Badland Development Research Articles

Timing of gully development in a structurally controlled badland landscape, western Turkey

The development of badlands at a global scale has become an increasingly relevant research topic in various earth science disciplines with respect to climate change and extensive erosion over the past few decades. Not only understanding badland forming processes but also investigating the potential causes and timing of badlands at a spatio-temporal scale is of great importance to unravel the genesis of badlands. To address these key aspects, this work focuses on a multi-method study in a Mediterranean badland landscape, Kula Badlands, western Turkey, exposed in two tributary catchments of the Gediz river. The Kula Badlands is recognised with its dense gully network deeply incised into fine grain and weakly consolidated Miocene and Quaternary sediments. These badlands are known to have developed within the extensional tectonic regime of a mini-graben system. However, the genesis, timing and incision history of the gully and badland development of the Kula Badlands require further investigation. In this work, timing and behaviour of gully erosion and sedimentation are studied with age control using appropriate luminescence and radiocarbon dating methods combined with geological and geomorphological observations. Sedimentation pattern and age results demonstrate a staircase-like form resembling river terraces in badland gullies. Sediment burial ages of badland deposits show an estimated age range of 140 ka to 0.5 ka. An accelerated incision is observed during the mid-Holocene with alternating erosion and sedimentation waves in response to upstream erosion. This period coincides with increased human activity in the area. Although, an apparent link between the timing of the preserved deposition and climate change could not be observed. A volcanic damming and subsequent breaching, and an interplay between tectonics and climate are likely to have triggered and accelerated the badland erosion and sedimentation activity within the spatial gully network pattern along the fault lines.

Assessing landscape features and geomorphic processes influencing sediment dynamics in a geomorphologically highly active Mediterranean agroecosystem: The upper Val d'Arda case study (Northern Apennines, Italy)

The management of Mediterranean Agroecosystems is crucial to prevent or mitigate sediment-related threats like soil erosion, water quality issues, and reservoir sedimentation. Hence, the identification of type, extent, and location of sediment sources and sinks, in relation to geological and landscape features, is a key prerequisite for identifying erosion hot spot areas and assessing sediment dynamics at catchment scale. This study was carried out in the upper Val d'Arda catchment (Northern Apennines, Italy). We applied geomorphological field mapping together with multi-temporal photointerpretation, GIS-based hydrological modelling, terrain analysis and photogrammetry. Our approach was aimed at exploring the main landscape features, as well as identifying the variety of processes influencing sediment dynamics. In this poorly studied area, we identified a high heterogeneity in terms of type and extent of sediment sources and related processes. Landslides are the most common processes contributing to the sediment yield. Their morphogenesis, extent and location are controlled mainly by lithology and topography. Large ancient earthflows have been the most important geomorphic factor in shaping the landscape, strongly influencing the surficial drainage pattern and the morphological evolution of the main fluvial systems. Upland rill-interrill erosion is another main sediment source, particularly on arable lands. Piping and gullying locally contribute to the development of badlands, and have a high potential for soil loss and sediment production. Finally, fluvial processes significantly contribute to the sediment yield with several active fluvial erosion scarps and bank erosion source areas. Alluvial sediments are locally stored in transient landforms such as bars or more permanent sinks such as floodplains or river terraces. Our study shows that an integrated methodology based on fieldwork, geomorphological mapping, GIS applications and proximal sensing methods is an effective approach to characterize complex geomorphic systems in the Northern Apennines.

Structurally Controlled Landscape Evolution in Kula Badlands, Western Turkey

Badlands are extensively eroded landscapes consisting of weakly consolidated deposits within highly dense drainage systems. Their controlling and shaping factors can differ in relation to various internal and external conditions and processes that are not always well understood. This study focuses on the development of a badland landscape affecting Miocene and Quaternary sand-clay sediments in the extensional tectonic regime of Western Turkey with a multidisciplinary approach. The area between Kula and Selendi towns exhibits a badland topography with extensively eroded surface features, deepened gullies within poorly consolidated, sand clay-sized sediments. The results of structural field mapping and morphometric analyses using a 5 m resolution DEM to study the role of structural control in the development of badlands are presented in this study. Field data analysis supported by the quantitative assessment of longitudinal gully profiles illustrates the role of pre-existing structures as faults, their orientation and geometry in net erosion-sedimentation and the development of deepened gully networks. Representative illustrations, field photographs and block diagrams are presented to show the relationship between the rock structure and badland landscape. The connection between the extensional tectonics, erosional dynamics and geomorphology point to a structurally-controlled landscape in the Kula badlands in Western Turkey.

Regional distribution and characteristics of major badland landscapes in Turkey

Badlands are extremely rugged, outstanding landscapes that can be seen in all ice-free climate regions over erosion-susceptible unconsolidated materials, and they have drawn attention with their spectacular and iconic forms. Unlike nearly all badlands researches conducted at the experimental site and watershed scale, so far, the broader-scale evaluation has been neglected in the analysis of badland distribution, characteristics, and dynamics. Our study provides an integrative new insight into badland landscapes by investigating the distribution, characteristics and controlling factors of Turkish badlands on a broad, regional scale. We inventoried Turkish badlands using aerial imagery and studied their distribution using K-means clustering, an unsupervised machine learning algorithm, based on a set of major conditional geo-environmental factors that control the regional distribution and characteristics of badlands, including tectonics, lithology, topography, climate, and vegetation. Here, we identified, a total of 4494 km2 of badland areas which are non-uniformly distributed across Turkey, substantially clustered in the Central Anatolian Plateau (CAP). According to our regional analyses, we have determined a total of five badland regions comprising three major types classified as Semi-arid, Mediterranean, and Montane (humid), together with two transitional types in-between the Semi-arid and Montane badland regions. Our results indicate that temperature seasonality (0.83), mean annual precipitation (0.83), and precipitation seasonality (0.76) are predominantly assigned to the badlands clusters. The clastic rocks are revealed as the most crucial and inevitable factor for the development of Turkish badlands, which are represented in a wide geologic time-scale (Cretaceous to Quaternary) and diverse lithological units (i.e., lacustrine, volcaniclastics, and terrestrial). Neogene and Paleogene terrestrial clastics (77 %) constitute the majority of the lithologic settings of these badland landscapes. The active and complex tectonic history of Turkey has portrayed the fundamental frame of the identified badland regions, by providing a susceptible environment (i.e., development of sedimentary basins) and promoting badland development through successive base-level changes. Furthermore, tectonically-modulated (i.e., formation of orogenic belts, and uplifting of CAP) climate dynamics outline the distribution pattern and differentiation of the regional characteristics of badlands in Turkey. Overall, our regional-scale approach to badland mapping and regional synthesis may decipher not only the tectonic and climatic conditions of the identified badlands regions, but it may also contribute to the implementation of future effective strategies for the detection and mapping of erosion susceptible and high sediment flux areas in very broad spatial contexts of similar unexplored territories.

Hydrogeomorphic assessment of badlands in part of the Mandakini River watershed, Chitrakoot, India

Badlands are a hydrogeomorphological feature with operative processes leading to intense erosion. This study utilizes the morphometric methods with the help of remote sensing data in a GIS environment to determine the characteristics of the badlands of Mandakini River watershed and their interpretation to explore the factors responsible for the formation of the typical landforms. Objective interpretation of morphometric data of badlands with the help of statistical Pearson’s correlation coefficient (PCC) and dendrogram cluster may be made to emphasize the controlling factors. The morphometric parameters like the total number of streams (Nu), bifurcation ratio (Rb), drainage density (Dd), drainage frequency (Fs), drainage texture (Dt), and infiltration number (If) and their correlation in the study area plays a significant role in the advancement of rills and gullies. In the present area, the total number of streams (Nu) is very significantly related with the lengths of the first-order (L1), the second-order (L2), and the third-order streams (L3) along with the total stream length of all orders (Lu) in the third-order and the fourth-order sub-watersheds. Bifurcation ratio (Rb) is strongly correlated with L1, L2, L3, L4, and drainage texture (Dt) in the fourth-order sub-watershed. These correlations insinuate a tectonic influence in the basin and show an ultrafine drainage texture that ultimately forms badland topography. The relation between Dd-Lg-C-If-Rn produces a self-enhancing system of badland development, which promotes erosion in the area under study. These correlations provide a well-figured observation of the sub-watershed that, due to the increase in infiltration number (If), the drainage density (Dd) also increases, which leads to enhancement of channel cutting and erosion rates (low Lg and C value). This correlation coefficient of Rn is moderately low, indicating a single storey type of badlands. The badlands seem to have formed owing to setting up of self-enhancing erosive system on paleo wetlands, as evidenced by the presence of calcretes. Calcretes have been related to the presence of wetlands’ conditions. These have been related to fall in water levels, therefore, indicating much higher water levels nearly close to ground surfaces before setting up badlands conditions. Thus, the badlands which have shallow calcretes horizons can be said to have been wetlands in the past.

Cause-and-effect in Mediterranean erosion: The role of humans and climate upon Holocene sediment flux into a central Anatolian lake catchment

The debate in historical geomorphological studies about the causes of erosion in regions such as the Mediterranean has been long-standing. The relative roles of climate change and human impacts can be difficult to disentangle in the absence of highly resolved chronologies. Here we reconstruct the erosion history of a small lake catchment in central Anatolia, located on the edge of one of the Mediterranean's most iconic badland landscapes in Cappadocia. Because these lake sediments are annually laminated, precisely dating clastic inwash layers and calculating recurrence intervals and flux rates is possible. Lake cores have been analysed for μXRF elemental geochemistry and via thin sections, along with proxies for hydroclimate (oxygen isotopes) and land cover (pollen). Peaks in titanium, along with other detrital elements, and changes in clastic layers indicate increased sediment influx into Nar Lake between 9300 and 8000 cal BP (ceramic Neolithic, when obsidian mining took place nearby) and again, more importantly, during the last 2500 years (Iron Age to modern), the latter exhibiting three phases of enhanced catchment erosion. Multiproxy comparisons show that these phases were related primarily to periods of increased human impact on vegetation and soils around the lake. Most sediment influx has been in the form of turbidites, linked to the presence of a fan delta at the lake edge, although this store does not appear to have significantly delayed sediment delivery from eroding hillslopes to the lake bed. The marked increase in detrital influx during the late Holocene implies that badland development in the lake catchment is recent and largely anthropogenic, rather than ancient and of climatic causation, and probably involving stream capture. The record also shows that sediment influx diminished markedly at times when human land use disintensified, which in turn indicates that hillslope degradation is reversible with appropriate land management.

Badland susceptibility assessment in Volterra municipality (Tuscany, Italy) by means of GIS and statistical analysis

Badlands can be defined as complex and peculiar types of erosional formations that develop in clayey environments and are mainly favoured by lithological and topographic features, as well as by markedly seasonal climate. This work aims at assessing badland susceptibility in Volterra municipality located in Tuscany region (Italy) by means of bivariate statistical analysis implemented in a geographic information system. The Volterra municipality is affected by intense soil erosion processes, including rill and gully erosion usually turned out as badland forms, mostly occurring on Pliocene–Pleistocene clayey sediments. Firstly, an inventory of 234 badland areas was produced on the basis of an available pre-existing database, integrated with the interpretation of aerial photographs and supported by a field survey. Badlands were distinguished in type A and type B, according to different evolutional stage, vegetation presence and consequently different landforms. Then, nine geoenvironmental factors supposed to be predisposing for badland occurrence were chosen and combined with the spatial frequency of badland areas derived from the inventory, through Information Value Statistic approach. The result was a badland susceptibility map that highlights a strong control of lithology, slope gradient and land use in conditioning badland development in the investigated area. The effectiveness of the performed model was demonstrated by a validation test computed through a receiver operating characteristics analysis. The outcomes of this work provide an updated badland database that is useful for soil erosion management and further land-use planning within the Volterra municipality.

Assessing soil erosion hazard in a key badland area of Central Italy

In this work, an integrated methodology was applied to assess the water erosion hazard in Upper Orcia Valley, an area of Southern Tuscany (Italy), greatly affected by severe denudation processes, that caused the development of widespread badlands. Prediction of areas prone to calanchi badland development was carried out by applying a susceptibility assessment method based on conditional statistical analysis, preceded by a bivariate statistical analysis aimed at selecting the most influential causal factors of erosion. Water erosion rates at badland sites were estimated by means of an empirical statistical method, implemented to evaluate the erosion intensity (Tu denudation index) and based on some geomorphic parameters as independent variables. This methodology allows associating the denudation intensity to the spatial prediction. The validation procedure, based on a random partition of calanchi badland areas, confirmed the efficiency of the spatial zonation of the erosion hazard values. Moreover, the comparison of the estimated erosion rates with the results of decadal investigations on denudation processes affecting the study area, performed by different monitoring methods, showed the effectiveness of the estimation model. These results allowed concluding that the proposed procedure represents a useful tool to be applicable for soil protection strategy planning in land management of Mediterranean areas characterized by similar morphoclimatic features, even when direct erosion rate measures are not available.

A 13‐year record of erosion on badland sites in the Karoo, South Africa

AbstractLand degradation in South Africa has been of concern for more than 100 years with both climate change and inappropriate land management (overgrazing) being proposed as primary drivers. However, there are few quantitative studies of degradation and, in particular, few of erosion by water. Badlands, taken here to be the landform which results from extreme erosion, have been notably neglected. We report on 13 consecutive years of erosion pin measurements of badland erosion on 10 study sites in the Sneeuberg uplands of the eastern Karoo in South Africa. The study sites are on Holocene colluvium which mantles footslopes. They have been subject to overgrazing for at least 100 years, c. 1850–1950. Currently they are lightly grazed by sheep. The area receives about 500 mm rainfall per year. The sites are remote, with only informal, farmer‐operated, daily raingauges nearby. The nearest sub‐daily raingauge is c. 55 km distant. Also we report on an analysis of the erosion pin data which focuses on establishing the origins and context of the badlands, including the relationship between study sites and adjacent valley‐bottom gully systems; compare erosion rates on our study sites with rates determined by erosion pins on other badland sites; and discuss the implications of these erosion rates for landscape development and off‐site impacts. Net erosion rates on the study sites are relatively high compared with global badland rates and range from 3.1 to 8.5 mm yr‐1 which may be extrapolated to 53 to 145 t ha yr‐1 (using a measured bulk density of 1.7 g cm‐3). However, comparisons with badland sites elsewhere are difficult because of different measuring methodologies, lithologies, climate and dominant processes. Erosion rates on the study sites are strongly influenced by rainfall amounts and, in particular, by daily rainfall events which exceed ~10 mm: this is the threshold intensity at which runoff has been observed to commence on badlands. Of significance, but of lesser influence, is weathering, mainly by wetting and drying: this prepares bare surfaces for erosion. However, questions remain regarding the role of site characteristics, and of processes at each site, in determining between‐site differences in erosion rate. Crude extrapolation of current rates of erosion, in conjunction with depths of incision into the badlands, suggests that badland development started around 200 years ago, probably as a response to the introduction of European‐style stock farming which resulted in overgrazing. We assume, but cannot quantify, the additional influence of periods of drought and burning in the erosional history of the area. Intermittent connection of these badlands to valley‐bottom gullies and therefore to small farm dams and ultimately to large water storage reservoirs increases their impact on local water resources. Copyright © 2015 John Wiley & Sons, Ltd.

Geomorphological evolution of badlands based on the dynamics of palaeo-channels and their implications

The badlands along the lower Chambal valley represent the worst case of water erosion in India. These badlands are believed to have developed due to neo-tectonic activities and, probably, strengthening of southwest monsoon in late Pleistocene–Holocene. Due to neo-tectonic activities, the Chambal River has undergone many changes before reaching to its present planform. This study reports palaeo-channels on the Chambal River’s right flank along its lower reaches. Salient features of the palaeo-channels and their relation to present spatial pattern of badlands are studied. These palaeo-channels have significantly influenced the development of badlands along the lower Chambal River and have given them distinct and conspicuous spatial patterns. In the light of the evidences, a modified schematic geomorphic evolution of badlands development is also proposed starting from a pre-incision scenario till the present day situation. A major modification in the proposed model is the multi-channel planform of the Chambal River before its incision.

Una revisión de los procesos de sufosión o piping en España

The papers referred to the development of piping processes in Spain are reviewed. Most of papers are focused on semi-arid environments of the Ebro Depression and South-East Spain, where large collapses occur favouring the evolution of gullies. In many cases, piping is related to the presence of badlands. Piping is particularly relevant on soils and poorly consolidated materials on soft rocks (marls and lutites), with abundant expansive clays and high sodium content. The existence of strong hydraulic gradients (linked to bench-terracing of cultivated soils, or to gully incision) is a necessary factor. Many of the problems related to piping are generated in old cultivated fields or even in irrigated fields. In mountain areas the presence of subsurface drainage networks has been cited as a consequence of the presence of micro-mammals burrowing or dead roots, though they do not lead to the development of badlands.

Multivariate erosion risk assessment of lateritic badlands of Birbhum (West Bengal, India): A case study

Each geomorphic hazard involves a degree of risk which incorporates quantification of the probability that a hazard will be harmful. At present, the categorization of sub-watersheds into erosion risk is considered as the fundamental step to conserve the soil loss. Development of badlands over the laterites of Birbhum district is an indicative of excessive soil loss in the monsoonal wet-dry type of climate. Slope erosion and channel erosion have generated huge amount of sediment from the small watersheds during intense monsoonal rainfall (June–September). The adjoining areas of Rampurhat I Block, Birbhum (West Bengal) and Shikaripara Block, Dumka (Jharkhand) have lost the lateritic soil cover at a rate of 20–40 ton/ha/year (Sarkar et al. 2005). In order to estimate the progressive removal of soil particles from the gully-catchments of the above-mentioned area, different morphometric parameters, soil parameters, hydrologic parameters and empirical models are employed. Side by side, the study is carried out to categorize the gully-catchments into different magnitude of erosion risk using several multivariate statistical techniques.

CHANGING SEDIMENT YIELD AND SEDIMENT DYNAMICS IN THE KAROO UPLANDS, SOUTH AFRICA; POST‐EUROPEAN IMPACTS

ABSTRACTWe provide an overview of published results and a significant body of new data from an ongoing research programme designed to reconstruct sediment yields and sources in small (<60 km2) catchments in the Eastern Cape, South Africa over the last 150 years. Our analysis of four catchments has determined that sediment yield increased significantly in the latter half of the 20th century but that the exact timing of these increases was different in each of the four catchments. In two high altitude locations, sediment yield increases were not associated with a significant change in sediment source although, in one case, areas of former cultivation appear to have made a slightly greater contribution since the 1960s. In a third catchment, increases in sediment yield appear to have been driven by the development of badlands and by an increase in connectivity between the badlands and the main channel network in the 1960s. In the fourth catchment, increased connectivity between the main catchment and dam occurred as a result of the construction of a causeway to carry a main road and by the construction of culverts beneath the road. Occasional changes in sediment source have also been identified in the sedimentary record, but these were not linked directly to road construction. Research to date shows the complexity of sediment delivery in these semi‐arid catchment systems and emphasises the need to combine sediment yield with source ascription to better understand the dynamics of these systems. Copyright © 2012 John Wiley & Sons, Ltd.

RECONSTRUCTING RECENT LAND DEGRADATION IN THE SEMI‐ARID KAROO OF SOUTH AFRICA: A PALAEOECOLOGICAL STUDY AT COMPASSBERG, EASTERN CAPE

ABSTRACTThis paper forms part of an ongoing, multidisciplinary study of land degradation in the Eastern Cape, South Africa. A series of studies of erosion, runoff and the development of gullies, badlands and sediment delivery to small farm reservoirs in the Sneeuberg uplands have shown that the semi‐arid Karoo is vulnerable to soil erosion. Cereal cultivation and increased livestock numbers are thought to have played a major role in triggering erosion over the last 200 years. To test this assumption, we analysed pollen, non‐pollen palynomorphs and microscopic charcoal from sediments that have infilled one farm dam since the 1930s and which is located in the Sneeuberg uplands of the Eastern Cape. The results, supported by sediment source tracing, indicate that soil erosion was closely associated with agricultural activity. The reconstructions appear to be in agreement with historical documentary records. However, records of livestock stocking densities were found to be insufficiently detailed to enable direct matching against microfossil proxies for grazing, especially the coprophilous fungal spore, Sporormiella type. This study demonstrates the importance of combining sediment tracing techniques with palynological analyses to provide a more informed interpretation of land use changes as recorded by lake and reservoir sediments. Copyright © 2012 John Wiley & Sons, Ltd.

A reconstruction of historical changes in sediment sources, sediment transfer and sediment yield in a small, semi-arid Karoo catchment, semi-arid South Africa

Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.

Dendrochronological and geomorphological investigations to assess water erosion and mass wasting processes in the Apennines of Southern Tuscany (Italy)

Abstract The Tyrrhenian side of the Central Apennines is located in a lively geological context, in which uplift/denudation dynamics played a key role in landscape evolution. Intense water erosion and gravitational processes led to the development of spectacular badlands on the widespread clayey hillslopes. The Crete d'Arbia badlands (as part of the Crete Senesi of Southern Tuscany) represent one of the most beautiful examples of these landforms developed on Pliocene clays. On the other hand, these rapidly evolving landforms endanger the artistic heritage of the area, as with the Monte Oliveto Maggiore Abbey that was constructed on the top of a badland hillslope and confers additional value to the landscape. In the perspective of monitoring and reconstructing some significant phases of the relief evolution of this area an integrated approach has been used, which is based on dendrogeomorphology and geomorphological monitoring techniques. In particular, the correspondence between the data from dendrogeomorphological indicators and the measured denudation rates on badland hillslopes was tested. The sampling for dendrogeomorphological analysis has been performed in two stages on 45 trees of the Pinus pinea L. species, on hillslopes affected by soil creep and shallow landslides, in order to identify annual ring growth anomalies, compression wood and roots exposure. Trees' local behaviour is not homogeneous but some common trends have been detected on the basis of the anomaly index and compression wood. Since 1993 several monitoring stations at badland denudation “hot spots” have been equipped with erosion pins; quantitative data from monitoring stations, compared to pluviometric series, indicated critical phases of denudation that were supported by dendrochronological data. The integrated approach between dendrogeomorphology and geomorphological monitoring techniques allowed calibration of both tools in order to extend the analysis in the period preceding the field measurements. This kind of approach, capable of implementation in many contexts, could be particularly helpful in order to forecast the relief evolutionary trend.

Why Mississippi floods were expected

A combination of bad weather, ocean conditions and land development conspired to produce high waters.

Effect of precipitation on the geological development of badlands in arid regions

The main objective of this paper was to study the effect of precipitation on the geological development of badlands in arid regions. Field observations and laboratory investigations were carried out to characterize the surface soils of the Avonlea badlands in southern Saskatchewan, Canada, which is currently experiencing a rapid development in infrastructure. Three distinct surface sediments were identified: an upper slope of cemented sandstone, a mid-slope on weathered mudrock and a relatively flat basal pediment. Each of these soils reacts differently to rainfall events. Precipitation results in grain size reduction which, together with the consistency limits, explains the water sensitivity of the soils; the fines increased by 16% in the cemented sandstone, 78% in the weathered mudrock and 33% in the basal pediment. Erosion susceptibility was highest in the basal pediment (2% clays) followed by cemented sandstone (cementation by 6% active clays) and then by weathered mudrock (cohesion due to the 40% clay).

Geomorphological dynamics of subhumid mountain badland areas — weathering, hydrological and suspended sediment transport processes: A case study in the Araguás catchment (Central Pyrenees) and implications for altered hydroclimatic regimes

This study investigates the geomorphological dynamics of badland areas in the Araguás catchment (0.45 km2) in the Central Pyrenees. The genesis and development of badlands in the Central Pyrenees is favoured by the presence of Eocene marls and a markedly seasonal climate. The Araguás catchment has been monitored since 2004. Analysis of weathering processes and regolith dynamics showed that alternating freeze-thaw and wetting-drying cycles are the main causes of regolith development and weathering, and effectiveness and intensity of these processes is maximum in winter and summer. Evolution of the badland surfaces is related to regolith moisture level and temperature, closely associated with the season and slope exposure, which cause cyclical variations in regolith physical conditions. The most important effect associated with regolith dynamics is the temporal delay between maximum rainfall erosivity and variation in maximum surface runoff generation, reflected in seasonal differences in sediment transport. The dynamics of weathering and erosion processes affecting badland areas are the principal factors controlling geomorphological development, and the extreme hydrological and sedimentological responses of badlands are the main effects of such morphologies. From a hydrological point of view, badlands increase water production, and flood frequency relative to neighbouring areas; from a sedimentological point of view, suspended sediment transport from badland areas can reach amounts two or three orders of magnitude higher than other nearby environments. Given these results, possible responses of badland dynamics to altered hydroclimatic regime are briefly discussed.

Evidence from field-based studies of rates of soil erosion on degraded land in the central Karoo, South Africa

Degradation in Sneeuberg Region of the central Karoo, South Africa, is characterized by the development of badlands on the footslopes of upland areas and by gully systems in valley bottoms. Evidence from aerial photographs suggests that there has been a slight decrease in degraded areas between 1945 and 2002, although gully systems have increased in density, if not in length. Field measurements were carried out using a grid pattern of erosion pins at ten sites over a three-year period. On interfluves within existing degraded areas erosion continues at an average rate of 5.6 mm yr − 1 . On channels, footslopes, and sidewalls erosion rates are 2.6 mm, 4.7 mm and 16.7 mm respectively. The overall figure masks the high degree of cut and fill experienced within degraded areas. In channels, approximately eight times as much sediment is being moved compared to the overall loss at the end of 3 years. These figures indicate that the relief of most badland areas is decreasing. Erosion pin results are compared with losses from stones on pedestals and from the area around shrubs. There is evidence that rainfall has increased in amount and intensity over the last century which would promote erosion on existing bare ground. At the same time stock numbers have continued to decrease since a high point in the 1930s, reducing grazing pressure. This, coupled with the fact that most available colluvial footslopes are already degraded, may explain the overall decrease in the extent of degraded areas. However, monitoring results, observational evidence and sedimentation in dams indicate that badlands remain active and an important source of sediment.