Constant Rainfall Rate Research Articles

Experimental Study of Rainfall Infiltration in an Analog Fracture‐matrix System

In this study, an experimental apparatus was developed to investigate unsaturated infiltration in an analog fracture‐matrix system. Fracture and adjacent matrix is simulated by sands with various particle sizes. Four rainfall infiltration experiments were performed on the analog fracture‐matrix system at a constant rainfall rate of 100 mm/h. The process of rainfall infiltration is measured by a combination method of tensiometers and quick moisture apparatus. The measured results reveal that fracture‐matrix interactions certainly exert influences on the hydraulic behaviour of unsaturated fractured matrix, and the fluid flow mainly infiltrates along the nonuniform paths within the matrix. Moreover, it is observed that the influences are greater when using a coarser sand to mimic the fracture. Specifically, the wetting phase in the matrix moves faster than that in the fracture; the fracture, therefore, acts as a vertical capillary barrier, but there exists lateral water exchange from the matrix to the fracture. Overall, this study has demonstrated the importance of fracture/matrix interactions, which should be considered when dealing with unsaturated flow through permeable matrices.

Removal of Heavy Metals from Stormwater Using Porous Concrete Pavement

This study aimed to investigate the heavy metals, i.e. Cu, Pb, Ni, and Zn removal efficiency from stormwater runoff of a porous concrete pavement (PCP). A model of PCP was designed with the porosity and co-efficient of permeability of the pavement were 27.2% and 1.83 cm/sec, respectively. Artificial stormwater containing heavy metals are passed through the pavement at a constant rainfall rate to mimic the stormwater rainfall-runoff condition. The artificial stormwater infiltrated through the pavement were then collected at two different pavement layers at different time instances. From the experimental investigations, it is observed that Cu, Pb, Ni and Zn concentrations are significantly reduced in the treated stormwater. At the first collection point which is located below the sub-base layer and coarse sand layer of the pavement, the concentrations of Cu, Pb and Zn reduced 56%, 67% and 93% respectively compared to their initial concentration, Ni concentration reduced only 20%. At the second collection point which is located below the coarse and fine sand layers beneath the pavement, the concentrations of Cu, Pb, Zn, and Ni are reduced 92%, 89%, 100%, 100%, respectively.

Modelling of drainage dynamics influence on sediment routing system in a fold‐and‐thrust belt

AbstractDrainage networks link erosional landscapes and sedimentary basins in a source‐to‐sink system, controlling the spatial and temporal distribution of sediment flux at the outlets. Variations of accumulation rates in a sedimentary basin have been classically interpreted as changes in erosion rates driven by tectonics and/or climate. We studied the interactions between deformation, rainfall rate and the intrinsic dynamics of drainage basins in an experimental fold‐and‐thrust belt subjected to erosion and sedimentation under constant rainfall and shortening rates. The emergence of thrust sheets at the front of a prism may divert antecedent transverse channels (perpendicular to the structural grain) leading to the formation of longitudinal reaches, later uplifted and incorporated in the prism by the ongoing deformation. In the experiments, transverse incisions appear in the external slopes of the emerging thrust sheets. Headward erosion in these transverse channels results in divide migration and capture of the uplifted longitudinal channels located in the inner parts of the prism, leading to drainage network reorganization and modification of the sediment routing system. We show that the rate of drainage reorganization increases with the rainfall rate. It also increases in a nonlinear way with the rate of uplift. We explain this behaviour by an exponent > 1 on the slope variable in the framework of the stream power erosion model. Our results confirm the view that early longitudinal‐dominated networks are progressively replaced by transverse‐dominated rivers during mountain building. We show that drainage network dynamics modulate the distribution of sedimentary fluxes at the outlets of experimental wedges. We propose that under constant shortening and rainfall rates the drainage network reorganization can also modulate the composition and the spatial distribution of clastic fluxes in foreland basins.

Transport Time Scales in Soil Erosion Modeling

Core Ideas Erosion timescales inherent in the Hairsine–Rose soil erosion are exposed. Both fast and slow timescales are isolated and can be estimated a priori. The maximum sediment settling rate controls the possible range of timescales. In practice, the full range of erosion timescales are not seen in flume experiments. Unlike sediment transport in rivers, erosion of agricultural soil must overcome its cohesive strength to move soil particles into suspension. Soil particle size variability also leads to fall velocities covering many orders of magnitude, and hence to different suspended travel distances in overland flow. Consequently, there is a large range of inherent timescales involved in transport of eroded soil. For conditions where there is a constant rainfall rate and detachment is the dominant erosion mechanism, we use the Hairsine–Rose (HR) model to analyze these timescales, to determine their magnitude (bounds) and to provide simple approximations for them. We show that each particle size produces both fast and slow timescales. The fast timescale controls the rapid adjustment away from experimental initial conditions—this happens so quickly that it cannot be measured in practice. The slow timescales control the subsequent transition to steady state and are so large that true steady state is rarely achieved in laboratory experiments. Both the fastest and slowest timescales are governed by the largest particle size class. Physically, these correspond to the rate of vertical movement between suspension and the soil bed and the time to achieve steady state, respectively. For typical distributions of size classes, we also find that there is often a single dominant timescale that governs the growth in the total mass of sediment in the non‐cohesive deposited layer. This finding allows a considerable simplification of the HR model, leading to analytical expressions for the evolution of suspended and deposited layer concentrations.

How will increases in rainfall intensity affect semiarid ecosystems?

AbstractModel studies suggest that semiarid ecosystems with patterned vegetation can respond in a nonlinear way to climate change. This means that gradual changes can result in a rapid transition to a desertified state. Previous model studies focused on the response of patterned semiarid ecosystems to changes in mean annual rainfall. The intensity of rain events, however, is projected to change as well in the coming decades. In this paper, we study the effect of changes in rainfall intensity on the functioning of patterned semiarid ecosystems with a spatially explicit model that captures rainwater partitioning and runoff‐runon processes with simple event‐based process descriptions. Analytical and numerical analyses of the model revealed that rainfall intensity is a key parameter in explaining patterning of vegetation in semiarid ecosystems as low mean rainfall intensities do not allow for vegetation patterning to occur. Surprisingly, we found that, for a constant annual rainfall rate, both an increase and a decrease in mean rainfall intensity can trigger desertification. An increase negatively affects productivity as a greater fraction of the rainwater is lost as runoff. This can result in a shift to a bare desert state only if the mean rainfall intensity exceeds the infiltration capacity of bare soil. On the other hand, a decrease in mean rainfall intensity leads to an increased fraction of rainwater infiltrating in bare soils, remaining unavailable to plants. Our findings suggest that considering rainfall intensity as a variable may help in assessing the proximity to regime shifts in patterned semiarid ecosystems and that monitoring losses of resource through runoff and bare soil infiltration could be used to determine ecosystem resilience.

A Spatiotemporal Correlation Technique to Improve Satellite Rainfall Accumulation

AbstractA spatiotemporal correlation technique has been developed to combine satellite rainfall measurements using the spatial and temporal correlation of the rainfall fields to overcome problems of limited and infrequent measurements while accounting for the measurement accuracies. The relationship between the temporal and spatial correlation of the rainfall field is exploited to provide information about rainfall beyond instantaneous measurements. The technique is developed using synthetic radar data. Nine months of Operational Program for the Exchange of Weather Radar (OPERA) data are used on grid sizes of 100, 248, and 500 km with pixel resolutions of 8, 12, and 24 km to simulate satellite fields of view and are then applied to the real satellite data over the Southwest to calculate 3-h rainfall accumulations. The results are compared with the simple averaging technique, which takes a simple mean of the measurements as a constant rainfall rate over the entire accumulation period. Using synthetic data, depending on the time separation of the measurements and their accuracy, a spatiotemporal correlation technique has shown the potential to yield improvements of up to 40% in absolute error and up to 25% in root-mean-square error when compared with the simple averaging technique. When applied to the real satellite data over the Southeast, the technique showed much less skill (general improvement of only 2%–6%).

Paved Area Reduction Factors under Temporally VariedRainfall and Infiltration

Best management practices (BMPs) for storm water drainage systems are used to increase storm water quality and reduce the amount of storm water runoff that is generated from a developed watershed. Paved area reduction factors, referred to as PARFs, are developed in this study to determine the reduction of storm water runoff when storm water BMPs are incorporated into storm water designs. PARFs determine the amount of runoff reduction by evaluating the effective impervious values of a watershed compared to the impervious value that is commonly determined by weighting the impervious and pervious areas. This study shows that there is a difference between the effective imperviousness and area-weighted imperviousness of a watershed. It also investigates PARFs that are developed under temporally varied rainfall and infiltration parameters and presents how they can vary from PARFs that are derived using constant rainfall and infiltration rates. This study creates an effective line to relate site-effective imperviousness with the infiltration to rainfall index that was developed in previous studies. The effective line provides an easy application to determine site-effective imperviousness from area-weighted impervious values. This study also quantifies the incentives of storm water BMPs by defining the net present value when imperviousness is a basis for storm water fees. It is found that a cost savings in storm water fees can be used to encourage storm water BMPs, and that applying temporally varied rainfall and infiltration for computing PARFs can show an increase in cost savings over previous methods.

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.

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.

Soil erosion due to rainfall impact with no inflow: a numerical solution with spatial and temporal effects of sediment settling velocity characteristics

Dynamic changes take place in the nature of sediment eroded from bare soil at low slopes by rainfall impact when there is no inflow of water at the top of the eroding slope. This relates initially to fine soil sediment not settling back onto the soil after the rainfall impact. Coupled partial differential equations describing such dynamic changes have been solved numerically for a bed of soil, bounded at its upper end, and subject to a constant rainfall rate. This solution allows prediction of the change with time and downslope distance in the concentration and settling velocity (or size) characteristics of eroding sediment, allowing critical evaluation of the assumption of space-independent sediment characteristics made in prior approximate analytical solutions of the equations involved. Following the determination of as yet unpredictable soil-related parameters in the equations, the solution was tested by comparison with experimented data on two soils of contrasting structural stability, namely a vertosol [The Australian Soil Classification (1996)] and a aridisol. Investigations included the determination of a minimum number of sediment size classes required to adequately describe the settling velocity characteristics, based on the shape of the underlying basic settling velocity characteristic, which is used to predict the dynamics of sediment deposition. The effect on the solution of observed structural breakdown in soil aggregation due to rainfall impact was investigated, leading to more accurate predictions of the settling velocity characteristics of eroded sediment. Other sources of discrepancy between theory and observation remain to be determined.

Determination of cloud and precipitation characteristics in the monsoon region using satellite microwave and infrared observations

We have studied the cloud and precipitation features in the Indian summer monsoon region based on satellite microwave and infrared observations. Emphases are particularly given to the differences between stratiform and convective rains and between rains over land and over ocean. In the studied region, average rainfall rate of convective clouds is about 6 times higher than for stratiform clouds while the latter covers 4 to 5 times more area than the former. As a result, convective rains produce higher rain total than stratiform rains with a ratio of about 3 : 2. The difference between convective and stratiform rains is evident virtually by any satellite signatures – cloud top temperature, and microwave emission, scattering and combined signatures. Cloud top temperature appears no skill to reflect surface rainfall rates for stratiform rains while colder cloud top temperatures correspond to higher rainfall rates for convective clouds. As rainfall rate increases, microwave emission signature reaches saturation much quicker for stratiform rains than for convective rains. For convective rains, the rainfall rate – scattering signature relation shows a distinct difference between rains over land and over ocean. Corresponding to the same rainfall rate, the scattering signature over land is about twice as high as that over ocean. The mean vertical precipitation profiles showed that stratiform rains have a constant rainfall rate below freezing level and a sharp drop-off above, regardless over land or ocean. Convective rain profiles, on the other hand, often have the maximum rainfall rate below the freezing level, implying a significant growth of raindrops by warm microphysical processes, such as coalescence. It is also found that given the same surface rainfall rate, the amount of ice particles above freezing level is substantially greater for convective rains over land than over ocean, which explains the difference of scattering signatures between rains over the two different surface types. It is also demonstrated that the sub-pixel variability of rains is largely responsible for the mismatch between plane-parallel model simulations and actual satellite observations.

Landscape response to climate change: Insights from experimental modeling and implications for tectonic versus climatic uplift of topography

Research Article| February 01, 2003 Landscape response to climate change: Insights from experimental modeling and implications for tectonic versus climatic uplift of topography Stéphane Bonnet; Stéphane Bonnet 1Géosciences Rennes, Université de Rennes 1, UMR CNRS 6118, Campus de Beaulieu, 35 042 Rennes cedex, France Search for other works by this author on: GSW Google Scholar Alain Crave Alain Crave 1Géosciences Rennes, Université de Rennes 1, UMR CNRS 6118, Campus de Beaulieu, 35 042 Rennes cedex, France Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (2): 123–126. https://doi.org/10.1130/0091-7613(2003)031<0123:LRTCCI>2.0.CO;2 Article history received: 24 May 2002 rev-recd: 01 Oct 2002 accepted: 03 Oct 2002 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Stéphane Bonnet, Alain Crave; Landscape response to climate change: Insights from experimental modeling and implications for tectonic versus climatic uplift of topography. Geology 2003;; 31 (2): 123–126. doi: https://doi.org/10.1130/0091-7613(2003)031<0123:LRTCCI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We present the results of an experimental investigation of the concurrent action of tectonic uplift and climate variation on relief evolution. We designed an experimental apparatus that allows the study of erosion of laboratory-scale topographies that evolve under given uplift and rainfall rates. For constant uplift and rainfall rates, the experimental topography evolves toward a statistical steady state defined by a mean elevation constant with time. Starting from such a steady state and keeping the input uplift rate constant, a subsequent change in the rainfall rate yields a change in the mean elevation of the landscape to a new equilibrium elevation. An increase in precipitation yields a lower mean steady-state elevation, whereas for a decrease in precipitation the surface is uplifted. We define this phenomenon as a climatically induced surface uplift, as opposed to a tectonically induced surface uplift. The climatically and tectonically induced surface uplifts correspond to different dynamics of denudation so that it is theoretically possible to differentiate between the climatic or tectonic causes of surface uplift from records of output sediment fluxes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

When is Rain Steady?

Abstract By definition, steady rain should have a nearly constant rainfall rate. Thus far, however, the criteria for determining when rain is steady remain qualitative and arbitrary. The authors suggest a definition for steadiness that can be used to quantify the elusive notion of natural variability. In particular, the logical criteria for steadiness imply statistical stationarity and lack of correlation between raindrops in neighboring volumes, requirements identical to those for the drops being distributed according to a Poisson process at all scales. Hence, steady rain is Poissonian. Explicit equations for the variance σ2R of the rainfall rates are developed. They show that, in general, raindrop clustering enhances the variance beyond that for Poissonian rain (σ2P). It is also demonstrated by using observations that this enhancement is augmented further when the rain is statistically nonstationary. Identifying steady rain is important. To be specific, because steady rain is statistically stationary, t...

Areal Infiltration Modeling over Soils with Spatially Correlated Hydraulic Conductivities

We study the problem of field-scale infiltration over soils where spatial variability of saturated hydraulic conductivity is represented by a homogeneous correlated lognormal random field. The Green-Ampt equation was used to describe infiltration at the local scale. Cumulative infiltration, F, was initially used as the independent variable to develop expressions for the ensemble mean and variance of field-scale infiltration under both constant and time-dependent rainfall rates. Analytical expression was derived for the expected time it takes for a given areal depth of water to infiltrate into the soil. Approximate expressions based on a series expansion and a parameterization of the local cumulative infiltration were also presented for describing the ensemble-averaged field-scale infiltration. These results were compared with extensive sets of Monte Carlo simulations for a wide variety of cases. The simulations revealed that the proposed formulations provide an adequate estimate of field-scale infiltration, and that the variance of field-scale infiltration could be parameterized through a simple scaling relationship in terms of the correlation length of the saturated hydraulic conductivity field. Simplified expressions for the variance under asymptotic correlation lengths were also presented.

A Simple Treatment of Physical Nonequilibrium Water Flow in Soils

Water flow in soils with sufficiently large aggregate size or pore‐class heterogeneity may exhibit a nonequilibrium between the actual water content and that given by the water retention curve. The result is deeper penetration of infiltrating water than predicted using classical infiltration theory. Models of this process usually divide the soil into two or more exchanging flow regions. A simpler treatment is possible by combining Richards' equation with a dynamic description of the approach to equilibrium. We present a first‐order time constant equilibration model of infiltration into a hypothetical structured soil and use the model to describe published outflow responses to constant rate rainfall on six large, undisturbed cores. Using measured hydraulic properties and varying only the A and B horizon time constants, the model was fitted to cumulative outflow from one particular soil core that had measured time domain reflectometry (TDR) water contents at the 0.05‐ and 0.5‐m depths recorded during the experiment. Cumulative outflow was fitted using time constants of 4 and 5 h for A and B horizons, respectively, and this also gave good agreement with TDR measured water contents. Cumulative outflow and runoff from a further four of the six cores was described using the same A and B horizon time constants and varying only the macropore hydraulic conductivity. The remaining core contained a decayed root, which conducted water rapidly with little opportunity for lateral exchange. A description of cumulative outflow required both the macropore hydraulic conductivity and the time constant to be altered.

Reply [to “Comment on ‘Analytical integration of the kinematic equation for runoff on a plane under constant rainfall rate and Smith and Parlange infiltration’ by J. V. Girfildez and D. A. Woolhiser”

Water Resources ResearchVolume 36, Issue 3 p. 827-827 CommentariesFree Access Reply [to “Comment on ‘Analytical integration of the kinematic equation for runoff on a plane under constant rainfall rate and Smith and Parlange infiltration’ by J. V. Girfildez and D. A. Woolhiser”] J. V. Giráldez, J. V. GiráldezSearch for more papers by this authorD. A. Woolhiser, D. A. WoolhiserSearch for more papers by this author J. V. Giráldez, J. V. GiráldezSearch for more papers by this authorD. A. Woolhiser, D. A. WoolhiserSearch for more papers by this author First published: 01 March 2000 https://doi.org/10.1029/1999WR900313Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume36, Issue3March 2000Pages 827-827 ReferencesRelatedInformation

Comment on “Analytical integration of the kinematic equation for runoff on a plane under constant rainfall rate and Smith and Parlange infiltration” by J. V. Giráldez and D. A. Woolhiser

Comment on “Analytical integration of the kinematic equation for runoff on a plane under constant rainfall rate and Smith and Parlange infiltration” by J. V. Giráldez and D. A. Woolhiser

A STUDY ON PONDING TIME AND INFILTRATION CAPACITY DURING STEADY RAINFALL

Natural rainfall has the variation in rainfall intensity during its event. However, the various infiltration models are subjected to rainfall intensities that are higher than the infiltration capacity of the soil at a given location. Diskin and Nazimov (J. Hydrol., 172: 313-330, 1995) proposed recently the infiltration model which is a simple conceptual model and can express the relationship between rainfall intensity and ponding time.‘Ponding time’ is the period from the beginning of rainfall until the occurrence of ponding. This model also can compute the variation in the infiltration capacity for constant or variable rainfall rates. A simple conceptual model is valuable for carrying out the stormwater runoff analysis.The purpose of this paper is to investigate the ponding time and the infiltration capacity for field infiltration data measured using a rainfall simulator under steady rainfall and to evaluate the above infiltration model proposed by Diskin and Nazimov. Comparison of the model calculations with experimental data shows reasonably good for the relationship between rainfall intensity and ponding time and excellent agreement for the infiltration decay curves.

Evaluation of a simplified dynamical rainfall forecasting model from rain events simulated using a meteorological model

This paper presents an evaluation of a simplified dynamical model from simulated rain events. This model is based on conservation of the rainwater content of an atmospheric column and uses mull-scan radar data and surface meteorological observations. A test of the model using radar data from Oklahoma City (USA) and the Cevennes region (France) has not clearly shown the model efficiency compared to the simple extrapolation of radar observations. This statement can be explained by the limited number of rain events available for testing the model and errors inherent in radar measurements. The proposed evaluation is based on a mono-dimensional microphysical and meteorological model, which serves to simulate reference rainfall. The outputs of the meteorological model: rainwater content, cloud top temperature, surface temperature, pressure and dew point are used for initialising the simplified dynamical model as in the case of observed rain events. The evaluation of the simplified dynamical model is performed by comparing forecasts to reference rainrates. This comparison shows that the simplified dynamical model performs better than the simple extrapolation method for short lead-times up to 30 min. This time is related to the response time of the rainwater atmospheric column. For longer lead-tithes, the dynamics of the simplified model tends to a steady state characterised by a constant rainfall rate controlled by the source term. This result which has still to be confirmed makes the model adapted to requirements of urban hydrology.

Rain-induced crosspolarisation on line-of-sight systems at 38 GHz

Factors affecting rain-induced depolarisation at 38 GHz have been investigated. The effect of raindrop canting on the crosspolar signal levels has been examined together with other, more minor, factors such as water temperature and drop shape model. The intervening medium between the two terminals is assumed to have constant rainfall rate and the crosspolar effects are evaluated for various link separations and for various rain intensities. Additionally, data obtained from the Chilbolton radar are used and the depolarisation effects due to typical precipitation events are assessed. Results indicate that, for a standard 38 GHz PCN (personal communication network) system, the use of linear, orthogonal polarisations is not likely to present operational problems. Compared with the copolar fading of the wanted signal and the depolarisation introduced by antennas typically used by the operators, the effects of rain-induced crosspolarisation are shown to be almost negligible.