Constant Rainfall Research Articles

Theory-Based SCS-CN Method and Its Applications

This study, by incorporating the Philip infiltration solution, constructs from a theoretical perspective an alternative model to replace the Soil Conservation Service curve-number (SCS-CN) method and provides an in-depth analysis of its variants in order to understand their limitations and accuracy. Variants under analyses include the nonlinear Ia-R relation of Jain et al. and the general and modified Mishra-Singh models which, in spite of favorable consistency with observed data, are obtained by approximation, leaving several odd results unexplained. Along with the crucial assumptions embedded in the SCS-CN method, vital factors dominating model accuracy are examined at constant rainfall intensity. Soil-infinite storage is avoided to reflect the actual situation in most vadose zones, which amends the SCS method and allows the theoretical exploration of the range in which CN usually falls. Using different soils, this study compares the differences and common features of all the models in order to test their proficiency. Finally, the features of a unit hydrograph are integrated into the alternative model to perform a simple evaluation of the impact of catchment urbanization on the river stage.

Climate information from C, N and O stable isotope analyses of mammoth bones from northern Siberia

Nineteen Late Pleistocene samples of fossil mammoth and four of horse and bison from the Leptev Sea area were studied for their C, N and O stable isotope composition. The majority of the samples have interstadial (MIS 3) ages and only two have late-glacial ages. The carbon and nitrogen isotope values are in good agreement with those previously measured on other mammoths from the same area. They seem to indicate, for the interstadial period, a stability of the climate conditions characterised by low and constant rainfall with only few oscillations. Only after the LGM are more humid conditions apparent. The calculated oxygen isotope composition of water are several per mill more positive than those of modern meteoric water in the area. They do not seem to correlate with well-established Late Pleistocene temperature changes but rather with aridity. The temporal pattern indicates a rapid increase of dry conditions after around 34 ka BP. Only the two samples dated after the LGM might indicate an effective increase in temperature.

Phosphorus losses in water and sediments in runoff of the water erosion in oat and vetch crops seed in contour and downhill

In contour cultivations, the ability of the plants to retain sediments suspended in flowing water and the marks in the soil caused by preparation, promotes the deposition of these sediments in the furrows. The objective of this work was to quantify the level of extractable P in the erosion sediments and in the surface of the soil, the level of soluble P in the runoff water and the level of extractable P in the different sized sediments transported in the runoff water, and the P total losses by water erosion. The work was carried out under simulated rainfall between April and November 2006 in an INCEPTISOL soil, under conventional cultivation. The combination of three factors was studied; type of crop: oats ( Avena strigosa) and vetch ( Vicia sativa), method of seedling (downhill and in contour) and a simulated rainfall test (five tests with constant rainfall intensity of 64 mm h −1 for a duration of 1 h). The first four rainfall tests were made on the crops during their cycle, and the fifth one on the crop residues, which were maintained on the soil surface. The levels of P in the soil and in the runoff sediments were positively correlated; these levels in soil diminish from 60.7 mg kg −1 at the beginning of the crop cycle until 33.6 mg kg −1 at the end of the cycle, and increase to 61.5 mg kg −1 when measured in the crop residues; while, the P levels in runoff sediments diminishing from 27.5 mg kg −1 at the beginning of the crop cycle until 18.0 mg kg −1 at the end of the cycle, and increase to 30.8 mg kg −1 when measured in the crop residues. Seedling in contour produced sediments with a greater level of P (24.6 mg kg −1) than seedling downhill (21.4 mg kg −1); however, the P total losses were smaller in the contour (37.1 g ha −1) than downhill (51.4 g ha −1). The P level in the runoff sediments increased with the reduction in particle size; within one size class, the P level was greater in contour seedling than downhill. The level of soluble P in the runoff water was inversely proportional to the concentration of sediments in this water.

Rainfall Infiltration Pattern in an Unsaturated Silty Sand

One-dimensional infiltration tests were conducted to investigate the effects of rainfall intensity and initial water content on the transient infiltration pattern of unsaturated silty sand. For a constant rainfall intensity greater than the saturated permeability but smaller than the maximum infiltration capacity of soil, the infiltration curve is divided into preponding and postponding stages. The time to ponding reduces with increasing rainfall intensity and initial water content. After ponding, the infiltration rate reduces with time and its reducing rate increases with rainfall intensity but does not vary significantly with initial water content. The infiltration pattern can be simulated qualitatively by solving Richard’s equation numerically with the use of the flux and head type boundary conditions at the soil surface in the preponding and postponding stages, respectively.

Theoretical relationships between first flush of roof runoff and influencing factors

Considering the short length of building roofs, a theoretical analysis of the first flush of roof runoff was conducted based on the kinematic wave and pollutant erosion equations. This mathematical derivation with analytical solutions predicts pollutant mass first flush (MFF), mean concentration of initial runoff (MCIF), mean concentration of roof runoff (MCRR) with diversion of initial portion and residual mass available on the bed surface (RS) after the entire runoff under the condition of constant excess rainfall. And the effects of the associated influencing factors (roof length, roof gradient, roof surface roughness, rainfall intensity, rainfall duration, and erosion coefficients) on them were discussed while the values of parameters referred to the previous studies. The results showed that for roofs whose length is shorter than 20 m, both the increase in roof length and roof gradient and the decrease in roof surface roughness result in larger MFF and MCIF and smaller MCRR and RS, which is beneficial to water reuse and pollution reduction. The theoretical relationship between the first flush and the influencing factors may aid the planning and design of roof in terms of rainwater utilization or diffuse pollution control.

Rhizome rot of ginger (Zingiber officinale) caused byPythium myriotylumin Fiji and Australia

Observations on the etiology of rhizome rot of ginger are presented for Fiji and Australia. In Fiji, the disease generally develops during hot, wet conditions in March and April, and often causes losses of more than 50% in seed crops. In Australia, the disease was observed for the first time during the wet summer of 2007–08, almost totally destroying the immature ginger crop in one field and causing 8–30% losses in other fields. Measurements taken when soils were saturated due to almost constant rainfall indicated that many plants died within 3 weeks of showing the first signs of yellowing, with the disease spreading down slopes at rates of up to 4.5 m/day. Pathogenicity tests indicated that the disease was caused by Pythium myriotylum and that the pathogen was capable of destroying ginger rhizomes in 1–2 weeks in saturated soils at temperatures of 26–30°C. The role of the environment in exacerbating the disease is considered and implications for management are discussed.

Climate and parent material controls on organic matter storage in surface soils: A three-pool, density-separation approach

Physically- and biochemically-distinct fractions of soil organic matter (SOM) can be separated by density to yield: (i) low-density plant detritus fraction easily separable from soil minerals (f-LF), (ii) low-density materials strongly associated with minerals (m-LF), and (iii) high-density fraction (HF) rich in microbially-processed organic matter strongly associated with minerals. The factors controlling the pool size and chemistry in these fractions, especially those in m-LF, are unclear. We examined the influence of climate and parent material on SOM in these fractions using two sets of forest soils (0–10 cm mineral horizon) developed from contrasting parent materials (metasedimentary vs. ultrabasic igneous rock) along an altitudinal gradient in Mt. Kinabalu, Borneo. From 700 m to upper altitudes (1700, 2700 m), where mean annual temperature decreases from 24 to 12 °C with roughly constant rainfall, surface soil C stocks on both parent materials increased from 2.6–2.8 to 5.4–7.5 kg m − 2 with progressively greater proportions in m-LF and, to less extent, fresher plant detritus fractions. In HF, C and N concentrations increased with altitude though their stocks were roughly constant due to progressively lower bulk density. Labile C assessed by laboratory incubation of bulk soils correlated better with C concentrations in the two LF pools than in HF, especially at the lowest altitude where most SOM is strongly associated with minerals as HF. These results suggest that LF pools are more labile and more sensitive to altitude-induced, climate differences as compared to the HF pool that is protected by the mineral matrix. The C:N ratios of HF on metasedimentary rock increased with altitude (11 to 17) while those on ultrabasic rock remained essentially constant (14–15), implying interactive influence of altitude and parent material on stoichiometry. Unusually high C:N and alkyl-C in m-LF were found in mid-altitude soils, suggesting selective preservation of inherently recalcitrant materials in addition to, or instead of, mineral coating or aggregate occlusion of partially-degraded LF by microbial metabolites.

Non‐invasive monitoring of water infiltration in a silty clay loam soil using Spectral Induced Polarization

An experimental investigation was undertaken to study the ability of Spectral Induced Polarization (SIP) to monitor water infiltration in a silty clay loam soil. It was based on the coupled acquisition of tensiometer data and Spectral Induced Polarization (SIP) spectra (1.46 Hz to 12 kHz) during the infiltration event created by an artificial constant rainfall rate of about 15 mm/h. The approach, which was applied both in the field and in a soil column, confirms the existence of a significant phase drop in the high‐frequency domain (typically greater than 1 kHz) during the first infiltration cycles. The interpretation of the tensiometer and SIP data show that this phase drop is correlated with the water filling of pores in the [30–85] μm diameter range. The phase drop is qualitatively and quantitatively interpreted as a Maxwell‐Wagner effect associated with the electrical heterogeneity of the soil. It could correspond to the transition between two physical states. In the first state before the arrival of the wetting front, highly polarized and wet aggregates are embedded in an electrically isolating phase, i.e., air. In the second state after the arrival of the wetting front, structural pores between the aggregates are filled with a connected and conducting phase, i.e., water, leading macroscopically to a decrease in bulk soil polarizability. The experimental and theoretical results of this study suggest strongly that the SIP method can be used to monitor the water filling of structural or draining pores in the field. This original result requires validation in other sites.

Rainfall and tillage effects on transport of fecal bacteria and sex hormones 17β-estradiol and testosterone from broiler litter applications to a Georgia Piedmont Ultisol

Poultry litter provides nutrients for crop and pasture production; however, it also contains fecal bacteria, sex hormones (17β-estradiol and testosterone) and antibiotic residues that may contaminate surface waters. Our objective was to quantify transport of fecal bacteria, estradiol, testosterone and antibiotic residues from a Cecil sandy loam managed since 1991 under no-till (NT) and conventional tillage (CT) to which either poultry litter (PL) or conventional fertilizer (CF) was applied based on the nitrogen needs of corn ( Zea mays L) in the Southern Piedmont of NE Georgia. Simulated rainfall was applied for 60 min to 2 by 3-m field plots at a constant rate in 2004 and variable rate in 2005. Runoff was continuously measured and subsamples taken for determining flow-weighted concentrations of fecal bacteria, hormones, and antibiotic residues. Neither Salmonella, nor Campylobacter, nor antimicrobial residues were detected in litter, soil, or runoff. Differences in soil concentrations of fecal bacteria before and after rainfall simulations were observed only for Escherichia coli in the constant rainfall intensity experiment. Differences in flow-weighted concentrations were observed only for testosterone in both constant and variable intensity rainfall experiments, and were greatest for treatments that received poultry litter. Total loads of E. coli and fecal enterococci, were largest for both tillage treatments receiving poultry litter for the variable rainfall intensity. Load of testosterone was greatest for no-till plots receiving poultry litter under variable rainfall intensity. Poultry litter application rates commensurate for corn appeared to enhance only soil concentrations of E. coli, and runoff concentrations of testosterone above background levels.

A minimal model of soil water–vegetation interactions forced by stochastic rainfall in water-limited ecosystems

A minimal model of soil water–vegetation interaction in dryland ecosystems is developed as a vehicle to show how stochastic differential equations can be applied to this problem. In contrast to previous works, which assume a constant rainfall, the system is forced using stochastic rainfall, and the stationary probability distributions of the soil water content and the vegetation density are derived analytically. Thence, a sensitivity analysis of the stationary probability distributions on rainfall and model parameters has been carried out. This analysis points out the influence of the rainfall process, soil and vegetation properties on the stationary probability distributions of soil water and vegetation. The approach can potentially be extended to address more complex models.

Variable Rainfall Intensity and Tillage Effects on Runoff, Sediment, and Carbon Losses from a Loamy Sand under Simulated Rainfall

The low-carbon, intensively cropped Coastal Plain soils of Georgia are susceptible to runoff, soil loss, and drought. Reduced tillage systems offer the best management tool for sustained row crop production. Understanding runoff, sediment, and chemical losses from conventional and reduced tillage systems is expected to improve if the effect of a variable rainfall intensity storm was quantified. Our objective was to quantify and compare effects of a constant (Ic) intensity pattern and a more realistic, observed, variable (Iv) rainfall intensity pattern on runoff (R), sediment (E), and carbon losses (C) from a Tifton loamy sand cropped to conventional-till (CT) and strip-till (ST) cotton (Gossypium hirsutum L.). Four treatments were evaluated: CT-Ic, CT-Iv, ST-Ic, and ST-Iv, each replicated three times. Field plots (n=12), each 2 by 3 m, were established on each treatment. Each 6-m2 field plot received simulated rainfall at a constant (57 mm h(-1)) or variable rainfall intensity pattern for 70 min (12-run ave.=1402 mL; CV=3%). The Iv pattern represented the most frequent occurring intensity pattern for spring storms in the region. Compared with CT, ST decreased R by 2.5-fold, E by 3.5-fold, and C by 7-fold. Maximum runoff values for Iv events were 1.6-fold higher than those for Ic events and occurred 38 min earlier. Values for Etot and Ctot for Iv events were 19-36% and 1.5-fold higher than corresponding values for Ic events. Values for Emax and Cmax for Iv events were 3-fold and 4-fold higher than corresponding values for Ic events. Carbon enrichment ratios (CER) were <or=1.0 for ST plots and >or=1.0 for CT plots (except for first 20 min). Maximum CER for CT-Ic, CT-Iv, ST-Ic, and ST-Iv were 2.0, 2.2, 1.0, and 1.2, respectively. Transport of sediment, carbon, and agrichemicals would be better understood if variable rainfall intensity patterns derived from natural rainfall were used in rainfall simulations to evaluate their fate and transport from CT and ST systems.

Nitrogen and Phosphorus Runoff Losses from Variable and Constant Intensity Rainfall Simulations on Loamy Sand under Conventional and Strip Tillage Systems

Further studies on the quality of runoff from tillage and cropping systems in the southeastern USA are needed to refine current risk assessment tools for nutrient contamination. Our objective was to quantify and compare effects of constant (Ic) and variable (Iv) rainfall intensity patterns on inorganic nitrogen (N) and phosphorus (P) losses from a Tifton loamy sand (Plinthic Kandiudult) cropped to cotton (Gossypium hirsutum L.) and managed under conventional (CT) or strip-till (ST) systems. We simulated rainfall at a constant intensity and a variable intensity pattern (57 mm h(-1)) and collected runoff continuously at 5-min intervals for 70 min. For cumulative runoff at 50 min, the Iv pattern lost significantly greater amounts (p < 0.05) of total Kjeldahl N (TKN) and P (TKP) (849 g N ha(-1) and 266 g P ha(-1) for Iv; 623 g N ha(-1) and 192 g P ha(-1) for Ic) than did the Ic pattern. However, at 70 min, no significant differences in total losses were evident for TKN or TKP from either rainfall intensity pattern. In contrast, total cumulative losses of dissolved reactive P (DRP) and NO3-N were greatest for ST-Ic, followed by ST-Iv, CT-Ic, and CT-Iv in diminishing order (69 g DRP ha(-1) and 361 g NO3-N ha(-1); 37 g DRP ha(-1) and 133 g NO3-N ha(-1); 3 g DRP ha(-1) and 58 g NO3-N ha(-1); 1 g DRP ha(-1) and 49 g NO3-N ha(-1)). Results indicate that constant-rate rainfall simulations may overestimate the amount of dissolved nutrients lost to the environment in overland flow from cropping systems in loamy sand soils. We also found that CT treatments lost significantly greater amounts of TKN and TKP than ST treatments and in contrast, ST treatments lost significantly greater amounts of DRP and NO3-N than CT treatments. These results indicate that ST systems may be losing more soluble fractions than CT systems, but only a fraction the total N (33%) and total P (11%) lost through overland flow from CT systems.

Exploring the use of a column model for the characterization of microphysical processes in warm rain: results from a homogeneous rainshaft model

Abstract. A study of the evolution of raindrop spectra (raindrop size distribution, DSD) between cloud base and the ground surface was conducted using a column model of stochastic coalescense-breakup dynamics. Numerical results show that, under steady-state boundary conditions (i.e. constant rainfall rate and DSD at the top of the rainshaft), the equilibrium DSD is achieved only for high rain rates produced by midlevel or higher clouds and after long simulation times (~30 min or greater). Because these conditions are not typical of most rainfall, the results suggest that the theoretical equilibrium DSD might not be attainable for the duration of individual rain events, and thus DSD observations from field experiments should be analyzed conditional on the specific storm environment under which they were obtained.

Impact of different land uses on the migration of two herbicides in a silt loam soil: unsaturated soil column displacement studies

SummaryDisplacement experiments of bromide and two herbicides, isoproturon and metribuzin, were performed in unsaturated undisturbed soil cores sampled on a unique site under (i) conventional wheat/maize rotation, (ii) 10‐year‐old grassed strip and (iii) 80‐year‐old oak/chestnut forest. Steady state conditions at constant rainfall intensity were used to compare the effect of the different land uses on soil herbicide transport and dissipation parameters. For each herbicide, mobility was similar between grassed strip and cultivated soils while it was reduced in the forest soils. The descriptive and moment analyses of the experimental breakthrough curves of bromide and herbicides demonstrated a similar degree of physical non‐equilibrium transport for the cropped and grassland soil columns, with transport ranging from a less intense physical non‐equilibrium status to the complete physical equilibrium state for the forest soil columns. Chemical non‐equilibrium transport was shown for the three situations. Degradation occurred in some columns as demonstrated by the elution of a metabolite of isoproturon. Previous data on sorption and degradation of isoproturon on the same soils were used to explain the differences observed in the analysis of the elution curves between grassed strip, forest and cultivated soil. Averaging Kd values from individual soil layers of each profile gave a satisfying understanding of isoproturon retardation factors. Sorption on soil organic matter was the main factor in herbicide mobility. However, other phenomena such as degradation and formation of non‐extractable residues were involved in the differences observed in leached masses of isoproturon between the three situations.

Effects of Tropical Rainfall Patterns with Constant Rainfall Erosivity on Soil and Nitrogen Losses

Effects of Tropical Rainfall Patterns with Constant Rainfall Erosivity on Soil and Nitrogen Losses

Use of the Connectivity of Runoff Model (CRUM) to investigate the influence of storm characteristics on runoff generation and connectivity in semi‐arid areas

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

Numerical modeling of surface runoff and erosion due to moving rainstorms at the drainage basin scale

Summary A physically-based distributed erosion model (MEFIDIS) was applied to evaluate the consequences of storm movement on runoff and erosion from the Alenquer basin in Portugal. Controlled soil flume laboratory experiments were also used to test the model. Nine synthetic circular storms were used, combining three storm diameters (0.5, 1 and 2 times the Alenquer basin’s axial length) with three speeds of storm movement (0.5, 1 and 2 m/s); storm intensities were synthesized in order to maintain a constant rainfall depth of 50 mm. The model was applied to storms moving downstream as well as upstream along the basin’s axis. In all tests, downstream-moving storms caused significantly higher peak runoff (56.5%) and net erosion (9.1%) than did upstream-moving storms. The consequences for peak runoff were amplified as the storm intensity increased. The hydrograph shapes were also different: for downstream-moving storms, runoff started later and the rising limb was steeper, whereas for upstream moving storms, runoff started early and the rising limb was less steep. Both laboratory and model simulations on the Alenquer basin showed that the direction of storm movement, especially in case of extreme rainfall events, significantly affected runoff and soil loss.

Effects of intra-storm variations in rainfall intensity on interrill runoff and erosion

Five simulated rainstorms, each with a different rainfall intensity pattern but all delivering the same total kinetic energy to the soil surface, were applied to three different soils in a laboratory flume. The storm patterns were: constant rainfall intensity, increasing intensity, decreasing intensity, increasing then decreasing intensity and decreasing then increasing intensity. The three soils were: a clay loam, a sandy loam and a sandy soil. No differences in total runoff were observed that were consistent across the three soil types. However, consistent differences were observed in the amount and size distribution of the eroded sediment. In particular, the constant-intensity storm yielded an average soil loss of 75% of the varying-intensity storms, and the eroded sediment from the constant-intensity storms had a lower clay content than that from the varying-intensity storms. In contrast to the differences in amount and size distribution of eroded sediment, splashed sediment exhibited much smaller differences. Interrill erosion rates are widely assumed to vary with rainfall intensity to the power 2, but this relationship has been obtained from experiments over a range of rainfall intensities, but in which rainfall intensity has been constant in each experiment. The experiments reported here, undertaken using variable rainfall intensity within each experiment, indicates an exponent of 2.55. The experiments demonstrate that the assumption that a given rainfall intensity falling on a given soil for a given amount of time will result in a given amount of runoff and erosion is unsound. They point to the need for a greater understanding of the processes of interrill sediment detachment and transport in order to model successfully erosion under temporally varying rainfall.

Spatial Modelling of Sediment Transport over the Upper Citarum Catchment

This paper discusses set up of a spatial model applied in Geographic Information System (GIS) environment for predicting annual erosion rate and sediment yield of a watershed. The study area is situated in the Upper Citarum Catchment of West Java. Annual sediment yield is considered as product of erosion rate and sediment delivery ratio to be modelled under similar modeling tool. Sediment delivery ratio is estimated on the basis of sediment resident time. The modeling concept is based on the calculation of water flow velocity through sub-catchment surface, which is controlled by topography, rainfall, soil characteristics and various types of land use. Relating velocity to known distance across digital elevation model, sediment resident time can be estimated. Data from relevance authorities are used. Bearing in mind limited knowledge of some governing factors due to lack of observation, the result has shown the potential of GIS for spatially modeling regional sediment transport. Validation of model result is carried out by evaluating measured and computed total sediment yield at the main outlet. Computed total sediment yields for 1994 and 2001 are found to be 1.96×10 6 and 2.10×10 6 tons/year. They deviate roughly 54 and 8% with respect to those measured in the field. Model response due to land use change observed in 2001 and 1994 is also recognised. Under presumably constant rainfall depth, an increase of overall average annual erosion rate of 11% resulted in an increase of overall average sediment yield of 7%.

Apparent Contact Angle Effects of Homogeneous Dry Sand on Fingered Flow Growing Under a Constant Rainfall Condition

Apparent Contact Angle Effects of Homogeneous Dry Sand on Fingered Flow Growing Under a Constant Rainfall Condition