摘要:

AbstractGlen Canyon Dam, located on the Colorado River 24km upstream from Grand Canyon National Park, has affected downstream alluvial sand deposits which are used as campsites by recreational boaters. Inventories of campsite numbers and sizes conducted in 1973, 1983 and 1991, and comparison of aerial photograph series taken in 1965, 1973, 1984 and 1990 show that there has been a system‐wide decrease in the number and size of campsites. Campsites are unevenly distributed along the river, and availability is regarded as ‘critical’ along reaches comprising 45% of the river, based on interviews with river guides. During the first 10 years of Glen Canyon Dam operations, at least 30% of all campsites decreased in size. During the next 18 years, between 1973 and 1991, 32% of all campsites decreased in size, and campsite capacity decreased by 44%. High annual dam releases in excess of power plant capacity in 1983 caused a net system‐wide increase in the number of campsites, but decreased campsite capacity in two critical reaches. The ‘benefit’ of sand aggradation due to the 1983 high flow was short‐lived, and by 1991 only a few campsites were larger than they had been in 1973. In contrast, other sites, especially in critical reaches, were eroded by the 1983 high flows and have not recovered in size. Options for future dam management must consider the variable response of campsites to high flows in critical and non‐critical reaches and the duration over which ‘beneficial’ high f

ISSN:0886-9375    

DOI:10.1002/rrr.3450090302

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe increasing involvement of fluvial geomorphology in river channel management has highlighted the desirability of being able to predict spatially differentiated river channel adjustment in relation to prevailing drainage basin characteristics. An exploratory analysis, using data derived from geomorphological reconnaissance surveys and maps, was carried out with the aim of characterizing river channel adjustments in four catchments within the Thames basin. As many of the variables are categorical in nature, logistic regression is utilized to generate multivariate equations which relate four styles of adjustment to catchment characteristics describing rock type, gradient, land use and channel management. Using only the variables which are statistically significant provides a goodness of fit of around 50%. Geomorphological interpretations of the characterizations are provided and, in general, indicate the varying balance between areally extensive natural controls and more localized human influences in shaping the individual styles of adjustment. In the studied lowland environment it appears that few channels are capable of recovering their sinuosity after channel management, thus highlighting the importance of conserving currently sinuous channels and the restoration of previously straightened reaches. Low gradient rural channels set on Chalk or clay favour deposition and thus may be targeted for maintenance operations. Erosive enlargement of the cross‐section is promoted where channel straightening takes place in zones of high gradient; an option which should be minimized to reduce further management expenditur

ISSN:0886-9375    

DOI:10.1002/rrr.3450090303

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Instream Flow Incremental Methodology (IFIM) is a procedure that has been applied to the rivers of many countries to determine the relationship between discharge and a measure of the physical habitat area available to aquatic species. PHABSIM is a software package that is used to perform the calculations required for the IFIM procedure. Published data on instream macrophyte growth in chalk streams are used here to test the seasonal effects of plant growth in a hypothetical channel. The results show how these effects can significantly distort PHABSIM results. The predicted weighted useable area can differ by as much as 34% depending on the season used for the principal calibration of the Water Surface Profile module (WSP) of PHABSIM. An algorithm is proposed for use with PHABSIM which allows the effects of changes in macrophyte biomass to be included.

ISSN:0886-9375    

DOI:10.1002/rrr.3450090304

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450090305

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450090301

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY