摘要:

AbstractThe Green River is a major tributary of the Colorado River with a drainage area of 115 770 km2in Colorado, Utah and Wyoming. The influence of Flaming Gorge Dam on sediment transport and the potential for future channel change were studied using comparative analysis of historical aerial photographs from 1952 to 1987 and geographical information systems, published sediment (1951‐86) and discharge (1965‐87) records, and sediment data collected during 1986‐8. Since the closure of the dam in 1964, new equilibrium channel widths were apparently achieved by 1974 in the reach 161‐279 km below Flaming Gorge Reservoir and by 1981 in the reach 465‐509 km below the reservoir. Recent high flows have resulted in an increase in average channel width in both reaches as measured on aerial photographs taken in 1986 and 1987. Sediment data from US Geological Survey gauges on the Green River and its primary tributaries and three sites established on the Green River for this study suggest that bed material sediment transport in the Green River has now attained a quasi‐equilibrium, with the river transporting just the load supplied to it. The potential for future channel changes exists, as evidenced by the response of the channel (i.e. channel widening) to the increased flows during 1983, 1984 and 1986. Future adjustments in channel characteristics should be limited to responses to changes in discharge and sediment supply and transport i

ISSN:0886-9375    

DOI:10.1002/rrr.3450070302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractEmbankments of the last century and contemporary channelization and development of urban and industrial areas along the Rhone Valley have greatly changed the river. The impacts of these on three biological descriptors of the hydrosystem (benthic invertebrates, fish communities and aquatic birds) have been studied. A reduction in the morphological diversity of the regulated hydrosystem has caused a reduction in biological diversity. This system has become a slow potamic system as a consequence of the more uniform environmental conditions: the benthic macroinvertebrate fauna has become eurytopic and pollution tolerant, with very localized potamic species; fish communities are dominated by limnophilic cyprinids; and water bird communities are limited by the absence of typical species of fluvial areas, such as terns.

ISSN:0886-9375    

DOI:10.1002/rrr.3450070303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn analysis of old maps and documentary sources reveals that major changes in river channel planform have occurred over the last 200 years on the River Tay system, Scotland, UK. Reaches showing natural river channel planform change, however, are relatively small and a stable planform is characteristic of many sections of the river. River planform instability appears to be controlled by channel bed slope, sediment load and the enhanced vulnerability of former river channel courses to erosion. Flood protection embankments built in the 19th and 20th centuries modified unstable multichannel wandering gravel bed river sections to narrower single‐channel reaches, with limited lateral migration. On the River Tummel, 20th century impoundment has caused further geomorphological change in response to clearwater erosion close to the dam and aggradation processes within the regulated river downstream, but isolation of the effects of impoundment from those of channelization are problematic. An examination of the geomorphic effects of a high magnitude flood event in 1990 and historical accounts of earlier large floods reveal that the 1990 flood was the third largest since 1800 in the study area. Despite river regulation and bank protection the zones naturally characterized by instability are still susceptible to planform changes causing flood embankments to be breached, channel shifts and development of gravel bar

ISSN:0886-9375    

DOI:10.1002/rrr.3450070304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractExtensive river training works were undertaken on the upper Hunter River, Australia between 1956 and 1978 in response to rapid lateral migration and channel widening caused by a series of large floods between 1949 and 1955. River training involved artificial cutoffs, extensive realignment, structural bank protection works and tree planting. Channel length and hence sinuosity (ratio of channel length to valley length) decreased throughout each of six reaches located in the 78.9 km long study area as a direct result of the artificial cutoffs and realignment. Although the overall length reduction was less than 5%, one section experienced a 17% reduction. Localized channel straightening directly increased slope, decreased roughness and consequently increased flow velocity. The structural works have generally succeeded, converting an actively migrating stream into a laterally stable channel. Largely because of channel straightening and reduced sediment supply by floodplain reworking, the river has responded by eroding its bed by up to 1.1 m since the 1950s. Bed erosion preferentially removed the sand and fine gravel fraction producing an armour layer of coarse gravel. This armour layer halted further erosion by protecting the underlying fine material and is now only episodically mobilized by floods with return periods greater than 5.6 years on the annual maximum series. Unfortunately degradation was not predicted before the river training works were undertaken and it was only the fortuitous formation of the bed armour layer which prevented the degradation from becoming a major problem.

ISSN:0886-9375    

DOI:10.1002/rrr.3450070305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe floodplains of the lower Rhine are situated in a densely populated area of the Netherlands. Although they are used intensively the floodplains still fulfill important ecological functions. The lower Rhine is the downstream sedimentation zone of the River Rhine and its floodplains are characterized by river‐transported vascular flora originating from southern and eastern Europe. Using multivariate methods data from previously published work and field data on grasslands and former river beds have been analysed to determine trends in ecological changes. The consequence of continued sedimentation and decreased erosion is an increased drying out of the floodplains. Excavation and recultivation of formerly excavated land does not reverse the losses in flora and vegetation. Statistically there is a negative relationship between the characteristic flora and recultivated land. The natural transversal river gradient also disappears, together with its characteristic ecological diversity. Aquatic environments in the floodplains have been changed completely since regulation work started in the 19th century. Most former river beds have disappeared due to silting up. Data on short‐term vegetation succession confirm the long term analysis of map d

ISSN:0886-9375    

DOI:10.1002/rrr.3450070306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractOn the upper reaches of the Ishite River, Japan the stream water is diverted completely at about 3 km above the Ishitegawa Reservoir, except under flood conditions. The chemical composition of the regenerated streamflow 2.4 km downstream from the diversion was determined 70 times during two years (1986‐7) to investigate the effects of the diversion on water chemistry. Factor analysis suggested that two main factors controlled the water chemistry. Factor 1 explained 45.7% of the total variance and was correlated positively with the concentrations of Ca2+, Mg2+, Na+, HCO−3, SO2−4and Cl−, which seemed to reflect the leaching of dominant ions from the catchment soil. The factor 1 score was correlated negatively with the ecological ‘Ca‐Mg index’ (r2= 0.912), a low value of which is necessary to avoid phosphorus enrichment by phytoplankton in the downstream reservoir. The diversion seemed to contribute to this purpose because the log flow‐rate value was correlated positively with the index (r2= 0.730). On the other hand, factor 2 explained 10.2% of the total variance and was correlated positively with NO−3concentration and negatively with pH. Factor 2 was considered in relation to the partial pressure of dissolved CO2gas in the stream water and appeared to be a complex biological factor that reflected CO2production in the catchment soil and consumpt

ISSN:0886-9375    

DOI:10.1002/rrr.3450070307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY