摘要:

AbstractThe primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments (‘inputs’) from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr−1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in‐channel reservoir increased by 60 Mg yr−1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction (<3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in‐channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr−1for the entire basin (based on a sediment output of 7430 Mg km−2yr−1and a measured bulk density of 1.35 Mg m−3). However, this masked the actual rates of 1.2 to 7.1 mm yr−1in subbasin primary source areas, and rates of 0.6 to 17 mm yr−1for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well‐integrated drainage network for rapid conveyance of sediments from the hillslope subs

ISSN:0197-9337    

DOI:10.1002/esp.3290160502

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractDaily rainfall data for four stations in Europe and east Africa are used to obtain, by means of magnitude‐frequency analysis, a measure of the Cumulative Erosion Potential (CEP) that takes into account rainfall characteristics, soil water storage, and granulometric properties of soils. The CEP has the advantage of being calculated from generally available published rainfall data, so that wide regional coverage is possible. Together with additional data on the surface configuration and on seasonal variations of rainfall and plant cover, the CEP can provide a basis for estimating hillslope erosion by overland flo

ISSN:0197-9337    

DOI:10.1002/esp.3290160503

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the Whitehall Forest of Georgia during the 1985‐86 non‐growing season soil CO2varied with soil depth, varied spatially at constant depth, and varied temporally with changing environmental conditions. Variations with depth in the upper 1.4 m of the soil were of greater magnitude than temporal variations and spatial differences at 30 cm depth were of lesser magnitude. Mean soil CO2in evergreen forest was higher (0.207 per cent) than in deciduous and mixed forest (0.157 per cent). There were no trends in soil CO2along hillslopes or with changes in soil texture, bulk density, moisture content, or temperature. Soil CO2did increase near trees possibly due to increased root densities and/or more numerous pockets of microbial activity. For CO2at 30 cm depth, two variables–the mean daily temperature range in the month before measurement and actual evapotranspiration in the week before measurement (AET7)–explained 76 per cent of the variation in mean soil CO2. At the profile site, where soil CO2was measured at five depths, 66 per cent of the variability in CO2was explained by soil depth, AET7, and the average daily temperature range in the two months before meas

ISSN:0197-9337    

DOI:10.1002/esp.3290160504

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractGeographical Information Systems (GIS) and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard.From a small drainage basin located in Central Italy, relevant geological and geomorphological factors were collected and processed by applying GIS technology. In particular, modules were used which both generate high‐fidelity digital terrain models and automatically partition the terrain into main slope‐units. The resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope‐unit. Although not lacking drawbacks, the method proved to be a feasible and cost‐effective approach to landslide susceptibility assessment and

ISSN:0197-9337    

DOI:10.1002/esp.3290160505

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBedload pulses in gravel‐bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small‐scale generic model of braided gravel‐bed streams. Two experiments are described in which braided channels developed in a 14 m × 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three‐dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly id

ISSN:0197-9337    

DOI:10.1002/esp.3290160506

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractAlternate bars were formed by sediment transport in a flume with Froude‐modelled flow and relative roughness characteristic of gravel‐boulder channels with steep slopes. The flume (0.3 m wide × 7.5 m long) was filled with a sand‐gravel mixture, which was also fed into the top of the flume at a constant rate under constant discharge. Channel slope was set at 0.03. Initially, coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream. Sorting in the pool directed coarse particles onto the next bar head downstream. Alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting, flow, and channel morphology. During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited. Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar‐head erosion and bedload transport over bars. Likely factors leading to bar‐head stabilization in modelled gravel‐bed channels are coarse mixed‐size sediment, steep channel gradients, and

ISSN:0197-9337    

DOI:10.1002/esp.3290160507

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInDevelopments in a non‐destructive method of determining rock strength, Allison (1990) compares data collected using an ultrasonic apparatus with data obtained from Schmidt hammer tests. He concludes that the Schmidt hammer data shows a wide degree of scatter and that its accuracy as field technique is questionable. No discussion is made of how the Schmidt hammer was used or of the total number of readings taken and the range of values. The graphs presented comparing data derived from some samples using ultrasonic equipment do not appear markedly at variance from the Schmidt hammer‐derived data but true comparison is not possible because the graphs use different measurement criteria. No information is given on comparative time and financial costs, which must be significantly different for the two techniq

ISSN:0197-9337    

DOI:10.1002/esp.3290160508

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn a previous publication (Allison, 1989), a non‐destructive method for indirectly determining rock strength by measuring Dynamic Young's Modulus was described. Data were presented to assess the Grindosonic apparatus in relation to standard laboratory techniques. A further Short Communication (Allison, 1990) evaluated the non‐destructive test as a field technique, in part achieved by comparing the Grindosonic results with data collected using the Schmidt hammer. The Schmidt hammer is a widely used field technique in geomorphology for determining rock strength (see for example Day and Goudie, 1977; Day, 1981). Allison (1989, 1990) also suggested that the elastic properties of materials are becoming increasingly important in geomorphological studies. The opportunity to provide additional information and comments here is apprecia

ISSN:0197-9337    

DOI:10.1002/esp.3290160509

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMeasures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of Schmidt hammer rebound (R‐) values and degree of weathering. However, weathering and roughness are intimately related, so the latter cannot be seen simply as a source of error limiting the utility of the Schmidt hammer. Only where surfaces had similar textures prior to weathering can R‐values be compared directly. Even where surface texture is well controlled, differences in R‐values should be viewed critically rather than assigned indiscriminately to differences in degree of weath

ISSN:0197-9337    

DOI:10.1002/esp.3290160510

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160511

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY