摘要:

AbstractThis paper investigates the spatial and temporal variations of runoff, erosion and rate of sediment transport on an agricultural field submitted to natural rainfalls. The site, located in the Eastern Townships (Québec, Canada), is a corn field (10000 m2) where sheetwash erosion is active. Water (Q) and sediment (Qs) discharges were measured from June to October at eight locations on the field and for ten rainfall events. Analysis of the data was carried out on an aggregate data set and on the distributed measurements in time and space. The results showed that changes in vegetation, soil compaction and crusting are critical in determining temporal variations of runoff and erosion. Until August, the increase in soil compaction reduced infiltration capacity and depression storage and generated greater runoff for a given rainfall intensity (I). Sediment transport decreased as particle detachment is less likely to occur when vegetation breaks the drop impact and the soil surface is sealed. Later in the season, we observed an increase in sediment concentration associated with the presence of burrowing insects and harvest activity, providing loose sediments to the broken down surface. Intercepts and slopes of the relationship betweenQandQsalso vary during the period of measurement. High sediment availability over the soil surface in June and October gives high intercept values. The slope of the relationship is more stable but difficult to estimate for extreme events (high values ofIor lowQvalues) where the number of sampled points are small. During a rainfall, the response of the field is dominated by the topography and drainage area. The largest amount of runoff and erosion occurred on straight and steep slopes with small drainage areas, and on converging gentle slopes with large drainage areas. Although aggregate runoff and erosion values are decreasing with drainage area, parameters of theQs‐Qrelationship for different locations on the field are not statistically different. These results bear important consequences for models of sheetwash erosion on agricultural fiel

ISSN:0885-6087    

DOI:10.1002/hyp.3360070103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWater temperature behaviour in a small upland Exmoor catchment (the Black Ball Stream) has been studied over a 14‐year period since January 1976. Results from continuous records revealed annual mean stream temperatures to have a coefficient of variation of less than 5 per cent, and values of 5,10 and 15°C to be equalled or exceeded 90,41.8 and 4 per cent of the time respectively. The annual regime of water temperature was relatively predictable but diel cycles of varying magnitude were superimposed on the seasonal march. A clear seasonal hysteresis was evident whereby diel range in spring exceeded that in autumn by typically more than 2°C. Trend analysis of monthly temperature time series highlighted the stability of the thermal regime in recent years, although investigation of air‐water temperature relationships indicated that an increase in mean surface air temperature projected for southwest England by the Year 2050 would result in a rise of mean winter and summer stream temperatures by 1.6 and 1.3°C respectively. Analysis of streamflow effects on water temperature suggested that future indirect impacts of climatic change on thermal regime via changes in stream discharge are likely to be

ISSN:0885-6087    

DOI:10.1002/hyp.3360070104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractBypass flow in structured soils is dominated by soil hydrological processes, such as rain intensity, initial pressure head of the soil, surface storage of rain, horizontal contact area and absorption rate, and hydraulic conductivity of the soil matrix. This study was conducted to determine the relative impact of these processes in different soil types. A quasi 3‐dimensional simulation model was used to calculate the effects of these soil hydrological input parameters on surface infiltration, macropore flow (with related horizontal absorption) and drainage. For light textured soils, surface infiltration was the most important term in the water balance. Heavy textured soils, in contrast, had drainage as the main term. In the latter soils bypass flow, when occurring, was almost equal to the amount of rain applied, indicating that absorption processes were strongly reduced. Lateral absorption on macropore walls was a minor fraction in the total mass balances, due to limited contact area and relatively weak diffusivity forces. Surface infiltration is a crucial parameter in bypass flow and is mainly dependent on rain intensity, initial pressure head and conductivity of the soil matrix. This requires measurement methods for hydraulic conductivity that specifically consider the effect of macropore

ISSN:0885-6087    

DOI:10.1002/hyp.3360070105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA hydrologic model for urban areas has been developed which incorporates distributed parameter modelling concepts and functions in the context of a geographic information system. In the proposed model, the watershed is represented as a cascade of grid cells, whose size can be specified by the user. Preliminary processing includes the determination of overland flow directions for each cell. An automated procedure is used to establish the cell‐to‐cell connectivity scheme, which is used to order the computations within each time step. Infiltration is computed using the Green‐Ampt equation, while runoff rates are computed using a coupling of the continuity equation and Manning's equation for turbulent flow. Storm sewer flows are routed using time‐shift routing. The model is capable of simulating flow through streets and offers the possibility of predicting the downstream movement of sewer system overflows. In preliminary testing on a small residential watershed, the model was able to reproduce measured hydr

ISSN:0885-6087    

DOI:10.1002/hyp.3360070106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThinly stratified sedimentary deposits in a heterogeneous field were investigated to obtain basic physical data for the simulation of water flow. A procedure is described which translates a thinly stratified soil profile into a number of functional layers using functional hydrological properties. A functional layer is defined as a combination of one or more soil horizons and should (i) be recognizable during a soil survey using an auger and (ii) show significantly different functional hydrological properties when compared with another functional layer. This procedure gave three easily recognizable functional layers. Sets of hydrological characteristics of these three functional layers were obtained by physical measurements of the soil and by estimation, using textural data for classification into a standard Dutch series. The performance of several combinations of these sets was tested by comparing simulated and measured soil matric potentials for seven plots during one year. The best simulation results were obtained if measured soil hydraulic characteristics were used for relatively homogeneous functional layers and if the soil hydraulic characteristics were estimated at each location for the most heterogeneous layer.

ISSN:0885-6087    

DOI:10.1002/hyp.3360070107

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe portable surface capacitance insertion probe was used to measure thein situwater content of near surface soil layers. The probe readings were calibrated against gravimetric samples collected over a wide range of water contents, and were found to be very closely correlated. The capacitance probe was used repeatedly in time and space at a field site where ridges and furrows ensured a regular pattern of soil water variations. The observed spatial variations of the water content were related to topography and land mangement. The degree of variability was dependent on the average water content.

ISSN:0885-6087    

DOI:10.1002/hyp.3360070108

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractLarge infiltration ponds (10–15 m2) were used, in conjunction with a ring infiltrometer and a well permeameter, to determine the infiltration characteristics of a complex lateritic soil profile in the jarrah (Eucalyptus marginata) forest of Western Australia. Simultaneous measurements of soil water content and soil water potential allowed a description of the infiltration and redistribution in the soil profile. The infiltration ponds effectively measured the conductivity of a subsurface lateritic duricrust which was found to have a relatively high saturated hydraulic conductivity (Ks) of 2.7 m d−1, despite its apparently massive and extensive nature. Removal of the topsoil identified large (≈1 m2) infilled holes penetrating the duricrust over about 6% by area. Measurements indicated that these large ‘holes’ had a highKsvalue (≈ 10 m d−1), whereas the remaining duricrust had a lowerKsvalue (≈ 2m d−1). These results have implications for probable maximum flood design calculations and assessing the hydrological impact of extensive open

ISSN:0885-6087    

DOI:10.1002/hyp.3360070109

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough littoral regions in northern lakes may sustain fish spawning grounds, little is known of the temporal or spatial aspects of their thermal and chemical regimes. This shortcoming is due in part to the difficulty in properly sampling these regions throughout the year with adequate spatial resolution. This problem is especially critical in lakes affected by episodic acidification during the spring snowmelt, a period of substantial importance to fisheries recruitment. A device was constructed to alleviate the problems associated with conventional water quality sampling of littoral regions. Constructed of thick walled polyvinyl chloride and permanently installed in the nearshore regions of an Adirondack lake, the episodic event sampler (EES) provided finely resolved (0.25 m) temperature and water chemistry data during the spring snowmelt period (February to May) of 1989. Although the construction and installation of the sampler represented a significant investment in labour and materials, this was offset by the high quality of the data collected. As the samplers were relatively undamaged by freeze‐thaw activity, it is expected that they will continue to provide excellent information for several year

ISSN:0885-6087    

DOI:10.1002/hyp.3360070110

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe composition and amount of colloidal and suspended participate matter transported during a small flood event in Magela Creek in tropical northern Australia was investigated. The flood studied constituted approximately 3 % of the total annual flow, most (90%) of which occurred between mid‐January and mid‐February of the study year. Three fractions were separated from water samples using a sequential method involving a continuous flow centrifuge to separate suspended particulate matter (SPM; nominally>1 μm) followed by hollow fibre filtration, first using a 0.1 μm filter to separate course colloidal matter (CCM; nominal size 1–0.1 μm) and then a 0–015 μm filter to separate fine colloidal matter (FCM; nominal size 0.1–0.015 μm). The SPM was predominantly inorganic (organic matter 21 %), whereas the colloidal fractions were dominantly organic matter (CCM 60%; FCM 83%). Analysis of individual particles using electron microprobe and automated image analysis indicated that the mineral fractions in both the SPM and CCM were dominated by iron‐enriched aluminosilicates (including kaolinite) (72–82%) and quartz (9–10%), indicative of a highly weathered and extensively laterized catchment. Surprisingly there was very little difference in the composition of the SPM or CCM fractions during the flood event studied, which may indicate either that sediment availability was restricted following the major run‐off events in January and February, or that all the sediment sources within the catchment are geochemically similar.Approximately the same amounts of particulate (20 tonne), colloidal (21 tonne) and dissolved material (17 tonne) were transported during the 25 hour period of the main flood peak; over 90% of the colloidal matter was 0.1–1.0 μm in size. These data suggest that previous estimates of the amounts of particulate (and colloidal) matter transported by Magela Creek, which were based on suspended solids measurements, may have underestimated the particulate matter load by as much as 50%. It is possible that the relatively high proportion of colloidal matter is unique to Magela Creek because coagulation and aggregation of colloidal matter to particulate matter is slow due to the very low concentations of calcium and magnesium in these waters. However, if the result is more widespread, there are important implications for the global estimates of fluvially transported particulate and dissolved materials as many of the previous studies may have underestimated the particulate load and overest

ISSN:0885-6087    

DOI:10.1002/hyp.3360070111

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360070102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY