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A tension-saturated capillary fringe above the water table in drained lands gives rise to lower water tables than would occur in its absence. Results of a conformal mapping solution for the flow from uniform steady rainfall rates on the soil surface to deep drains installed above an impermeable bed when the soil above the drains is wholly tension-saturated show that the effect on the water table is greater the nearer the drain is to the impermeable floor. The effect becomes less with increasing rainfall rate. For the very deep tension-saturated soils assumed in the analysis (that implies a very large negative value for the air-entry pressure for the soil), the results obtained give lower bounds for the water-table heights in real soils with finite air-entry values that lie between the calculated ones and those obtained by theory neglecting a capillary fringe. [ABSTRACT FROM AUTHOR]

This paper describes laboratory experiments that provide evidence of infiltration of excess runoff water from upstream areas that moves downslope over unsaturated areas (run-on process). The experiments were carried out using a tilting tank that was packed with two different natural soils to a depth of 70 cm and subjected to artificial rainfalls from a rainfall simulator. Different rainfall patterns were generated over the surface at different slope settings. Measurements of overland flow, deep flow, and soil water content, together with photographs of soil surface, were used to quantify the main features of the run-on process. The results indicate that the interaction between Hortonian overland flow and local infiltration over the permeable areas can be appropriately described by representing the flow depth per unit time as an “additional” rainfall rate. Thus, these experimental results support the representation of the run-on process that was adopted in previous numerical studies that evaluated the effects of the run-on process. [ABSTRACT FROM AUTHOR]

Prediction of flood hydrographs in semiarid regions is a complex task due to limited rainfall-runoff observations. The application of complex loss models that have intensive input data requirements can be impractical for such regions. The performance of three loss models, namely, initial and constant rate (IC), Soil Conservation Service (SCS), and constant fraction (CF), in prediction of flood events in a 37.2-km2 semiarid watershed was evaluated using deterministic and probabilistic hydrologic models. We quantified the performance in terms of bias, error, and correlation via relative error (RE), Nash–Sutcliff efficiency (NSE), and percent bias (PBIAS) for 14 events with dry prestorm conditions and a range of rainfall properties (duration, depth, and temporal pattern) and runoff characteristics (peak, volume, and time to peak). The NSE values of the deterministic model ranged from 0.61 to 0.90 and −0.50 to 0.63 for calibration and validation, respectively, in the best model (IC). The results suggest that the performance of loss models was inconsistent in terms of hydrograph attributes. The IC model was best in terms of peak flow according to both deterministic and probabilistic models and best in terms of volume according to the deterministic model, but similar to SCS and better than the CF based on the probabilistic model. The CF model mostly underestimated the runoff volume and peak flow. The performances of the loss models were almost identical in the prediction of the time to peak. These results suggested that deterministic models may be insufficient for selecting the best loss models. Probabilistic models, incorporating the parametric uncertainty, are needed to further evaluate the performance of loss models. There was no correlation between the performance of models and the size of events. Rainfall temporal pattern was found to be an effective factor in the accuracy of flood hydrology predictions. The results can guide the selection of loss models in semiarid watersheds. [ABSTRACT FROM AUTHOR]

Rainfall erosion can cause environmental and economic damage by decreasing the storage capacity of water reservoirs because of the detachment of soil particles. The purpose of this study was to develop a one-dimensional physicomathematical model that can help predict the effects of rainfall erosion on the banks of water reservoirs. The model was developed using the Mein–Larson model to describe water infiltration, the kinematic wave approximation to represent overland flow generation, and the steady state sediment continuity equation to estimate sediment transport. The model was validated using rainfall simulator tests and lateritic soil samples with a bimodal soil–water retention curve. The results showed conformity with the experimental data, identifying a threshold in the models for discharge per unit area and sediment yield rate, as well as a linear increase in the models for total runoff and sediment load per unit area. However, the model failed to capture the peak in sediment yield rate owing to raindrop impact during the initial minutes of rainfall. Parametric analysis highlighted the impact of increasing the calibration constant of splash erosion, erodibility coefficient, and critical shear stress on the slope of the sediment load per unit area model. Despite its limitations, the model demonstrates satisfactory predictive capability for sediment load per unit area under high-intensity rainfalls, achieving an R2 greater than 0.92 in five of the six cases examined. [ABSTRACT FROM AUTHOR]

In this paper, models for short-term prediction of influent flow rate in a wastewater-treatment plant are discussed. The prediction horizon of the model is up to 180 min. The influent flow rate, rainfall rate, and radar reflectivity data are used to build the prediction model by different data-mining algorithms. The multilayer perceptron neural network algorithm has been selected to build the prediction models for different time horizons. The computational results show that the prediction model performs well for horizons up to 150 min. Both the peak values and the trends are accurately predicted by the model. There is a small lag between the predicted and observed influent flow rate for horizons exceeding 30 min. The lag becomes larger with the increase of the prediction horizon. [ABSTRACT FROM AUTHOR]

The Soil Conservation Service (SCS) method is widely used to estimate runoff from small- to medium-sized watersheds. The most critical assumption of the SCS method is that the ratio of actual retention to potential retention is the same as the ratio of actual runoff to potential runoff; however, this assumption has not been empirically validated. The paper develops a framework to test this proportionality assumption that underpins the SCS method. Using data on rainfall intensity and storm runoff from 210 site events from Australia and Southeast Asian countries, this paper shows that a strong relationship exists between maximum retention on the basis of the SCS equation and the product of effective storm duration and spatially averaged maximum infiltration rate, and empirical support exists for the proportionality assumption for runoff estimation. Relating the maximum retention to the effective storm duration and maximum infiltration rate provides additional avenues for prediction of storm runoff amount and peak runoff rate, which are the key design parameters for storm water control and management. [ABSTRACT FROM AUTHOR]

A simplified model for estimating the hydrologic response to rainfall events at basin scale is developed in this study. It involves an abstraction of the real basin geometry based on networks of planes and channels and three semianalytical components that give the expected areal-average infiltration rate at field scale, the surface runoff hydrograph as lateral inflow into the channel network, and the water flow routing through the channel network. The model was tested by comparison with Monte Carlo simulations that relied on a detailed representation of spatial variation of excess rainfall and numerical solutions of water routing through planes and channels. The peak flow and the shape of the hydrographs were generally well reproduced. The results were less accurate for cases involving low volumes of effective rainfall, but these are of less importance in hydrologic practice. In spite of the complexity of the processes represented, such as the spatial heterogeneity of soil saturated hydraulic conductivity and rainfall rate as random variables over each subwatershed, the model requires a low computational effort that makes it suitable for application at all levels of spatial discretization. [ABSTRACT FROM AUTHOR]

The dependence between temporal sampling error in satellite-derived rainfall estimates and rainfall rate is of scientific and practical interest. We explore the use of copulas to construct the needed joint distribution between the sampling error and the corresponding rainfall rate. Our approach is to first estimate the marginal distribution functions in a parametric way, and then use these with a number of copula functions in search of the one most appropriate. We use maximum likelihood to estimate the parameters of the copulas. We select the best-fitted parametric copula function as the one that gives the largest likelihood. Our findings have important implications for the interpretation and propagation studies of remote sensing precipitation uncertainties. [ABSTRACT FROM AUTHOR]

A model is presented that can simulate infiltration from rainstorms on areas exhibiting random variation in saturated hydraulic conductivity KS. Heterogeneity in the capillary drive (or length scale) parameter G can be treated as well. The method is based on a point infiltration model that includes the Green-Ampt or Smith-Parlange infiltration functions. The runoff area is characterized as an ensemble of infiltrating points or flow path strips that provides runoff to a receiving channel. The model is developed by simulation of a large ensemble using Latin hypercube sampling. The infiltration expression is responsive to a changing rainfall rate r and is easily characterized using the basic infiltration parameters KS and G, plus a third parameter based only on the coefficient of variation of KS or G. Areal heterogeneity causes a rainfall-dependent change in the areal effective value for KS, called Ke(r). The infiltration expression contains rainfall rate as a variable, and observed storms with temporal rainfall patterns may easily be treated. Moreover, the new expression eliminates the explicit concept of ponding time as a separate calculation. The effect of heterogeneous infiltration parameters is demonstrated using several field cases. [ABSTRACT FROM AUTHOR]

To mitigate flood damage in cities, pervious concrete has been developed as a viable and sustainable alternative to traditional concrete to facilitate drainage. Previous studies have tended to evaluate the drainage capacity of pervious blocks through permeability and drainage tests in simplified conditions, giving little consideration to multiple environmental factors such as rainfall rate and temporal changes in the blocks' drainage capacity. This study presents experimental results of the runoff and drainage capacity of pervious blocks subjected to time-dependent evaporation and corresponding changes in their degree of saturation. Different levels of repeated water charging at designated time intervals simulated the urban environment, and both runoff and drainage were continuously monitored. The results highlight that runoff can take place after certain time intervals despite the same water charge because of evaporation and prewetting-induced changes in waterretention capacity. The effects of the surface layer, the bedding layer, and clogging (all part of the urban areas) on the drainage were also observed. The findings underscore the significance of the actual, rather than the simplified laboratory-based, drainage capacity in urban areas. [ABSTRACT FROM AUTHOR]

An important goal of combining weather radar with rain gauge data is to provide reliable estimates of rainfall rate and accumulation and to further identify intense precipitation and issue flood warnings. Scanning radars provide the ability to observe precipitation over wider areas within shorter timeframes compared to rain gauges, leading to improved situational awareness and more accurate and reliable warnings of future precipitation and flooding events. The focus of this study is on evaluating the performance of the multi-radar multi-sensor (MRMS) system with and without the impact of a local gap filling radar. The challenge of using radar and rain gauges to provide accurate rainfall estimates in complex terrain is investigated. The area of interest is the Russian River basin north of San Francisco, CA, which lies within the National Oceanic and Atmospheric Administration (NOAA) Hydrometeorology Testbed (HMT). In this complex mountainous terrain, the challenge of obtaining reliable quantitative precipitation estimations (QPEs) is hindered by beam blockage and overshooting, as well as the enhancement of rainfall on the windward side of mountain ranges. The effectiveness of several local radars, which include four S-band National Weather Service (NWS)Weather Surveillance Radar-1988 Doppler (WSR-88DP) radars and a C-band gap filling TV station radar (i.e., KPIX), are considered for deriving QPE over this region. The precipitation estimation methodologies used the MRMS algorithms and an independent KPIX-only (Z - R) based QPE algorithm. In addition, a time series analysis is conducted in order to illustrate the radargauge rainfall difference caused by radar beam height. The sampling relative to precipitation vertical structure is also considered in regards to the depth of the precipitation and the height of the bright band. The quantitative evaluation of different QPE products is presented. [ABSTRACT FROM AUTHOR]

Infiltration-based sustainable urban drainage systems (i-SUDS) often turn out to be simple and effective solutions for on-site runoff and pollution control. Their ability to limit the discharge to sewer networks or receiving waters can be broadly assessed in terms of (pluri)annual stormwater volume reduction. Although accepted as a relevant efficiency metric, this long-term volume reduction does not integrate well in design practices that have traditionally relied on event-based approaches. This article introduces a modeling framework, involving a hydrological model and machine-learning emulation, from which a web app was developed to allow practitioners to investigate the relation between i-SUDS design and pluriannual volume reduction efficiencies. The theoretical basis for modeling and a description of the web app are first provided. A diagnosis of the hydrological model is then conducted. The uncertainty caused by model parameters that do not directly relate to i-SUDS design is evaluated through a sensitivity analysis performed over multiple design scenarios. The latter is found to be highly variable and potentially significant, thereby justifying its explicit consideration in the web app. As part of this diagnosis, the impact of a shallow groundwater or a low-permeability layer on simulated volume reduction efficiencies is later evaluated to clarify the validity domain of the model. Practical recommendations on the minimum distance to shallow groundwater or low permeability layer, for the rainfall conditions considered in the web app, are given as a function of project size and the permeability of the soil media. The applicability of the web app is later illustrated from a selection of outputs. Its outcomes are finally compared to those of a simple design rule based on the combination permanent storage (as rainfall depths) and drawdown duration targets. Results confirm the inability of such simple design rules to fully capture pluriannual volume reduction efficiency and point out the risk of oversizing i-SUDS. Stormwater infiltration in small vegetated systems can effectively reduce runoff and pollutant discharge to surface waters. A well-accepted performance objective for such systems is to achieve a significant reduction of the rainfall volume at the annual scale. However, integrating (pluri)annual volume reduction targets in design practices remains difficult as they do not accommodate well with the back-of-the-napkin, event-based calculations traditionally used by the stormwater profession. This paper introduces a web app that allows practitioners to easily investigate the relation between the design characteristics of infiltration-based solutions and pluriannual volume reduction efficiencies. The approach shows how machine learning can be used to replicate at low computational cost the outputs of specialized hydrological models and be incorporated in larger-audience tools. Through an analysis of the validity domain of the app, the study also points out the potential reduction of efficiency that may result from the presence of a shallow groundwater or a low-permeability layer, an aspect often overlooked in the design of infiltration-based systems. The applicability of the app is illustrated from different usage situations. The relevance of the proposed approach is finally demonstrated through a comparison to a simpler, event-based design method, which proves unable to adequately capture pluriannual volume reduction efficiency. [ABSTRACT FROM AUTHOR]

Here, the author expands on the results of the paper “Explicit Solution to Green and Ampt Infiltration Equation” by Serrano published in 2001. Specifically, new simple expressions are given for the cumulative infiltration depth and the infiltration rate that include more terms in the decomposition series. These expressions improve the results and overcome the transcription errors in Eqs. (16) and (17) in the paper by Serrano. A criterion for the convergence of the series is given with graphical illustrations of applications. Generally, the decomposition solution is accurate for a wide range of soil and hydrologic parameters. Important errors occur when the rainfall rate is very high relative to the soil hydraulic conductivity (e.g., high rainfall intensity on clayey soils). As time increases, the errors decrease and the decomposition solution is accurate. [ABSTRACT FROM AUTHOR]

Discusses a study which proposed a theoretical approach to justify the SCS method for runoff estimation. Derivations of SCS runoff equations; Alternative approach for justifying the SCS method; Analytical results.

Intense rain events and sprawling urbanization have contributed to more frequent flash flooding in cities, often due to the pressurization of drainage systems. Stormwater collection networks (SCNs) can become pressurized if their conveyance capacity is exceeded, leading to on-street flooding through backflow out of curb inlets. Due to the complexity of SCN geometry and spatiotemporal rainfall variability, studies evaluating pressurization in stormwater systems have previously been conducted for relatively simple geometries and inflow conditions. Thus, to date there have been few network-scale insights into how pressurization develops, making it difficult to understand drivers that influence pressurization: slope, roughness, connectivity, and inflow rate. The present work evaluates the process of SCN pressurization using numerical modeling through a systematic variation of these variables. Herein, three distinct pressurization mechanisms were identified by using EPA SWMM 5.1 to model idealized SCN topology and junction inflows. New nondimensional flow indexes (NDFIs) are proposed to characterize the pressurization conditions after an initially empty stormwater system reaches steady state under application of hydrographs. This study provides a basis for further systematic evaluation of factors influencing drainage system pressurization, guiding future actions to mitigate urban flash flooding. [ABSTRACT FROM AUTHOR]

The influence of urban development on the volume of storm water runoff and on water temperature, and the associated impact on streams in urban watersheds, has generated a need for tools to predict the temperature of urban storm water runoff, particularly for the assessment of future urban development. To address this need, the Minnesota Urban Heat Export Tool (MINUHET) model was developed to simulate the flow of heat and storm water through a small urban watershed for a rainfall-runoff event. The tool includes process-based hydrological and thermal models for runoff from developed, undeveloped, or vegetated land uses, for various components of drainage networks, and for some best management practices such as detention and infiltration ponds, storm water vaults, and rock cribs. The primary output of MINUHET is a time series of the flow rate and temperature of runoff, which can be used to determine the heat content of the runoff at the outlet of the modeled watershed and aid in the assessment of the thermal impact on receiving waters. This paper provides an overview of the hydrologic and heat transfer processes simulated by MINUHET and presents a case study in which MINUHET is applied to a 5.06-hectare (12.5-acre) residential neighborhood in Plymouth, Minnesota for which runoff flow and temperature data were available for a series of rainfall events. The model was manually calibrated to several parameters, including saturated hydraulic conductivity, Manning's roughness, and thermal diffusivity and heat capacity of asphalt. Runoff flow rate, runoff temperature, and heat export (heat content of the runoff relative to a specified reference temperature) were accurately simulated for a total of four rainfall events using the calibrated parameters. A sensitivity analysis of the model revealed that simulations were especially sensitive to dew point (rainfall) temperature, rainfall rate and saturated hydraulic conductivity, and to thermal properties and thickness of asphalt. These results illustrate the importance of both data quality and a truthful representation of the modeled watershed in producing accurate simulations with MINUHET. [ABSTRACT FROM AUTHOR]

Rainfall results in the transfer of chemicals from soil to surface runoff. A physically-based solute transport model was developed for estimating the solute concentration in runoff originating from the soil surface. The model accounts for the effects of soil infiltration, raindrops, the water runoff rate, and the return flow, all of which influence the concentration of the solutes in the runoff. It was assumed that the depth of mixing zone changed with the varieties of the raindrop hits, return flow, and overland flow. It was also assumed that runoff and soil in the mixing zone mixed instantaneously and that the solute in the soil beneath the mixing zone was moved to the mixing zone by diffusion. The mixing zone was included in the model and was based on the deposited layer or shield concept. To test the model, laboratory experiments were carried out that used two soil types that were exposed to simulated rainfall. The results simulated by the model were highly correlated with the experimental data. In the first few minutes after rainfall began, the solute concentration in the runoff was mainly controlled by the rainfall rate and solute concentration in the mixing zone; higher solute levels in the mixing zone resulted in higher solute concentrations in runoff. When the solute concentration in the runoff stabilized, the solute concentration in the runoff was mainly controlled by the diffusion of solutes from the soil beneath the mixing zone. The simulated data showed a high level of correlation with the measured data for both runoff volume and solute concentration in the runoff. This demonstrates that the model captured the temporal behavior of the runoff and solute transport in the runoff. [ABSTRACT FROM AUTHOR]

When the flow in the capillary fringe above the water table is taken into account in land-drainage theory, water-table heights are lower than those predicted when incident rainfall on the surface is assumed to travel vertically through the vadose zone. An analytical solution is given here to the steady-state drainage problem of the flow of surface-incident rainfall to cylindrical drain channels for the situation of a completely tension-saturated soil above the water table. This gives the maximum effect that the unsaturated soil region above the water table can have on the water-table height for the given drainage system. Calculated results show that the water-table height above drain level is smaller for deeper drains below the soil surface and for larger drain radii than is the case when the effect of the capillary fringe is ignored. It follows that drainage design based on customary land-drainage theory ignoring the effect of a capillary fringe gives an overestimate for the drain spacing. [ABSTRACT FROM AUTHOR]

The influence of urban development on the volume of storm water runoff and on water temperature, and the associated impact on streams in urban watersheds, has generated a need for tools to predict the temperature of urban storm water runoff, particularly for the assessment of future urban development. To address this need, the Minnesota Urban Heat Export Tool (MINUHET) model was developed to simulate the flow of heat and storm water through a small urban watershed for a rainfall-runoff event. The tool includes process-based hydrological and thermal models for runoff from developed, undeveloped, or vegetated land uses, for various components of drainage networks, and for some best management practices such as detention and infiltration ponds, storm water vaults, and rock cribs. The primary output of MINUHET is a time series of the flow rate and temperature of runoff, which can be used to determine the heat content of the runoff at the outlet of the modeled watershed and aid in the assessment of the thermal impact on receiving waters. This paper provides an overview of the hydrologic and heat transfer processes simulated by MINUHET and presents a case study in which MINUHET is applied to a 5.06-hectare (12.5-acre) residential neighborhood in Plymouth, Minnesota for which runoff flow and temperature data were available for a series of rainfall events. The model was manually calibrated to several parameters, including saturated hydraulic conductivity, Manning's roughness, and thermal diffusivity and heat capacity of asphalt. Runoff flow rate, runoff temperature, and heat export (heat content of the runoff relative to a specified reference temperature) were accurately simulated for a total of four rainfall events using the calibrated parameters. A sensitivity analysis of the model revealed that simulations were especially sensitive to dew point (rainfall) temperature, rainfall rate and saturated hydraulic conductivity, and to thermal properties and thickness of asphalt. These results illustrate the importance of both data quality and a truthful representation of the modeled watershed in producing accurate simulations with MINUHET. [ABSTRACT FROM AUTHOR]

Hydrograph methods are used to identify functional dependencies of the rational-method runoff coefficient, and nested intensity-duration-frequency (IDF) rainfall distributions are used to evaluate the assumption that a uniform rainfall intensity with duration equal to the time of concentration leads to the maximum peak runoff rate. Key findings of this study are that the runoff coefficient can have a substantial dependence on both the IDF function and the time of concentration of the catchment, the runoff coefficient can take on values greater than one, and the peak runoff rate is underestimated by assuming a constant rainfall intensity of duration equal to the time of concentration. [ABSTRACT FROM AUTHOR]

Lysimeters constructed from polyethylene tanks were filled with Oldsmar fine sand soil. A single “Midsweet” orange on Carrizo citrange rootstock tree was planted in each lysimeter on May 5, 1991. Fertilization treatments included traditional fertilization using applications of dry-soluble fertilizer at 6-week intervals (TF), weekly fertigation applications (WF), and single annual applications of two different controlled-release materials (CR). Irrigation (by microsprinklers) and drainage volumes (collected weekly) were measured with totalizing flow meters. Trees fertilized with CR products achieved equivalent growth to trees on the TF and WF treatments, even though the CR treatment trees received only 44% of N as the other treatments. The fertigated trees averaged about 14% greater evapotranspiration (ET) during the period of study as compared to the nonfertigated trees. As the trees grew, the average ET increased from 2.8 and 2.3 mm day-1 during 1991/1992 for the fertigated and nonfertigated treatments, respectively, to 5.0 and 4.4 mm day-1, respectively, during 1993/1994. The percentage of the applied N leached ranged from 35% for the WF treatment to 53% with the TF treatment. The total N leached (NO3–N and NH4–N) with the WF trees was approximately two times greater than that for the CR treatments. TF applications resulted in approximately two and one-half times more N leached than from the CR materials. More than 65% of the total N was leached during the rainy summer months (June–November). Leaching was found to be directly related to the rainfall rate. [ABSTRACT FROM AUTHOR]

Using approximate analytical solutions of the nonlinear Richard’s equation, simple models for the simulation of water content, pressure head, hydraulic head, and infiltration rate profiles, subject to either constant conditions, time-variable rainfall, or redistribution, are developed. New practical expressions for the time to ponding and infiltration rate at the ground surface for a variable rainfall rate are proposed. These physically based expressions preserve the nonlinearity inherent in the differential equation, may be easily incorporated into storm-water management models, and do not require the concept of infiltration rate capacity. The results are obtained by adopting well-known expressions for the soil-water physical relationships and the simultaneous solution of the Richard’s and pressure gradient at the ground equations. To verify the analytical procedure, a new solution of the water-content-based Richard’s equation was developed and tested with respect to experimental values, Philip’s solution, and Parlange’s solution, with excellent agreement. In fact, the present model better predicted the location and shape of the wetting front and the tails after that, than did the classical solutions. The models were also compared with a limited finite-difference solution, with reasonable agreement, and with a solution to the linearized Richard’s equation, with poor agreement. Nonlinearity in the differential equation appears to be an important system feature. [ABSTRACT FROM AUTHOR]

A depth-integrated numerical model GP_Rain was developed to calculate the behavior of neutrally buoyant, highly soluble gases subjected to scavenging by rain. A neutrally buoyant release of hydrogen fluoride is used to illustrate the use of the model. The GP_Rain model was developed in two steps. The part without rain scavenging is based on AFTOX, a Gaussian puff/plume model. Then a first-order decay term for rain scavenging, which was developed by assuming a homogeneous rain field, was added to the concentration calculation for the puff. The model can predict the maximum release distance for a certain concentration limitation and a two-dimensional plume with or without rain. [ABSTRACT FROM AUTHOR]

An aeroengine must be able to work safely under severe weather such as rainy weather. The intake of excessive rainwater into the aeroengine can induce stall and surge in the compressor, and the performance changes of the compressor after water ingestion directly affect the work reliability of the aeroengine. The form of spatial distribution of rainwater at the compressor inlet is one of the important factors causing its performance changes, and the characteristic distribution of water droplets may lead to the occurrence of flow distortions at the inlet and inside the compressor. Therefore, this paper takes the water droplet distribution at the inlet of the compressor as the starting point and uses the full-flow CFD numerical method to investigate the changes of internal flow and characteristics of a multistage compressor under typical water ingestion conditions. The water droplet distribution index (Kθ), which describes the inhomogeneous distribution of water droplets along the circumferential direction of the compressor inlet, is defined in this study. The results show that the larger the water droplet distribution index is, the more obvious the performance degradation will be, and the narrower its stable working range will be. Additionally, the results also showed that the full inlet nonuniform and localized water ingestion can lead to flow field distortion characteristics inside the compressor. [ABSTRACT FROM AUTHOR]

Multimechanism floods (MMFs) are caused by the simultaneous occurrence of more than one flood mechanism such as storm surge, precipitation, tides, and waves. MMFs can lead to more severe or differing impacts than single-mechanism floods. As a result, comprehensive risk assessments require the ability to assess the multivariate probabilistic behaviors of hazards from MMFs. This study introduces a novel Bayesian-motivated approach for the probabilistic assessment of hurricane-induced hazards from the combination of the surge, precipitation, tides, and river antecedent flow. A Bayesian network (BN) is developed to capture the physical (conditional) relationship between variables and facilitate the generation of a hazard curve for river discharge that captures the contributions from multiple flood drivers. A case study located along the Delaware River is used to illustrate the proposed approach. Five computationally efficient representative predictive models are developed to estimate the conditional distributions required for the BN as a means of demonstrating the overall framework. The predictive models used in this study act as placeholders and can be replaced with more sophisticated and high-fidelity models depending on the desired accuracy level. While the predictive models are intended to be representative and illustrative, the model performance is evaluated using three historical storms that affected the area. Overall, the proposed framework is shown to be transparent, effective, and adaptable. [ABSTRACT FROM AUTHOR]

Flow-like landslides are recognized to be the most destructive slope movements and to threaten human life. They may occur in several geological settings, as is the case of the pyroclastic soil covers resting on either igneous, or carbonate, bedrocks. The pyroclastic soil strata involved in these shallow landslides typically are partially saturated over the whole year. Intense rainfall, considered at hourly time scale, represents the triggering factor because it causes the decrease in matric suction and the consequent decrease in soil shear strength. However, it is recognized as the role of the hydromechanical slope behavior, the vegetation cover, and the geomorphological irregularities on shallow landslide hazard. These factors should be properly simulated in physically based predictive models of the failure onset to set up a reliable early warning system (EWS). This paper presents a new coupled thermohydraulic modeling of a pyroclastic soil cover in Campania, accounting for several slope factors that may predispose landslide activation, including the geomorphological local irregularities. The Mount Faito test site, in the Lattari Mountains (Southern Italy), has been adopted as a prototype slope for the geomorphological and hydromechanical scenarios of reference because of the extensive field and laboratory characterizations of the soil strata already available from previous studies. Once validated with these data, the numerical model has been used to estimate the slope response to critical rainfall scenarios. Such numerical estimations have been then compared to the instability predictions currently provided by empirical approaches, defined in terms of the intensity and duration of rainstorms threshold of shallow landslide activations. By comparison between the empirical and physically based approaches, the crucial role of antecedent slope hydraulic conditions and the geological setting for implementing reliable EWS, reducing false alarms, is proved. [ABSTRACT FROM AUTHOR]

To reduce life threats and financial losses under hurricane weather and traffic conditions, stakeholders need to make a sequence of decisions (e.g., enforcing traffic control and/or broadcasting travel advisory) with the presence of various uncertainties, which could be formulated as a Markov decision process (MDP). To effectively solve the MDP for optimal operation of hurricane-impacted transportation networks, a risk-informed decision-support framework is proposed consisting of both a decision-making environment and tool. The decision-making environment involves essentially three coupled modules of hurricane hazard, transportation infrastructure, and traffic flow, where the uncertainties from natural environment, built environment, and human behavior are examined. Specifically, multiple correlated hazards for each specific storm are capsulated in the hurricane hazard module, representative hurricane-vulnerable infrastructure components and associated moving vehicles are evaluated in the transportation infrastructure module, and network-level traffic relations are addressed in the traffic flow module. In view of the complexity and intractability of a hurricane-transportation infrastructure-traffic system through full model representation, the efficient low-dimensional modeling approaches including both physics-based analytical and data-driven surrogate models are utilized in all these three simulation modules. Considering an explicit probabilistic model for the decision-making environment (and hence state transition function) is not available, the operation optimization (involving competing objectives of traffic safety and mobility) is accomplished through a deep reinforcement learning-based decision-making tool that learns to act optimally (involving both traffic control and travel advisory actions) by directly interacting with the environment. A hypothetical case study is conducted to verify the applicability and effectiveness of the proposed framework as a testbed for optimal operation of hurricane-impacted transportation networks. [ABSTRACT FROM AUTHOR]

It is time to shift our paradigm of small watershed design from a graphic (or tabular) to a theoretical method, because (1) the recent general unit hydrograph (UH) model can convert a design hyetograph to a design hydrograph simply, accurately, and theoretically; (2) the Natural Resources Conservation Service (NRCS) has recommended that the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 rainfall data of depths and distributions at a specific site, which is often called the NRCS-NOAA rainfall distributions, should be used for small watershed design if runoff data are unavailable; and (3) in this paper, we have presented a design procedure that formulates design hydrographs from the NRCS-NOAA Atlas 14 rainfall distributions and the general UH model automatically, using the MATLAB convolution function. A literature review indicated that the current practice for design hydrographs in small watersheds from hyetographs is laborious because both hyetographs and UHs are discrete. By contrast, the theoretical general UH model can significantly simplify this process. In this research, we first found analytic design hydrographs from rectangular and triangular hyetographs, which were next used to validate the MATLAB convolution method. We then proposed a double exponential rainfall distribution for both asymmetric and symmetric hyetographs. After that, we modified the symmetric exponential distribution model to describe NRCS-NOAA Atlas 14 data for site-specific hyetographs, which are finally convolved with the general UH model for site-specific design hydrographs, using the MATLAB convolution function. It is noteworthy that the proposed method extends the classic rational method from the peak discharge to the whole hydrograph; and it is valid for both continuous and discrete hyetographs. Hence, it provides a powerful tool in urban development, agriculture land use, roadway planning, and airport construction; it can also be used to evaluate an existing drainage system under various meteorologic–hydrologic conditions. Finally, we expect that this research will shift our current design practice and university UH teaching from an empirical to a theoretical paradigm in the near future. [ABSTRACT FROM AUTHOR]

Rapid and efficient infrastructure restoration is critical to reducing the impacts of extreme events on community lifelines. Following a large-scale extreme event, infrastructure restoration at various stages is carried out simultaneously by agencies at various government levels and jurisdictions. Since each agency has different roles, responsibilities, and boundaries within which it operates, coordination and communication among them are challenging. With the overall goal of providing a common operating picture and facilitating concerted planning and action among emergency response agencies, this research proposes a data-driven and equity-centered framework that links the various stages—damage identification, restoration scheduling, and monitoring and control—of infrastructure restoration. This study takes a particular focus on the highway restoration caused by flood inundation. In detail, the framework is composed of three parts, including (1) a systematic data-driven approach that quickly provides spatially distributed estimates of highway inundation, (2) an equity-centered restoration scheduling strategy that prioritizes restoration tasks based on community social vulnerability, and (3) a Bayesian-based approach that provides an up-to-date indication of the impacts of component level changes on the overall restoration progress. A case study on highway inundation in Harris County during Hurricane Harvey was conducted to demonstrate the feasibility and applicability of the proposed framework. In the case study, multisource data, including physical highway topology, geospatial information, field inspection results, and socioeconomic and demographic data, were used. Our framework generates outputs that can be used for rapid damage identification, automated restoration scheduling, and real-time progress updating. In practice, these outputs facilitate quick and shared situational awareness among the involved agencies, which is expected to ease communication and coordination and help overcome challenges resulting from parallel and fragmented restoration efforts. To the authors' best knowledge, this is the first framework that aims to support the management of infrastructure restoration by synthesizing various restoration stages. [ABSTRACT FROM AUTHOR]

The storage–discharge (S-Q) relation, widely employed in hydrology and hydraulics, is often derived from empirical data and is found to be hysteretic or looped, although approximated by a straight line or a curve in hydrologic modeling. The nature of hysteresis depends on geometric and hydraulic conditions. Despite its ubiquitous use, an analytical treatment discussing what causes the storage–discharge relationship to exhibit a looped behavior does not seem to have been reported. This study analyzes the S-Q relation analytically using kinematic wave approximation for a watershed represented by a plane, considering simultaneously rainfall, infiltration, and surface runoff or overland flow. For purposes of simplicity and tractability of analytical solutions, both rainfall intensity and infiltration rate are assumed to be constant. Depending on the duration of rainfall, two cases—equilibrium and partial equilibrium—are distinguished. The hysteretic S-Q relationship is different for these two cases and requires close scrutiny, which is pursued in this study. It is emphasized that the assumptions of constant rainfall intensity and infiltration rate, rectangular geometry, and kinematic wave approximation undermine the dynamics of hysteresis. [ABSTRACT FROM AUTHOR]

This paper aims to develop an accurate and efficient numerical model for three-dimensional transient thermal groundwater flow problems. The modified Richards equation and heat transport equation are considered to govern the thermal groundwater flows. For modeling water flows in the subsurface saturated-unsaturated porous media, we combined the method of characteristics (MOC) and a meshless localized radial basis function collocation method (LRBFCM). In order to implement the MOC scheme, the modified Richards equation is reformulated to an advection form and then computed by the particle tracking technique via MOC. We will then solve the heat equation and remaining terms of the temporal Richards equation by the LRBFCM. Seven benchmark subsurface flow problems with and without temperature effects are simulated and discussed to verify the feasibility and efficiency of this novel three-dimensional (3D) numerical model. [ABSTRACT FROM AUTHOR]

Baseflow separation from rainfall and streamflow data is a fundamental problem in applied hydrology, unsolved despite extensive investigations. For example, a part of baseflow is interflow, which results from rainfall infiltration, but almost all of the existing baseflow separation methods, such as graphic and filter methods, have nothing to do with it, which is a serious flaw from the viewpoint of science. The objective of this research is thus to present an innovative baseflow separation method based on the recent general unit hydrograph (UH) model and the classic Green-Ampt infiltration equation. Specifically, we divided a rainfall hyetograph into two parts using the Green-Ampt infiltration equation: one for surface flow that generates direct runoff and the other for subsurface flow that recharges groundwater and generates interflow. As with direct runoff from the surface system, we approximated the subsurface system as a linear system and thus applied the general UH model for interflow in the unsaturated soil zone, where excess infiltration is defined by analogy to excess rainfall. We assumed that groundwater flow could be described by the classic recession curve; we then added interflow and the groundwater flow to obtain the baseflow. We validated the proposed method with six real-world case studies representing four interflow patterns. Particularly, we found that, unlike direct runoff, the interflow UH model parameters are not unique, depending on stream stages. This implies that the subsurface system is a time-variant linear system, which can even make a negative interflow if groundwater is recharged from streams. We expect that this research will provide a better baseflow separation method and thus improve our understanding of watershed processes. [ABSTRACT FROM AUTHOR]

Traditional land development stormwater management replaces natural pervious surfaces with impervious surfaces such as pavements and buildings. This increases the rate of runoff that is typically then managed through drainage systems and controlled at or near the site discharge location. This approach often leads to increases in total runoff volume, which can lead to higher peak flows in downstream stormwater systems. Low impact development (LID) technologies, such as porous pavements and green roof systems, provide an alternate approach to managing site runoff by mimicking the pervious surfaces they replace. However, these technologies are often used alongside traditional stormwater infrastructure because their entire hydrologic benefit has not been fully explored. Herein we examine the reduction in peak discharge and total runoff volume achieved through the use of porous pavements and green–blue roof systems (a green roof with an underlying storage volume) on three land developments located on the coastal plain of South Carolina. Model results show that the inclusion of green–blue roof systems can significantly reduce peak discharge compared to traditional roof systems and common modular green roof systems, although they have negligible impact on the total volume discharged. Porous pavements significantly reduce total volume discharged, even when placed over low infiltration soils, but have less impact on peak flow depending on their design. The implementation of LID technologies has the potential to improve site performance beyond standard design rainfall depths, indicating that the use of LID may offset the impact of climate change–induced increases in extreme rainfall event depth and intensity. [ABSTRACT FROM AUTHOR]

Contemporary sewer system operation heavily relies on urban drainage model results. In a case study near Leuven, Belgium, this research investigates the potential of a cost-effective local area weather radar (LAWR) for providing rainfall input to sewer models. Before rainfall estimation was possible, the radar was calibrated using tipping bucket rain gauge measurements. Various calibration methods were investigated, and a nonlinearly regressed power law function taking range to the radar into account was most suitable in this case study. Rainfall estimations could be slightly improved by rendering the calibration dependent on radar output. Fifty-seven events were simulated using the InfoWorks CS modeling software, and the effect of radar input on model results was investigated. There were large quantitative deviations, but the qualitative course of time series observed in conduits was reproduced well. Although certain events show a higher correspondence between measured and simulated time series when using radar-driven input, the gauge-driven input generally outperforms the former in this case study and the accompanying model. [ABSTRACT FROM AUTHOR]

Permeable friction course (PFC) is a porous asphalt pavement placed on top of a regular impermeable roadway. Under small rainfall intensities, drainage is contained within the PFC layer; but under higher rainfall intensities, drainage occurs both within and on top of the porous pavement. A computer model-the permeable friction course drainage code (Perfcode)-is developed to study this two-dimensional unsteady drainage process. Given a hyetograph, geometric information regarding the roadway layout, and hydraulic properties of the PFC media, the model predicts the variation of water depth within and on top of the PFC layer through time. The porous layer is treated as an unconfined aquifer using Darcy's law and the Dupuit-Forchheimer assumptions. Surface flow is modeled using the diffusion wave approximation to the Saint-Venant equations. A mass balance approach is used to couple surface and subsurface phases. Straight and curved roadway geometries are accommodated via a curvilinear grid. The model is validated using steady-state solutions that were obtained independently. Perfcode was applied to a field monitoring site near Austin, Texas, and hydrographs predicted by the model were consistent with field measurements. For a sample storm studied in detail, PFC reduced the duration of sheet flow conditions by 80%. In a second sample storm, PFC prevented sheet flow conditions completely. The model may be used to improve the drainage design of PFC roadways. [ABSTRACT FROM AUTHOR]

A two-dimensional rainfall-runoff model is used to systematically explore the aggregate effect of spatially heterogeneous saturated hydraulic conductivity, Ks, on Hortonian runoff generation. The fully dynamic model integrates overland flow and infiltration to allow for the “interactive infiltration” process (run-on). Rainfall events varying in time and intensity were simulated on synthetic hillslopes with random and spatially correlated Ks fields. Model grid size discretization recommendations are developed to fully capture the variation in Ks and avoid limiting the spatial interactive infiltration opportunities as found in analysis of the effects of model grid size on spatially uncorrelated hillslopes. Our results show that on highly correlated Ks fields, relative to the hillslope length, the infiltration due to interaction is less than half that of uncorrelated fields for low intensity events. Previous findings, are also substantiated and further explored, with explicit consideration of model discretization, that the variation in Ks increases interaction by increasing the infiltration opportunity time, simultaneously, increasing runoff. Finally we investigate the rainfall durations, which produce maximum interaction, and find interaction peaks for rainfall events approximately 1.5 times longer than the hillslope average time to ponding. [ABSTRACT FROM AUTHOR]