Search

Estimation of peak outflow resulting from dam failure is of paramount importance for flood risk analysis. This paper presents a new hybrid clustering model based on artificial neural networks and genetic algorithms (ANN-GA) for improving predictions of peak outflow from breached embankment dams. The input layer of the ANN-based model comprises height and volume of water behind the breach at failure time plus a new parameter of cluster number. The cluster number is obtained from partitioning the input data set using the kk-means clustering technique. The model is demonstrated using the data samples collected from the literature and compared with three benchmark models by using a cross-validation method. The benchmark models consist of a conventional regression model and two ANN models trained by nonlinear techniques. Results indicate that the suggested model is able to estimate the peak outflows more accurately, especially for big flood events. The best prediction for the current database was obtained from a five-clustered ANN-GA model. The uncertainty analysis shows the five-clustered ANN-GA model has the lowest prediction error and the smallest uncertainty.

The effect on the solution of dynamic link journey time was investigated under various levels of discretization of dividing link into several segments. The outflow was given by using of the widely used model of relationship between whole link journey time and link flow in dynamic traffic assignment (DTA) models based on given inflows. Under the condition of traffic flow satisfying the rule of first in and first out (FIFO), a link was divided into a few segments, based on whole link journey time model, the discretized journey -time model and the discretized outflow model of every segment was deduced, and whose solutions were proved closely approximating the LWR solutions. Finally, Case 1 numerically compare the precision in calculation of solution of discretized journey-time model under different levels of discretization, and in Case 2 the journey time simulation method was given by use of detected traffic flow.

This paper describes results of an advanced suction controlled triaxial test device on a loessial soil in an attempt to define the constitutive relationship between suction stress and matric suction (Suction Stress Characteristic Curve) for highly collapsible soils. Due to the presence of void spaces with different degrees of collapse potential within the soil matrix, the collapse phenomenon in loess is believed to be a continuous-stepwise reduction in volume rather than a sudden drop during wetting. Due to this unique volume change behavior, the definition of the suction stress characteristic curve for loess may require a soil-specific experimental testing approach capable of making precise and continuous measurements of volume change and water outflow during loading. The testing approach includes a pressure-feedback control loop to provide the required pressure equilibrium in the system in the case of any change in pressure due to pore structure collapse and two independent digitized volume change measurement devices to measure possible changes in soil/water volume during testing. Based on the experimental measurements, depending on the applied unsaturated stress state variables (e.g., net stress and matric suction), and the consequent magnitude of wetting-induced collapse, the soil specimen may show different behavior during shear. For higher matric suctions, soil specimens experience small changes in volume during the suction equilibrium stage and shear strength curves show a dilative and brittle behavior as shearing proceeds. At lower levels of matric suction or higher magnitudes of net stress, a ductile behavior in the shear stress curves is observed and most specimens experience a decrease in volume during shear. Experimental results indicate a unique critical state line for specimens sheared under varying stress state conditions when defining the SSCC using the measured shear strength data in this study.

Grassed swales or drainage ditches are an attractive BMP since they can reduce runoff volume by infiltrating water into the soil, filter sediments and associated pollutants out of the water, and settle solids onto the soil surface. Infiltration rate is a controlling factor for the water quality performance of swales. In this study infiltration measurements were taken at 108 locations in a swale which is located in Madison, WI. A model has been developed to estimate the infiltration of direct rainfall and roadway stormwater runoff into the soil of that swale for observed rainfall events, and thereby facilitate the calculation of volume and rate of outflow from the swale. This model is based on the Green-Ampt equation for the infiltration calculation. The model takes into consideration the antecedent moisture condition of the soil and the Green-Ampt parameters for the soil. With this model the outflow rate of the swale was estimated for the monitored rainfall intensity of a selected storm using the saturated hydraulic conductivity measurements that were taken in the field, and compared with actual outflow rate from that swale. This paper will show how our measured infiltration parameters can be used to determine the stormwater mitigation performance of a given swale.

This paper describes the development of a numerical model, called CSTCRS1, for one-dimensional coupled contaminant transport and large strain consolidation under constant rate of strain (CRS) loading conditions. Numerical simulations using CSTCRS1 indicate that concentration boundary conditions can have an important effect on contaminant transport during CRS consolidation. For the conditions considered, zero concentration gradient and reservoir boundary conditions yielded the same contaminant mass outflows regardless of the transport mechanisms (i.e., diffusion, mechanical dispersion, and sorption). However, these transport mechanisms become important when a zero concentration boundary condition is specified. Additional simulations indicate that applied strain rate also has an important effect on the coupled CRS consolidation and contaminant transport. A higher strain rate will generally yield more non-uniform local strain profiles, smaller contaminant mass outflow, and a larger concentration gradient within specimen.

A numerical model, called CSTCRS1, is presented for coupled onedimensional large strain consolidation and solute transport under constant rate of strain (CRS) loading conditions. The model is based on a dual-Lagrangian framework that tracks separately the motions of fluid and solid phases. A series of numerical simulations indicates that transport boundary conditions can have an important effect on the solute transport during CRS consolidation. The zero concentration boundary condition yielded the largest solute mass outflows, the reservoir boundary condition yielded intermediate values, and the zero concentration gradient boundary condition yielded the smallest outflows. Additional simulations indicate that, for conditions considered, increasing the applied strain rate will generally decrease solute mass outflow.

Hydraulic simulation of earthquake damaged water distribution system (WDS) is essential to evaluate seismic service capacity of WDS. This paper first deduces outflow models of the damages (leaks and breaks) induced by earthquake with the help of flow pattern analysis, then presents comparisons on outflow models of pipeline damages and topology models of damaged-pipeline networks. The transformations between leakage outflow and breakage outflow is obtained by conversions of minor head loss at the leak and the frictional head loss along the disconnected pipelines of the break. Model comparisons and application results shown that the outflow of the pipe leakage and breakage can be deduced from the minor head loss at the leak and the frictional head loss along the disconnected pipe respectively.

Circular dropshafts, commonly used in urban storm water systems for energy dissipation and flow control, are characterized by significant flow aeration. In the laboratory, a series of experiments were performed in a circular dropshaft having two identical horizontal inflow and outflow circular channels having diameters of d=0.12 m, and a circular drop chamber having diameter of D=0.358 m for observing flow patterns and measuring air bubble entrainment flow parameters. Experimental observations showed distinct flow regimes associated with nappe impact in the shaft pool, in the outflow channel, or in the opposite shaft wall. New detailed air-water flow measurements were conducted in a circular dropshaft with using double-tip fiber optical probe. Measurements of void fractions, bubble frequencies and bubble sizes were conducted for different flow conditions of the circular inflow channel. In the shaft pool, the results obtained from measurements demonstrated the complexity of different air entrainment mechanisms.

Piping is one of the most important causes of dam failure. Concentrated leak erosion, which occurs in cracks or a system of interconnecting voids, accounts for a large percentage of dam failures. A physically-based numerical model for simulating piping in earth dams due to concentrated leak erosion is developed in this research. The evolution of piping includes surface erosion and collapses of the soils on the pipe wall, which is controlled by hydraulic conditions and soil properties. The outflow hydrograph and piping characteristics (i.e. pipe geometry and formation time) can be predicted using this model, which helps assess the flood hazard downstream. The failure of Teton Dam in Idaho, USA is simulated using the model. The simulation results approximately reproduce the piping failure process of the dam.

ASCE Numerical unsteady-flow simulations were used to investigate the breach outflow hydrographs produced by hypothetical canal embankment failures, considering the interaction of canal hydrodynamic effects and the rate of breach development. The studies led to the development of appraisal-level procedures for estimating the peak outflow rate and other breach outflow hydrograph characteristics as a function of canal hydraulic properties, breach development rate, the length of the affected canal reach, and the location of the breach relative to upstream and downstream check structures. These procedures will help water managers identify canal reaches and specific breach locations that have potential to produce large peak outflow rates. INTRODUCTION The Bureau of Reclamation has constructed more than 8,000 miles of irrigation water delivery canals since 1902. Although typically reliable, canal failures have occurred on occasion throughout Reclamation's history. Threats to canals include animal burrows, tree roots, embankment and foundation issues, pipe penetrations, seismic events, internal erosion under static loading, hydrologic events, and operational incidents. Canal failures can have significant consequences, and potential consequences are increasing as urban development surrounds formerly rural canals. To understand the risks associated with individual canals, modeling of potential failures is needed. Tools for predicting peak outflow from traditional embankment dams do not account for the upstream hydraulic boundary conditions imposed by a canal of finite cross section and volume. The ability of a canal to convey water to the site of a breach limits the potential peak outflow. To gain a better understanding of canal breach processes and develop guidance and tools for evaluating flooding risks associated with potential canal breaches, Reclamation has carried out scale model canal breach tests in the hydraulics laboratory (Wahl and Lentz 2010). These tests demonstrated that breach development rates are related to measurable soil erodibility parameters. However, due to space limitations in the laboratory, the physical model tests could not evaluate the interaction between canal hydrodynamics and the rate of breach development. Numerical modeling was undertaken to examine this relationship and develop predictive tools for estimating peak canal breach outflow.

The objective of the present research is to provide a more comprehensive hydraulic analysis of flow pattern around emergency spillways of the levee systems and also recommend an optimum pattern for installation of fuse plug spillways. The design of fuse plug spillways is usually based on very simple assumptions or 1-D models which neglect the influence of flow pattern around a fuse plug spillway on the neighboring spillways. These assumptions may lead to improper design of a set of emergency spillways. Application of 2-D models is highly recommended for the assessment of those effects. In this study, MIKE21 is used as a 2-D model to study the flow pattern around a set of fuse plug spillways. MIKE21 model is based on numerical solution of 2-D depth averaged Navier-Stokes equations. The modeling results are used to recommend the optimum pattern of fuse plug spillways. The results also show that installation of separate spillways decrease the total outflow about 1.01% to 1.35% compared to single a spillway. As a case study, Helleh River in Iran was considered. Several patterns for fuse plugs were modeled and the optimum pattern was selected based on economic and technical criteria. The influence of the flow patterns around each spillway on the neighboring spillways and the flood propagation on dry bed in the flood plain are presented as graphs and animations. The results of this study demonstrate the performance of MIKE21 for these types of the modeling and also may be helpful for designers of the flood protection levees in similar cases.

The water distribution systems management often requires the definition of the relationship between leak outflow and flow conditions inside the pipe. To explore this relationship, several tests were carried out at the Water Engineering Laboratory of the University of Perugia (Italy). To analyze the leak outflow dependence on functioning conditions for different pipe materials, leaks with the same geometry were machined on steel and polyethylene pipes. The results of the test on the polyethylene pipe confirm the viscoelastic behavior of the leaks in these pipes, i.e. the leakage dependence on the functioning conditions time-history. On the contrary, the tests in the steel pipes of different thickness seem to confirm an elastic or elastoplastic behavior of the leaks. Since the considered test conditions are similar to those of functioning systems, it seems reasonable that the shown effects of the material properties on the leakage, especially for polyethylene pipes, can be relevant for water distribution systems management.

Traditional water distribution system models, which are referred to as demand-driven analysis (DDA) are normally analyzed under the assumption that water demands at nodes are known and always satisfied, i.e., they are equal to nodal outflows regardless of the pressure at nodes. Nodal pressures are then calculated by an iterative algorithm such as Newton-Raphson or a similar method. This formulation is valid under normal/design conditions. However, in many situations such as pipe burst or pump outage or insufficient water supply, the nodal outflows affected by low pressure will decrease. Therefore, network simulation under deficient pressure conditions using conventional DDA can cause large deviation from actual situations. The purpose of this paper is to combine several pressure-dependent demand (PDD) formulations with the EPANET Toolkit to simulate deficient-network performance more realistically. An extension of EPANET which implements repetitive modifications to nodal outflows based on PDD formulations (EPANET-MNO), is also developed. First a comparison is made between respective performances of four different pressure-dependent demand functions (PDDFs) with the defined required pressure and minimum service pressure. Then pipe bursts are simulated using emitters in conjunction with PDD analysis. The paper demonstrates that good modeling performance of EPANET-MNO has been achieved for simulating deficient-network considering pressure-dependent demand.

Many projects of long-distance water transmission have been built to resolve the problem of the shortage of urban water resources. But, the water hammer will be presented as the result of excluding air fleetly at the process of water-filled at first time in the projects of gravity flow. The process of water-filled at first time is divided into 3 steps according to the target of operation in project, filling water, excluding air and enhancing flow, which are benefit for the application of study result and guide of operation. In the first step, the target of filling water is to exclude part air in the pipelines and to outflow water at the end of pipelines. The key parameter of control is the flow rate which is solved by the method of flow of non-collecting air. In the second step, the target of excluding air is to exclude all the air from air valve in the pipeline by water pressure, the key of this step is the operation process. In the third step, the target of enhancing flow is to increase velocity of flow for reaching the design flow. The method of filling water at the first time has applied in the long-distance water transmission project located in the northeast of China, the operation status shows that the method could ensure the security and order in the 1620 ICPTT 2011 © 2011 ASCE

Bioretention, a key structural practice of Low Impact Development (LID), has been proven to decrease peak flow rates and volumes, promote infiltration and evapotranspiration and improve water quality. Exactly how well bioretention mimics pre-development (or natural) hydrology is an important research question. Do bioretention outflow rates mirror shallow groundwater inter-event stream recharge flow associated with natural or non-urban watersheds? Streamflow from three small, non-urban watersheds, located in the Piedmont of central North Carolina, was compared to bioretention outflow from four cells also in North Carolina's Piedmont region. Each benchmark watershed drained to a small stream, where flow rate was monitored for an extended period of time. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream inter-event flow. Results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 hours following the commencement of flow. Similarly, there is no statistical difference between the cumulative volumes released by the two systems during the 48 hours following the start of flow. These results indicate that bioretention cells behave comparably to watersheds in natural or non-urban conditions with respect to both flow rates and flow volumes and suggest that bioretention outflows may mirror post storm event shallow groundwater inter-event stream recharge flow. Solely considering bioretention outflow as a conjugate to runoff may be a misinterpretation of a flowrate that actually resembles shallow interflow.

Gravel formation is the most common formation in the Taichung area in Taiwan, where most of the gravels are hard and have high strength and strong interlock between gravels. Methods used for underground constructions in gravel formation are still under exploration due to lack of experience. Thus, the objective of this study is to focus on investigation of Taichung base waste water outflow pipeline construction using pipe jacking method. The analyzed data during tunnel construction include attrition and repair of the machine, torque applied at the cutter face, thrust forces used to push the pipes, encountered problems, and tunnel advancing rate are synthesized and analyzed. For drive distance less than 90 m, the thrust forces used to push the pipes are around 400 to 500 tons. The frictional resistance between the pipe, the outside diameter is 2.85m, and ground is around 0.6 to 1.0 ton/m2. The average advancing rate, time used to push each pipe and torque applied at the cutter head are 20.6 mm/min, 2.9 hours and 260 t-m, respectively.

Bioretention, a key structural practice of Low Impact Development (LID), has been proven to decrease peak flow rates and volumes, promote infiltration and evapotranspiration and improve water quality. Exactly how well bioretention mimics pre-development (or natural) hydrology is an important question that continues to be researched. Do bioretention outflow rates mirror shallow groundwater inter-event stream recharge flow associated with natural watersheds? Three small, undeveloped watersheds, located in the piedmont of central North Carolina, were chosen to represent natural hydrology. These watersheds ranged from 50 to 78ha and were comprised primarily of forest and pastureland. Each drained to a small stream, where flow rate was monitored for an extended period of time. Data collected from the natural watersheds was compared to outflow rates from four bioretention cells. The cells selected are located within the piedmont region and drain predominantly urban watersheds ranging from 0.2 to 0.9ha in size. Flow rates and cumulative volumes were determined for each site at the following intervals after stormflow/outflow began: 3, 6, 12, 18, 24, 30, 36, 42 and 48 hours. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream inter-event flow. Nonparametric statistical analyses were performed on the datasets using the Wilcoxon signed rank test. Results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 hours following the commencement of flow. Similarly, there is no statistical difference between the cumulative volumes released by the two systems during the 48 hours following the start of flow. These results indicate that bioretention cells behave comparably to natural, undeveloped conditions with respect to both flow rates and flow volumes and that bioretention outflows somewhat mirrow post storm event shallow groundwater recharge.

This study describes the application and verification of the two-dimensional hydrodynamic model MIKE21, the simulation of flow around levee breaches and mapping of flooded areas beyond the breach points. MIKE21 model is based on numerical solution of two-dimensional depth averaged Navier-Stokes equations. The experimental data from a levee breach (laboratory scale) from the previous studies were used to assess the performance of MIKE21 in levee break simulation. The experimental setup included a tilting laboratory flume with a lateral floodplain added to the flume letting the outflow propagate outside the breach. Comparison of experimental data and MIKE21 results at several stations near the breach showed that two-dimensional depth averaged approximation is quite suitable to capture the flow pattern around the breach. Nevertheless, at some points especially in regions of highly turbulent flow or sharp water surface gradients, the flow is three-dimensional and the two-dimensional approximation may not be accurate. As a case study, the Helleh River with levee system in Bushehr province was simulated. Using MIKE21, the proper locations for emergency breaching (i.e., fuse plugs spillways) in the levee system was studied and presented in some detail. Apart from MIKE21, a one-dimensional model of the river was developed using HEC-RAS. Finally the propagation of the flood waves through the breaches is shown as maps and animations.

This study aims to evaluate observed and modeled performance data to develop a design strategy to size LID vegetative filter strips for use as highway stormwater BMPs. Vegetative filter strips are uniformly graded and densely vegetated sections of open space, engineered to reduce and treat overland sheet flows primarily through infiltration. In green highway design and redevelopment, this LID technology (also classified as a structural BMP) creates functionally equivalent hydrologic landscapes. These BMPs are installed in highway right-of-way to maintain, replicate or minimize the change in pre-development hydrologic regime and manage stormwater runoff on site therefore reducing the need for conventional drainage structures. All data in the study is measured by mass balance, a function of inflow and outflow, which are in turn functions of the drainage area, storm intensity, runoff volume, and VFS features. To this end, these factors influencing performance are further analyzed through an application of the scientific theories governing the measured parameters. Specifically, drainage area, and storm magnitude and duration, complied in design scenarios as the Water Quality Volume (acre-feet), WQ v , are massed again to calculate the flow rate (cfs), Q , in an application of Darcy's Law that governs VFS mechanics and the mass balance. VFS sizing is then determined based infiltrating the WQ v . Units are consistent with those from the collected data.

This paper presents a methodology to measure the impact of stormwater controls on the receiving stream using a series of discrete events to represent the long-term hydrologic regime as a simpler alternative to continuous simulation. Hydromodification impacts on channel morphology are best evaluated using flow and shear stress duration curves, which typically require continuous simulation. The methodology proposed herein allows the development of these duration curves using discrete events. The methodology was tested in a hypothetical development in the City of Columbia, Missouri. Design assumptions were made for a typical residential development and a typical stream. Various stormwater controls were designed for this site, including conventional detention, a water quality volume and channel protection volume basin, and bioretention. The outflow from each design scenario was analyzed to determine the effectiveness of different levels of stormwater controls. The objective was to compare the effect of each scenario using duration curves to measure its ability of mimic the original hydrology. The study indicates that LID most closely replicates the original regime and that detention provides some benefits when water quality and channel protection are included, although its effect does not reproduce the original hydrology. Detention criteria based on extreme events, such as the 100-year storm event, are ineffective for this purpose.

Most urban watershed models developed to comply with various regulatory programs can only be used to approximate LID implementation in their existing configuration. These models were developed in order to simulate flow through the thousands of acres that together make up each water pollution control facility (WPCF) service. Consequently, the resolution of the original models is relatively coarse. For example, tens of square blocks are aggregated into single hydrologic units called subcatchments, and only the WPCP's head works, interceptors, major trunk sewers, and large diameter sewer pipes are included in the sewer network. Because of these approximations, and the fact that LID technologies would alter flow patterns and pollutant mobilization rates within the large-scale subcatchments, LID retrofits cannot be directly simulated in many existing urban scale hydrologic and hydraulic models. This paper will present initial work on the development and calibration of a high resolution hydraulic and hydrologic model that is being used to simulate the impact of low impact development retrofits on wet weather flowrates in the combined sewer system of a dense urban watershed. The two-block, Bronx, NY study site was selected due to its location at the hydrologic edge of the sewer service area, and also because of the extent to which its soils, slopes, open space, and building stock and vintage reflected average values for New York City, as confirmed using various statistical analyses. In the model, developed using SWMM 5.0, separate subcatchments are defined for each roof, sidewalk, backyard, and street present in the study area. Realistic routing is also incorporated in the hydrologic representation. Model calibration is accomplished by systematically varying subcatchment properties and comparing time series flowrate predictions at the downstream end of the study area with actual sewer flow observations, using precipitation time series also measured on site. The subcatchment attribute combinations associated with all sets of predictions are recorded, and parameter regions associated with reasonable and unreasonable predictions are identified. Presented are some initial attempts to simulate the effects of green roof retrofits on the outflow hydrograph from the study site. A discussion of how the resolution of subcatchment discretization affects model predictions is also provided.

The capacity to infiltrate stormwater is an important aspect of many low impact development practices. Quantitative evaluation of infiltration capacity has typically been performed by monitoring the inflow and outflow of various storms, and determining the infiltration through a mass balance. Monitoring programs, however, are typically of long duration (i.e. one or more field seasons), require intensive effort, and frequently do not yield useful data for individual LID practices. We propose a new approach for assessment of stormwater LID practices that includes controlled testing as a key component in a Four Level assessment program. In increasing order of effort, the four levels are: (1) visual inspection, (2) infiltration capacity testing, (3) synthetic runoff testing, and (4) monitoring.

The purpose of this analysis is to develop a dispersive mixing parameterization method and specific dispersion coefficients used to predict salinity in a one-dimensional tidally-averaged transport model. Longitudinal dispersive mixing is parameterized based on the analysis of three-dimensional simulations spanning a range of freshwater inflows in the San Francisco Estuary. The three-dimensional simulation results were analyzed at 28 cross-sections in the San Francisco Estuary to calculate salt fluxes, salinity gradients and other information required for the parameterization method. This method represents the spatial variability of dispersion and includes dependence on horizontal Richardson Number, Delta outflow and other environmental variability. These parameterizations are incorporated into a tidally-averaged one-dimensional model for predicting salinity in Central San Francisco Bay, San Pablo Bay, Suisun Bay and the Sacramento-San Joaquin Delta. This simplified model was developed for the Delta Risk Management Strategy (DRMS) project, funded by the California Department of Water Resources, in order to simulate thousands of levee failure scenarios. The dispersion coefficients are currently applied in the simplified model to represent all dispersive transport in most of the model domain. The resulting simplified model accurately predicts observed monthly-averaged salinity through the San Francisco Estuary for a 15 year simulation period.

A high resolution three-dimensional numerical model, COCIRM, was adapted and optimized to predict the potential impact of the Waneta Expansion Project (WEP) on the flow conditions at the confluence of the Columbia and Pend d’Oreille rivers. Flows in this confluence area represent important habitat features for white sturgeon, including the well-developed low-speed Waneta Eddy for sturgeon rearing and feeding, and the jet-like high-speed Pend d’Oreille River outflow for sturgeon spawning. Extensive model calibrations and validations were carried out to render the model a useful and reliable tool for the WEP environmental impact assessment. The model results are in good agreement with extensive in situ observations in terms of the patterns of the Waneta Eddy, Pend d’Oreille outflow and its associated standing waves as well as water temperatures.

The limited length of instrumental streamflow data impacts the true magnitude of natural interdecadal variability of water delivered from the UGRB. This limited period of instrumental record can be expanded by utilizing proxy records (reconstructed streamflow) derived from tree rings. Two reconstructed streamflow datasets are now available for the Green River near Green River, UT (Stockton and Jacoby, 1976; Woodhouse et al., 2006), and a new preliminary reconstruction has been developed for the Green River near Green River, Wyoming (Woodhouse et al., 2006). Also, recent research has resulted in the development of nine streamflow reconstructions spatially located throughout the UGRB (Barnett et al., 2008). The proposed research would use these streamflow reconstructions to assess patterns (temporal and spatial) and sources of streamflow variability in the UGRB. An investigation of long-term streamflow variability, focusing on extreme events such as mega-droughts, will be performed. The research will result in the development of probabilistic drought forecasts. Salas et al. (2005) provides drought definitions and equations that can be utilized by water planners in storage dependent systems. Loaiciga (2005) utilized the compound renewal process, which generalizes the Poisson process, to calculate return periods for drought events. This may result in frequency – duration curves for UGRB drought. Such probability curves can then be analyzed in light of Compact agreements to answer questions such as, “How often might the outflow from the UGRB fail to meet 10-year delivery obligations?”

This paper presents the results of an experimental investigation of consolidation-induced solute transport. Diffusion and large strain consolidation tests were conducted on composite specimens of kaolinite slurry consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Solute breakthrough curves and final concentration profiles indicate that both diffusion and consolidation-induced advection can make important contributions to solute transport and that faster consolidation can increase the rate of solute mass outflow. The results of this study indicate that transient advection effects should be considered for transport analyses involving the large strain consolidation of soft contaminated clays.

Peak-flow attenuation is important in urban stormwater management because runoff from post-development increases in magnitude and volume and may cause flooding to downstream areas. The standard practice in the United States is to require that the peak flow after development does not exceed predevelopment peak flow for specified design storms. The purpose of detention basins is to capture high runoff rates from post-development and control the peak discharge of the outflow using orifices and weirs. However, the use of detention basins in Korea is not used in new developments due of high land costs. As a result, many existing urban areas experience an increased frequency of flooding due to urbanization upstream in the watershed. This study investigates how variations in pond size, orifices and weirs could be used to reduce the peak-flows from a new 11 hectare development in the Ulsan-Hwabong region of Korea. This development is typical of new developments that are being constructed on the fringe of existing urban areas in Korea. In this study, the required volume and land area of a detention pond was determined in order to control the development outflow peaks for the 2-year, 10-year and 100-year design storms. Three cases detention pond designs are compared in terms of economics. The rainfall-runoff simulation model used in the design of these three detention ponds is the Storm Water Management Model (SWMM) 5, which is the latest updated version for windows.

Since the watershed of the Mekong River is situated under the typical monsoon climate, the Mekong River presents a distinct variation in its water levels between the dry and rainy seasons, and causes heavy inundation in the Delta area along the river every year. In order to analyze the flow phenomena and inundation process for agricultural practice in the Mekong Delta, this study tried to establish three models: the combine of “3*4+1-type” model and the ARMA time series model, Tonle Sap Lake Storage Model and Delta Water Balance Model. The “3*4+1- type” Model was employed to calculate the runoff of the Lower Mekong River Basin from Chiang Saen to Kompong Cham and its sub catchments. The ARMA time series model was applied to the residuals of the Tank Model application in order to obtain 1 day to 5 days ahead flow forecasting after the present day based on the available data of the present day. The inflow to the Tonle Sap Lake was also estimated by the “3*4+1- type” Model, whereas outflow of the lake was formulated based on the relationship between storage volumes and water level of the Lake surface. The application of the ARMA to the “3*4+1-type” model was found effective to improve flood forecasting at the outlets point of each sub-catchment. The established storage model for the Tonle Sap Lake could calculate well for simulating the outflow and the seasonal water balance of the Tonle Sap area. Deltaic area was divided into four zones, and water balance of each zone was formulated by considering the zone’s inflow/outflow between rivers and flooding areas. The establishment of these three models could provide a basic framework for modeling the Mekong Delta, Cambodia.

The current SCS dimensionless rainfall distribution patterns (Type I, IA, II, and III) are thought to be over conservative and in need of replacement. This study develops new dimensionless design rainfall patterns for the state of South Carolina for various durations. The rainfall data from various sources dating back to 1971 was collected and analyzed. Different storm separation methods were reviewed and a modification of an existing method was adopted for the study. The rainfall events were combined into 21 different groups ranging from 2 to 51 hours. The top fifty events (by volume) within each group were selected to determine the dimensionless rainfall pattern. Similar dimensionless rainfall patterns for various groups were combined to create representative time-duration patterns for the state of South Carolina. The results showed that two distinct dimensioless rainfall patterns could be established. The new rainfall patterns were compared to the SCS rainfall curves and rainfall patterns developed by other states. The impact of these new dimensionless rainfall patterns on design practice was assessed. The new rainfall patterns were used to evaluate the response of hydraulic structures to rainfall events. In particular, the basin rainfall-runoff volume and detention pond performance were evaluated and compared to the results from the SCS rainfall patterns. For the basin test, the runoff volume, peak discharge, and time to peak were compared. For the pond test, the stage versus time and the ratio of storage volume to runoff volume were compared. The impact of varying the outflow culvert size on pond storage requirement was also investigated. The comparison showed that new rainfall patterns resulted in lower peak flow and different peak time for the runoff hydrograph. The new rainfall patterns resulted in lower peak stage and detention pond storage volume.

Because bioretention areas have the ability to fulfill both landscape and water quality needs in a small area, they have received increased recognition as an integral part of Low Impact Development (LID); however, questions on design guidelines persist. Two paired, field-scale bioretention studies (Greensboro and Louisburg) have been conducted in North Carolina to study removal of phosphorus and nitrogen, hydraulic retention, the effectiveness of an induced saturated zone, and the impact of low P-Index fill media. Both bioretention pairs comprise nominally 5% of their respective watersheds and are planted with trees and shrubs. In Greensboro, one conventionally drained cell and one cell containing an induced saturated zone (previously termed anaerobic zone) of 0.45m were continuously monitored from June, 2002, to December, 2004. Lower outflow frequency was found for the induced saturated zone design. During outflow events, TP concentrations were significantly lower (P

The purpose of this paper is to model the behavior of water demand in water distribution systems as a separate process. The contribution of a tank to the water demand at a node is defined as the difference in the tank outflow with and without the demand at the node. This does not correspond with the physical contribution of water from the tank to the node, but allows the demand contribution to the tank to be mathematically separated from the hydraulics of the system without demands. It is shown theoretically that for a simple two tank system, the demand contributions of the tanks are proportional to the total demand, and independent of the tank levels. For a two tank system with two demands, the total contribution of a tank to the demand can be determined through susperposition. For more complex systems the independence of the demand distribution with tank level is lost, but superposition can still be used to determine the demand contribution of a tank. Demand distribution has application in network simplification and extended-period simulation of water distribution using the Explicit Integration method.

Nature's inherent ability to cleanse itself is at the heart of Monitored Natural Attenuation (MNA). The complexity comes when one attempts to measure and calculate this inherent ability, called the Natural Attenuation Capacity (NAC), and determine if it is sufficient to cleanse the system to agreed upon criteria. An approach that is simple in concept for determining whether the NAC is sufficient for MNA to work is the concept of a mass balance. Mass balance is a robust framework upon which all decisions can be made. The inflows to and outflows from the system are balanced against the NAC of the subsurface system. For MNA to be acceptable, the NAC is balanced against the contaminant loading to the subsurface system with the resulting outflow from the system being in a range that is acceptable to the regulating and decision-making parties. When the system is such that the resulting outflow is not within an acceptable range, the idea of taking actions that are sustainable and that will bring the system within the acceptable range of outflows is evaluated. These sustainable enhancements are being developed under the Enhanced Attenuation (EA) concept.

A drainage swale hydraulic analysis was conducted by WEST Consultants, Inc. as part of a dispute regarding a proposed subdivision. The primary purpose of the study was to evaluate the adequacy of the proposed drainage improvements. The downstream portion of the flow system consisted of: a steep triangular channel discharging into a debris basin, a chute-like flow over a retaining wall, and a hydraulic jump (formed on the adverse slope of the street) combined with a distributed lateral (sheet) outflow along the road. Due to the complex nature of the flow (steep slope, lateral spreading, hydraulic jump with distributed outflow), standard hydraulic modeling tools, such as the HEC-RAS program, could not be used to accurately determine flow characteristics. A straightforward numerical procedure, which overcomes present limitations of HEC-RAS, was developed instead to solve flow resistance equations using a simple Excel spreadsheet. The elements of this procedure and the hydraulic modeling results are presented here.

Although the numerical algorithms for solution of the St. Venant Equations are similar; substantial differences exist between these two commonly used models with respect to how the river geometry is sampled, interpreted and represented digitally for model use. HEC-RAS utilizes cross section descriptions in distance-elevation format, with associated transverse roughness distribution. NWS-FLDWAV utilizes a cross section description based upon user-input tables of top width and Manning's n values as functions of elevation. This paper reports the procedures used to prepare comparable NWS-FLDWAV data from an existing HEC-RAS dam break flood routing application and the differences and similarities in the resulting simulations. The results demonstrate that the computed breach outflow hydrograph is similar for the two models. It is concluded that the differences in the interpretation and approximation of river geometry is the primary source of the differences in the model simulations. The two models employ numerous different assumptions regarding formulation of the finite difference approximations to the various terms in the governing unsteady flow equations. A number of data representations were examined to identify and evaluate the differences in the models for computations, data handling and model features.

An existing traffic island at Villanova University was retrofitted to become a bioinfiltration BMP serving a drainage area of 1.3 acres, one-half of which is impervious parking and roadway area. It is part of the Villanova Urban Stormwater Partnership Best Management Demonstration Park. Designed to infiltrate 70 to 80% of the yearly rainfall, the facility mitigates the delivery of nonpoint source pollution and streambank-eroding surges to Darby Creek downstream. Construction was completed in early 2002 and instruments were installed to record rainfall and pool level at 5 minute intervals. A v-notch weir was added to measure outflow volumes and a model for the system was developed in HEC-HMS. The model uses Green-Ampt and kinematic wave methods to predict runoff and infiltration volumes and outflow hydrograph shapes. With three years of data collection, observation, and model calibration, a clearer picture is emerging of the physical processes at work within the basin and its watershed. This understanding will be useful in the design of similar systems in the urban landscape.

Over the past half-century, the USDA has assisted in the design and construction of approximately 11,000 flood control and multipurpose dams. As these dams approach the end of their planned service life, sediment pools fill and sediment deposition in the flood pool reduces flood storage. Simultaneously, development in the watershed may increase runoff while development downstream of the dam increases the consequences of failure. Therefore, there is an increased need for improved procedures for predicting performance of overtopped earth embankment dams. Field experience and laboratory experiments indicate that the erosion process for overtopped earth embankment dams can be divided into sequential stages or phases for computational purposes. These stages include: 1) an initial stage prior to the failure of the vegetal cover or other protection on the downstream slope, 2) a breach development stage during which the resulting headcut or overfall moves from the point of formation through the dam crest, 3) a breach stage during which the headcut advances into the reservoir, and 4) a drawdown stage during which the breach continues to widen as the stored water in the reservoir is released. The flow geometry and the relations describing the discharge and erosion processes vary with stage. This report discusses the dominant characteristics of the identified stages of the progressive breach process and the impact of the resulting geometry on discharge prediction. Results of an idealized study of breach outflow during headcut entry into the reservoir are briefly discussed.