ISSN:0197-9337    

DOI:10.1002/esp.3290160402

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160403

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe influence of the seasons of the year on beach changes is well documented in the literature. One generalization which has emerged is that beaches are ‘combed down’ in winter and ‘built up’ in summer. Some workers have disagreed with this dictum because field evidence does not necessarily support the assertion.This study, located in the humid tropics, shows, with the aid of graduated pegs emplaced perpendicularly to the shoreline, that the magnitude and frequency of beach changes are greater in the wet, than in the dry season. Furthermore, there is a net loss of beach materials in the wet season and a net gain in the dry season, even though erosion and accretion occur throughout the year with no statistically significant difference in their magnitudes.Erosion prevails at the northern half of the beach while accretion is dominant to the south. The upper and lower foreshore zones are more prone to changes than the mid‐t

ISSN:0197-9337    

DOI:10.1002/esp.3290160404

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm3cm−1yr−1and average bedrock lowering rates of about 0.07 mm yr−1for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr−1calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin‐wide denudation rates of between 0.05 and 0.08mm yr−1, suggesting an approximate steady‐state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km2, suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in

ISSN:0197-9337    

DOI:10.1002/esp.3290160405

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractRainfall, peak discharges, and suspended sediment transport were surveyed for 280 events in three small (0.8 to 10 km2) catchments in a hilly area derived from Neogene marls, silts, and sands.Under similar hydrological input conditions, stream flow behaviour and sediment delivery differed considerably from one catchment to another, depending on topography, lithology, land use, and especially sediment availability. Analytical treatment of data showed a good fit between sediment yield and peak flow discharge. Less good, although still significant, was the correlation between sediment concentration and discharge values for different flow stages. Rainfall peak/basin lag time and rainfall/discharge showed poor or no correlation, mainly due to strong variations in rainfall distribution.Sediment concentration in the catchments varied enormously according to season, from zero up to 334 g 1−1; sediment yield was 160‐900 tonnes km−2yr−1in the two major catchments, and over 5200 tonnes km−2yr−1in the headwater catchment, stressing the importance of small tributaries not only in inducing floods in downstream channels, but also in sedi

ISSN:0197-9337    

DOI:10.1002/esp.3290160406

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves. To date, no study has attempted to unequivocally establish on stratigraphical, sedimentological, and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences. This paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest England. Sand layers of varying thickness are present within Holocene lagoonal and peat sequences of several shallow lakes of the Scilly Isles. Detailed analysis of Big Pool, St Agnes, indicates that the basal peats date from around 1000 BP. Within the basal peats are numerous thin sand layers. Above the basal peat is an extensive sand layer 15 to 40 cm thick. The base of this latter layer probably dates from the early to mid 18th century. Particle size, grain surface morphology, diatom, and mineral magnetic studies are used to try and determine the most likely mode of deposition. The results of all analyses are inconclusive, but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of Atlantic storms during the Little Ice Age superimposed upon a rising sea level. The thick sand layer may have been deposited by the tsunami wave generated by the Lisbon earthquake of November 1,1755. Due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves, it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments.

ISSN:0197-9337    

DOI:10.1002/esp.3290160407

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFew studies have precisely documented the response of stream channels to short‐term flow variability. This paper examines the impact of sequential flows of various magnitudes on the morphology of a low‐energy river in northeastern Illinois, U.S.A. Between June 1986 and November 1988 channel cross‐sections were surveyed on a semiannual basis at 26 locations along a 7.2 km stretch of the Des Plaines River. During this period an estimated 100‐year flood, several bankfull flows, and an extreme low flow associated with a severe drought occurred. The response of the river channel to each of these events was relatively minor. Mean changes for the reach were generally less than 3 per cent for mean depth and less than 1 per cent for width. Statistical analysis indicates that net changes in width and depth over the entire period were not significantly different from zero. This lack of geomorphic response is attributable to low stream power, low hydrologic variability, fine bed materials, and cohesive banks along this stretch of river. Although dramatic changes in channel morphology did not occur, subtleties in geomorphic response were observed that reflect the temporal ordering of hydrologic

ISSN:0197-9337    

DOI:10.1002/esp.3290160408

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMiniature sorted patterned ground features (nets and stripes) occur at an elevation ofca. 35 m in the L'Antioja valley, East Falkland. The features have developed following recent soil erosion and display many of the characteristics associated with the operation of frost‐related processes in regolith materials. The patterns are currently active and indicate that in cool oceanic climates the distribution of frost‐sorted patterns is controlled by the presence of bare ground on suitable regolith rather than by altit

ISSN:0197-9337    

DOI:10.1002/esp.3290160409

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160410

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160412

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY