Estimating field‐saturated soil hydraulic conductivity by a simplified Beerkan infiltration experiment

Field‐saturated soil hydraulic conductivity, K_fs, is highly variable. Therefore, interpreting and simulating hydrological processes, such as rainfall excess generation, need a large number of K_fs data even at the plot scale. Simple and reasonably rapid experiments should be carried out in the field. In this investigation, a simple infiltration experiment with a ring inserted shortly into the soil and the estimation of the so‐called α* parameter allowed to obtain an approximate measurement of K_fs. The theoretical approach was tested with reference to 149 sampling points established on Burundian soils. The estimated K_fs with the value of first approximation of α* for most agricultural field soils (α* = 0.012 mm^?1) differed by a practically negligible maximum factor of two from the saturated conductivity obtained by the complete Beerkan Estimation of Soil Transfer parameters (BEST) procedure for soil hydraulic characterization. The measured infiltration curve contained the necessary information to obtain a site‐specific prediction of α*. The empirically derived α* relationship gave similar results for K_fs (mean = 0.085 mm s^?1; coefficient of variation (CV) = 71%) to those obtained with BEST (mean = 0.086 mm s^?1; CV = 67%), and it was also successfully tested with reference to a few Sicilian sampling points, since it yielded a mean and a CV of K_fs (0.0094 mm s^?1 and 102%, respectively) close to the values obtained with BEST (mean = 0.0092 mm s^?1; CV = 113%). The developed method appears attractive due to the extreme simplicity of the experiment. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil degradation in central Spain due to sheet water erosion by low‐intensity rainfall events

Runoff and sediment lost due to water erosion were recorded for 36 (1 m²) plots with varying types of vegetative cover located on sloping gypsiferous fields in the South of Madrid. 75% of the events had maximum 30‐minute intensity (I₃₀) less than 10 mm h^?1 in the period studied (1994–2005). As for the vegetative cover, maximum correlation between runoff and soil loss was found in the least protected plots (0–40% cover) during the most intense rainfall events; however, a significant positive correlation was also observed in plots with greater coverage (40–60%). If coverage exceeded 60%, rainfall erosivity declined. The average amount of sediment produced in high‐intensity events was significantly greater (approximately 7 g m^?2 per I₃₀ event >10 mm h^?1) than that produced in the rest of the moderate‐intensity events (approximately 3 g m^?2 per I₃₀ event <10 mm h^?1), but due to the high rate of occurrence of the latter throughout the year sediment loss during the period studied totaled 128 g m^?2. By comparison, only 40 g m^?2 was produced by the I₃₀ events greater than 10 mm h^?1. Even though the amount of soil lost is relatively insignificant from a quantitative standpoint, the organic matter content lost in the sediment (six times more than in the soil) is a permanent loss that threatens the development of the surface of the soil in this area when the vegetative cover is less than 40%. The soil here experiences a chronic loss of 0·02 mm annually as a consequence of frequent, moderate events, in addition to any loss produced by extraordinary events, which, though less frequent, are much more erosive. If moderate events are ignored, an important part of soil loss will be lost in the long run. Copyright © 2007 John Wiley & Sons, Ltd.     

Infiltration and runoff generation processes in fire‐affected soils

Post‐wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire‐affected soils to predict time‐to‐start of runoff and peak runoff rate at the plot scale (1 m²). Time series of soil‐water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one‐dimensional post‐wildfire numerical model, which was then used as a ‘virtual instrument’ to provide estimates of the saturated hydraulic conductivity and high‐resolution (1 mm) estimates of the soil‐water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting‐front depth indicated that post‐wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, K_s, near the soil surface ranged from 0.1 to 5.2 mm h^?1. Because of the relatively small values of K_s, the time‐to‐start of runoff (measured from the start of rainfall), t_p, was found to depend only on the initial soil‐water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92–97% of the variance of t_p, and the numerical infiltration model explained 74–91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that t_p in fire‐affected soils (which often have low values of K_s) is probably controlled more by the storm profile and the initial soil‐water saturation deficit than by soil hydraulic properties. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Effects of initial soil water content and saturated hydraulic conductivity variability on small watershed runoff simulation using LISEM

Abstract

Soil water content (θ) and saturated hydraulic conductivity (K_s) vary in space. The objective of this study was to examine the effects of initial soil water content (θ_i) and K_s variability on runoff simulations using the LImburg Soil Erosion Model (LISEM) in a small watershed in the Chinese Loess Plateau, based on model parameters derived from intensive measurements. The results showed that the total discharge (TD) and peak discharge (PD) were underestimated when the variability of θ_i and K_s was partially considered or completely ignored compared with those when the variability was fully considered. Time to peak (TP) was less affected by the spatial variability compared to TD and PD. Except for TP in some cases, significant differences were found in all hydrological variables (TD, PD and TP) between the cases in which spatial variability of θ_i or K_s was fully considered and those in which spatial variability was partially considered or completely ignored. Furthermore, runoff simulations were affected more strongly by K_s variability than by θ_i variability. The degree of spatial variability influences on runoff simulations was related to the rainfall pattern and θ_i. Greater rainfall depth and instantaneous rainfall intensity corresponded to a smaller influence of the spatial variability. Stronger effects of the θ_i variability on runoff simulation were found in wetter soils, while stronger effects of the K_s variability were found in drier soils. For accurate runoff simulation, the θ_i variability can be completely ignored in cases of a 1-h duration storm with a return period greater than 10 years, while K_s variability should be fully considered even in the case of a 1-h duration storm with a return period of 20 years.

Editor D. Koutsoyiannis; Associate editor A. Fiori     

Plot‐scale measurement of soil erosion at the experimental area of Sparacia (southern Italy)

Obtaining good quality soil loss data from plots requires knowledge of the factors that affect natural and measurement data variability and of the erosion processes that occur on plots of different sizes. Data variability was investigated in southern Italy by collecting runoff and soil loss from four universal soil‐loss equation (USLE) plots of 176 m², 20 ‘large’ microplots (0·16 m²) and 40 ‘small’ microplots (0·04 m²). For the four most erosive events (event erosivity index, R_e ≥ 139 MJ mm ha^?1 h^?1), mean soil loss from the USLE plots was significantly correlated with R_e. Variability of soil loss measurements from microplots was five to ten times greater than that of runoff measurements. Doubling the linear size of the microplots reduced mean runoff and soil loss measurements by a factor of 2·6–2·8 and increased data variability. Using sieved soil instead of natural soil increased runoff and soil loss by a factor of 1·3–1·5. Interrill erosion was a minor part (0·1–7·1%) of rill plus interrill erosion. The developed analysis showed that the USLE scheme was usable to predict mean soil loss at plot scale in Mediterranean areas. A microplot of 0·04 m² could be used in practice to obtain field measurements of interrill soil erodibility in areas having steep slopes. Copyright © 2003 John Wiley & Sons, Ltd.     

Measurement Method Has a Larger Impact Than Spatial Scale For Plot-Scale Field-Saturated Hydraulic Conductivity (Kfs) After Wildfire and Prescribed Fire in Forests

Wildfires raise risks of floods, debris flows, major geomorphologic and sedimentologic change, and water quality and quantity shifts. A principal control on the magnitude of these changes is field-saturated hydraulic conductivity (K_fs), which dictates surface runoff generation and is a key input into numerical models. This work synthesizes 73 K_fs datasets from the literature in the first year following fire at the plot scale (≤ 10 m²). A meta-analysis using a random effects analysis showed significant differences between burned and unburned K_fs. The reductions in K_fs after fire, expressed by the ratio of K_{fs Burned}/K_{fs Unburned}, were 0.46 (95% confidence interval of 0.31-0.70) combining wildfire and prescribed fire and 0.3 (95% confidence interval of 0.13-0.71) for wildfire. No significant differences for K_fs were observed between wildfire and prescribed fire or moderate and high fire severity. Both K_fs magnitude and variability depended more on measurement method than measurement support area at the plot scale, with methods applying head ≥0.5 cm producing larger estimates of K_fs. It is recommended that post-fire efforts to characterize K_fs for modeling or process-based interpretations use methods that reflect the dominant infiltration processes: tension infiltrometers and simulated rainfall methods when soil matrix flow dominates and ponded head methods when macropore flow is critical. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.     

Hillslope hydrology in tropical rainforest steeplands in Brunei

Many remaining areas of tropical rainforest in south‐east Asia are located on landscapes dominated by deep valleys and very steep slopes. Now that logging activities are extending into these steeplands, it is essential to understand how the natural rainforest system behaves if any kind of realistic assessment of the effects of such disturbance is to be made. This paper examines the hydrological behaviour of an undisturbed rainforest system on steep topography in the Temburong District of Brunei, north‐west Borneo. The physical and hydrological properties of the regolith material are generally typical of tropical residual soils. The regolith has a clay texture and a low dry bulk density beneath a superficial litter/organic horizon. The infiltration capacity of the surface soil was several hundred mm h⁻¹. That of the exposed mineral subsoil was an order of magnitude less, similar to the saturated hydraulic conductivity (K_sat) of around 180 mm h⁻¹ at a depth of 150 cm. There was no indication that K_sat reduced with depth except very near the bedrock interface. Soil tensions were measured using a two‐dimensional array of tensiometers on a 30° slope. During dry season conditions, infiltrating rain‐water contributes to soil moisture, and drying of the soil is dominated by transpiration losses. During wet season conditions, perched water tables quickly develop during heavy rainfall, giving rise to the rapid production of return flow in ephemeral channels. No infiltration excess or saturation overland flow was observed on hillslopes away from channel margins. Subsurface storm flow combined with return flow produce stream flow hydrographs with high peak discharges and very short lag times. Storm event runoff coefficients are estimated to be as high as 40%. It is concluded that the most distinctive feature of the hydrology of this ‘steepland rainforest’ is the extremely ‘flashy’ nature of the catchment runoff regime produced by the combination of thin but very permeable regolith on steep slopes. Copyright © 2000 John Wiley & Sons, Ltd.     

A comparison between the single ring pressure infiltrometer and simplified falling head techniques

Testing the relative performances of the single ring pressure infiltrometer (PI) and simplified falling head (SFH) techniques to determine the field saturated soil hydraulic conductivity, K_fs, at the near point scale may help to better establish the usability of these techniques for interpreting and simulating hydrological processes. A sampling of 10 Sicilian sites showed that the measured K_fs was generally higher with the SFH technique than the PI one, with statistically significant differences by a factor varying from 3 to 192, depending on the site. A short experiment with the SFH technique yielded higher K_fs values because a longer experiment with the PI probably promoted short‐term swelling phenomena reducing macroporosity. Moreover, the PI device likely altered the infiltration surface at the beginning of the run, particularly in the less stable soils, where soil particle arrangement may be expected to vary upon wetting. This interpretation was supported by a soil structure stability index, SSI, and also by the hydraulic conductivity data obtained with the tension infiltrometer, i.e. with a practically negligible disturbance of the sampled soil surface. In particular, a statistically significant, increasing relationship with SSI and an unsaturated conductivity greater than the saturated one were only detected for the K_fs data obtained with the PI. The SFH and PI techniques should be expected to yield more similar results in relatively rigid porous media (low percentages of fine particles and structurally stable soils) than in soils that modify appreciably their particle arrangement upon wetting. The simultaneous use of the two techniques may allow to improve K_fs determination in soils that change their hydrodynamic behaviour during a runoff producing rainfall event. Copyright © 2013 John Wiley & Sons, Ltd.     

Using live vegetation volume to analyze the effects of plot Pinus massoniana Lamb on water and soil conservation under natural rainfall events

The 3-D spatial distributions of vegetation are of great significance for water and soil conservation but are rarely concerned in literatures. The live vegetation volume （LVV） was used to relate to water/soil loss under 144 natural erosive rainfall events from 2007 to 2010 in a typical water-eroded area of southern China. Quadratic polynomial regression models were established for five pure tree （Pinus massoniana Lamb） plots between LVV and water （rtmoff）/soil conservation effects （RE/SE）. RE/SE corresponds to the ratios of runoff depth/soil loss of the pure tree plots to that of the control plot under each rainfall event. Increasing LVV exhibits descending （DS）, descending-ascending （DA）, ascending-descending （AD）, and ascending （AS） trends in the LVV-RE and LVV-SE curves. The effects of soil conservation on the plots were generally more noticeable than the effects of water conservation, and most of the RE and SE values reflected the positive effects of water and soil conservation. The effects were mainly positive under heavy rains （e.g., rainfall erosivity, R = 140 MJ mm ha-l h, maximum 30 min intensity, I30 = 16 mm h-l）, whereas the effects were mainly negative under light rains （e.g., R = 45 MJ mm ha-1 h, I30 = 8 mm h-l）. The trees＇ water/soil conservation effects notably transformed when rainfall erosivity and intensity were lower than the positive or negative effects to a certain threshold. About 50% rainfall events led to obvious transform effects when LVVs were near 0.5 or 0.6. These results are able to aid in the decision making on the forest reconstruction in water-eroded areas.     

A portable rainfall simulator for field assessment of splash and slopewash in remote locations

This paper describes the design, operation and performance of a field‐portable ‘drip‐type’ simulator and erosion measurement system. The system was constructed specifically for soil erosion research in the humid tropics and has been used extensively in Malaysian Borneo. The simulator is capable of producing replicable storms of up to 200 mm h^?1 intensity and 20–30 minutes duration with a drop‐size distribution close to that of natural storms of such intensity (D₅₀ of simulated rainfall is 4·15 mm at 200 mm h^?1 and 3·65 mm at 160 mm h^?1, D⁵⁰ measured during natural rainfall = 3·25 mm). The simulator is portable and simply constructed and operates without a motor or electronics, thus making it particularly useful in remote, mountainous areas. The erosion measurement system allows assessment of: (1) rainsplash detachment and net downslope transport from the erosion plot; (2) slopewash (erosion transported by overland flow); and (3) infiltration capacity and overland flow. The performance of the simulator–erosion system compared with previous systems is assessed with reference to experiments carried out in primary and regenerating tropical rainforest at Danum Valley (Malaysian Borneo). The system was found to compare favourably with previous field simulators, producing a total storm kinetic energy of 727 J m^?2 (over a 20‐minute storm event) and a kinetic energy rate of 0·61 J m^?2 s^?1, approximately half that experienced on the ground during a natural rainfall event of similar intensity, despite the shorter distance to the ground. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of grass soil cover on water runoff and soil detachment under rainfall simulation in a sub‐humid South African degraded rangeland

In most regions of the world overgrazing plays a major role in land degradation and thus creates a major threat to natural ecosystems. Several feedbacks exist between overgrazing, vegetation, soil infiltration by water and soil erosion that need to be better understood. In this study of a sub‐humid overgrazed rangeland in South Africa, the main objective was to evaluate the impact of grass cover on soil infiltration by water and soil detachment. Artificial rains of 30 and 60 mm h^?1 were applied for 30 min on 1 m² micro‐plots showing similar sandy‐loam Acrisols with different proportions of soil surface coverage by grass (Class A: 75–100%; B: 75–50%; C: 50–25%; D: 25–5%; E: 5–0% with an outcropping A horizon; F: 0% with an outcropping B horizon) to evaluate pre‐runoff rainfall (Pr), steady state water infiltration (I), sediment concentration (SC) and soil losses (SL). Whatever the class of vegetal cover and the rainfall intensity, with the exception of two plots probably affected by biological activity, I decreased regularly to a steady rate <2 mm h^?1 after 15 min rain. There was no significant correlation between I and Pr with vegetal cover. The average SC computed from the two rains increased from 0·16 g L^?1 (class A) to 48·5 g L^?1 (class F) while SL was varied between 4 g m^?2 h^?1 for A and 1883 g m^?2 h^?1 for F. SL increased significantly with decreasing vegetal cover with an exponential increase while the removal of the A horizon increased SC and SL by a factor of 4. The results support the belief that soil vegetation cover and overgrazing plays a major role in soil infiltration by water but also suggest that the interrill erosion process is self‐increasing. Abandoned cultivated lands and animal preferred pathways are more vulnerable to erosive processes than simply overgrazed rangelands. Copyright © 2011 John Wiley & Sons, Ltd.     

Near‐saturated surface soil hydraulic properties under different land uses in the St Denis National Wildlife Area,Saskatchewan, Canada

Surface soil hydraulic properties are key factors controlling the partition of rainfall and snowmelt into runoff and soil water storage, and their knowledge is needed for sound land management. The objective of this study was to evaluate the effects of three land uses (native grass, brome grass and cultivated) on surface soil hydraulic properties under near‐saturated conditions at the St Denis National Wildlife Area, Saskatchewan, Canada. For each land use, water infiltration rates were measured using double‐ring and tension infiltrometers at ?0·3, ?0·7, ?1·5 and ?2·2 kPa pressure heads. Macroporosity and unsaturated hydraulic properties of the surface soil were estimated. Mean field‐saturated hydraulic conductivity (K_fs), unsaturated hydraulic conductivity at ?0·3 kPa pressure head, inverse capillary length scale (α) and water‐conducting macroporosity were compared for different land uses. These parameters of the native grass and brome grass sites were significantly (p < 0·1) higher than that of the cultivated sites. At the ?0·3 kPa pressure head, hydraulic conductivity of grasslands was two to three times greater than that of cultivated lands. Values of α were about two times and values of K_fs about four times greater in grasslands than in cultivated fields. Water‐conducting macroporosity of grasslands and cultivated fields were 0·04% and 0·01% of the total soil volume, respectively. Over 90% of the total water flux at ?0·06 kPa pressure head was transmitted through pores > 1·36 × 10^?4 m in diameter in the three land uses. Land use modified near‐saturated hydraulic properties of surface soil and consequently may alter the water balance of the area by changing the amount of surface runoff and soil water storage. Copyright © 2004 John Wiley & Sons, Ltd.     

Runoff initiation in a preserved semiarid Caatinga small watershed,Northeastern Brazil

This study analyses some hydrological driving forces and their interrelation with surface‐flow initiation in a semiarid Caatinga basin (12 km²), Northeastern Brazil. During the analysis period (2005 – 2014), 118 events with precipitation higher than 10 mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on‐site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface‐water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60‐min rainfall intensity (I₆₀). Runoff always occurred when rainfall surpassed 31 mm, but it never occurred for rainfall below 14 mm or for I₆₀ below 12 mm h^?1. The fact that the duration of the critical intensity is similar to the basin concentration time (65 min) and that the infiltration threshold value approaches the river‐bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27% of the events. It is possible that surface‐flow initiation in the Caatinga biome is strongly influenced by the root‐system dynamics, which changes macro‐porosity status and, therefore, initial abstraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Impacts of annual precipitation extremes on soil and nutrient losses in vineyards of NE Spain

The objective of this research was to characterise annual precipitation extremes in a Mediterranean vineyard region. The number of exceptional events (P > 95th percentile) and annual extreme events (P > 99th percentile), as well as their strength, erosive character and return period were analysed for 2000–2004. The erosive character was evaluated according to the R‐factor (kinetic energy × maximum intensity in 30‐min periods). Soil and nutrient losses caused by these events were evaluated by combining field sampling and a hydrological model to estimate total runoff in a vineyard plot. The results show a clear increase in the number of very wet days and extreme events (P > 95th percentile), which represented up to 88% of annual rainfall. The severity of the extreme events (TS = precipitation event P > 99th percentile) reached values higher than 50 mm almost every year. These values were far exceeded in 2000, when one extraordinary event recorded 50% of the annual rainfall, with TS of 189 mm, about 80% of total rainfall being lost as runoff. Annual erosivity was driven not only by extreme events, but also by short events of less depth but high intensity. During some of the years analysed, rainfall erosivity was two or three times the average in the area. Most soil and nutrient losses occurred in a small number of events: one or two events every year were responsible for more than 75% of the annual soil and nutrient losses on average. Antecedent soil moisture conditions, runoff rates, and events with a return period higher than two years were responsible for the higher erosion rates. Apart from an exceptional event recorded in 2000, which produced more than 200 Mg ha^?1 soil losses, annual soil losses up to 25 Mg ha^?1 were recorded, which are much higher than the soil loss tolerance. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrological and erosional response to natural rainfall in a semi‐arid area of south‐east Spain

A better knowledge of soil erosion by water is essential for planning effective soil and water conservation practices in semi‐arid Mediterranean environments. The special climatic and hydrological characteristics of these areas, however, make accurate soil loss predictions difficult, particularly in the absence of minimal data. Two zero‐order experimental microcatchments (328–759 m²), representative of an extensive semi‐arid watershed with a high potential erosion risk in the south‐east of Spain, were selected and monitored for 3 years (1991–93) in order to provide information on the hydrological and erosional response. A pluviogram and hydrograph recorded data at 1‐min intervals during each storm, after which the soil loss was collected and the particle size of the sediment was analysed. Runoff coefficients of about 9% and soil losses of between 84·83 and 298·9 g m^?2 year^?1 were observed in the area. Rapid response times (geometric mean values lower than 2 h) and low runoff thresholds (mean values between 3·5 to 5·9 mm) were the norm in the experimental areas. A rain intensity of over 15 mm h^?1 was considered as ‘erosive rainfall’ in these areas because of the total soil loss and the transport capacity of the overland flow. Differences in pore‐size distribution explained the different hydrological responses observed between areas. The erosional response was more complex and basically seemed to be determined by soil aggregate stability and topographical properties. A greater proportion of finer particles in the eroded material than in the soil matrix indicated selective erosion and the transport of finer material. Copyright © 2001 John Wiley & Sons, Ltd.     

Sediment and solute transport on soil slope under simultaneous influence of rainfall impact and scouring flow

Soil erosion and nutrient losses with surface runoff in the loess plateau in China cause severe soil quality degradation and water pollution. It is driven by both rainfall impact and runoff flow that usually take place simultaneously during a rainfall event. However, the interactive effect of these two processes on soil erosion has received limited attention. The objectives of this study were to better understand the mechanism of soil erosion, solute transport in runoff, and hydraulic characteristics of flow under the simultaneous influence of rainfall and shallow clear‐water flow scouring. Laboratory flume experiments with three rainfall intensities (0, 60, and 120 mm h⁻¹) and four scouring inflow rates (10, 20, 30, and 40 l min⁻¹) were conducted to evaluate their interactive effect on runoff. Results indicate that both rainfall intensity and scouring inflow rate play important roles on runoff formation, soil erosion, and solute transport in the surface runoff. A rainfall splash and water scouring interactive effect on the transport of sediment and solute in runoff were observed at the rainfall intensity of 60 mm h⁻¹ and scouring inflow rates of 20 l min⁻¹. Cumulative sediment mass loss (Ms) was found to be a linear function of cumulative runoff volume (Wr) for each treatment. Solute transport was also affected by both rainfall intensity and scouring inflow rate, and the decrease in bromide concentration in the runoff with time fitted to a power function well. Reynolds number (Re) was a key hydraulic parameter to determine erodability on loess slopes. The Darcy–Weisbach friction coefficients (f) decreased with the Reynolds numbers (Re), and the average soil and water loss rate (M_l) increased with the Reynolds numbers (Re) on loess slope for both scenarios with or without rainfall impact. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of soil‐hydraulic properties and infiltration timescales in wildfire‐affected soils

We collected soil‐hydraulic property data from the literature for wildfire‐affected soils, ash, and unburned soils. These data were used to calculate metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity (S) and wetting front potential (Ψ_f) were significantly different (lower) in burned soils compared with unburned soils, whereas field‐saturated hydraulic conductivity (K_fs) was not significantly different. The magnitude and duration of the influence of capillarity during infiltration was greatly reduced in burned soils, causing faster ponding times in response to rainfall. Ash had large values of S and K_fs but moderate values of Ψ_f, compared with unburned and burned soils, indicating ash has long ponding times in response to rainfall. The ratio of S²/K_fs was nearly constant (~100 mm) for unburned soils but more variable in burned soils, suggesting that unburned soils have a balance between gravity and capillarity contributions to infiltration that may depend on soil organic matter, whereas in burned soils the gravity contribution to infiltration is greater. Changes in S and K_fs in burned soils act synergistically to reduce infiltration and accelerate and amplify surface runoff generation. Synthesis of these findings identifies three key areas for future research. First, short timescales of capillary influences on infiltration indicate the need for better measurements of infiltration at times less than 1 min to accurately characterize S in burned soils. Second, using parameter values, such as Ψ_f, from unburned areas could produce substantial errors in hydrologic modeling when used without adjustment for wildfire effects, causing parameter compensation and resulting underestimation of K_fs. Third, more thorough measurement campaigns that capture soil‐structural changes, organic matter impacts, quantitative water repellency trends, and soil‐water content along with soil‐hydraulic properties could drive the development of better techniques for numerically simulating infiltration in burned areas.     

Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin

Ten representative research sites were selected in eastern Spain to assess soil erosion rates and processes in new citrus orchards on sloping soils. The experimental plots were located at representatives sites on limestone, in areas with 498 to 715 mm year^?1 mean annual rainfall, north‐facing slopes, herbicide treated, and new (less than 3 years old) plantations. Ten rainfall simulation experiments (1 h at 55 mm h^?1 on 0·25 m² plots) were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates. The 100 rainfall simulation tests (10 × 10 m) showed that ponding and runoff occurred in all the plots, and quickly: 121 and 195 s, respectively, following rainfall initiation. Runoff discharge was one third of the rainfall, and sediment concentration reached 10·4 g L^?1. The soil erosion rates were 2·4 Mg ha^?1 h^?1 under 5‐year return period rainfall thunderstorms. These are among the highest soil erosion rates measured in the western Mediterranean basin, similar to badland, mine spoil and road embankment land surfaces. The positive relationship between runoff discharge and sediment concentration (r² = 0·83) shows that the sediment availability is very high. Soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable. Copyright © 2009 John Wiley & Sons, Ltd.     

Severe soil erosion during a 3‐day exceptional rainfall event: combining modelling and field data for a fallow cereal field

Exceptional rainfall events cause significant losses of soil, although few studies have addressed the validation of model predictions at field scale during severe erosive episodes. In this study, we evaluate the predictive ability of the enhanced Soil Erosion and Redistribution Tool (SERT‐2014) model for mapping and quantifying soil erosion during the exceptional rainfall event (~235 mm) that affected the Central Spanish Pyrenees in October 2012. The capacity of the simulation model is evaluated in a fallow cereal field (1.9 ha) at a high spatial scale (1 × 1 m). Validation was performed with field‐quantified rates of soil loss in the rills and ephemeral gullies and also with a detailed map of soil redistribution. The SERT‐2014 model was run for the six rainfall sub‐events that made up the exceptional event, simulating the different hydrological responses of soils with maximum runoff depths ranging between 40 and 1017 mm. Predicted average and maximum soil erosion was 11 and 117 Mg ha^?1 event^?1, respectively. Total soil loss and sediment yield to the La Reina gully amounted to 16.3 and 9.0 Mg event^?1. These rates are in agreement with field estimations of soil loss of 20.0 Mg event^?1. Most soil loss (86%) occurred during the first sub‐event. Although soil accumulation was overestimated in the first sub‐event because of the large amount of detached soil, the enhanced SERT‐2014 model successfully predicted the different spatial patterns and values of soil redistribution for each sub‐event. Further research should focus on stream transport capacity. Copyright © 2014 John Wiley & Sons, Ltd.     

Infiltration,runoff and soil loss in Andisols affected by forest fire (Canary Islands,Spain)

Depending on the severity of the fire, forest fires may modify infiltration and soil erosion processes. Rainfall simulations were used to determine the hydrological effects of fire on Andisols in a pine forest burned by a wildfire in 2007. Six burned zones with different fire severities were compared with unburned zones. Infiltration, runoff and soil loss were analysed on slopes of 10% and 30%. Forest floor and soil properties were evaluated. Unburned zones exhibited relatively low infiltration (23 and 16 mm h^?1 on 10% and 30% slope angles, respectively) and high average runoff/rainfall ratios (43% and 50% on 10% and 30% slope angles, respectively), which were associated with the extreme water repellency of the forest floor. Nonetheless, this layer seems to provide protection against raindrop impact and soil losses were found to be low (8 and 16 g m^?2 h^?1 for 10% and 30% slope angles, respectively). Soil cover, soil structure and water repellency were the main properties affected by the fire. The fire reduced forest floor and soil repellency, allowing rapid infiltration. Moreover, a significant decrease was noted in soil aggregate stabilities in the burned zones, which limited the infiltration rates. Consequently, no significant differences in infiltration and runoff were found between the burned and the unburned zones. The decrease in post‐fire soil cover and soil stability resulted in order‐of‐magnitude increases in erosion. Sediment rates were 15 and 31 g m^?2 h^?1 on the 10% and 30% slope angles, respectively, in zones affected by light fire severity. In the moderate fire severity zones, these values reached 65 and 260 g m^?2 h^?1 for the 10% and 30% slope angles, respectively. Copyright © 2012 John Wiley & Sons, Ltd.