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Infiltration Rates (infiltration + rate)
Selected AbstractsCauses and consequences of fire-induced soil water repellencyHYDROLOGICAL PROCESSES, Issue 15 2001J. Letey Abstract A wettable surface layer overlying a water-repellent layer is commonly observed following a fire on a watershed. High surface temperatures ,burn' off organic materials and create vapours that move downward in response to a temperature gradient and then condense on soil particles causing them to become water repellent. Water-repellent soils have a positive water entry pressure hp that must be exceeded or all the water will runoff. Water ponding depths ho that exceeds hp will cause infiltration, but the profile is not completely wetted. Infiltration rate and soil wetting increase as the value of ho/hp increases. The consequence is very high runoff, which also contributes to high erosion on fire-induced water-repellent soils during rain storms. Grass establishment is impaired by seeds being eroded and lack of soil water for seeds that do remain and germinate. Extrapolation of these general findings to catchment or watershed scales is difficult because of the very high temporal and spatial variabilities that occur in the field. Copyright © 2001 John Wiley & Sons, Ltd. [source] Spatial variability of soil and nutrient characteristics of semi-arid grasslands and shrublands, Jornada Basin, New MexicoECOHYDROLOGY, Issue 1 2008Eva Nora Mueller Abstract Heterogeneity of vegetation and soil properties is characteristic of semi-arid and arid environments. The potential underlying causes of the dynamics that create this spatial variability, with consequent impacts on landscape connectivity and thus ecological and ecohydrological processes, are not clearly understood. An investigation was carried out into the spatial variability of ponded infiltration rate, soil moisture, soil-aggregate stability, vegetation cover, random roughness and nutrient content in the soil (ammonium, nitrate and phosphorus) at grassland and shrubland sites for two spatial scales in the Jornada Basin, in the northern part of the Chihuahua desert. At the plant-interplant scale, statistically significant differences exist between vegetated and non-vegetated sites for soil moisture and infiltration rate within both shrublands and grasslands. The spatial distributions of all other parameters follow a more complex scheme at this scale. At the landscape scale, distinct differences exist for most parameters between the grasslands and the shrubland sites. Geostatistical analysis revealed that the autocorrelation lengths are not simply a function of average shrub sizes, but may be caused by a more complex pattern probably related to the spatial layout of rill and inter-rill areas and other localized transfers of soil resources through the redistribution of water and wind. These results demonstrate the importance of understanding spatial linkages of processes within the landscape in understanding dryland ecosystem dynamics. Copyright © 2007 John Wiley & Sons, Ltd. [source] Non-equilibrium water flow characterized by means of upward infiltration experimentsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2001Summary Upward infiltration experiments under tension were used to demonstrate the presence of non-equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non-aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single-porosity Richards equation, as well as a variably saturated, dual-porosity model and a dual-permeability model for characterizing non-equilibrium water flow. The laboratory experiments were carried out on 0.10-m-long soil cores having an internal diameter of 0.10 m. Constant pressure heads of ,0.10 and ,0.01 m were used as the lower boundary condition. Each infiltration was followed by a single-rate evaporation experiment to re-establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus-1D software) with a Marquardt,Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non-equilibrium flow. This behaviour could be well characterized using a model of physical non-equilibrium that divides the medium into inter- and intra-aggregate pores with first-order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis. [source] A probabilistic investigation of infiltration in the vadose zone: proposal for a new formula of infiltration rateHYDROLOGICAL PROCESSES, Issue 21 2007Erick Carlier Abstract The infiltration rate in the unsaturated zone is analysed from a probabilistic point of view. It is shown that the empirical formulas of Horton and Kostiakov, without apparent physical basis, are explained in a probabilistic approach. Horton's formula reflects a Markovian process contrary to Kostiakov's formula. This approach made it possible to explain why Kostiakov's formula is more powerful than that of Horton. A new equation of infiltration is proposed. The three formulas were compared, for four types of soil, with the model of van Genuchten based on the Richards equation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Mobility of major ions and nutrients in the unsaturated zone during paddy cultivation: a field study and solute transport modelling approachHYDROLOGICAL PROCESSES, Issue 20 2007N. Rajmohan Abstract Study of the movement of water and solute within soil profiles is important for a number of reasons. Accumulation of prominent contaminants from agricultural chemicals in the unsaturated zone over the years is a major concern in many parts of the world. As a result, the unsaturated zone has been a subject of great research interest during the past decade. Hence, an intensive field study was conducted in a part of Palar and Cheyyar river basins to understand the variation of major ions and nutrients in the soil zone during paddy cultivation. The chloride and nitrate data were used to model the movement of these chemicals in the unsaturated zone using the HYDRUS-2D model. The field study shows that fertilizer application and irrigation return flow increases the major ions and nutrients concentration in the unsaturated zone. Further, the nutrient concentrations are regulated by plant uptake, fertilizer application and infiltration rate. Additionally, denitrification and soil mineralization processes also regulate the nitrogen concentration in the unsaturated zone. The solute transport modelling study concluded that the simulated results match reasonably with the observed trends. Simulated concentrations of chloride and nitrate for a 5-year period indicate that the concentrations of these ions fluctuate in a cyclic manner (from 60 to 68 mg l,1 and from 3·4 to 3·5 mg l,1 respectively in groundwater) with no upward and downward trend. The influence of excessive fertilizer application on groundwater was also modelled. The model predicts an increase of about 17 mg l,1 of chloride and 2·3 mg l,1 of nitrogen in the groundwater of this area when the application of fertilizers is doubled. The model indicates that the present level of use of agrochemicals is no threat to the groundwater quality. Copyright © 2007 John Wiley & Sons, Ltd. [source] Infiltration into effluent irrigation-induced repellent soils and the dependence of repellency on ambient relative humidityHYDROLOGICAL PROCESSES, Issue 17 2007R. Wallach Abstract As a result of water scarcity and as a means of wastewater disposal, reuse of treated sewage effluent in irrigated agriculture is practiced worldwide. Among the detrimental aspects of wastewater re-use in agriculture is the possibility that soils will be rendered water repellent. The current study focuses on time dependent variation of infiltration rate in effluent-induced repellent soils, and time dependent variation in water repellency at different levels of ambient relative humidity (RH). The shape of the cumulative infiltration curve of water was found to depend on the repellency degree (concave for wettable and slightly repellent soils, convex for severely repellent soil). Compared with infiltration rates in the wettable and slightly repellent soils, infiltration rates in the severely repellent soil were very low at the beginning and then increased. When the liquid-vapor surface tension was reduced by means of ethanol addition to the infiltrating solution, the cumulative infiltration curve of the severely repellent soil also became concave. Repellency degree (as measured by WDPT) was found to be essentially constant over a large range of ambient RH values (<10 , ,81%), and to increase sharply at values above 90%. The relative increase in water drop penetration time (WDPT) at high RH was greatest for the least repellent soil (10-fold increase in WDPT), and least for the most repellent soil (2-fold increase in WDPT). At RH > 90%, the time to reach equilibrium with respect to WDPT and soil moisture content was similar. In contrast, at values of ambient RH ranging from < 10 to 81%, WDPT was invariant over the course of reaching equilibrium with respect to moisture content. However, after reaching moisture content equilibrium, WDPT declined with increasing time. Copyright © 2007 John Wiley & Sons, Ltd. [source] A field-scale infiltration model accounting for spatial heterogeneity of rainfall and soil saturated hydraulic conductivityHYDROLOGICAL PROCESSES, Issue 7 2006Renato Morbidelli Abstract This study first explores the role of spatial heterogeneity, in both the saturated hydraulic conductivity Ks and rainfall intensity r, on the integrated hydrological response of a natural slope. On this basis, a mathematical model for estimating the expected areal-average infiltration is then formulated. Both Ks and r are considered as random variables with assessed probability density functions. The model relies upon a semi-analytical component, which describes the directly infiltrated rainfall, and an empirical component, which accounts further for the infiltration of surface water running downslope into pervious soils (the run-on effect). Monte Carlo simulations over a clay loam soil and a sandy loam soil were performed for constructing the ensemble averages of field-scale infiltration used for model validation. The model produced very accurate estimates of the expected field-scale infiltration rate, as well as of the outflow generated by significant rainfall events. Furthermore, the two model components were found to interact appropriately for different weights of the two infiltration mechanisms involved. Copyright © 2005 John Wiley & Sons, Ltd. [source] Assessing burn severity and comparing soil water repellency, Hayman Fire, ColoradoHYDROLOGICAL PROCESSES, Issue 1 2006Sarah A. Lewis Abstract An important element of evaluating a large wildfire is to assess its effects on the soil in order to predict the potential watershed response. After the 55 000 ha Hayman Fire on the Colorado Front Range, 24 soil and vegetation variables were measured to determine the key variables that could be used for a rapid field assessment of burn severity. The percentage of exposed mineral soil and litter cover proved to be the best predictors of burn severity in this environment. Two burn severity classifications, one from a statistical classification tree and the other a Burned Area Emergency Response (BAER) burn severity map, were compared with measured ,ground truth' burn severity at 183 plots and were 56% and 69% accurate, respectively. This study also compared water repellency measurements made with the water drop penetration time (WDPT) test and a mini-disk infiltrometer (MDI) test. At the soil surface, the moderate and highly burned sites had the strongest water repellency, yet were not significantly different from each other. Areas burned at moderate severity had 1·5 times more plots that were strongly water repellent at the surface than the areas burned at high severity. However, the high severity plots most likely had a deeper water repellent layer that was not detected with our surface tests. The WDPT and MDI values had an overall correlation of r = ,0·64(p < 0·0001) and appeared to be compatible methods for assessing soil water repellency in the field. Both tests represent point measurements of a soil characteristic that has large spatial variability; hence, results from both tests reflect that variability, accounting for much of the remaining variance. The MDI is easier to use, takes about 1 min to assess a strongly water repellent soil and provides two indicators of water repellency: the time to start of infiltration and a relative infiltration rate. Copyright © 2005 John Wiley & Sons, Ltd. [source] Saline Drainage Water, Irrigation Frequency and Crop Species Effects on Some Physical Properties of SoilsJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2001Y. A. Al-Nabulsi This field study evaluated the effects of water quality, irrigation frequency and crop species on some physical properties of soils. The experiment had a split-split-plot design, with three irrigation water qualities (normal water, drainage water and a 1 : 1 mixture of freshwater and drainage water) as the main treatments, two irrigation frequencies (at 7- and 14-day intervals) as the subtreatments and two crops (barley and alfalfa) as the subsubtreatments. The soil infiltration rate was highest in the barley plot receiving freshwater irrigation at weekly intervals. The lowest soil infiltration rate was found in alfalfa plots receiving saline irrigation water at 14-day intervals. Bulk density and proportions of micropores [pore radius (r) < 1.4 µm] were higher and the proportion of macropores (r > 14.4 µm) was lower in barley than in alfalfa. Saline irrigation caused the greatest decrease in total porosity. The soil infiltration rate was higher with more frequent irrigation, and was highest in alfalfa plots receiving freshwater irrigation. The decrease in soil bulk density and infiltration rate was greater with saline drainage water, irrespective of the crop grown and the irrigation frequency. Salzhaltiges Drainagewasser, Bewässerungshäufig-keit und Kulturpflanzenarten mit Wirkung auf einige physikalische Eigenschaften des Bodens Eine Felduntersuchung wurde vorgenommen, um dem Einfluss der Wasserqualität, der Bewässerungshäufigkeit und Kulturpflanzenarten auf einige physikalische Eigenschaften von Böden zu untersuchen. Die Infiltrationrate mit Frischwasser in wöchentlichen Abständen unter Gerste war hoch. Eine Behandlung mit Salzwasser in 14 tägigen Abständen unter Luzerne zeigte eine geringere Infiltrationsrate des Bodens. Bodendichte und der Anteil der Mikroporen (Poren mit einem Radius von r < 1,4 mm) waren größer und der Anteil der Makroporen (r > 14,4 mm) war unter Gerste geringer. Bewässerung mit Salzwasser verursachte die stärkste Abnahme in der Gesamtporosität. Die Infiltrationsrate des Bodens nahm mit der Häufigkeit der Bewässerung zu und zeigte den höchsten Wert bei Luzerne und einer Frischwasserbewässerung. Die Abnahme in der Bodendichte und der Infiltrationseigenschaften waren bei Salzwasserdrainage unabhängig von der Kulturpflanzenart und der Bewässerungshäufigkeit höher. [source] Immediate effects of prescribed burning, chopping and clearing on runoff, infiltration and erosion in a shrubland area in Galicia (NW Spain)LAND DEGRADATION AND DEVELOPMENT, Issue 5 2008C. Fernández Abstract The immediate effects of three different fuel management treatments on runoff, infiltration and erosion were evaluated in a mixed heathland in Galicia (NW Spain). The treatments compared were: prescribed burning, shrub chopping and shrub clearing. Rainfall simulations were conducted immediately before and after fuel reduction treatments. A rainfall rate of 67,mm,h,1 was applied for 30,min to each runoff plot. Application of treatments significantly affected runoff and infiltration, but the parameter most affected by treatment was soil erosion, especially after prescribed burning. However, sediment yields measured immediately after treatments were low in all the cases, varying from 32,kg,ha,1 after shrub clearing to 248,kg,ha,1 after prescribed burning. In the rainfall simulation plots subjected to prescribed burning, the maximum temperatures reached at mineral soil surface during burns significantly affected soil losses. The organic layer remaining after treatments and soil moisture contents appeared to be critical variables in controlling runoff and erosion during the first rainfall event following fuel reduction treatments. When the remaining organic layer was removed just after treatments and a new rainfall simulation was carried out, mean infiltration rate trended to decrease and cumulative runoff and sediment yield tended to increase. The above information could be useful for determining whether fuel management prescriptions are compatible with fire hazard reduction and soil conservation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Fodder production and soil health with conjunctive use of saline and good quality water in ustipsamments of a semi-arid regionLAND DEGRADATION AND DEVELOPMENT, Issue 2 2007R. K. Yadav Abstract Food and fodder shortage in arid and semi-arid regions force farmers to use marginal quality water for meeting the water requirement of crops which result in low quality, reduced production and an adverse impact on soil properties. A field study on loamy-sand (Hyperthermic Typic Ustipsamments) saline soil was conducted during 1999,2001 at Central Institute for Research on Buffaloes, Hisar. This involved assessment of effects of conjunctive use of saline water, EC,=,4·6,7·4,dSm,1, SAR,=,14,22 ((mmol,1)½ with good quality water on five fodder crop rotations: oat-sorghum (Avena sativa- ,Sorghum bicolor), rye grass,sorghum (Loleum rigidum,Sorghum bicolor), Egyptian clover,sorghum (Trifoleum alexandrinum,Sorghum bicolor), Persian clover,sorghum (Trifoleum resupinatum,Sorghum bicolor) and Indian clover,sorghum (Melilotus indica,Sorghum bicolor) and certain soil properties associated with it. Leguminous winter fodder crops were more sensitive to poor quality water use. Reductions in fodder yield with use of saline water alone throughout season were 85, 68, 54, 42, 36 and 26 per,cent in Indian clover, Egyptian clover, Persian clover, oat, rye grass and sorghum respectively as compared to good quality water. Leguminous fodder crops produced protein rich (12,14 per,cent) and low fibre (18,20 per,cent) fodder as compared to poor quality grassy fodder under good quality water irrigation but their quality deteriorated when saline water was used. These leguminous crops accumulated proportionately higher Na+ (1·58 per,cent) resulting in adverse impact on their growth as compared to grassy fodder crops. Higher soil salinity (12·2,dSm,1), SAR,=,20 (mmol,1)½ was recorded with saline water irrigation; and slight adverse impact was noticed on infiltration rate and contents of water dispersible clay. Alternate cyclic use of canal and saline water could be an option for fodder production under such conditions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Rehabilitation of degraded sodic lands during a decade of Dalbergia sissoo plantation in Sultanpur District of Uttar Pradesh, IndiaLAND DEGRADATION AND DEVELOPMENT, Issue 5 2002A. Mishra Abstract The ameliorative effect of Dalbergia sissoo, planted on sodic land at Sultanpur (26° 10,,26° 40,N, 81° 45,,82° 30,E), India, in a tropical environment, was studied at 3, 6 and 9 years of age. The soil properties of the sites improved significantly, showing marked reduction in pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP) and an increase in organic carbon, nitrogen and availability of nutrients in the soil. The significant reduction in Na ion was found in all the age groups. Results showed an improvement in the soil moisture regime due to increased infiltration rate (cm,hr,1), soil permeability (cm2), water-holding capacity, field capacity and pore space whereas, the bulk density decreased significantly after successive years of planting. The effect on soil attributes was confined to surface soil in the young plantation and deeper in older plantation. Therefore, the study clearly indicated that the sodic soil could be desodified by growing D. sissoo plantations on these degraded sites. Copyright © 2002 John Wiley & Sons, Ltd. [source] Success of Ultrasound-guided Peripheral Intravenous Access with Skin MarkingACADEMIC EMERGENCY MEDICINE, Issue 8 2008Jessica R. Resnick MD Abstract Objectives:, The most effective technique for ultrasound-guided peripheral intravenous access (USGPIVA) is unknown. In the traditional short-axis technique (locate, align, puncture [LAP]), the target vessel is aligned in short axis with the center of the transducer. The needle is then directed toward the target under real-time ultrasound (US) guidance. Locate, align, mark, puncture (LAMP) requires the extra step of marking the skin at two points over the path of the vein and proceeding with direct visualization as in LAP. The difference in success between these two techniques was compared among variably experienced emergency physician and emergency nurse operators. Methods:, Subjects in an urban academic emergency department (ED) were randomized to obtain intravenous (IV) access using either LAP or LAMP after two failed blind attempts. Primary outcomes were success of the procedure and time to complete the procedure in variably experienced operators. Results:, A total of 101 patients were enrolled. There was no difference in success between LAP and LAMP, even among the least experienced operators. Of successful attempts, LAMP took longer than LAP (median 4 minutes, interquartile range [IQR] 4,10.5 vs. median 2.9 minutes, IQR 1.6,7; p = 0.004). Only the most experienced operators were associated with higher levels of success (first attempt odds ratio [OR] 6.64; 95% confidence interval [CI] = 2 to 22). Overall success with up to two attempts was 73%. Complications included a 2.8% arterial puncture rate and 12% infiltration rate. Conclusions:, LAMP did not improve success of USGPIVA in variably experienced operators. Experience was associated with higher rates of success for USGPIVA. [source] Extreme events controlling erosion and sediment transport in a semi-arid sub-andean valleyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2002R. Coppus Abstract The importance of extreme events in controlling erosion and sediment transport in semi-arid areas has long been appreciated but in practice being by definition rare and episodic they are difficult to study. When they are observed this is frequently in catchments for which little data are available. Another difficulty is that even when catchments are being monitored the instruments that record discharge, sediment load and hillslope sediment fluxes perform inaccurately or unpredictably during extreme weather conditions. This paper describes slope and channel processes that were actually observed by the authors during a (at least) 1 : 30 year 30 minute event with a rainfall intensity of 240 mm h,1 in a second-order tributary of the Rio Camacho near Tarija in southern Bolivia. During the event, it could be observed how different tributary streams and slope sections contributed sediments and flow to the main channel. Evidence for these contributions did not survive the event, which has implications for both modelling and monitoring. Before the onset of the event open erosion plots were functioning on the slopes where rainfall and runoff were being measured. Rainfall experiments were used to obtain infiltration rates. The storm began with a moderate intensity of about 5 cm per hour but increased after 5 minutes to 30 cm per hour and continued for 30 minutes. At this time, the rainfall intensity greatly exceeded the infiltration capacity and water started draining the steep slopes. The ephemeral channel rapidly filled up with runoff. Erosion by hailstones was considerable. Provisionally, the discharge during peak runoff was estimated at 43·7 m3 s,1 (Manning equation). On the basis of sediment loads carried by previous storms, (average concentration of 21 g l,1) the total suspended load discharge during the storm would have been 15 ton ha,1. Within the ephemeral channel, 10 to 50 cm thick layers of coarse sediments were deposited. The collectors of the open erosion plots could not handle the large amounts of runoff and sediment and were completely filled to overflowing. Comparing these data with soil losses during less intense storms it can be concluded that extreme events largely contribute to erosion and sediment transport and that the majority of the rainstorms play only a minor role. The results also show how limited the values of rainfall experiments are in understanding geomorphic events. This makes modelling of erosion and soil losses a difficult and hazardous task. Copyright © 2002 John Wiley & Sons, Ltd. [source] Soil infiltration, runoff and sediment yield from a shallow soil with varied stone cover and intensity of rainEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005Uttam Kumar Mandal Summary Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side-effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi-arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour,1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour,1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l,1 for 64.7% stone cover with rainfall of 48.5 mm hour,1 to 70 g l,1 for 3.5% stone cover with rain falling at 136.8 mm hour,1. The soil loss rate was less than 2 t ha,1 hour,1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour,1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size. [source] The Lisse Effect RevisitedGROUND WATER, Issue 6 2002Edwin P. Weeks The Lisse effect is a rarely noted phenomenon occurring when infiltration caused by intense rain seals the surface soil layer to airflow, trapping air in the unsaturated zone. Compression of air by the advancing front results in a pressure increase that produces a water-level rise in an observation well screened below the water table that is several times as large as the distance penetrated by the wetting front. The effect is triggered by intense rains and results in a very rapid water-level rise, followed by a recession lasting a few days. The Lisse effect was first noted and explained by Thal Larsen in 1932 from water-level observations obtained in a shallow well in the village of Lisse, Holland. The original explanation does not account for the increased air pressure pushing up on the bottom of the wetting front. Analysis of the effect of this upward pressure indicates that a negative pressure head at the base of the wetting front, ,f, analogous to that postulated by Green and Ampt (1911) to explain initially rapid infiltration rates into unsaturated soils, is involved in producing the Lisse effect. Analysis of recorded observations of the Lisse effect by Larsen and others indicates that the water-level rise, which typically ranges from 0.10 to 0.55 m, should be only slightly larger than |,f| and that the depth of penetration of the wetting front is no more than several millimeters. [source] A new saturated/unsaturated model for stormwater infiltration systemsHYDROLOGICAL PROCESSES, Issue 25 2008Dale Browne Abstract Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one-dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front-tracking model that innovatively combines a soil-moisture-based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non-iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd. [source] Field and laboratory estimates of pore size properties and hydraulic characteristics for subarctic organic soilsHYDROLOGICAL PROCESSES, Issue 19 2007Sean K. Carey Abstract Characterizing active and water-conducting porosity in organic soils in both saturated and unsaturated zones is required for models of water and solute transport. There is a limitation, largely due to lack of data, on the hydraulic properties of unsaturated organic soils in permafrost regions, and in particular, the relationship between hydraulic conductivity and pressure head. Additionally, there is uncertainty as to what fraction of the matrix and what pores conduct water at different pressure heads, as closed and dead-end pores are common features in organic soil. The objectives of this study were to determine the water-conducting porosity of organic soils for different pore radii ranges using the method proposed by Bodhinayake et al. (2004) [Soil Sci. Soc. Am. J. 68:760,769] and compare these values to active pore size distributions from resin-impregnated laboratory thin sections and pressure plate analysis. Field experiments and soil samples were completed in the Wolf Creek Research Basin, Yukon. Water infiltration rates were measured 16 times using a tension infiltrometer (TI) at 5 different pressure heads from , 150 to 0 mm. This data was combined with Gardiner's (1958) exponential unsaturated hydraulic conductivity function to provide water-conducting porosity for different pore-size ranges. Total water-conducting porosity was 1·1 × 10,4, which accounted for only 0·01% of the total soil volume. Active pore areas obtained from 2-D image analysis ranged from 0·45 to 0·60, declining with depth. Macropores accounted for approximately 65% of the water flux at saturation, yet all methods suggest macropores account for only a small fraction of the total porosity. Results among the methods are highly equivocal, and more research is required to reconcile field and laboratory methods of pore and hydraulic characteristics. However, this information is of significant value as organic soils in permafrost regions are poorly characterized in the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source] Infiltration into effluent irrigation-induced repellent soils and the dependence of repellency on ambient relative humidityHYDROLOGICAL PROCESSES, Issue 17 2007R. Wallach Abstract As a result of water scarcity and as a means of wastewater disposal, reuse of treated sewage effluent in irrigated agriculture is practiced worldwide. Among the detrimental aspects of wastewater re-use in agriculture is the possibility that soils will be rendered water repellent. The current study focuses on time dependent variation of infiltration rate in effluent-induced repellent soils, and time dependent variation in water repellency at different levels of ambient relative humidity (RH). The shape of the cumulative infiltration curve of water was found to depend on the repellency degree (concave for wettable and slightly repellent soils, convex for severely repellent soil). Compared with infiltration rates in the wettable and slightly repellent soils, infiltration rates in the severely repellent soil were very low at the beginning and then increased. When the liquid-vapor surface tension was reduced by means of ethanol addition to the infiltrating solution, the cumulative infiltration curve of the severely repellent soil also became concave. Repellency degree (as measured by WDPT) was found to be essentially constant over a large range of ambient RH values (<10 , ,81%), and to increase sharply at values above 90%. The relative increase in water drop penetration time (WDPT) at high RH was greatest for the least repellent soil (10-fold increase in WDPT), and least for the most repellent soil (2-fold increase in WDPT). At RH > 90%, the time to reach equilibrium with respect to WDPT and soil moisture content was similar. In contrast, at values of ambient RH ranging from < 10 to 81%, WDPT was invariant over the course of reaching equilibrium with respect to moisture content. However, after reaching moisture content equilibrium, WDPT declined with increasing time. Copyright © 2007 John Wiley & Sons, Ltd. [source] Runoff and suspended sediment yields from an unpaved road segment, St John, US Virgin IslandsHYDROLOGICAL PROCESSES, Issue 1 2007Carlos E. Ramos-Scharrón Abstract Unpaved roads are believed to be the primary source of terrigenous sediments being delivered to marine ecosystems around the island of St John in the eastern Caribbean. The objectives of this study were to: (1) measure runoff and suspended sediment yields from a road segment; (2) develop and test two event-based runoff and sediment prediction models; and (3) compare the predicted sediment yields against measured values from an empirical road erosion model and from a sediment trap. The runoff models use the Green,Ampt infiltration equation to predict excess precipitation and then use either an empirically derived unit hydrograph or a kinematic wave to generate runoff hydrographs. Precipitation, runoff, and suspended sediment data were collected from a 230 m long, mostly unpaved road segment over an 8-month period. Only 3,5 mm of rainfall was sufficient to initiate runoff from the road surface. Both models simulated similar hydrographs. Model performance was poor for storms with less than 1 cm of rainfall, but improved for larger events. The largest source of error was the inability to predict initial infiltration rates. The two runoff models were coupled with empirical sediment rating curves, and the predicted sediment yields were approximately 0·11 kg per square meter of road surface per centimetre of precipitation. The sediment trap data indicated a road erosion rate of 0·27 kg m,2 cm,1. The difference in sediment production between these two methods can be attributed to the fact that the suspended sediment samples were predominantly sand and silt, whereas the sediment trap yielded mostly sand and gravel. The combination of these data sets yields a road surface erosion rate of 0·31 kg m,2 cm,1, or approximately 36 kg m,2 year,1. This is four orders of magnitude higher than the measured erosion rate from undisturbed hillslopes. The results confirm the importance of unpaved roads in altering runoff and erosion rates in a tropical setting, provide insights into the controlling processes, and provide guidance for predicting runoff and sediment yields at the road-segment scale. Copyright © 2006 John Wiley & Sons, Ltd. [source] Sediment infiltration traps: their use to monitor salmonid spawning habitat in headwater tributaries of the Cascapédia River, QuébecHYDROLOGICAL PROCESSES, Issue 20 2005André E. Zimmermann Abstract Sediment infiltration can clog salmon nests and reduce egg survival. As a countermeasure, environmental managers often deploy infiltration traps to monitor sediment infiltration. Traps provide a repeatable means of measuring infiltration and enable comparisons to be made between sites. Results from infiltration rates measured with traps have also been used to estimate infilling rates into salmon nests. Application of these data is questionable, as the composition of the bed and the amount of fine sediment within the bed is known to affect infiltration rates. Thus, infiltration rates measured with infiltration traps may differ from the infiltration rates occurring in redd and riffle gravels. To examine how relationships between sediment infiltration rates varied between four watersheds, we continuously monitored suspended sediment transport, shear stress and infiltration rates at four sites over 5 months. We also compared infiltration rates measured with infiltration traps with changes in the hydraulic conductivity and subsurface grain size distribution of adjacent artificially constructed salmon nests and natural riffle gravels. Among the four watersheds, clear differences in sediment infiltration rates were observed. The differences correlated with the subsurface silt content but no strong relationship existed between land-use or basin physiography/geology. Despite observing an average of 30 kg m,2 of sediment finer than 2 mm being deposited in the infiltration traps during the study, no change in redd or riffle substrate was observed. If the deposition rates measured with the traps reflect the processes in redds, enough sediment would have been deposited to inhibit egg emergence. However, no reduction in egg survival to the eyed stage was observed. In summary, our results show that infiltration traps with clean gravels can be used to detect intersite differences in sediment transport regimes. Extrapolations of sediment infiltration rates measured with such collectors to estimate infiltration rates in redds or riffles is, however, flawed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Infiltration, runoff and sediment production in blanket peat catchments: implications of field rainfall simulation experimentsHYDROLOGICAL PROCESSES, Issue 13 2002J. Holden Abstract 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. [source] Unsaturated slope stability analysis with steady infiltration or evaporation using elasto-plastic finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2005D. V. Griffiths Abstract The paper presents results of unsaturated slope stability analyses using elasto-plastic finite elements in conjunction with a novel analytical formulation for the suction stress above the water table. The suction stress formula requires four parameters, three for the soil type and one for the steady infiltration (or evaporation) due to environmental effects. The suction stress approach enables the analysis to proceed in the context of classical effective stress, while maintaining the advantages of a general non-linear finite element approach in which no advance assumptions need to be made about the shape or location of the critical failure surface. The results show the extent to which suctions above the water table can increase the factor of safety of a slope for a variety of different soil types and infiltration rates. All stability analyses that include the effects of suction stresses are contrasted with more traditional approaches in which water pressures above the water table are ignored. Copyright © 2005 John Wiley & Sons, Ltd. [source] Organic mound-building ants: their impact on soil properties in temperate and boreal forestsJOURNAL OF APPLIED ENTOMOLOGY, Issue 4 2008M. F. Jurgensen Abstract Ants are important components of most soil invertebrate communities, and can affect the flow of energy, nutrients and water through many terrestrial ecosystems. The vast majority of ant species build nests in the mineral soil, but a small group of ants in temperate and boreal forests of Eurasia and North America build large parts of their nests above-ground using organic materials collected from the surrounding soil. Many studies have shown that ants nesting in mineral soil can affect water infiltration rates, soil organic matter (OM) content, and nutrient cycling, but much less is known on how mound-building ants influence soil physical and chemical properties. In this paper we summarize what is known on the soil impacts of organic mound-building ants in temperate and boreal forests, and how these ants could be affected by ecosystem disturbance and future climate change. Much of this information comes from studies on Formica rufa group ants in Europe, which showed that CO2 emissions and concentrations of C, N, and P are usually higher in ant mounds than in the surrounding forest soil. However, ant mounds are a minor component of total soil C and nutrient pools, but they do increase spatial heterogeneity of soil water and available nutrients. Mound-building ants can also impact tree growth, which could change the quantity and quality of OM added to soil. Forest management, fire, and projected climate change, especially in boreal forests, could affect mound-building ant population dynamics, and indirectly, soil properties. [source] INFILTRATION OF WASTEWATER AND SIMULATED RAINWATER AS AFFECTED BY POLYACRYLAMIDE,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2002Duane T. Gardiner ABSTRACT: Irrigation reduces infiltration rates for subsequent irrigations or rains, thus decreasing the efficiency of water use and impacting watersheds in agricultural areas. Reduced infiltration causes greater runoff with its accompanying erosion, pollution, and sedimentation. Small rates of polyacrylamide (PAM) improve infiltration and reduce erosion on irrigated fields. The effects of PAM on infiltration of rainwater, the longevity of the effects of various rates of PAM, and the effects of repeated or intermittent PAM applications are not understood. This study measured the effects of four PAM application rates (0, 10, 25, and 40 ppm) on the subsequent infiltration of wastewater or simulated rainwater for seven weeks following the initial treatments. Also, effects of repeated and intermittent PAM applications on infiltration were determined. Hydraulic conductivity was determined for each soil column using the falling head method. Two soil types from the coastal plain of south Texas were tested , a soil high in clay (Victoria) and a sandy loam (Willacy). Effects of PAM rates were significant, but effects of water type were not (P > 0.05). Benefits from single PAM applications disappeared within two weeks. Water enriched with PAM is so viscous and infiltrates so slowly that applying PAM in every irrigation event may not be feasible. However, repeating PAM applications every two weeks maintained high infiltration rates on the alternate weeks. This intermittent application of PAM may be a practical approach for improving infiltration rates on irrigated lands. [source] Comparison between effects of open grazing and manual harvesting of cultivated summer rangelands of northern Iran on infiltration, runoff and sediment yield,LAND DEGRADATION AND DEVELOPMENT, Issue 6 2007S. H. R. Sadeghi Abstract The effects of grazing and cultivation management on infiltration, runoff and sediment yield on storm basis were quantified for summer rangeland in the Matash mountains (Talesh Region), northern Iran. The infiltration experiments were made using double cylinder infiltrometer with five replicates within each study treatment. The runoff generation and sediment yield were measured using standard plots (1·83,m,×,22·18,m) in three replications. The peak and the terminal instantaneous infiltration, and runoff and sediment rates were compared using independent and paired sample t -test in two aforesaid treatments, respectively. The terminal and the peak instantaneous infiltration rates of 39·6 and 342·9,mm/h showed a respective significant increase (p,<,0·001) of 32 and 39 per cent in cultivated areas compared to those in open grazing treatments. The results of runoff analysis also showed that there was a significant difference (p,<,0·001) in runoff generation in two above-mentioned areas. The runoff water was also found to be 5·63-folds more in case of open grazing treatment in comparison with that generated by cultivated plots. A significant difference (p,<,0·001) in sediment yield between two study treatments was also proved by the results obtained through sediment yield study. The soil loss in open grazing treatment was found to be 26·6 times more than of that occurred in cultivated plots. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hip holes: kangaroo (Macropus spp.) resting sites modify the physical and chemical environment of woodland soilsAUSTRAL ECOLOGY, Issue 5 2002D. J. Eldridge Abstract Hip holes are shallow, reniform-shaped depressions found next to the trunks of many trees and shrubs in arid and semi-arid Australia. They are constructed by kangaroos (Macropus spp.), who use them as diurnal resting sites, particularly during hot weather. Physical and chemical properties of soils in hip holes were compared with non-hole microsites adjacent to the trunk (,trunk'), microsites below the canopy (,canopy') and microsites out in the open (,open') under two trees (Eucalyptus intertexta, Alectryon oleifolius) and one shrub (Dodonaea viscosa) in a semi-arid woodland in eastern Australia. Overall, there were few effects under D. viscosa apart from a greater (10-fold) mass of litter in the hip holes compared with the trunk microsite. Hip holes under E. intertexta and A. oleifolius, however, contained six times more dung compared with the trunk microsite. For the two tree species, soils in the hip holes were significantly more erodible, as measured by aggregation levels, compared with the other microsites, but there were no significant differences in bulk density nor pH. Steady-state infiltration rates at the hip hole and trunk microsites were significantly greater than those in the open, but there was no significant hip hole effect. Soils in the hip holes contained greater levels of exchangeable calcium and magnesium (E. intertexta) and greater exchangeable sodium (A. oleifolius) compared with trunk microsites. Hip holes under E. intertexta contained approximately 68% more organic carbon, total carbon and nitrogen, and 86% more sulfur compared with trunk microsites. Similarly, hip holes under A. oleifolius contained on average 38% more organic and total carbon, and 47% more nitrogen than trunk microsites. Given the density of hip holes and their impact on soil chemistry, kangaroos are considered to be important elements in the maintenance of heterogeneity in these woodlands. [source] Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin,1: method assessmentLAND DEGRADATION AND DEVELOPMENT, Issue 6 2004M. E. Grismer Abstract Revegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion-control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS-plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ,60,mm,h,1, approximating the 100-yr, 15-min design storm, was applied over replicated 0·64,m2 plots in each treatment type and over bare-soil plots for comparison. Simulated rainfall had a mean drop size of ,2·1,mm and approximately 70% of ,natural' kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45,,m) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2,12 as compared to 0·3,3,g,m,2,mm,1 for granitic soils. Pine-needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross-slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||