A simplified model for estimating field‐scale surface runoff hydrographs

The problem of obtaining field‐scale surface response to rainfall events is complicated by the spatial variability of infiltration characteristics of the soil and rainfall. In this paper, we develop and test a simplified model for generating surface runoff over fields with spatial variation in both rainfall rate and saturated hydraulic conductivities. The model is able to represent the effects of local variation in infiltration, as well as the run‐on effect that controls infiltration of excess water from saturated upstream areas. The effective rainfall excess is routed to the slope outlet using a simplified solution of the kinematic wave approximation. Model results are compared to averaged hydrographs from numerically‐intensive Monte–Carlo simulations for observed and design rainfall events and soil patterns that are typical of Central Italy. The simplified model is found to yield satisfactory results at a relatively small computational expense. A proposal to include a simple channel routing scheme is also presented as a prelude to extend this conceptualization to watershed scales. Copyright © 2006 John Wiley & Sons, Ltd.     

Measurement of runoff and soil loss from two differently sized plots in a subtropical environment (Brazil)

Studies of soil erosion on small plots present upscaling problems. The results in the literature on the effect of slope length (i.e. scale) on runoff and soil erosion are contradictory. Furthermore, most studies that examine scale effects measured through erosion plots have been conducted in Mediterranean environments. The objective of this study was to assess the effects of plot size on runoff and soil loss in a subtropical environment. Other measurements were taken to appraise the topsoil property changes inside the plots. The soil was ploughed twice, the surface was leveled with a hoe and it was kept bare during the experiment. Data were collected from 10 paired plots, five plots measuring 10 m × 1 m and five plots measuring 1 m × 1 m, installed in the same pedo‐geomorphologic unit. Measurements were carried out from November 2008 to November 2009. During this period, 97 natural storms were registered. The results indicate that the small plots tended to have higher runoff (30% higher) compared to larger plots, especially during periods of greater rainfall volume, duration and intensity. The soil loss was similar in both the 1 m² plots (6·33 kg/m²) and the 10 m² plots (6·26 kg/m²). Moreover, the dynamics of the soil loss during the experiment was relatively similar across both plot sizes. The large plots tended to have a greater internal complexity. In these plots, the steps retreat were higher, the overland flow scars were more frequent, and points of rill initiation and protochannels emerged in several parts of the plots. The results of the small plots were comparable to the results obtained on the large plots, especially in relation to soil loss. These plots were useful for short‐term assessments of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

两种不同DEM处理方法提取的水系比较

水系不但是重要的自然地理要素,而且对防洪减灾、资源开发等有着重要意义。基于DEM的坡面径流法是最为常用的水系提取方法,其提取精度直接取决于DEM中洼地的处理方法。为了比较不同DEM处理方法对水系提取精度的影响,本文以江西省潦河流域为例,利用基于DEM数据的J＆D算法及基于辅助数据的AGREE方法来处理实验区DEM,然后利用坡面径流法提取水系。结果表明,经两种方法后均可以提取出连续的水系,且提取水系的等级、数量及长度相差不大;在提取精度上,在受人类活动影响较小的山地丘陵地区两种方法提取的水系比较吻合,而在平坦地区或受人类活动影响较大的地区提取的水系差异较大,且AGREE方法处理后提取的水系精度较高。     

Factors influencing surface runoff generation from two agricultural hillslopes in central Pennsylvania

The variable source area (VSA) concept provides the underlying paradigm for managing phosphorus losses in runoff in the north‐eastern USA. This study sought to elucidate factors controlling runoff along two hillslopes with contrasting soils, including characterizing runoff generation mechanisms and hydrological connectivity. Runoff monitoring plots (2 m × 1 m) were established in various landscape positions. Footslope positions were characterized by the presence of a fragipan that contributed to seasonally perched water tables. In upslope positions without a fragipan, runoff was generated primarily via the infiltration‐excess (IE) mechanism (96% of events) and was largely disconnected from downslope runoff. Roughly 80% of total runoff originated from the north footslope landscape position via saturation‐excess (SE) (46% of events; 62% of runoff) and IE (54% of events; 38% of runoff) mechanisms. Runoff from the north hillslope was substantially greater than the south hillslope despite their proximity, and apparently was a function of the extent of fragipan representation. Results demonstrate the influence of subsurface soil properties (e.g. fragipan) on surface runoff generation in variable source area hydrology settings, which could be useful for improving the accuracy of existing runoff prediction tools. Published in 2009 by John Wiley & Sons, Ltd.     

Using a transient infiltrometric technique for intensively sampling field‐saturated hydraulic conductivity of a clay soil in two runoff plots

The point measurement of soil properties allows to explain and simulate plot scale hydrological processes. An intensive sampling was carried out at the surface of an unsaturated clay soil to measure, on two adjacent plots of 4 × 11 m² and two different dates (May 2007 and February–March 2008), dry soil bulk density, ρ_b, and antecedent soil water content, θ_i, at 88 points. Field‐saturated soil hydraulic conductivity, K_fs, was also measured at 176 points by the transient Simplified Falling Head technique to determine the soil water permeability characteristics at the beginning of a possible rainfall event yielding measurable runoff. The ρ_b values did not differ significantly between the two dates, but wetter soil conditions (by 31%) and lower conductivities (1.95 times) were detected on the second date as compared with the first one. Significantly higher (by a factor of 1.8) K_fs values were obtained with the 0.30‐m‐diameter ring compared with the 0.15‐m‐diameter ring. A high K_fs (> 100 mm h^?1) was generally obtained for low θ_i values (< 0.3 m³m^?3), whereas a high θ_i yielded an increased percentage of low K_fs data (1–100 mm h^?1). The median of K_fs for each plot/sampling date combination was not lower than 600 mm h^?1, and rainfall intensities rarely exceeded 100 mm h^?1 at the site. The occurrence of runoff at the base of the plot needs a substantial reduction of the surface soil permeability characteristics during the event, probably promoted by a higher water content than the one of this investigation (saturation degree = 0.44–0.62) and some soil compaction due to rainfall impact. An intensive soil sampling reduces the risk of an erroneous interpretation of hydrological processes. In an unstable clay soil, changes in K_fs during the event seem to have a noticeable effect on runoff generation, and they should be considered for modeling hydrological processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Scale effects of Hortonian overland flow and rainfall–runoff dynamics in a West African catena landscape

Hortonian runoff was measured from plots with lengths of 1·25 and 12 m, and at watershed level for rainstorms during the 1996 rainy season in cental Côte d'Ivoire, Africa. A clear reduction in runoff coefficients was found with increasing slope lengths, giving order of magnitude differences between runoff measurements at point level (1 m²: 30–50% of total rain) and watershed level (130 ha: 4% of total rain). Runoff reduction from 1·25 and 12 m slopes was reproduced for each major runoff‐producing rainstorm at two different sets of plots, but the reduction was erratic for rainfall events which produced little runoff. In addition, runoff reduction varied wildly from one rainstorm to the next. In the analysis, we show that the spatial variability of runoff parameters causes the erratic behaviour during rainstorms with little runoff. During the more important, larger runoff‐producing events, which give 78% of total runoff, the temporal dynamics of the rainfall–runoff process determine the reduction of runoff coefficients from longer slopes. A simple infiltration/runoff model was used to simulate the field results, thereby confirming the importance of rainfall dynamics as an explanatory factor for measured reduction of runoff coefficients. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental study of water fluxes in a residential area: 2. Road infiltration,runoff and evaporation

Lack of accurate data has led some hydrologists and city planners to assume that urban infiltration is zero and runoff is 100% of the rainfall. These assumptions lead to an over estimation of road runoff volume and an underestimation of direct recharge to groundwater, which is already rising under some UK cities. This study investigates infiltration and runoff processes and quantifies the percentage of rainfall that contributes to storm drainage, and that which infiltrates through different types of road surface. Access tubes were installed for measuring soil water content using a neutron probe in three car parks, a road and a grass site at the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford. Storm drainage was recorded at the exit of the Thamesmead Estate in Crowmarsh Gifford, just before the drain joins the River Thames at Wallingford. Rainfall and water table depth were also recorded. Weekly measurements of soil moisture content indicated that the top 40 cm layer is not influenced by water‐table fluctuations and, therefore, positive changes in soil moisture could be attributed to infiltration of rainfall through the surface. Depending on the nature of the surface, subsurface layers, level of traffic, etc., between 6 and 9% of rainfall was found to infiltrate through the road surfaces studied. The storm drainage generated by road runoff revealed a flow pattern similar to that of the receiving watercourse (River Thames) and increased with the increase of infiltration and soil water content below the road surface. The ratio of runoff to rainfall was 0·7, 0·9 and 0·5 for annual, winter (October–March) and summer (April–September) respectively. As the results of the infiltration indicated that 6 to 9% of annual rainfall infiltrates through the road surface, this means that evaporation represents, 21–24% of annual rainfall, with more evaporation taking place during summer than winter. Copyright © 2003 John Wiley & Sons, Ltd.     

Thresholds of land cover to control runoff and soil loss

This research focused on the determination of land cover thresholds that have a significant impact on runoff generation and soil loss at the pedon scale. For this purpose, six erosion micro-plots were set up on grassland and shrubland types of rangeland in the northeast of Iran, and the amounts of vegetation cover, litter, runoff and soil loss on them were measured. A factorial statistical analysis was carried out on the completely randomized design using land cover and rainfall factors. The results show that the effect of rainfall on soil loss and runoff was greater than that of land cover. Also, the effect of land cover on soil loss was greater than that on runoff generation. Furthermore, two specific thresholds were identified: the first was from 10 to 30% of landcover and the second from 50 to 70%.     

Grid size effects analysis and hydrological similarity of surface runoff in flatland basins

The effects of grid-size modification on the derived topographic attributes are analysed and a procedure for scaling model parameters and similarity assessment between flow variables is proposed. Hydrological simulations are performed with a physically-based and spatially-distributed quasi-2D mathematical model. The scaled model parameters are the effective roughness coefficient associated with overland flow (n_ov) and the transverse slope in the cell (TSC). To scale the selected parameters, the criterion of equilibrium storage conservation between the different grid sizes is applied. Three basins of the central-east region of Argentina are modelled. The spatial variability of basin geomorphology is quantified using the entropy concept. The simulation results show that when grid size is increased, to obtain similar hydrological responses it is necessary to increase the n_ov or to reduce the TSC. In terms of similarity, the best results are achieved when TSC is scaled, particularly when water depths are considered.     

Plot and small‐watershed scale runoff from two reclaimed surface‐mined watersheds in Alberta

Infiltration excess overland flow has been identified as the dominant flow pathway in recently reclaimed surface mined watersheds as a result of compaction and sorting during the reclamation procedure. Therefore, there could be a fairly direct relationship between runoff generated from the hillslopes to that measured at the watershed outlet. A 3‐year study was initiated in 1993 to determine how well surface runoff at a watershed scale could be predicted from 1‐m² runoff frames placed on hillslopes in two reclaimed surface‐mined watersheds in central Alberta. Runoff from the hillslope frames suggests outlet discharge should be high from the 3\4‐ha Sandy Subsoil Watershed and much less for the 9\8‐ha West Watershed, but the opposite occurred. Most of the hillslope runoff from the Sandy Subsoil Watershed infiltrated once it reached the channel and depression storage played an insignificant role in determining runoff. In contrast, most of the runoff from the West Watershed originated from rain falling directly on the saturated channel (depression storage) or near‐channel saturated areas, rather than the hillslopes. Neither watershed runoff magnitude nor timing could be predicted from the same parameters for hillslope runoff frames for either reclaimed watershed. Copyright © 2000 John Wiley & Sons, Ltd.     

Quality assessment from a hydrological perspective of a digital elevation model derived from WorldView-2 remote sensing data

Abstract

A digital elevation model (DEM) derived from a stereo pair of WorldView-2 (WV-2) images was assessed against ground-truth GPS point datasets. Two assessment methods were used: (a) vertical accuracy assessment and (b) hydrological assessment of surface runoff variables. Three agricultural plots with different topographic slopes were selected to perform a vertical accuracy assessment, followed by a comparative assessment of a set of hydrological variables. The results show an overall vertical accuracy of 0.45 m, confirming the potential of WV-2 stereo images to extract elevation information at high spatial resolution. Concerning plot-scale micro-topographic features, the WV-2 DEM performed better on the plot with rolling slopes (5–10%), extracting variables such as the total length and drainage area of flow paths with relative errors lower than 20%. However, some limitations were detected in the extraction of variables such as terrain slope, drainage points of flow paths and terrain depressions in areas of flatter slopes (<5%).

Editor Z.W. Kundzewicz; Associate editor D. Gerten     

An approach to analysing plot scale infiltration and runoff responses to rainfall of fluctuating intensity

Simulated rainfall of fluctuating intensity was applied to runoff plots on bare dryland soils in order to explore a new method for analysing the non‐steady‐state responses of infiltration and overland flow. The rainfall events all averaged 10 mm/h but included intensity bursts of up to 70 mm/h and lasting 5–15 min, as well as periods of low intensity and intermittency of up to 25 min. Results were compared with traditional steady‐state estimates of infiltrability made under simulated rainfall sustained at a fixed intensity of 10 mm/h. Mean event infiltration rate averaged 13.6% higher under fluctuating intensities, while runoff ratios averaged only 63% of those seen under constant intensity. In order to understand the changing soil infiltrability, up to three affine Horton infiltration equations were fitted to segments of each experiment. All equations had the same final infiltrability f_c, but adjusted values for coefficients f₀ (initial infiltrability) and K_f (exponential decay constant) were fitted for periods of rainfall that followed significant hiatuses in rainfall, during which subsurface redistribution allowed near‐surface soil suction to recover. According to the fitted Horton equations, soil infiltrability recovered by up 10–24 mm/h during intra‐event rainfall hiatuses of 15 to 20‐min duration, contributing to higher overall event infiltration rates and to reduced runoff ratios. The recovery of infiltrability also reduced the size of runoff peaks following periods of low intensity rainfall, compared with the predictions based on single Horton infiltration equations, and in some cases, no runoff at all was recorded from late intensity peaks. The principal finding of this study is that, using a set of affine equations, the intra‐event time variation of soil infiltrability can be tracked through multiple intensity bursts and hiatuses, despite the lack of steady‐state conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Delineating runoff processes and critical runoff source areas in a pasture hillslope of the Ozark Highlands

The identification of runoff contributing areas would provide the ideal focal points for water quality monitoring and Best Management Practice (BMP) implementation. The objective of this study was to use a field‐scale approach to delineate critical runoff source areas and to determine the runoff mechanisms in a pasture hillslope of the Ozark Highlands in the USA. Three adjacent hillslope plots located at the Savoy Experimental Watershed, north‐west Arkansas, were bermed to isolate runoff. Each plot was equipped with paired subsurface saturation and surface runoff sensors, shallow groundwater wells, H‐flumes and rain gauges to quantify runoff mechanisms and rainfall characteristics at continuous 5‐minute intervals. The spatial extent of runoff source areas was determined by incorporating sensor data into a geographic information‐based system and performing geostatistical computations (inverse distance weighting method). Results indicate that both infiltration excess runoff and saturation excess runoff mechanisms occur to varying extents (0–58% for infiltration excess and 0–26% for saturation excess) across the plots. Rainfall events that occurred 1–5 January 2005 are used to illustrate the spatial and temporal dynamics of the critical runoff source areas. The methodology presented can serve as a framework upon which critical runoff source areas can be identified and managed for water quality protection in other watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Stone cover and slope factors influencing hillside surface runoff and infiltration: laboratory investigation

In this study, laboratory rainfall simulation in an extensive area was used to study the infiltration, and interception and storage from surface runoff in points with different stone cover percentages (0, 10, 20 and 30%) and slopes (5°, 10° and 20°). The experimental results of this study showed that the interrelationships among the slope, stone cover percentage, groundwater level, surface runoff amount, and interception and storage of the ponds were varied and irregular. No systematic patterns were detected for the change in the groundwater level, surface runoff amount, and interception and storage of the ponds with different stone cover percentages at different slopes and no threshold values were apparent. For a 5° slope, if the stone cover percentage was increased, the amount of surface runoff was reduced, the infiltration and the groundwater level experienced no significant change, and the interception and storage of the ponds increased. For a 10° slope, if the stone cover percentage was increased, the amount of surface runoff increased, the infiltration decreased, the groundwater level experienced no significant change or decreased slightly at certain points, and the interception and storage of the ponds increased. For a 20° slope, if the stone cover percentage was increased, the amount of runoff increased, the infiltration decreased, the groundwater level experienced no significant change or decreased slightly at certain points, and the interception and storage of the ponds increased. With or without stone cover, when the hydraulic conductivity of the top material is close to that of fine sand or laterite, an increase in the slope gradient decreased the amount of surface runoff and increased the storage amount of the ponds. As for the stone distribution, an interlaced style showed better performance in the interception and storage of ponds than that of a regular style. There was no significant change in the groundwater level. Copyright © 2000 John Wiley & Sons, Ltd.     

Estimation of surface runoff and water‐covered area during filling of surface microrelief depressions

During the filling of surface microrelief depressions the precipitation excess (precipitation minus infiltration and interception) is divided between surface storage and runoff, i.e. runoff starts before the surface depressions are filled. Information on the division of precipitation excess is needed for modelling surface runoff during the filling of surface depressions. Furthermore, information on the surface of the area covered with water is needed for calculating infiltration of water stored in soil surface depressions. Thirty‐two soil surface microreliefs were determined in Danish erosion study plots. The slope was c. 10% for all plots. Data were treated initially by removing the slope, after which 20 ‘artificial’ slopes (1–20%) were introduced producing 640 new data sets. Runoff during filling of the microrelief storage was calculated for each of the 640 data sets using a model developed for calculating surface storage and runoff from grid elevation measurements. Runoff started immediately after the first addition of water for all data sets. On a field scale, however, runoff has to travel some distance as overland flow and storage in smaller and larger depressions below the runoff initiation point must be taken into consideration. The runoff increases by intermittent steps. Whenever a depression starts to overflow to the border of the plot, the runoff jumps accordingly. In spite of the jumps, the distribution between surface storage and runoff was closely related to the quotient between precipitation excess and depression storage capacity. Surface area covered with water was exponentially related to the amount of water stored in surface depressions. Models for calculating surface storage and runoff from grid elevation measurements are cumbersome and require time‐consuming measurements of the soil surface microrelief. Therefore, estimation from roughness indices requiring fewer measurements is desirable. New improved equations for such estimations are suggested. Copyright © 2000 John Wiley & Sons, Ltd.     

A flume design for the study of slope length effects on runoff

Recent publications from field and simulation studies indicate that runoff per unit area decreases as the length of the slope being observed is increased. This scale effect has been observed and documented for slopes with a uniform infiltration capacity as well as for slopes along which infiltration capacity is variable. This paper presents the design and testing of a laboratory flume for the study of the processes that lead to this scale effect, particularly for the case of slopes covered with crops. The features of the flume include reliable experimental control of soil water content prior to rainfall, high intensity rainfall without erosion, uniform crop growth along the slope, and the option of varying the infiltration rate independently of rainfall and soil characteristics. Copyright © 2001 John Wiley & Sons, Ltd.     

Variation in curve numbers derived from plot runoff data for New South Wales (Australia)

The curve number method is a simple one parameter (the curve number) rainfall runoff model. While its theoretical underpinning has been questioned it remains a powerful hydrological tool in the absence of detailed data and is therefore used extensively in hydrological models. This study aims to characterize the variation in maximum retention values (S), which underlie curve numbers, for a range of agricultural treatments across a large spatial area in New South Wales (NSW), Australia. The data used for the analysis spans several decades of rainfall runoff observations. A range of different derivation methods result in variation in mean and variance of S. In particular, methods that emphasize the larger storms result in greater S and thus lower runoff. For larger spatial scales, emphasis on larger storms gives more reliable estimates of S. Systematic variation in S arises from variations in treatment, pre‐runoff soil moisture, rainfall depth, and variations in cover. On the basis of the analysis, a table of curve number values for different land uses found in NSW is presented. The resulting distributions of S and curve numbers provide guidance for rainfall runoff modelling studies in the agricultural important areas of NSW. Copyright © 2011 John Wiley & Sons, Ltd.     

A simple two‐parameter model for scaling hillslope surface runoff

The objective of this research was to develop and parameterise a physically justified yet low‐parameter model to quantify observed changes in surface runoff ratios with hillslope length. The approach starts with the assumption that a unit of rainfall‐excess runoff generated at a point is a fraction β of precipitation P (m) which travels some variable distance down a slope before reinfiltrating, depending on the local rainfall, climate, soils, etc. If this random distance travelled Y is represented by a distribution, then a survival function will describe the probability of this unit of runoff travelling further than some distance x (m). The total amount of per unit width runoff Q (m²) flowing across the lower boundary of a slope of length λ (m) may be considered the sum of all the proportions of the units of rainfall excess runoff integrated from the lower boundary x = 0 to the upper boundary x = λ of the slope. Using these assumptions we derive a model Q(λ) = βPμλ/(μ + λ), (μ > 0, 0 ≤ β ≤ 1, λ ≥ 0) that describes the change in surface runoff with slope length, where μ (m) is the mean of the random variable Y. Dividing both sides of this equation by Pλ yields a simple two‐parameter equation for the dimensionless hillslope runoff ratio Q_h(λ) = βμ/(μ + λ). The model was parameterised with new rainfall and runoff data collected from three replicates of bounded 2 m wide plots of four different lengths (0.5, 1.0, 2.0 and 4.0 m) for 2 years from a forested SE Australian site, and with 32 slope length–runoff data sets from 12 other published studies undertaken between 1934 and 2010. Using the parameterised model resulted in a Nash and Sutcliffe statistic between observed and predicted runoff ratio (for all data sets combined) of 0.93, compared with –2.1 when the runoff ratio was fixed at the value measured from the shortest plot. Copyright © 2014 John Wiley & Sons, Ltd.     

Evidence of large rainfall partitioning patterns by banana and impact on surface runoff generation

In this article the effect of redistribution of rainfall by banana on local water fluxes and the possible impact of these fluxes on surface runoff has been studied. First the water redistribution by a banana canopy at three development stages (vegetative, flowering, and bunch stage) was measured. The results showed a considerable stemflow, proportional to the leaf area index (LAI), which represented 18 to 26% of the incident rainfall volume according to the age of the crop. Consequently, the rainfall rate was 28‐fold higher at the plant collar for a fully developed banana canopy. For the throughfall, on average, the higher the LAI, the lower the mean throughfall. In addition, the spatial distribution of the throughfall varied according to the distance from the pseudostem. Notably, for the earlier stages, the area between the pseudostem and 0·5 m from it received weak throughfall. Secondly, simulations were carried out with a simple two‐compartment model simulating the total surface runoff volume. The simulations showed stemflow combined with the agronomical practice of furrowing has an effect on runoff compared to bare soil. A relative increase in surface runoff volume of three‐fold was encountered on a plot with a fully developed banana and a infiltration rate of 60 mm h^?1. However, the absolute increase was only a few percentage of the incident rainfall volume, although it represented large water volumes given the tropical rains. These features must be taken into account for hydrological management of such systems. Copyright © 2007 John Wiley & Sons, Ltd.