1,721,036 research outputs found
River habitat mapping using Airborne Imaging Spectrometry (CASI-3)
No full textA Compact Airborne Spectrographic Imager (CASI-2) is used to map the depth of the River Test, a chalk stream in southern England. Lyzenga’s (1981) method is used to decouple variations in water depth from changes in bed material type. The results show that atmospheric correction improves the relationship between water depth and the logarithm of CASI reflectance, especially in visible wavelengths. The estimated accuracy of water depth was ± 20 cm, but validation was difficult due to the need to precisely co-locate the ground samples and the CASI data
The hydraulic impact and performance of a lowland rehabilitation scheme based on pool-riffle installation: the River Waveney, Scole, Suffolk, UK
No full textPool-riffle installation is increasingly becoming the standard form of river habitat enhancement undertaken, largely for the benefit of fisheries. This study documents the effect of riffle installation on the morphological and hydraulic diversity of a low gradient engineered river. Despite their prevalence there have to date been few published studies of the impacts of these features on channel hydraulics, despite concerns as to their potential impact on flood levels. In this paper the impacts of the installation of gravel bedforms on water surface elevations and flow resistance are considered. The performance of the riffle-pool sequences is assessed against a set of criteria derived from the scientific literature. The analysis reveals that the gravel bedforms do display the hydraulic functionality associated with natural pool-riffle sequences. At bankfull discharge, water surface elevation is not significantly increased over those existing prior to installation, and physical habitat is shown to be more diverse following rehabilitation. The stability and appropriate classification of the gravel bedforms created in the scheme are discussed, together with the implications for floodplain and river rehabilitation in general
Impacts of river restoration on small-wood dynamics in a low-gradient headwater stream (in Special Issue: Wood In World Rivers)
No full textWood is an important element in many river systems, interacting with channel and floodplain geomorphology, hydrology and ecology. Restoration practices are increasingly re-introducing wood into streams and researchers have started to study the geomorphic and ecological effects of re-introducing wood into rivers. However, little research has attempted to quantify the impacts of river restoration (including the addition of wood jams) on wood retention. Based on tracing dowels to simulate small wood (ranging in length from 0·184 to 1·06 m and diameter from 0·006 to 0·035 m) in three study reaches before and after restoration, this study provides a detailed representation of the influence of restoration on small-wood transport and the relative importance of different trapping sites within a low-order meandering stream in the New Forest, UK. The research specifically addresses the following questions. (i) Does restoration reduce transport of small wood? (ii) Does restoration increase the frequency and type of small-wood trapping sites? (iii) Do wood jams trap more small wood than other trapping sites? (iv) Do shorter pieces of wood travel further than long pieces? The study has demonstrated that (i) different types of restoration have different effects on the frequency and type of small-wood trapping mechanisms, and hence also on small-wood transport; (ii) wood jams were the most effective structures for trapping small wood in this environment; (iii) shorter pieces of wood travelled further than long pieces. Channel-floodplain interactions were also found to be important, allowing the floodplain to function as a trapping site
Environmental change in river channels: a neglected element. Towards geomorphological typologies, standards and monitoring
No full textRivers integrate the impacts of change in atmospheric and terrestrial systems; they then deliver these to the coast. En route geomorphological processes create dynamic and diverse habitats, both in-stream and in riparian/floodplain ecotones. The dynamics of channel change conflict with human resource development, the outcome is that many river and riparian environments have been significantly modified, complicating the interpretation of change. Collection of geomorphological data on both form and process has to date been overwhelmingly an academic pursuit; standard measurement networks and long-term monitoring have, as a result been largely absent-as in the Environmental Change Network (ECN), despite the emerging requirements of legislation such as the EU Water Framework Directive. In this paper, we utilise a unique set of repeat channel surveys and long-term bed-load sediment yields to provide guidance on both definitions of change and those variables and survey techniques which might form the basis, in future, of improved national-scale monitoring. The Environment Agency's River Habitat Surveys suggest the basis for channel typologies that could structure a sampling framework and rationalise the variables to be monitored. We also point to the value of more detailed geomorphological procedures in use at the catchment/project scale-Catchment Baseline Surveys and Fluvial Audits-as a standardised basis for monitoring the detail of change in the fluvial sediment system. A perfect opportunity to lay foundations for such monitoring activity has been provided in England and Wales by the winter floods of 2000/2001
Event bed load yield measurement with load cell bed load traps and prediction of bed load yield from hydrograph shape
No full textOne of the goals of sediment transport research is to predict the bed load yield of ungauged catchments. However, what little field data exist are characterized by temporal fluctuations in the record of event yield. Attempts to model the process of transport typically involve the derivation of empirical relationships between commonly measured variables such as stream discharge and the rate of bed load transport. Such approaches fail to account for the effect of sediment supply on the process of transport, which is known to contribute to the variability in records. This paper sets out a conceptual model of sediment transport that establishes a link between the form of the stream hydrograph and the effectiveness of an event as indexed by sediment yield. The model is then tested against a dataset of 60 bed load transport events recorded using a new type of load-cell pit trap. Total event power is shown to be capable of explaining 70% of the variance in event yields for a small woodland stream
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The application of palaeohydrology in river management
No full textThis paper reviews recent changes in river management. These changes are characterised by a move from the notion of rivers as stable equilibrium forms to one of dynamic responsive ecosystems. Coupled to these changes are a series of scientific questions that provide the context for reviewing the role that palaeohydrology might have in supporting contemporary and future river management. Palaeohydrology is shown to be capable of providing important and relevant information to river managers. Furthermore a series of emerging frameworks for incorporating geomorphology in river management exist wherein palaeohydrological data and analysis can be directly interfaced with the river management process. The paper therefore concludes that within specific limits, palaeohydrology is in much stronger position to support and communicate with the river management agencies than has previously been the case
Guidebook of applied fluvial geomorphology: Defra/Environment Agency Flood and Coastal Defence R&D Programme
No full textEU Life Environment Project on Wise Use of Floodplains: Cherwell catchment restoration scenarios: final report
No full textFinal report to NERC on processes controlling the effectiveness of river restoration as a means of enhancing lotic biodiversity
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