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1.
The paper focusses on connectivity in the context of infiltration‐excess overland flow and its integrated response as slope‐base overland flow hydrographs. Overland flow is simulated on a sloping surface with some minor topographic expression and spatially differing infiltration rates. In each cell of a 128 × 128 grid, water from upslope is combined with incident rainfall to generate local overland flow, which is stochastically routed downslope, partitioning the flow between downslope neighbours. Simulations show the evolution of connectivity during simple storms. As a first approximation, total storm runoff is similar everywhere, discharge increasing proportionally with drainage area. Moderate differences in plan topography appear to have only a second‐order impact on hydrograph form and runoff amount. Total storm response is expressed as total runoff, runoff coefficient or total volume infiltrated; each plotted against total storm rainfall, and allowing variations in average gradient, overland flow roughness, infiltration rate and storm duration. A one‐parameter algebraic expression is proposed that fits simulation results for total runoff, has appropriate asymptotic behaviour and responds rationally to the variables tested. Slope length is seen to influence connectivity, expressed as a scale distance that increases with storm magnitude and can be explicitly incorporated into the expression to indicate runoff response to simple events as a function of storm size, storm duration, slope length and gradient. The model has also been applied to a 10‐year rainfall record, using both hourly and daily time steps, and the implications explored for coarser scale models. Initial trails incorporating erosion continuously update topography and suggest that successive storms produce an initial increase in erosion as rilling develops, while runoff totals are only slightly modified. Other factors not yet considered include the dynamics of soil crusting and vegetation growth. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
In semi‐arid environments, the characteristics of the land surface determine how rainfall is transformed into surface runoff and influences how this runoff moves from the hillslopes into river channels. Whether or not water reaches the river channel is determined by the hydrological connectivity. This paper uses a numerical experiment‐based approach to systematically assess the effects of slope length, gradient, flow path convergence, infiltration rates and vegetation patterns on the generation and connectivity of runoff. The experiments were performed with the Connectivity of Runoff Model, 2D version distributed, physically based, hydrological model. The experiments presented are set within a semi‐arid environment, characteristic of south‐eastern Spain, which is subject to low frequency high rainfall intensity storm events. As a result, the dominant hydrological processes are infiltration excess runoff generation and surface flow dynamics. The results from the modelling experiments demonstrate that three surface factors are important in determining the form of the discharge hydrograph: the slope length, the slope gradient and the infiltration characteristics at the hillslope‐channel connection. These factors are all related to the time required for generated runoff to reach an efficient flow channel, because once in this channel, the transmission losses significantly decrease. Because these factors are distributed across the landscape, they have a fundamental role in controlling the landscape hydrological response to storm events. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

3.
Extensive loess covered areas characterize the mildly arid areas of western Israel, where average annual rainfall is 280 mm. Hydrological data point to a peculiar hydrological behavior of the ephemeral streams. The frequency of sporadic flash floods is very high. However, even in extreme rain events peak discharges are extremely low. Hydrographs are usually characterized by very steep rising and falling limbs, representative of saturated areas, extending over a limited part of the watershed. Following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself, with negligible contribution from the adjoining hillslopes. The study was based on two complementary approaches. The hydrological approach was based on the detailed analysis of rainfall–runoff relationships in a small watershed (11 km2) and on the analysis of the hydrological characteristics of the drainage network. The second approach was based on the toposequence concept. Several boreholes were dug along a hillslope 400 m long. Chemical data obtained show no significant difference in the downslope direction. Similar results were also obtained for the particle size distribution and soil moisture content. Data obtained perfectly fit the concept of ‘Partial Area Contribution’ as it presents an extreme case of hydrological discontinuity at the hillslope–channel interface. The lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel. The limited connectivity is attributed to the prevalence of low rain intensities in the study area. The present study is also relevant to our understanding of pedological processes in dryland areas. The high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances, and casts doubt on the general application of the toposequence approach. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

4.
This paper reports results from field experiments and hydrological modelling on the dynamics of runoff generation in highly convergent parts of the landscape in a logged and burnt eucalypt forest in south‐eastern Victoria, Australia. Large‐scale rainfall simulation experiments were conducted to explore runoff generating mechanisms from harvested areas, and to assess the effectiveness of standard water quality protective measures, here a disturbed filter strip, in preventing accession of sediment to near‐stream areas. We then examined the likely effects of varying antecedent moisture conditions on surface and subsurface runoff generating mechanisms. Very small volumes of surface runoff were generated only at very high rainfall intensity rates that exceeded a 100 year recurrence interval event during the simulated experiments. There was little or no identifiable impact of either compaction from logging operations or fire‐induced hydrophobicity on surface infiltration or generation of surface runoff. Measured soil hydraulic properties and soil depths explained the paucity of surface runoff, and the dominance of subsurface storm flow as the prime runoff generating mechanism. Deep lateral subsurface flow was observed from the cut‐face of a fire access track and into a streamhead downslope of the experimental plots. Water balance modelling using Topog_Dynamic indicated the conditions under which saturated overland flow in this environment could be generated are rare, but that care should be taken in siting of roads and tracks in lower parts of convergent landscapes. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

5.
Surface runoff on agricultural fields arises when rainfall exceeds infiltration. Excess water ponding in and flowing through local microtopography increases the hydrological connectivity of fields. In turn, an increased level of hydrological connectivity leads to a higher surface runoff flux at the field boundaries. We investigated the functional hydrological connectivity of synthetical elevation fields with varying statistical properties. For this purpose, we developed an object-oriented ponding and redistribution model to which Philip’s infiltration model was coupled. The connectivity behaviour is determined by the presence of depressions with a large area and spatial organization of microtopography in rills or channels. The presence of microdepressions suppresses the effect of the spatial variation of infiltration properties. Connectivity behaviour of a field with a varying spatial distribution of infiltration properties can be predicted by transforming the unique connectivity function that was defined for a designated microtopography.  相似文献   

6.
Seasonally dry forests in tropical regions show over 300% inter-annual biomass variability that directly affects the runoff and erosion dynamics. However, biomass fluctuation is mostly overlooked in hydrosedimentological analysis, including in connectivity analysis. The aim of this paper is to understand how the dryland vegetation seasonality in Brazilian drylands affects the potential runoff and sediment connectivity using the Index of Connectivity (stream and outlet targets). Two main analytical steps were used to identify the influence of dry forest biomass fluctuation on connectivity: Creation of vegetation scenarios based on the relationship between rainfall patterns and NDVI fluctuations (Landsat images); Identification of the effect of the vegetation scenarios on Index of Connectivity. The method was applied to a 90 km2 watershed in NE Brazil, creating a daily vegetation classification using five vegetation scenarios related to rainfall parameters, with average NDVI values from 0.18 during very dry scenarios (<20 mm of antecedent rainfall) to 0.62 in very wet scenario (>500 mm of antecedent rainfall). The primary connectivity behaviour is controlled by a continuous connectivity decrease, reaching 32%, related to increase of humidity and vegetation biomass. At the same time, due to rainfall irregularity, high magnitude rainfall events can occur even during very dry scenarios, when the watershed shows very high potential connectivity. It indicates that connectivity in runoff-dominated regions is temporally variable due to the highly seasonal vegetation and variable incidence of intense rainstorms.  相似文献   

7.
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8.
Hydrological processes in karst basins are controlled by permeable multimedia, consisting of soil pores, epikarst fractures, and underground conduits. Distributed modelling of hydrological dynamics in such heterogeneous hydrogeological conditions is a challenging task. Basing on the multilayer structure of the distributed hydrology‐soil‐vegetation model (DHSVM), a distributed hydrological model for a karst basin was developed by integrating mathematical routings of porous Darcy flow, fissure flow and underground channel flow. Specifically, infiltration and saturated flow movement within epikarst fractures are expressed by the ‘cubic law’ equation which is associated with fractural width, direction, and spacing. A small karst basin located in Guizhou province of southwest China was selected for this hydrological simulation. The model parameters were determined on the basis of field measurement and calibrated against the observed soil moisture contents, vegetation interception, surface runoff, and underground flow discharges from the basin outlet. The results show that due to high permeability of the epikarst zone, a significant amount of surface runoff is only generated after heavy rainfall events during the wet season. Rock exposure and the epikarst zone significantly increase flood discharge and decrease evapotranspiration (ET) loss; the peak flood discharge is directly proportional to the size of the aperture. Distribution of soil moisture content (SMC) primarily depends on topographic variations just after a heavy rainfall, while SMC and actual ET are dominated by land cover after a period of consecutive non‐rainfall days. The new model was able to capture the sharp increase and decrease of the underground streamflow hydrograph, and as such can be used to investigate hydrological effects in such rock features and land covers. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
Much attention has been given to the surface controls on the generation and transmission of runoff in semi‐arid areas. However, the surface controls form only one part of the system; hence, it is important to consider the effect that the characteristics of the storm event have on the generation of runoff and the transmission of flow across the slope. The impact of storm characteristics has been investigated using the Connectivity of Runoff Model (CRUM). This is a distributed, dynamic hydrology model that considers the hydrological processes relevant to semi‐arid environments at the temporal scale of a single storm event. The key storm characteristics that have been investigated are the storm duration, rainfall intensity, rainfall variability and temporal structure. This has been achieved through the use of a series of defined storm hydrographs and stochastic rainfall. Results show that the temporal fragmentation of high‐intensity rainfall is important for determining the travel distances of overland flow and, hence, the amount of runoff that leaves the slope as discharge. If the high‐intensity rainfall is fragmented, then the runoff infiltrates a short distance downslope. Longer periods of high‐intensity rainfall allow the runoff to travel further and, hence, become discharge. Therefore, storms with similar amounts of high‐intensity rainfall can produce very different amounts of discharge depending on the storm characteristics. The response of the hydrological system to changes in the rainfall characteristics can be explained using a four‐stage model of the runoff generation process. These stages are: (1) all water infiltrating, (2) the surface depression store filling or emptying without runoff occurring, (3) the generation and transmission of runoff and (4) the transmission of runoff without new runoff being generated. The storm event will move the system between the four stages and the nature of the rainfall required to move between the stages is determined by the surface characteristics. This research shows the importance of the variable‐intensity rainfall when modelling semi‐arid runoff generation. The amount of discharge may be greater or less than the amount that would have been produced if constant rainfall intensity is used in the model. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

10.
Information on the spatial and temporal origin of runoff entering the channel during a storm event would be valuable in understanding the physical dynamics of catchment hydrology; this knowledge could be used to help design flood defences and diffuse pollution mitigation strategies. The majority of distributed hydrological models give information on the amount of flow leaving a catchment and the pattern of fluxes within the catchment. However, these models do not give any precise information on the origin of runoff within the catchment. The spatial and temporal distribution of runoff sources is particularly intricate in semi‐arid catchments, where there are complex interactions between runoff generation, transmission and re‐infiltration over short temporal scales. Agents are software components that are capable of moving through and responding to their local environment. In this application, the agents trace the path taken by water through the catchment. They have information on their local environment and on the basis of this information make decisions on where to move. Within a given model iteration, the agents are able to stay in the current cell, infiltrate into the soil or flow into a neighbouring cell. The information on the current state of the hydrological environment is provided by the environment generator. In this application, the Connectivity of Runoff Model (CRUM) has been used to generate the environment. CRUM is a physically based, distributed, dynamic hydrology model, which considers the hydrological processes relevant for a semi‐arid environment at the temporal scale of a single storm event. During the storm event, agents are introduced into the model across the catchment; they trace the flows of water and store information on the flow pathways. Therefore, this modelling approach is capable of giving a novel picture of the temporal and spatial dynamics of flow generation and transmission during a storm event. This is possible by extracting the pathways taken by the agents at different time slices during the storm. The agent based modelling approach has been applied to two small catchments in South East Spain. The modelling approach showed that the two catchments responded differently to the same rainfall event due to the differences in the runoff generation and overland flow connectivity between the two catchments. The model also showed that the time of travel to the nearest flow concentration is extremely important for determining the connectivity of a point in the landscape with the catchment outflow. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
Among the studies on runoff connectivity of soils with heterogeneous properties, the need to understand the relationships between soil heterogeneity and the associated runoff organization and amount is frequently mentioned. In this study, we simulate the stationary runoff–runon process on bi‐dimensional (2D) flat slopes for five infiltrability distributions, one of them correlated, as a function of rainfall intensity and flow dimension. We define flow dimension by 1 + ε, where ε is the outflow fraction transferred from one pixel to each of the two lateral downslope pixels. Our aim is to assess the effect of ε and soil heterogeneity on the connectivity function compared to the mean runoff flow rate, the wet area and the number of runoff patterns. The analysis of connectivity is carried within the percolation framework. The results show that the integral connectivity scale is more sensitive to the flow dimension and soil heterogeneity compared to the other variables. The wet area fraction does not depend on ε. Unlike previous studies, we find that increased runoff production is not necessarily related to increased connectivity. The use of the connectivity function within the percolation framework appears to be a valuable method for assessing the impact of soil heterogeneity and flow dimension on the runoff organization during a rainfall event. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

12.
Upgrading agriculture in semi-arid areas and ensuring its sustainability require an optimal management of rainfall partition between blue and green waters in the farmed water harvesting catchment. The main objective of this study is to analyze the influence of heterogeneous land use on the spatial and temporal variation of rainfall partitioning and blue water production within a typical farmed catchment located in north-eastern Tunisia. The catchment has an area of 2.6 km2 and comprises at its outlet a dam, which retains the runoff water in a reservoir. Overland flow and soil water balance components were monitored during two cropping seasons (2000/2001 and 2001/2002) on a network of eleven plots of 2 m2 each with different land use and soil characteristics. The hydrological balances of both the catchment and reservoir have been monitored since 1994.Observed data showed a very large temporal and spatial variability of overland flow within the catchment reflecting the great importance of total rainfall as well as land use. During the 2001/2002 season the results showed a large variation of the number of observed runoff events, from 27 to 39, and of the annual overland flow depths, from 8 mm (under vineyard on calcaric cambisols) up to 43 mm (under shrubs-pasture on haplic regosols), between the plots. The annual runoff amounts were moderate; they always corresponded to less than 15% of the annual rainfall amount whatever the observation scale. It was also observed that changes in land use in years with similar rainfall could lead to significant differences in blue water flow. An attempt for predicting the overland flow by the general linear regression approach showed an r2 of 31%, the predictors used are the class of soil infiltration capacity, the initial moisture saturation ratio of the soil surface layer and the total rainfall amounts.These experimental results indicate that the variation in land use in a semi-arid catchment is a main factor of variation in soil surface conditions and explain the major role played by the former on hydrological behavior of the upstream area and on rainfall partition between overland flow and infiltration. Therefore, to predict the water harvesting capacities in terms of blue water production of a farmed catchment in semi-arid areas it seems essential to consider precisely its land use and its temporal evolution related to management practices.  相似文献   

13.
Observed scale effects of runoff on hillslopes and small watersheds derive from complex interactions of time-varying rainfall rates with runoff, infiltration and macro- and microtopographic structures. A little studied aspect of scale effects is the concept of water depth-dependent infiltration. For semi-arid rangeland it has been demonstrated that mounds underneath shrubs have a high infiltrability and lower lying compacted or stony inter-shrub areas have a lower infiltrability. It is hypothesized that runoff accumulation further downslope leads to increased water depth, inundating high infiltrability areas, which increases the area-averaged infiltration rate. A model was developed that combines the concepts of water depth-dependent infiltration, partial contributing area under variable rainfall intensity, and the Green–Ampt theory for point-scale infiltration. The model was applied to rainfall simulation data and natural rainfall–runoff data from a small sub-watershed (0.4 ha) of the Walnut Gulch Experimental Watershed in the semi-arid US Southwest. Its performance to reproduce observed hydrographs was compared to that of a conventional Green–Ampt model assuming complete inundation sheet flow, with runon infiltration, which is infiltration of runoff onto pervious downstream areas. Parameters were derived from rainfall simulations and from watershed-scale calibration directly from the rainfall–runoff events. The performance of the water depth-dependent model was better than that of the conventional model on the scale of a rainfall simulator plot, but on the scale of a small watershed the performance of both model types was similar. We believe that the proposed model contributes to a less scale-dependent way of modeling runoff and erosion on the hillslope-scale.  相似文献   

14.
A statistically based runoff‐yield model is proposed in this paper. The model considers spatial heterogeneities of rainfall, soil infiltration capacity and soil water storage capacity that are main factors controlling runoff‐yield process. It assumes that the spatial variation of rainfall intensity at each time step can be characterized by a probability density function, which is estimated by matching the hyetograph through goodness‐of‐fit measure, whereas the spatial heterogeneities of soil infiltration capacity and soil water storage capacity are described by parabola‐type functions. Surface runoff is calculated according to infiltration excess mechanism; the statistical distribution of surface runoff rate can be deduced with the joint distribution of rainfall intensity and soil infiltration rate, thus obtaining a quasi‐analytical solution for surface runoff. Based on saturation excess mechanism, the groundwater flow (flows below the ground are collectively referred to as groundwater flow) is calculated by infiltration and the probability distribution of soil water storage capacity. Consequently, the total runoff is composed of infiltration excess and saturation excess runoff components. As an example, this model is applied to flood event simulation in Dongwan catchment, a semi‐humid region and a tributary of Yellow River in China. It indicates that the proposed runoff‐yield model could achieve acceptable accuracy. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
Precipitation runoff is a critical hillslope hydrological process for downslope streamflow and piedmont/floodplain recharge. Shimen hillslope micro‐catchment is strategically located in the central foothill region of Taihang Mountains, where runoff is crucial for water availability in the piedmont corridors and floodplains of north China. This study analyzes precipitation‐runoff processes in the Shimen hillslope micro‐catchment for 2006–2008 using locally designed runoff collection systems. The study shows that slope length is a critical factor, next only to precipitation, in terms of runoff yield. Regression analysis also shows that runoff is related positively to precipitation, and negatively to slope length. Soil mantle in the study area is generally thin and is therefore not as critical a runoff factor as slope length. The study shows a significant difference between overland and subsurface runoff. However, that between the 0–10 and 10–20 cm subsurfaces is insignificant. Runoff hardly occurs under light rains (<10 mm), but is clearly noticeable under moderate‐to‐rainstorm events. In the hillslope catchment, vertical infiltration (accounting for 42–84% of the precipitation) dominates runoff processes in subsurface soils and weathered granite gneiss bedrock. A weak lateral flow (at even the soil/bedrock interface) and the generally small runoff suggest strong infiltration loss via deep percolation. This is critical for groundwater recharge in the downslope piedmont corridors and floodplains. This may enhance water availability, ease water shortage, avert further environmental degradation, and reduce the risk of drought/flood in the event of extreme weather conditions in the catchment and the wider north China Plain. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
Runoff generative process and runoff yield from arid talus mantled slopes   总被引：3，自引：0，他引：3  
Previous works dealing with the influence of a stone cover on runoff yield showed that runoff, attributed to the sealing effect of the topsoil by raindrops impact, was negatively related to the per cent of stone cover and stone size. These works were conducted on gentle slopes (3–11·5 degree) with a per cent of stone cover generally lower than 50 per cent, and composed of gravels. The present study deals with the runoff yield of steep talus slopes (26–36 degree) whose per cent of stone cover is very high (90–100 per cent), composed of cobbles and boulders. Three stimulated rainstorms were performed at various rainfall. intensities and durations on each one of six plots representative of the North eastern sector of Sinai. Although the contiguous stony cover prevented surface sealing by raindrops impact, runoff developed quite quickly on most slopes, and reached at peak discharge, after approximately ten minutes, up to 56 per cent of the rainfall. Differences between plots, in time lag, peak discharge and other hydrological variables, could be attributed mainly to the properties of the upper stony layer, with stone size as the most influential factor. Contrary to previous works, a positive relationship, was obtained between stone size to runoff yield. The result is explained by the process of water concentration. Each cobble and boulder behaves, on a smaller scale, like a bare rocky surface and yields per unit area water amounts beyond the infiltration rate of the limited uncovered areas. For a given stony cover the effect of water concentration is quicker with the big blocks than with gravels. A series of graphs trying to relate theoretically the relative importance of sealing and water concentration processes in runoff generation, at various conditions of stone cover and stone size, is proposed. The graphs enable to reconcile the results of the present study with those of previous works.  相似文献   

17.
This paper analyses the spatial and temporal variability of the hydrological response in a small Mediterranean catchment (Cal Rodó). The first part of the analysis focuses on the rainfall–runoff relationship at seasonal and monthly scale, using an 8‐year data set. Then, using storm‐flow volume and coefficient, the temporal variability of the rainfall–runoff relationship and its relationship with several hydrological variables are analysed at the event scale from hydrographs observed over a 3‐year period. Finally, the spatial non‐linearity of the hydrological response is examined by comparing the Cal Rodó hydrological response with the Can Vila sub‐catchment response at the event scale. Results show that, on a seasonal and monthly scale, there is no simple relationship between rainfall and runoff depths, and that evapotranspiration is a factor that introduced some non‐linearity in the rainfall–runoff relationship. The analysis of monthly values also reveals the existence of a threshold in the relationship between rainfall and runoff depths, denoting a more contrasted hydrological response than the one usually observed in humid catchments. At the event scale, the storm‐flow coefficient has a clear seasonal pattern with an alternance between a wet period, when the catchment is hydrologically responsive, and a dry summer period, when the catchment is much less reactive to any rainfall. The relationship between the storm‐flow coefficient and rainfall depth, rainfall maximum intensity and base‐flow shows that observed correlations are the same as those observed for humid conditions, even if correlation coefficients are notably lower. Comparison with the Can Vila sub‐catchment highlights the spatial heterogeneity of the rainfall‐runoff relationship at the small catchment scale. Although interpretation in terms of runoff processes remains delicate, heterogeneities between the two catchments seem to be related to changes in the ratio between infiltration excess and saturation processes in runoff formation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

18.
J. Holden  T. P. Burt 《水文研究》2002,16(13):2537-2557
Blanket peat covers the headwaters of many major European rivers. Runoff production in upland blanket peat catchments is flashy with large flood peaks and short lag times; there is minimal baseflow. Little is known about the exact processes of infiltration and runoff generation within these upland headwaters. This paper presents results from a set of rainfall simulation experiments performed on the blanket peat moorland of the North Pennines, UK. Rainfall was simulated at low intensities (3–12 mm h?1), typical of natural rainfall, on bare and vegetated peat surfaces. Runoff response shows that infiltration rate increases with rainfall intensity; the use of low‐intensity rainfall therefore allows a more realistic evaluation of infiltration rates and flow processes than previous studies. Overland flow is shown to be common on both vegetated and bare peat surfaces although surface cover does exert some control. Most runoff is produced within the top few centimetres of the peat and runoff response decreases rapidly with depth. Little vertical percolation takes place to depths greater than 10 cm owing to the saturation of the peat mass. This study provides evidence that the quickflow response of upland blanket peat catchments is a result of saturation‐excess overland flow generation. Rainfall–runoff response from small plots varies with season. Following warm, dry weather, rainfall tends to infiltrate more readily into blanket peat, not just initially but to the extent that steady‐state surface runoff rates are reduced and more flow takes place within the peat, albeit at shallow depth. Sediment erosion from bare peat plots tends to be supply limited. Seasonal weather conditions may affect this in that after a warm, dry spell, surface desiccation allows sediment erosion to become transport limited. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

19.
Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
A hydrological model (YWB, yearly water balance) has been developed to model the daily rainfall–runoff relationship of the 202 km2 Teba river catchment, located in semi‐arid south‐eastern Spain. The period of available data (1976–1993) includes some very rainy years with intensive storms (responsible for flooding parts of the town of Malaga) and also some very dry years. The YWB model is in essence a simple tank model in which the catchment is subdivided into a limited number of meaningful hydrological units. Instead of generating per unit surface runoff resulting from infiltration excess, runoff has been made the result of storage excess. Actual evapotranspiration is obtained by means of curves, included in the software, representing the relationship between the ratio of actual to potential evapotranspiration as a function of soil moisture content for three soil texture classes. The total runoff generated is split between base flow and surface runoff according to a given baseflow index. The two components are routed separately and subsequently joined. A large number of sequential years can be processed, and the results of each year are summarized by a water balance table and a daily based rainfall runoff time series. An attempt has been made to restrict the amount of input data to the minimum. Interactive manual calibration is advocated in order to allow better incorporation of field evidence and the experience of the model user. Field observations allowed for an approximate calibration at the hydrological unit level. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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