract: When rain forest is logged, rills and gullies are often initiated on heavily disturbed and compacted terrain components; whether and for how long they continue to enlarge following logging is critical as regards the recovery and sustainability of the regenerating forest. This paper examines these two issues in logged rain forest in northeastern Borneo. Results are presented of an investigation into how soil erosion rates and surface topography varies in selectively logged forests at different stages of regeneration (up to 15 years after logging) in Danum Valley, eastern Sabah, Malaysia. Measurements were made of changes in ground level and surface roughness at over 100 transect sites over periods of 1–15 years using the erosion bridge (microprofiler) technique. In the complex mosaic of the post-logging regenerating forest, attention focused on key features, notably abandoned logging tracks, gullies, heavily disturbed or compacted areas and road-related landslides and comparisons are made with primary forest terrain. The role of extreme rainstorms in controlling the temporal pattern of post-logging erosion in both regenerating and primary forest is demonstrated. The different situations in which rills and gullies initiated during or following logging enlarge or disappear in post-logging terrain are highlighted. The implications of the results for slope evolution and sustainable rain-forest management policies are briefly considered. [Copyright &y& Elsevier]

Gullying is a significant process in the long-term dynamics and evolution of both natural and rehabilitated (i.e. post-mining) landscapes. From a landscape management perspective it is important that we understand gully initiation and development, as it is well recognized that catchment disturbance can result in the development of gullies that can be very difficult to rehabilitate. This study examines gully position using geomorphic statistics relating to features such as depth, width and length in a catchment undisturbed by European activity in the Northern Territory, Australia. The results demonstrate that gullying occurs throughout the catchment and that a slope-area threshold does not exist and that gully position broadly follows the catchment area-slope relationship. Simple relationships relating catchment area and slope to gully depth, width and length provide poor results, despite these relationships having been found to apply for ephemeral gullies in cropland. The results suggest that gully initiation thresholds are low as a result of an enhanced fire regime. A threshold model for gully position that uses catchment area and slope to switch between gully and hillslope was evaluated and found broadly to capture gully position. [ABSTRACT FROM AUTHOR]

Headwater streams comprise 60 to 80 percent of the cumulative length of river networks. En hilly to mountainous terrain, they reflect a mix of hilislope and channel processes because of their close proximity to sediment source areas. Their morphology is an assemblage of residual soils, landslide deposits, wood, boulders, thin patches of poorly sorted alluvium, and stretches of bedrock. Longitudinal profiles of these channels are strongly influenced by steps created by sediment deposits, large wood, and boulders. Due to the combination of small drainage area, stepped shallow gradient, large roughness elements, and cohesive sediments, headwater streams typically transport little sediment or coarse wood debris by fluvial processes. Consequently, headwaters act as sediment reservoirs for periods spanning decades to centuries. The accumulated sediment and wood may be episodically evacuated by debris flows, debris floods, or gully erosion and transported to larger channels. In mountain environments, these processes deliver significant amounts of materials that form riverine habitats in larger channels. In managed steepland forests, accelerated rates of landslides and debris flows resulting from the harvest of headwater forests have the potential to seriously impact the morphology of headwater streams and downstream resources. [ABSTRACT FROM AUTHOR]

For southeastern Australia, arrival of the First Fleet in 1788 raises similar issues in environmental history as the 1492 landing of Columbus in the Americas. But Anglo-Australian settlement is younger and better documented, both in terms of scientific proxy data and historical sources, which include data on stocking rates that generally were light. Environmental concerns were voiced early, and a lively debate continues both among professionals and the lay public, with Australian geographers playing a major academic and applied role. This article addresses environmental degradation often attributed to early pastoralism (and implicit clearance) in the Tablelands of New South Wales. Methods include: (1) comparison of well-reported travel itineraries of 1817–1833 with modern land cover and stream channels; (2) critical reviews of high-resolution pollen profiles and the issues of Aboriginal vs. Anglo-Australian fire ecology; and (3) identification of soil erosion and gullying both before and after Anglo-Australian intrusion. The results indicate that (a) land cover of the Tablelands is little changed since prior to Contact, although some species are less common, while invasive genera of legumes have modified the ground cover; (b) the charcoal trace in pollen profiles prior to Contact supports an ecological impact of regular Aboriginal burning and rare, catastrophic fires; and (c) most stream channels were already entrenched (“gullied”) well before 1840, with repeated cut-and-fill cycles during the late Holocene, but before Contact. Land impairment has not been a major problem on the Tablelands, although the last two centuries have experienced cumulative and complex environmental change. This unexpected empirical picture suggests that, until high-technology intervention, increasing periodicity/magnitude of extreme drought/precipitation events had been the overriding trend in interior New South Wales, perhaps reinforced by burning. There is no support for an apocalyptic model of colonial environmental history. [ABSTRACT FROM AUTHOR]

Most discontinuous gullies overlying the almost tabular sedimentary strata of the Moldavian Plateau, Eastern Romania exhibit gullying by gully head advance and aggradation of the gully basin floor. According to Heede [Z. Geomorphol. N. F. 18 (1974) 260] the shape factor of the gullies, relating maximum to minimum depth, expresses both channel shape and hydraulic efficiency of channels.Based on a geomorphic approach, this paper shows that a better understanding of gully hydraulic efficiency may be assessed by another shape factor obtained by relating present to filled gully cross-section. A value of 1.0 for this shape factor, Sp/Sf, represents the threshold of hydraulic efficiency. Strong relationships were established between the shape factor and gully length. In addition, an appropriate substitute expressed as the ratio of gully bottom width (Wb) to gully top width (Wt) was found, which is easy to apply and very fast to determine in the field. [Copyright &y& Elsevier]

This paper presents a review of the coupling concept in fluvial geomorphology, based mainly on previously published work. Coupling mechanisms link the components of the fluvial system, controlling sediment transport down the system and the propagation of the effects of base-level change up the system. They can be viewed at several scales: at the local scale involving within-hillslope coupling, hillslope-to-channel coupling, and within-channels, tributary junction and reach-to-reach coupling. At larger scales, coupling can be considered as zonal coupling, between major zones of the system or as regional coupling, relating to complete drainage basins. These trends are illustrated particularly by the examples of hillslope-to-channel coupling in the Howgill Fells, northwest England, badland systems in southeast Spain, alluvial fans in Spain, USA and UAE, and base-level-induced dissection of Neogene sedimentary basins in southeast Spain. As the spatial scales increase, so do the timescales involved. Effective temporal scales relate to magnitude and frequency characteristics, recovery time and propagation time, the relative importance changing with the spatial scale. For downsystem coupling at the local scale, the first two are important, with propagation time increasing in importance in larger systems, especially in those involving upsystem coupling related to base-level change. The effective timescales range from the individual event, with a return period of decades, through decadal to century timescales for downsystem coupling, to tens to hundreds of thousands of years for the basinwide response to base-level change. The effective timescales influence the relative importance of factors controlling landform development. [Copyright &y& Elsevier]