摘要:

AbstractBadland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m2plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m2plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay‐rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed‐rock, which cause marked differences in hydrological response. North‐facing slopes respond more quickly, more frequently and produce more runoff than south‐facing slopes. Non‐uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation

ISSN:0360-1269    

DOI:10.1002/esp.3760050301

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe grass‐covered slopes on the southern flank of Mt Thomas, an upfaulted block of highly sheared sandstone and argillite 40 km NW of Christchurch, New Zealand, are presently undergoing severe erosion by a combination of mass‐wasting processes. Gully erosion, soil slips, and debris flows have carved out a number of steep, deeply incised ravines, from which coarse debris is transported (primarily by debris flows) to alluvial fans below. Geologic and historical evidence indicates that debris flows have been episodically active here for at least the last 20,000 years and have been the dominant process in fan building. This demonstrates that catastrophic geomorphic processes, rather than processes acting at relatively uniform rates, can be dominant in humid‐temperate areas as well as in arid and semi‐arid regions.In April 1978, debris flows were triggered in one of two unstable ravines in the Bullock Creek catchment by a moderate intensity, long duration rainstorm with a return period in excess of 20 years. Surges of fluid debris, moving at velocities up to 5 m/s, transported a dense slurry of gravel, sand, and mud up to 3·5 km over a vertical fall of 600 m. Deposition on the alluvial fan occurred when the flows left the confines of an entrenched fan‐head channel and spread out as a 0·16 km2sheet averaging 1·2 m thick. In all, 195,000 m3were deposited, roughly a third of that being reworked sediments from the head of the fan. Sediment yield from this one event would be equivalent to several thousand years worth of erosion at average sediment discharge rates for small South Island mountain catchments.Samples of viscous fluid debris during surges contained up to 84 per cent solids, composed of 70 per cent gravel, 20 per cent silt, and 4 per cent clay. Fluid density of the material ranged between 1·95 and 2·13 g/cm3, and it was extremely poorly sorted. Between surges the fluid was less viscous, less dense, and unable to carry gravel in suspension. Severe fan‐head entrenchment of the stream channel (approximately 10 m in less than 24 hours) was accomplished by the erosive action of the surges.Tectonic uplift of the Mt Thomas block and the weak, crushed condition of the bedrock appear to be ultimately responsible for the catastropic erosion of slopes in the Bullock Creek catchment. However, forest clearing within the last few centuries appears to have greatly increased the rate of mass wasting and gully erosion

ISSN:0360-1269    

DOI:10.1002/esp.3760050302

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractWalker Creek in Marin County, California is a coastal stream draining to Tomales Bay, which lies in the San Andreas Rift Zone. Its valley contains an alluvial fill with a basal gravel dated at 5000 years BP. In upstream parts of the watershed, channels are incised arroyo‐like in the fill leaving the valley floor standing as a high terrace averaging 5·5 m (18 ft) high. Below this terrace is an inner terrace of historic age that stands 2·4 m (8 ft) above the streambed. The stratigraphy and morphology of this valley are seen in others nearby, and indicate that in the last half of Holocene time in this region a single episode of valley alluviation was followed by two episodes of valley cutting.The second episode of valley cutting is occurring in the present time. During the last 60 years the flow has become seasonal, the stream has incised 1·5 m (5 ft) below the inner terrace in upstream reaches, aggraded 1·2 m (4 ft) in downstream reaches, and extended its estuary. Incision upstream has begun to re‐expose the bedrock valley floor and is associated with aggradation downstream that has caused the flood plain to overtop both terraces. This has decreased the stream's gradient.Using a stream that is currently effecting major changes in its valley and channel morphology, two aspects of hydraulic adjustment in fluvial systems are examined. The changes in the average slope of the longitudinal profile are small but measureable. Profile concavity has not changed measurably. The various profiles that have existed in Holocene time show that stream gradient can be, but is not necessarily, slightly adjusted during valley filling and cutting. Flow measurements at a high discharge show that the channel has begun to assume the hydraulic geometry of an ephemeral channel. Adjustments of depth, velocity, and roughness appear to be hydraulic adjustments in response to changing watershed con

ISSN:0360-1269    

DOI:10.1002/esp.3760050303

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractDownvalley sequences of slope profiles have been inferred to represent temporal sequences. Results from a simulation model are presented which demonstrate that for a slope system in dynamic equilibrium, the downvalley variation in form is best explained as a response to downvalley variation in basal conditions, and hence that in such an equilibrium system the direct substitution of time for space is not valid.

ISSN:0360-1269    

DOI:10.1002/esp.3760050304

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA general equation is proposed for the relationship between bedrock lowering and regolith thickness which includes, as special cases, hypotheses by Ahnert, Armstrong, Culling, Kirkby and Young, at least approximately.

ISSN:0360-1269    

DOI:10.1002/esp.3760050305

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractOpen ditching is a common and relatively cheap way of providing drainage for wet upland soils prior to afforestation or improved agriculture; it is sometimes also used to channelize moorland runoff into water storage schemes. In contrast to piped under‐drainage there is considerable danger of erosion in open ditches. Results are reported of investigations into the yield of bed‐load from ditched catchments; compared with unditched catchments there is a considerable increase in yield and this causes costly local problems of sedimentation. However, the implications of the erosion for downstream channel changes and reservoir sedimentation in the uplands are harder to predict without further study of the storage processes affecting bed‐load and of the influence of flood flows. The case studies are used to point to improvements in the design of open drainage net

ISSN:0360-1269    

DOI:10.1002/esp.3760050306

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMorphological and soil properties of terracettes have been examined using canonical correlation methods. Highly significant statistical relationships have been found linking some members of the soil property set to the morphological properties of the terracettes studied.

ISSN:0360-1269    

DOI:10.1002/esp.3760050307

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe factors affecting the relationship between channel discharge and volume of inundation are discussed. For many floodplains this relationship is not simple, but involves hysteretic effects which vary according to the hydrological characteristics of individual floods and the way in which these interact with the surface form of the floodplain reach. Some methods of deriving or estimating the extent of the hysteresis on floodplain reaches are suggested, although an acute lack of available data prevents detailed examination at present. Further investigations are required before floodplain conductivity relations can be used as an aid to flood routing procedures or in floodplain management problems. A major priority must be the acquisition of sequential inundation data.

ISSN:0360-1269    

DOI:10.1002/esp.3760050308

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3760050310

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3760050311

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY