Channel (geography)

About: Channel (geography) is a research topic. Over the lifetime, 3541 publications have been published within this topic receiving 81730 citations.

A classification of natural rivers

Abstract: A classification system for natural rivers is presented in which a morphological arrangement of stream characteristics is organized into relatively homogeneous stream types. This paper describes morphologically similar stream reaches that are divided into 7 major stream type categories that differ in entrenchment, gradient, width/depth ratio, and sinuosity in various landforms. Within each major category are six additional types delineated by dominate channel materials from bedrock to silt/clay along a continuum of gradient ranges. Recent stream type data used to further define classification interrelationships were derived from 450 rivers throughout the U.S, Canada, and New Zealand. Data used in the development of this classification involved a great diversity of hydro-physiographic/geomorphic provinces from small to large rivers and in catchments from headwater streams in the mountains to the coastal plains. A stream hierarchical inventory system is presented which utilizes the stream classification system. Examples for use of this stream classification system for engineering, fish habitat enhancement, restoration and water resource management applications are presented. Specific examples of these applications include hydraulic geometry relations, sediment supply/availability, fish habitat structure evaluation, flow resistance, critical shear stress estimates, shear stress/velocity relations, streambank erodibility potential, management interpretations, sequences of morphological evolution, and river restoration principles.

Biological Effects of Fine Sediment in the Lotic Environment

Abstract: / Although sedimentation is a naturally occurring phenomenon inrivers, land-use changes have resulted in an increase in anthropogenicallyinduced fine sediment deposition. Poorly managed agricultural practices,mineral extraction, and construction can result in an increase in suspendedsolids and sedimentation in rivers and streams, leading to a decline inhabitat quality. The nature and origins of fine sediments in the loticenvironment are reviewed in relation to channel and nonchannel sources andthe impact of human activity. Fine sediment transport and deposition areoutlined in relation to variations in streamflow and particle sizecharacteristics. A holistic approach to the problems associated with finesediment is outlined to aid in the identification of sediment sources,transport, and deposition processes in the river catchment. The multiplecauses and deleterious impacts associated with fine sediments on riverinehabitats, primary producers, macroinvertebrates, and fisheries are identifiedand reviewed to provide river managers with a guide to source material. Therestoration of rivers with fine sediment problems are discussed in relationto a holistic management framework to aid in the planning and undertaking ofmitigation measures within both the river channel and surrounding catchmentarea.KEY WORDS: Sedimentation; Fine sediment; Holistic approach; Ecologicalimpact; River restoration

Fractal River Basins: Chance and Self-Organization

Abstract: 1. A view of river basins 2. Fractal characteristics of river basins 3. Multifractal characteristics of river basins 4. Optimal channel networks: minimum energy and fractal structures 5. Self-organized fractal river networks 6. On landscape self-organization 7. Geomorphological hydrologic response 8. References.

PROFILE: Hungry Water: Effects of Dams and Gravel Mining on River Channels

Abstract: / Rivers transport sediment from eroding uplands to depositional areas near sea level. If the continuity of sediment transport is interrupted by dams or removal of sediment from the channel by gravel mining, the flow may become sediment-starved (hungry water) and prone to erode the channel bed and banks, producing channel incision (downcutting), coarsening of bed material, and loss of spawning gravels for salmon and trout (as smaller gravels are transported without replacement from upstream). Gravel is artificially added to the River Rhine to prevent further incision and to many other rivers in attempts to restore spawning habitat. It is possible to pass incoming sediment through some small reservoirs, thereby maintaining the continuity of sediment transport through the system. Damming and mining have reduced sediment delivery from rivers to many coastal areas, leading to accelerated beach erosion. Sand and gravel are mined for construction aggregate from river channel and floodplains. In-channel mining commonly causes incision, which may propagate up- and downstream of the mine, undermining bridges, inducing channel instability, and lowering alluvial water tables. Floodplain gravel pits have the potential to become wildlife habitat upon reclamation, but may be captured by the active channel and thereby become instream pits. Management of sand and gravel in rivers must be done on a regional basis, restoring the continuity of sediment transport where possible and encouraging alternatives to river-derived aggregate sources.KEY WORDS: Dams; Aquatic habitat; Sediment transport; Erosion; Sedimentation; Gravel mining

Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico

Abstract: An increase in the flux of nitrogen from the Mississippi river during the latter half of the twentieth century has caused eutrophication and chronic seasonal hypoxia in the shallow waters of the Louisiana shelf in the northern Gulf of Mexico. This has led to reductions in species diversity, mortality of benthic communities and stress in fishery resources. There is evidence for a predominantly anthropogenic origin of the increased nitrogen flux, but the location of the most significant sources in the Mississippi basin responsible for the delivery of nitrogen to the Gulf of Mexico have not been clearly identified, because the parameters influencing nitrogen-loss rates in rivers are not well known. Here we present an analysis of data from 374 US monitor ing stations, including 123 along the six largest tributaries to the Mississippi, that shows a rapid decline in the average first-order rate of nitrogen loss with channel size--from 0.45 day (-1) in small streams to 0.005 day (-1) in the Mississippi river. Using stream depth as an explanatory variable, our estimates of nitrogen-loss rates agreed with values from earlier studies. We conclude that the proximity of sources to large streams and rivers is an important determinant of nitrogen delivery to the estuary in the Mississippi basin, and possibly also in other large river basins.