摘要:

AbstractA fifteen year history of coastal dune recession at Magilligan, Northern Ireland has revealed both time and space contrasts in processes and morphology. Since 1968 ‘storm’ frequency has increased, while dune retreat reached a peak (5·4 m) in 1978–1979. Three types of dune eroding events are noted, resulting from particular wave/wind/tide combinations. The spatial variability in dune scarping is associated with vegetation and soil development, and slope failures range from granular avalanches to retrogressive rotational

ISSN:0197-9337    

DOI:10.1002/esp.3290140102

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractDredging and straightening of alluvial channels between 1959 and 1978 in West Tennessee caused a series of morphologic changes along modified reaches and tributary streams. Degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed‐levels by as much as 6·1 m. Following degradation, reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction. Aggradation downstream of the area of maximum disturbance reached 0·12 m per year with the greatest rates occurring near the stream mouths.The adjustment of channel geometry and phases of channel evolution are characterized by six process‐oriented stages of morphologic development—premodified, constructed, degradation, threshold, aggradation, and restabilization. Down‐cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded (threshold stage). Channel widening continues through the aggradation stage as the ‘slough line’ develops as an initial site of lower‐bank stability. The bank profile develops three dynamic elements (1) vertical face (70° to 90°), (2) upper bank (25° to 50°), and (3) slough line (20° to 25°). Alternate channel bars form during the restabilization stage and represent incipient mean

ISSN:0197-9337    

DOI:10.1002/esp.3290140103

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBedload transport measurements in two upland streams are considered as a function of the excess stream power exerted on the bed by the flow.During low flows when the framework gravels remain undisturbed, fine sediments are winnowed from the bed‐surface layer once a threshold of 3·4 W m−2is exceeded and the transport rate is strongly supply limited. However for stream powers in excess of 15 W m−2framework gravels are mobilized and the efficiency of the transport process approaches a local maximum of about 1 per cent for discharges up to 2/3 of bankfull.An inverse depth dependence in the efficiency of the transport process was noted but although bedload calibre increased as a function of discharge its influence on efficiency could not be demonstrated. However it was suspected that the size‐sorting relationships of the bed‐material in a number of rivers in relation to the transport efficiency might profitably be examin

ISSN:0197-9337    

DOI:10.1002/esp.3290140104

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIncreasing rates of bank erosion and sediment deposition have been reported from the Norfolk Broads since the early 19th century. The major sources of both suspended and deposited sediment in the rivers and Broads is quantified using sediment mineralogy, identified by X‐ray diffraction. This indicates that higher proportions of bank derived sediment are present in suspension in the waterway during the summer months, due primarily to bank erosion by motor craft. Dated sediment cores show how the sources of inorganic sediment have changed over time. Whilst in the past upland catchment sources dominated, at present material is mainly derived from river bank materia

ISSN:0197-9337    

DOI:10.1002/esp.3290140105

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractHeavy rainfall on the south side of the Rokko Mountains has often caused severe landslides and debris flows. Analysis of the annual summation of rainfall in excess of 100 mm/day shows that the rainfall in this area has dominant periodicities of about 25–30, 10–13, and 5–7 years. The period of about 25–30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall; years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area. Temporal change in this rainfall may provide a first approximation for erosional force. Analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25–30 years. Cross‐spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25–30 years; evidence that variations in the ring width may be used as proxy data for er

ISSN:0197-9337    

DOI:10.1002/esp.3290140106

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe suspended sediment yields of two adjacent, paired, catchments on blanket peat in mid‐Wales were compared before and after preafforestation drainage works. Catchment A was ploughed whilst an adjacent catchment (B) was left unploughed. After eight months Catchment B was also ploughed. The ploughing strategy in both catchments was designed to minimize sediment loss. However, suspended sediment loss increased 2·5 times following ploughing in Catchment A, whilst no such increase occurred at this time in Catchment B. Subsequently, suspended sediment yields in Catchment B increased 4·8 times after it was ploughed. Organic sediment was lost mainly from furrow sides, and erosion pins showed maximum ground recession in summer, due to peat wastage. Summer desiccation prepared sediment for transport, and organic suspended sediment loads were highest in the autumn. Sediment loads were limited by vegetation colonization and some reduction in sediment loss was due to the presence of unploughed strips adjacent to stream cour

ISSN:0197-9337    

DOI:10.1002/esp.3290140107

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSalt‐marsh cliffs in the muddy Severn Estuary are mostly strong and tall. They are retreating in response to the erosive attack of wave and tidal currents chiefly through toppling failures and rotational slips. In the sandy Solway Firth and Morecambe Bay systems, marsh cliffs are strong only in their upper parts, where a dense root‐mat of marsh grasses binds the sediments. Here cantilever and toppling failures are the main response of the cliffs to tidal and wave erosion The differences between the three estuarine systems in the mechanisms of marsh‐cliff erosion are partly reflected in the mode of preservation of the cliffs on the restoration of the conditions leading to renewal of marsh g

ISSN:0197-9337    

DOI:10.1002/esp.3290140108

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290140101

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY