A decision support system for identifying the habitat quality and rehabilitation potential of urban rivers

Few habitat survey, classification or assessment methodologies have been developed specifically for urban or heavily engineered rivers, and yet these rivers need careful assessment if management options are to be considered and prioritised in an economically and environmentally effective way. This paper presents a refinement of a previously proposed urban river survey (URS), which is a modification of the Environment Agency's River Habitat Survey. It then describes indices and classifications that have been developed from URS data and that provide a link between the type of engineering applied to a stretch of urban river and its habitat characteristics. Finally, some simple decision trees and scenario-modelling tools are presented that allow (i) newly surveyed urban stretches to be classified and (ii) some simple scenarios of channel management change to be assessed in order to prioritise management options for stretches of urban river across urban catchments

Initial adjustments within a new river channel: interactions between fluvial processes, colonizing vegetation, and bank profile development

A conceptual model of the morphological development of the riparian margins of newly cut river channels is presented, suggesting early feedbacks between vegetation growth and bank form. To test the model, observations of long and cross profiles, bank sediment and seed deposition, and bank vegetation development were collected over the first 2 years of river flows through a reach of the River Cole, West Midlands, UK. The newly created channel had a sinuous planform and varying asymmetric trapezoidal cross section in sympathy with the planform. No imposed bedforms or bank reseeding were included in the design. Over the 2 years, development of bedforms was rapid, with bed sediment sorting and bank profile adjustment occurring more steadily and progressively. Six classes of bank profile were identified by the end of the study period, illustrating close associations with sediment aggradation, vegetation colonization, and growth patterns. Vegetation colonization of the banks was seeded predominantly from local sources during the summer and from hydrochory (transport by the river) during the winter. Colonizing vegetation on the riverbanks appeared to act as a significant propagule source by the second summer and as an increasingly important roughness element, trapping both propagules and sediment, within the second year and providing early feedback into bank evolution. As a result, the time required for riparian margin development in the conceptual model was found to be considerably longer than observed in the study river. In addition, the role of surface wash/bank failure in modifying the bank profile and transporting seeds onto the upper bank face during the first year of bank development was found to be important in initiating rapid bank vegetation colonization and surface stabilization. This set of processes had not been incorporated in the initial conceptual model. In relation to channel restoration, this research illustrates that in small temperate rivers of modest energy the provision of an initial, sinuous corridor is sufficient to induce rapid development of fluvial features and vegetation cover without the need to construct bed forms or to seed the banks

Climate and Rivers

Over the last few decades as hydrologists have slowly raised their line of sight above the watershed boundary, it has become increasingly recognised that what happens in the atmosphere, as a major source of moisture for the terrestrial branch of the hydrological cycle, can strongly influence river dynamics at a range of spatial and temporal scales. Notwithstanding this, there is still a tendency for some in the river research community to restrict their gaze to the river channel or floodplain. However Geoff Petts, the person to which this special issue is dedicated, understood well and widely encouraged a holistic view of river catchment processes. This included an acknowledgment of the role of climate, in its broadest sense, in shaping what happens within and without the river channel. The purpose of this paper therefore is to offer a broad overview of the role of some aspects of climate science in advancing knowledge in river research. Topics to be addressed include the role of climate in influencing river flow regimes, a consideration of the large scale climate mechanisms that drive hydrological variability within river basins at inter-annual to decadal timescales and atmospheric rivers and their link to surface hydrology. In reviewing these topics a number of key knowledge gaps have emerged including attributing the causes of river flow regime changes to any one particular cause, the non-stationary and asymmetric forcing of river regimes by modes of climate variability and establishing links between atmospheric rivers, and terrestrial river channel processes, fluvial habitats, and ecological change