Antecedent Water Content Research Articles

Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model

This study simplifies the recession process, includes the hourly evapotranspiration, and modifies the surface layer of the green-roof hydrological model based on the Green-Ampt (G-A) method and Curve Number (CN) method. The existing G-A and CN methods are usually applied for event-total runoff. The results show that the proposed model improves the predicting accuracy of the outflow, and the model performs well for rainfall events with different intensities, duration, and hyetograph. the CN method performs as prominent as the G-A method but is more efficient. Based on observation, the retained volume and peak reduction are close to 50 % on average with a 1-to-2-hour peak delay. The results of the three-year simulation show that the retained volume and peak reduction reach 50 % for 75 % of the events when the antecedent water content is 30 %. Almost all rainfall is retained for events with rainfall amounts smaller than 20 mm when the antecedent water content is smaller than 30 %. On the other hand, 50 % (60 %) rainfall (peak) is retained (reduced) for events larger than 20 mm when the antecedent water content is smaller than 20 %. With the model verified using various rainfall events, the study generalizes an equation to estimate the rainwater retained by green roofs. Moreover, the stormwater-detention performance of a green roof in general is concluded quantitatively under different antecedent water content to assist the decision-making of irrigation concerning the goal of stormwater detention.

Analysis of Water Volume Required to Reach Steady Flow in the Constant Head Well Permeameter Method

The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively.

Retraction notice to “Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model” [Resour., Environ. Sustain. 13 (2023) 100125

Retraction notice to “Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model” [Resour., Environ. Sustain. 13 (2023) 100125

RETRACTED: Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model

RETRACTED: Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model

In situ water infiltration: Influence of cover crops after growth termination

AbstractCover crops (CCs) are known to influence water infiltration just prior to termination, but their effects on water infiltration over time are less known. This study investigated the influence of CCs on in situ water infiltration just prior to CC termination (during April) and again 2 mo after CC termination (during June). The multi‐species mixture of CCs used included hairy vetch (Vicia villosa Roth.), crimson clover (Trifolium incarnatum L.), winter wheat (Triticum aestivum L.), winter peas (Lathyrus hirsutus L.), oats (Avena sativa L.), triticale (Triticale hexaploide Lart.), barley (Hordeum vulgare L.), and flax (Linum usitatissimum L.). Infiltration rates were measured using double‐ring infiltrometers during April and June. The physically based Parlange and Green‐Ampt models were fitted to measured infiltration data. Cumulative infiltration was 52% higher in April and 68% higher in June under CC compared with no cover crop (NC) management. During April, the Parlange model–estimated saturated hydraulic conductivity parameter (Kdr) was 245% higher under CC compared with NC management. During the same sample period, the Green‐Ampt–estimated Kdr parameter was 383% higher under CC compared with NC management. The higher sorptivity parameter and lower antecedent water content under CC compared with NC management during both measurement periods suggest that CCs can significantly improve water infiltration into the soil, and this effect can last for up to 2 mo after CC termination.

Water balance modeling of Tandula (India) reservoir catchment using SWAT

The water availability assessment is an important aspect for planning and management of water resources in the basin; however, non-availability of observed runoff is an important issue often found in the developing countries. The farmers of irrigation projects incur more expenditure due to assured supply and suffer huge economic loss in dry years. In the present study, a water balance of reservoir for computation of runoff coupled with the application of spatially distributed Soil and Water Assessment Tool (SWAT) model, the SWAT model and SWAT–CUP application have been proposed for hydrological modeling can be used asses the inflows for efficient reservoir operation and planning of releases. The proposed methodology has been applied on Tandula reservoir catchment in Chhattisgarh state of India, which is well-known for its paddy cultivation and any short supply affect the economic status of marginal farmers in the command. The water balance of Tandula reservoir has been carried out for the period of 1991 to 2015 using daily reservoir levels, releases, evaporation, seepage, supplies from other sources, and spillway information. The percentage error in water balance analysis of Tandula reservoir varied between − 6.87 and 3.39% and seem reasonably well matched. The runoff obtained from water balance was checked with the SCS–CN technique and found close resemblance on the monthly and yearly basis. The digital image processing of remote sensing data has been used for determination of land uses and found that forest and agriculture land with rice cultivation are the principal land uses covering nearly 86% area of the catchment. The sensitivity analysis suggested that SCS curve number (r_CN2), saturated hydraulic conductivity (sol_k), soil antecedent water content (sol_AWC), and Manning’s N for the main channel (Ch_N2) are the most sensitive parameters. The sequential uncertainty fitting (SUFI2) technique has been used for calibration of model for the period of 1995 to 2007 and validated for 2008 to 2015. The model performance was adjudged using P-factor, r-factor, and Nash–Sutcliff efficiency, and best-fit model parameters were determined. The Nash–Sutcliff efficiency for calibration and validation were found as 0.75 and 0.65 respectively suggested that the developed model can be used for assessment of runoff from the catchment. The knowledge of the availability of water using the amalgamation of water balance, SWAT model, and SWAT CUP application can be used for reservoir operation, irrigation management, and assessment of the impact of climate and land use change on runoff from the catchment.

Mobility, Thickness, and Hydraulic Diffusivity of the Slow‐Moving Monroe Landslide in California Revealed by L‐Band Satellite Radar Interferometry

AbstractActive landslides cause fatalities and property losses worldwide. Landslide behaviors can be enigmatic in natural landscapes and therefore require high‐quality observations of their kinematics to improve our ability to predict landslide behavior. Here we use geodetic interferometric synthetic aperture radar (InSAR) observations to characterize the geometry and the spatio‐temporal deformation of the slow‐moving, deep‐seated Monroe landslide in northern California between 2007 and 2017. InSAR phase discontinuities show that the landslide is bounded by discrete strike‐slip faults at the lateral margins and segregated into distinct kinematic elements by normal and thrust faults. We find that the Monroe landslide has been moving consistently, with a maximum rate of about 0.7 m/year in the narrowest longitudinal center of the transport zone. The thickest landslide mass is estimated to be in a zone located between subsiding and the uplifting kinematic elements at the lower transport zone. The timing and magnitude of the landslide displacement are modulated by the intensity and duration of precipitation, as well as the antecedent water content of the landslide mass. In addition, we use a one‐dimensional pore‐water pressure diffusion model to estimate the rainfall‐modulated pore‐water pressure changes and hydraulic diffusivity. We find hydraulic diffusivity values between m2/s, which agrees with ground‐based measurements in this region. Displacement measurements on the hillslopes obtained from geodetic InSAR observations allow us to characterize the mobility, depth, and hydraulic diffusivity of slow‐moving landslides.

Diesel oil infiltration in soils with selected antecedent water content and bulk density

The effects of soil texture, initial water content and bulk density on diesel oil infiltration in fine sand and silty clay loam materials were evaluated. Three physical and two empirical equations express diesel oil infiltration through soils with time, with coefficients of determination greater than 0.99. Diesel oil infiltrates more quickly in the fine sand than in the silty clay loam material. Diesel oil infiltration rates are found to decrease with increasing initial water content and bulk density for the silty clay loam material. The infiltration rate of diesel oil in the fine sand material increases slightly with increasing initial water content. The diesel oil saturated conductivity (Kdiesel) decreases with increasing bulk density for the silty clay loam column. Diesel oil sorptivity(S) decreases linearly with increased initial water content and bulk density of the silty clay loam material. Changes in empirical parameters relative to initial water content and bulk density are similar to the parameter S.

Numerical evaluation of different landfill daily cover in semiarid areas - Jordan

Efficient and suitable daily landfill cover is considered the most important aspect for minimising the negative impact of landfills on the local environment and population, especially in arid and semiarid countries. In this study, numerical model, HYDRUS-2D/3D, was used to investigate the impact of landfill cover type, cover thickness and antecedent water content on the quantity and the rate of contaminant percolation through the Mafraq landfill in Jordan during a 30-year simulation period. Four different cover types (sandy loam, clay loam, silt and clay), three cover thicknesses (0, 50, 100 cm) and two antecedent soil water content values (θi = 0.12 and 0.20 m3m−3) were simulated. Initial chloride concentration of 665 mg/l which is equal to the measured concentration in Mafraq landfill leachate was used during simulation. Simulation results showed that maximum chloride concentration for different scenarios at all locations within the soil profile during the entire simulation period was less than the chloride concentration in the municipal solid waste (MSW) leachate. In addition, as the landfill cover thickness increases, the concentration of chloride at a certain location decreases. Meanwhile, the time required to reach this location increases. The simulation results also showed that the effect of θi on chloride concentration reduction increases as the cover thickness increases. A cover thickness of 50 cm is suitable in case of low θi.

Increased profile wettability in texture-contrast soils from clay delving: case studies in South Australia

Clay delving is becoming a popular practice to increase productivity of texture-contrast soils in southern Australia. The practice brings subsoil clay to the surface to be mixed with the sandy topsoil, and unlike clay spreading, it combines the addition of hydrophilic material with a ripping effect that disrupts the sharp boundary between the sandy topsoil and clayey subsoil. Our objective was to evaluate the magnitude of effects caused by delving on the spatial distribution of water through the profile for three Sodosols (Stagnic Solonetz soils) in the south-east of South Australia. We also wished to evaluate the extent to which clay delving might reduce water ponding at the A–B horizon interface. We wetted both delved and undelved texture-contrast soils with a Brilliant Blue dye solution under initially dry and wet conditions (to evaluate the effect of antecedent water content), and then took digital images of the stained profiles for quantitative comparison of the wetted areas. The stained soil profiles indicated that clay delving reduced preferential water flow (finger flow) and resulted in deeper and more uniform wetting of the A horizon, particularly under initially dry conditions. Under wet conditions (where water repellence was largely overcome), finger flow was significantly reduced regardless of delving but it still occurred to varying degrees depending on site characteristics. Delving significantly reduced ponding of water at the A–B horizon boundary and allowed greater penetration into the B horizon. At all sites, greater effects occurred directly on the delving lines and diminished with distance, implying that closer spacing of delving tines would increase uniformity of wetting throughout the profile. The effectiveness of delving on profile wetting was highly variable across the three sites, indicating that the outcome depends inter alia on the intrinsic soil characteristics and the delving equipment used in the field.

Forest Litter Interception Model for a Sessile Oak Forest

Abstract Models that describe hydrological processes in forests may help to estimate the consequences of forestry interventions or of climate change. The authors employed a hydrologic model for estimation of forest litter interception of a middle-aged sessile oak (Quercus petraea) stand. Antecedent water content and the storage capacity of the forest litter were the main parameters of the model. The antecedent water content of the litter was estimated by the daily precipitation and temperature data, collected in Hidegviz Valley research catchment in a three year measurement period (2006-2008). The measurements were done by an instrument we developed ourselves, where the undisturbed forest litter samples were enclosed in frames and measured in daily time steps.

Influence of cohesive and disruptive forces on strength and erodibility of tropical soils

Direct impact of intense tropical rainfall following deforestation and other deleterious land practices is one of the major causes of land degradation in the Caribbean. The susceptibility of the exposed soil to degradation depends on the cohesive strength of soil binding factors and the magnitude of disruptive forces produced by the intense rainfall. We propose that the combination of cohesive binding factors of clay and organic matter in a soil subjected to varying wetting conditions exert a strong influence on the resistance of the soil to sustained shearing stresses. Simulated rainfall experiments involving intense rainfall of 120mmh−1 were conducted on six Trinidad soils selected based on three levels of clay and two levels of organic matter. Samples were either left dry or pre-wetted with mist at slow (7.5mmh−1) and fast (75mmh−1) wetting rate to antecedent water content of 0.5 of field capacity and field capacity, followed by exposure to the intense simulated rainfall. We found that increase in clay content did not necessarily increase the cohesive strength of low organic matter soils since high clay soils shear and crust as much as low clay soils under the shearing stresses of intense rainfall and fast wetting. At high organic matter content, however, the resistance to shearing stresses increased at medium and high clay contents suggesting that high organic matter is required at these clay contents to reduce the surface tension of water entering the clay–organic matter matrix and thus increasing the cohesion of the clay particles. For medium to heavy textured soils of the humid tropics subjected to disruptive forces of intense rainfall, interaction rather than the individual effects of clay and organic matter control their erodibility.

Results of rainfall simulation to estimate sediment-bound carbon and nitrogen loss from an Atlantic Coastal Plain (USA) ultisol

Assessment of erosion impact on soil carbon and nitrogen loss and redistribution within landscapes is needed to develop estimates of soil carbon sequestration potential, soil quality management plans, and to evaluate potential for transport of sediment bound agrochemicals. We used variable intensity rainfall simulations to quantify the effects of tillage, conventional and strip, and antecedent soil water content on sediment-bound carbon and nitrogen loss from a Tifton loamy sand located in the southeastern Atlantic Coastal Plain (USA). Carbon and nitrogen loss via erosion of silt+clay sized versus sand sized sediment particles were quantified. Antecedent water content had no effect on mean sediment loss within tillage treatments, but losses from conventional till treatments were significantly greater than from strip till. Sediment lost as silt+clay was from 58 to 78% of the total under conventional and from 30 to 39% under strip tillage. The fraction of sediment lost as silt+clay versus sand was greater under conventional tillage than under strip tillage. Within-event sediment carbon enrichment compared to the top 2cm of soil was 0.9–7.2 for conventional and 0.6–3.7 for strip tillage. The strip till silt+clay fraction had significantly higher carbon content than the strip till sand fraction and the conventional till silt+clay fraction. Carbon loss from treatments was directly proportional to sediment loss. However, the conventional till treatments lost 4.6–6 times more carbon from the silt+clay sized fraction and 1.9–4.8 times more carbon from the sand sized fraction than strip till treatments. Results suggest that the higher proportion of silt+clay fraction sediment loss from conventional till may deplete nitrogen enriched organic matter while decreased erosion from strip till may serve to increase retention of organic nitrogen. Findings also indicate that an approach that adjusts loss estimates of organic carbon and nitrogen by using wet-sieved subsamples for analysis followed by standardization against total bulk sediment loss accounts for introduced errors from both sub-sampling efficiency and disturbance.

Modelling soil water and salt dynamics under pulsed and continuous surface drip irrigation of almond and implications of system design

The HYDRUS-2D model was experimentally verified for water and salinity distribution during the profile establishment stage (33 days) of almond under pulsed and continuous drip irrigation. The model simulated values of water content obtained at different lateral distances (0, 20, 40, 60, 100 cm) from a dripper at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140 and 160 cm soil depths at different times (5, 12, 19, 26 and 33 days of profile establishment) were compared with neutron probe measured values under both irrigation scenarios. The model closely predicted water content distribution at all distances, times and soil depths as RMSE values ranged between 0.017 and 0.049. The measured mean soil water salinity (ECsw) at 25 cm from the dripper at 30, 60, 90 and 150 cm soil depth also matched well with the predicted values. A correlation of 0.97 in pulsed and 0.98 in continuous drip systems with measured values indicated the model closely predicted total salts in the root zone. Thus, HYDRUS-2D successfully simulated the change in soil water content and soil water salinity in both the wetting pattern and in the flow domain. The initial mean ECsw below the dripper in pulsed (5.25 dSm−1) and continuous (6.07 dSm−1) irrigations decreased to 1.31 and 1.36 dSm−1, respectively, showing a respective 75.1 and 77.6% decrease in the initial salinity. The power function [y = ax−b] best described the mathematical relationship between salt removal from the soil profile as a function of irrigation time under both irrigation scenarios. Contrary to other studies, higher leaching fraction (6.4–43.1%) was recorded in pulsed than continuous (1.1–35.1%) irrigation with the same amount of applied water which was brought about by the variation in initial soil water content and time of irrigation application. It was pertinent to note that a small (0.012) increase in mean antecedent water content (θi) brought about 8.25–9.06% increase in the leaching fraction during the profile establishment irrespective of the emitter geometry, discharge rate, and irrigation scenario. Under similar θi, water applied at a higher discharge rate (3.876 Lh−1) has resulted in slightly higher leaching fraction than at a low discharge rate (1.91 Lh−1) under pulsing only owing to the variation in time of irrigation application. The influence of pulsing on soil water content, salinity distribution, and drainage flux vanished completely when irrigation was applied daily on the basis of crop evapotranspiration (ETc) with a suitable leaching fraction. Therefore, antecedent soil water content and scheduling or duration of water application play a significant role in the design of drip irrigation systems for light textured soils. These factors are the major driving force to move water and solutes within the soil profile and may influence the off-site impacts such as drainage flux and pollution of the groundwater.

Antecedent water content effects on runoff and sediment yields from two Coastal Plain Ultisols

The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m2 field plot received simulated rainfall at a variable rainfall intensity (Iv) pattern for 70 min (site 1) or a constant rainfall intensity (Ic) pattern for 60 min (site 2; Ic = 50.8 mm h−1). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0–2 (3–9-fold) and 2–15 (23–117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; Iv pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.

Drip Irrigation Water Distribution Patterns: Effects of Emitter Rate, Pulsing, and Antecedent Water

Drip irrigation is more effective and less expensive if a large amount of soil can be wetted with each emitter without losing water or nutrients below the root zone. The distance that water spreads horizontally from a drip line and the volume of soil wetted are limiting factors that determine the spacing and number of drip lines and emitters, the frequency of irrigation, and thus the cost of irrigation. We used numerical simulations and field trials to investigate the effects of application rate, pulsed water application, and antecedent water content on the spreading of water from drip emitters. Simulation results showed that pulsing and lower application rates produced minor increases in horizontal spreading at the end of water application. The small increases were primarily due to longer irrigation times, however, and not to flow phenomena associated with pulsing or low application rates. Moreover, the small increases mostly disappeared after the infiltrated water had redistributed for a period of 24 h. Field trials confirmed the simulation findings, with no statistically significant difference in wetting being found among five water application treatments involving pulsed applications and varying application rates. The simulations showed that higher antecedent water content increases water spreading from drip irrigation systems, but the increases were greater in the vertical direction than in the horizontal, an undesirable outcome if crop roots are shallow or groundwater contamination is a concern. Overall, soil texture (hydraulic properties) and antecedent water content largely determine the spreading and distribution of a given water application, with pulsing and flow rate having very little impact.

Abstraction from Infiltrating Water Content Waves during Weak Viscous Flows

Based on observations of constant wetting front velocities throughout a depth range of 1 to 2 m, we simplify infiltration as gravity‐driven weak viscous flow. In theory, time‐limited constant infiltration generates a sharp‐crested water‐content wave, WCW, at the surface that suddenly increases the soil water content as it arrives at a particular depth. This is in contrast to the more gradual increases produced by observed WCWs. The deviation between theoretical and observed WCWs is ascribed to water abstraction from the WCW to finer soil pores due to the gradient of capillary potential, ∇ψ. Water abstraction occurs across a finite time interval. The total amount of abstraction is the difference between the WCW's maximal water content and its antecedent water content, while its time interval lasts from the first increase to steady water content. The WCWs' maximal water contents are usually below complete saturation. The wave velocity multiplied by the time interval of abstraction yields the depth increment ZA of water abstraction during the passing of the wave. The frequency distribution of 215 ZA values was deduced from WCWs that were measured in situ under sprinkler irrigation. The ZA distribution covered a range from 0.2 to about 10 m, with its 50% midpoint at about 1 m. The limited depth range of increments indicates that abstraction is also a time‐limited process that may end before the pores surrounding the WCW are completely water saturated

Aggregate Stability and Erosion Response to Antecedent Water Content of a Loess Soil

Soil erosion processes are affected by the erodibility of the soil and by the erosivity of the rain. The effects of rain characteristics and invariant soil properties such as texture and organic matter content on soil erosion processes are well documented. The effect of antecedent soil water content (θa) on aggregate breakdown, seal formation, and subsequent soil erosion is much more disputable, however, as opposing effects have been reported. We conducted lab experiments with a rainfall simulator on a Belgian silt loam soil. The objectives were to determine the effect of θa on seal formation, runoff, and soil loss and to evaluate its effect on an empirical sediment transport equation. Air‐dried soil aggregates were subjected to θa of 0.04 (air‐dry aggregates), 0.12, and 0.19 m3 m−3 No runoff occurred on the soils with the highest θa, highest total runoff values were observed for intermediate θa, while intermediate amounts of total runoff were observed for the air‐dry aggregates. Soil loss, however, showed a different trend: highest values were found for the lowest θa, intermediate values for the intermediate θa, and no soil loss for the highest θa We further observed that θa had no influence on the final runoff rates and on the final infiltration rate through the soil surface. In using a water discharge and stream power equation to predict sediment transport, the intercept and exponent of the regression equations were found to be lower for θa of 0.19 than 0.12 m3 m−3, indicating decreasing erodibility with increasing θa We therefore suggest including θa as an additional variable to assess soil erodibility in deterministic event‐based water erosion models.

Runoff and solute mobilization processes in a semiarid headwater catchment

Runoff and solute transport processes contributing to streamflow were determined in a small headwater catchment in the eastern Murray‐Darling Basin of Australia using hydrometric and tracer methods. Streamflow and electrical conductivity were monitored from two gauges draining a portion of the upper catchment area (UCA) and a saline scalded area, respectively. Runoff in the UCA was related to the formation of a seasonally perched aquifer in the near‐surface zone (0–0.4 m). A similar process was responsible for runoff generation in the saline scalded area. However, saturation in the scald area was related to the proximity of groundwater rather than low subsurface hydraulic conductivity. Because of higher antecedent water content, runoff commenced earlier in winter from the scald than did the UCA. Additionally, areal runoff from the scald was far greater than from the UCA. Total runoff from the UCA was higher than the scald (15.7 versus 3.5 mL), but salt export was far lower (0.6 and 5.4 t for the UCA and scald area, respectively) since salinity of the scald runoff was far higher than that from the UCA, indicating the potential impact of saline scalded areas at the catchment scale. End‐member mixing analysis modeling using six solutes indicated that most runoff produced from the scald was “new” (40–71%) despite the proximity of the groundwater surface and the high antecedent moisture levels. This is a reflection of the very low hydraulic conductivity of soils in the study area. Nearly all chloride exported to the stream from the scald emanated from the near‐surface zone (77–87%). Runoff and solute mobilization processes depend upon seasonal saturation occurring in the near‐surface zone during periods of low evaporative demand and generation of saturated overland flow.

A laboratory study on the relative stability of the check‐dam system in the Loess Plateau, China

AbstractThe building of check‐dams is one of the most effective measures for the conservation of soil and water in the Loess Plateau of China, and the hydro‐sedimentologic balance is the most important factor influencing the relative stability of the check‐dam systems. This means that the soil and water in small watersheds controlled by the check‐dams will be absorbed internally, without the need for raising the height of the dams, if some given parameters have reached certain values. A runoff simulation experiment for a single check‐dam and a rainfall simulation experiment for the whole check‐dam system has been conducted, and the runoff/rainfall intensity and the parameter RV were determined through the annual erosion rate of the prototype watershed. The results indicated that the raising of the dam‐land altitude became slower, and the mean gradient of the gully was kept at a constant. The main reasons causing the check‐dam to show a good relative stability are the enlarging of the dam‐land area, the alleviating of erosion by the check‐dam, and the auto‐stabilizing mechanism of the gullies.This study presents a kind of scale‐down model experiment in which the ratio of the model geomorphological variable to the corresponding prototype variable keeps constant after the determinate runs of rainfalls, so that the soil and water erosion processes of the prototype could be monitored from the results of the model experiment. Four measures have been suggested for ensuring this ratio is a constant: (1) A bare‐land model with an appropriate erosion rate should be used in the experiment. (2) Dimensions of the landform, including the check‐dam, should normally be scaled down according to the prototype watershed. (3) Soil similar to those of the prototype should be used. (4) The antecedent water content before each rainfall simulation should be kept constant. Copyright © 2006 John Wiley & Sons, Ltd.