摘要:

AbstractErosion of natural river banks by boat‐generated waves is an increasingly serious problem on the navigable reaches of many rivers, particularly on the middle and estuarine reaches. An experiment designed to link bank erosion rates with easily measured wave characteristics, conducted on the scenic lower Gordon River in Tasmania, provides information useful for river management. Within a boat‐generated wave train a number of characteristics were measured and most showed a high correlation with measured rates of bank retreat. Maximum wave height within the train is the simplest measure and is associated with a major threshold in erosive energy on unconsolidated sandy alluvium at wave heights of 30 to 35 cm. At maximum wave heights above 35 cm all but the most resistant bank sediments erode. Reducing maximum wave heights to<30 cm by limiting boat speeds, and reducing the frequency of boat passages, caused a dramatic decline in bank erosion along the ri

ISSN:0886-9375    

DOI:10.1002/rrr.3450090102

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractFST hemispheres of identical size but varying density were used to evaluate the intensity and duration of near‐bottom shear stresses during peaking hydropower floods of various magnitudes (maximum 345 m3s−1; baseflow 2.75 m3s−1). The FST values at single points were recorded at rapid intervals along previously surveyed transects during the rising limb of flood events at various distances from the hydropower facility. Whole transect evaluations were ‐accomplished after the ‘flood’ level had stabilized.Measurements of over 1300 FST values were significantly correlated with mean water column velocity and complex hydraulic conditions such as turbulence, shear velocity and viscous sublayer. FST hemispheres are a rapid means of characterizing hydraulic conditions in medium order rivers. Changes in near‐substrate hydraulic conditions were patchy and could be classified in terms of risk to fauna of either dislodgement or physical damage. Low risk (class 1) changes occurred when FST values increased rapidly but returned to initial values after a short period of time (<90 minutes) from the arrival of the peaking wave. Medium risk (class 2) changes occurred when FST values increased rapidly and decreased after a short period of time, but remained at levels higher than before the arrival of the flood wave. High risk (class 3) changes occurred when FST values increased rapidly and remained at high levels during the entire flood event.It is suggested that floods that do not initiate significant bed movement create a mosaic of patches of variable disturbance risk to benthic fauna. Rapid evaluation by FST hemispheres could be used to characterize the overall disturbance potential for the channel by the construction of a weighted index based on the frequency of the various risk classes occurring in the reach being evaluated. A more appropriate analysis of impacts of peaking hydropower and other flood events must include the existence of hydraulic refugia and the movement patterns of both benthic species and those species that occupy the

ISSN:0886-9375    

DOI:10.1002/rrr.3450090103

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe pool‐riffle sequence as an important feature of river channels was described by Leopoldet al.(1964) to occur with a spacing of five to seven times the channel width. Subsequent work has generally confirmed this spacing, although more closely spaced pools and riffles are quoted for some channels in woodland basins and for some channelized streams. Although few detailed empirical studies have been made of adjustments of the pool‐riffle spacing, a detailed survey of a 6 km channel reach containing over 300 riffles in the New Forest, southern England indicates that despite the influence of woody debris and channelization, the interriffle distance generally falls within the range of five to seven channel widths. As substantial adjustments in channel dimensions have been widely observed downstream of channelization schemes, land‐use changes, and dams and reservoirs, the associated adjustments in pool‐riffle spacing should be a consideration in channel management and an ingredient of design for channel rest

ISSN:0886-9375    

DOI:10.1002/rrr.3450090104

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAlthough most of the world's river systems are regulated, the effects of river regulation on mammals and birds are little known. In fact, speculations are more common than empirical data. A review of this topic is presented, emphasizing northern rivers where most impacts have been described. Effects are related to the major causes of change. It is concluded that the two most disastrous effects of river regulation on mammals and birds are the permanent inundation of vast areas of land, and the disruption of the seasonal flood regime along the river. The design of future investigations to improve our knowledge is considered.

ISSN:0886-9375    

DOI:10.1002/rrr.3450090105

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe retention capacity of the floodplain and riparian zone for suspended matter and nitrogen has been investigated in the Adour River, a seventh order stream in south‐west France. Suspended matter and nitrogen fluxes through a 25 km meandering stretch of the river were measured during two flood events and compared with the amount of sediment trapped in the riparian zone (1.1 km2) and the major floodplain (16.8 km2) of the studied area. It was estimated that the floodplain and the riparian zone together retained between 10 and 20% of the suspended matter entering the stretch under study during the two main floods (138 700 Mg). Moreover, they retained about 11% of the total particulate nitrogen fluxes (640 Mg). Although the riparian zones are 15 times smaller than the major floodplain, the total suspended matter and particulate nitrogen deposition were, 50 and 17 times, respectively, larger in the riparian zone. The results obtained on the Adour River floodplain show that large river systems should not be considered only as export systems as riparian zones can retain a significant amount of suspended organic and mineral matter during flood

ISSN:0886-9375    

DOI:10.1002/rrr.3450090106

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe vertical and temporal distribution of coarse particulate organic matter (CPOM) larger than 1 mm from 0 to 70 cm depth within the substrate was observed at two different sites along a riffle in the River Morava. Samples of hyporheal sediments were taken by inserting a steel cylinder and a special grab. The amount of CPOM was determined by combustion. The maximum amount of CPOM was found at a depth of 30‐40 cm; lower levels of CPOM were observed in deeper horizons. The average amount of CPOM in 10cm layers (volume 1582.9 cm3) was 232.2 gm−3at station A and 691.3 gm−3at station B. The content of CPOM showed a maximum during the s

ISSN:0886-9375    

DOI:10.1002/rrr.3450090107

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractInvestigations were carried out into the contemporary distribution and structure of the vegetation communities at Gunthorpe, Nottinghamshire on the floodplain of the River Trent. A 60 km reach of the river was examined to determine the overall distribution and structure of vegetation communities; the Gunthorpe site was chosen as a representative example. Three hundred and thirty‐nine separate plots were examined and the site contained 132 species. It is clear that the extent of zones of discontinuity or transition (ecotones) between different vegetation patches has decreased due to long‐term land‐use management. The overall number of vegetation patches has also been reduced. A hierarchy relating boundaries to external influences is proposed and the relationship of ecotones to more clearly differentiated patch habitats identified. Highest species diversity is seen to be associated with the transition zones or ecotonal habitats, particularly under conditions of moderate disturbance intensity. It is concluded that the ecotones remaining still provide a habitat for a wide range of species with differing autecological requirements, but all typical of less disturbed alluvial meadows and marshes. These zones of transition potentially provide a pool for species expansion given improved ecological conditions following river restoration mea

ISSN:0886-9375    

DOI:10.1002/rrr.3450090108

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450090101

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY