摘要:

AbstractThis study examined the variation in soil erodibility along hillslopes in a Prairie landscape. The soil loss produced by simulated rainfall on undisturbed soils was used as an index of relative soil erodibility. Relative erodibility, and several soil properties, were measured at the summit, shoulder, midslope footslope and toeslope of 11 slope transects in an area of cultivated grassland soils on hummocky glacial till. The variation of erodibility with slope position was statistically significant, and slope position explained about 40 per cent of the variation in the erodibility measurements. Erodibility was 14 per cent higher on the shoulder and midslope, and 21 per cent lower on the toeslope, than on the summit and footslope. Local variation in erodibility along slopes was considered to be an important control on patterns of soil erosion in the landscape. The variation of erodibility along the slopes reflected soil property trends. The greatest erodibility was associated with upper slope positions where soils tended to be shallow, coarse, poorly leached and low in organic matter, while lower erodibility was found at lower slope positions with deep, organic‐rich and leached soils. Of the individual soil properties considered, silt and sand content were the most highly correlated with erodibility. The results, together with results from other studies, also suggest that net erosion and erodibility are positively relate

ISSN:0197-9337    

DOI:10.1002/esp.3290170602

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractLaboratory experiments, recent paleoenvironmental analyses of rock varnish, and surface exposure dating of geomorphic units have led to new insights into the process of entrenchment and segmentation of alluvial fans, and into the history of Quaternary sedimentation in Death Valley. Entrenchment begins at the fanhead. As the trench deepens, its down‐slope end migrates down‐fan, taking several tens of thousands of years to reach lower parts of the fan. Laboratory experiments suggest, however, that a new segment begins to grow at the toe long before the trench reaches this part of the fan. Furthermore, the initial slope of the segment is not the equilibrium slope. Field evidence supports this model. The tectonic tilting that caused entrenchment and segmentation in Death Valley may have been triggered by loading of the valley with water.Sedimentation on the salt pan in southern Death Valley is not, at present, in equilibrium with that on the fans. Rather, it seems to be adjusting to an increase in the amount of fine material reaching the playa, due in part to breaching of the outlet of Lake Tecopa somewhat after 600 ka BP, and in part to subsidence of different parts of the valley at different rates. Failure to recognize this disequilibrium resulted in errors in earlier estimates of the age of the segmentation eve

ISSN:0197-9337    

DOI:10.1002/esp.3290170603

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA prototype two‐dimensional finite element flow model for depth‐averaged free surface flows was developed for floodplain environments. Limited refinement of the model's physical representation was undertaken and the enhanced scheme applied to an 11 km river channel/floodplain reach in the U.K. Preliminary model results indicate that this modelling approach can be used to identify dynamic variations in the flow field parameters over length scales of the order of 10‐100 m. Potentially, such data have the ability to permit detailed analysis of short‐term floodplain sedimentary d

ISSN:0197-9337    

DOI:10.1002/esp.3290170604

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTopographic changes in two blowouts located in Island Beach State Park, New Jersey, USA were monitored over the winter of 1981‐1982. Elevation changes were measured with erosion pins, and sediment traps placed at comparable locations in each blowout monitored the amount of sand moved by the wind. Discrete wind events were identified from regional data, and morphological data for the intervals with the highest onshore and offshore wind speeds are examined in detail.Vegetation is the primary influence on the development of the two blowouts. Blowout A is characterized by eroding sidewalls, a stable base, and an accreting blowout rim. High rates of sediment transport occur through the blowout throat which results in accretion on the vegetated rim. This blowout is an active sediment transfer system. Vegetation causes a large amount of deposition in the throat of blowout B. As vegetation was buried over the winter, the area of deposition migrated inland. Sidewall erosion also occurred in blowout B. Little change was recorded on the blowout rim. Blowout B is a recovering system where sediment is delivered to the blowout floor from the beach by onshore winds and from the blowout rim by offshore winds where it is stabilized by vegetation.The development of foredune blowouts is governed largely by vegetation cover on the dune crest and by sidewall erosion during offshore and onshore winds. Blowout recovery depends on vegetation growth and sediment deposition in the throat, and on the role of the sidewalls as sources of sediment which is deposited elsewhere within the system. Foredune blowouts are dynamic systems in which positive feedbacks in sediment availability and vegetation growth lead to a cycle of development and closur

ISSN:0197-9337    

DOI:10.1002/esp.3290170605

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFires occur frequently in many biomes and generate high temperatures on the ground surface. There are many field examples of fire causing rock disintegration. The simulation of fire in the laboratory (using a furnace) and the monitoring of changes in rock modulus of elasticity (with a Grindosonic apparatus), reveal that different rocks respond differently to heating. Significant decreases in elasticity occur at temperatures as low as 200°C and granites display particularly marked reductions. Extended periods of heating are not required for significant reductions to occur. It is postulated that the degree of change in elasticity as a result of simulated fire is such that rock outcrops subjected to real fires are likely to be sufficiently modified as to increase their susceptibility to erosion and weathering processes

ISSN:0197-9337    

DOI:10.1002/esp.3290170606

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTravel distances in gravel‐bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge. Mean distance of movement, irrespective of grain size, is weakly correlated with stream power, especially near the threshold of movement. There may be several reasons for the weak correlation, including variable effects of bed structure, varying magnitudes of sediment mobilizing events and sampling problems. Grain size itself is of marginal significance. The virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period. Better results are obtained by relating the virtual rate of travel to the first peak of the flow event only. This implies that the initial seeding of the tagged particles dominates the observations. Nonetheless, an underlying general relation is indicated by the data, which are derived from a wide range of flow regime type

ISSN:0197-9337    

DOI:10.1002/esp.3290170607

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo methods that were recently proposed for calculating fractional bedload transport rates in gravel‐bed streams are examined closely. Both of them employ the Oak Creek bedload data. The Diplas (PD) method is guided by dimensional analysis and, therefore, can be used to predict bedload transport in different gravel rivers. The only requirement for using this method is the knowledge of the subsurface material size distribution of the stream of interest. The expression for the fractional bedload transport obtained by the Shih and Komar (SK) method for Oak Creek cannot be used for other streams. Its use for a given stream requires information that is rarely available. For the Oak Creek case both methods demonstrate similar predictive abilit

ISSN:0197-9337    

DOI:10.1002/esp.3290170608

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral points have been raised by Diplas concerning our analyses in Shih and Komar (1990) of bedload transport in gravel‐bed streams, and our comparisons with the approach developed by Diplas (1987) as a modification of the dimensional analysis first undertaken by Parkeret al.(1982). We disagree with Diplas' assessment that our approach [cannot be used for other streams] and that dimensional analysis necessarily expands the range of application of his analysis approach. We argue here that the dimensional analysis of Diplas obscures the relationship between the transport rate and grain size, and in fact leads to a complex and implausible dependence. In contrast, our approach allows one to better focus on the changing grain‐size distributions as the flow discharge and mean bottom stress incre

ISSN:0197-9337    

DOI:10.1002/esp.3290170609

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290170613

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290170614

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY