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River Courses (river + course)
Selected AbstractsTectonics and quaternary evolution of the Northern Apennines watershed area (upper course of Arno and Tiber rivers, Italy)GEOLOGICAL JOURNAL, Issue 1 2009Marco Bonini Abstract This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary Tuscan-Romagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1,Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle,Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Variability and management patterns of range resources in the Baro River plain, EthiopiaAREA, Issue 1 2008Daniel Kassahun The biophysical environment of rangelands in the arid and semi-arid lowland parts of Africa is customarily viewed as a homogenous entity. Such notion has encouraged employing a blanket management approach. However, there are perceptible variations within them which necessitate site-specific range management. This study has attempted to identify the variability of soil and forage attributes and assess the existing management practices of those resources in the Baro River plain, Ethiopia. Sample transects, representing pre- and post-fire conditions, were used to collect composite soil samples and vegetation attributes. Alongside the physical survey, a household survey was undertaken to validate the laboratory-generated information. The result showed significant differences of soil and forage attributes among different management regimes, distances from river course and dominant cover types. In general, the distribution of soil nutrients showed a ,distance decay effect', while the distribution of pH showed the reverse pattern. Application of heavy fire load and congested grazing are the principal range management related factors. About 80 per cent of sample pastoralists employ heavy fire without due consideration for the sustainability of the range resource and without considering the local variability. Recognition of site-specific information is the key to effective management of range resources in the study area. [source] Post-European settlement response gradients of river sensitivity and recovery across the upper Hunter catchment, AustraliaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2009Kirstie Fryirs Abstract Most analyses of river adjustment have focused on parts of catchments where metamorphosis has occurred. This provides a non-representative view of river responses to human-disturbance. Although many rivers have been subjected to systematic land-use change and disturbance, significant variability is evident in the form, extent and consequences of adjustment. This study documents the catchment-wide distribution of river sensitivity and adjustment in the upper Hunter catchment, New South Wales, Australia in the period since European settlement. The spatial distribution and timing of lateral, vertical and wholesale river adjustments are used to assess river sensitivity to change. The type and pattern of rivers, influenced largely by valley setting, have induced a fragmented pattern of river adjustment in the upper Hunter catchment. Adjustments have been largely non-uniform and localized, reflecting the predominance of bedrock-controlled rivers which have limited capacity to adjust and are resilient to change. Less than 20% of river courses have experienced metamorphosis. Phases of reach-scale geomorphic adjustment to human disturbance are characterized as a gradient of primary, secondary and tertiary responses. In general terms, primary responses such as cutoffs or straightening were followed by secondary responses such as channel expansion. These secondary responses occurred between 50,70 years after initial disturbance. A subsequent tertiary phase of river recovery, denoted as a transition from predominantly erosional to predominantly depositional geomorphic processes such as channel contraction, occurred around 70,120 years after initial disturbance. Such responses are ongoing across much of the upper Hunter catchment. Copyright © 2009 John Wiley & Sons, Ltd. [source] The river domain: why are there more species halfway up the river?ECOGRAPHY, Issue 2 2006Robert R. Dunn Biologists have long noted higher levels of species diversity in the longitudinal middle-courses of river systems and have proposed many explanations. As a new explanation for this widespread pattern, we suggest that many middle-course peaks in richness may be, at least in part, a consequence of geometric constraints on the location of species' ranges along river courses, considering river headwaters and mouths as boundaries for the taxa considered. We demonstrate this extension of the mid-domain effect (MDE) to river systems for riparian plants along two rivers in Sweden, where a previous study found a middle-course peak in richness of natural (non-ruderal) species. We compare patterns of empirical richness of these species to null model predictions of species richness along the two river systems and to spatial patterns for six environmental variables (channel width, substrate fineness, substrate heterogeneity, ice scour, bank height, and bank area). In addition, we examine the independent prediction of mid-domain effects models that species with large ranges, because the location of their ranges is more constrained, are more likely to produce a mid-domain peak in richness than are species with small ranges. Species richness patterns of riparian plants were best predicted by models including both null model predictions and environmental variables. When species were divided into large-ranged and small-ranged groups, the mid-domain effect was more prominent and the null model predictions were a better fit to the empirical richness patterns of large-ranged species than those of small-ranged species. Our results suggest that the peak in riparian plant species richness in the middle courses of the rivers studied can be explained by an underlying mid-domain effect (driven by geometric constraints on large-ranged species), together with environmental effects on richness patterns (particularly on small-ranged species). We suggest that the mid-domain effect may help to explain similar middle-course richness peaks along other rivers. [source] Response of the Rhine,Meuse fluvial system to Saalian ice-sheet dynamicsBOREAS, Issue 3 2008FREEK S. BUSSCHERS A new reconstruction of the interaction between the Saalian Drente glaciation ice margin and the Rhine,Meuse fluvial system is presented based on a sedimentary analysis of continuous core material, archived data and a section in an ice-pushed ridge. Optically Stimulated Luminescence (OSL) was applied to obtain independent age control on these sediments and to establish a first absolute chronology for palaeogeographical events prior to and during the glaciation. We identified several Rhine and Meuse river courses that were active before the Drente glaciation (MIS 11-7). The Drente glaciation ice advance into The Netherlands (OSL-dated to fall within MIS 6) led to major re-arrangement of this drainage network. The invading ice sheet overrode existing fluvial morphology and forced the Rhine,Meuse system into a proglacial position. During deglaciation, the Rhine shifted into a basin in the formerly glaciated area, while the Meuse remained south of the former ice limit, a configuration that persisted throughout most of the Eemian and Weichselian periods. An enigmatic high position of proglacial fluvial units and their subsequent dissection during deglaciation by the Meuse may partially be explained by glacio-isostatic rebound of the area, but primarily reflects a phase of high base level related to a temporary proglacial lake in the southern North Sea area, with lake levels approximating modern sea levels. Our reconstruction indicates that full ,opening' of the Dover Strait and lowering of the Southern Bight, enabling interglacial marine exchange between the English Channel and the North Sea, is to be attributed to events during the end of MIS 6. [source] | ||||||||||