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Summary: Global warming is expected to exacerbate the duration and intensity of droughts in the western United States, which may lead to increased tree mortality. A prevailing proximal mechanism of drought‐induced tree mortality is hydraulic damage, but predicting tree mortality from hydraulic theory and climate data still remains a major scientific challenge.We used forest inventory data and a plant hydraulic model (HM) to address three questions: can we capture regional patterns of drought‐induced tree mortality with HM‐predicted damage thresholds; do HM metrics improve predictions of mortality across broad spatial areas; and what are the dominant controls of forest mortality when considering stand characteristics, climate metrics, and simulated hydraulic stress?We found that the amount of variance explained by models predicting mortality was limited (R2 median = 0.10, R2 range: 0.00–0.52). HM outputs, including hydraulic damage and carbon assimilation diagnostics, moderately improve mortality prediction across the western US compared with models using stand and climate predictors alone.Among factors considered, metrics of stand density and tree size tended to be some of the most critical factors explaining mortality, probably highlighting the important roles of structural overshoot, stand development, and biotic agent host selection and outbreaks in mortality patterns. See also the Commentary on this article by Rowland et al., 230: 1685–1687. [ABSTRACT FROM AUTHOR]

Large wood (LW) jams are key riverine habitat features that affect hydraulic processes and aquatic habitat. The hydraulic influence of LW jams is poorly understood due to the complexity of fluid dynamics around irregular, porous structures. Here we validated a method for two‐dimensional hydraulic modeling of porous LW jams using the open‐source modeling software Delft3D‐FLOW. We sampled 19 LW jams at three reaches across the Columbia River Basin in the United States. We used computer‐generated porous plates to represent LW jams in the modeling software and calibrated our modeling method by comparing model outputs to measured depths and velocities at validation points. We found that modeling outputs are error‐prone when LW jams are not represented. By representing LW jams as porous plates we reduced average velocity root mean square error (RMSE) values (i.e., improved model accuracy) by 42.8% and reduced average depth RMSE values by 5.2%. These differences impacted habitat suitability index modeling. We found a 15.1% increase in weighted useable area for juvenile steelhead at one test site when LW jams were simulated vs. when they were ignored. We investigated patterns in average RMSE improvements with varying jam size, bankfull obstruction, porosity, and structure type, and river complexity. We also identified research gaps related to field estimation of LW jam porosity and porous structure modeling methods. Research Impact Statement: Hydraulic models are error‐prone where rivers interact with large wood jams. Our method for representing wood jams improves hydraulic model accuracy and ecohydraulic analysis. [ABSTRACT FROM AUTHOR]

The development of Watershed Management Plans (WMPs) in urban areas aids municipalities in allocating resources, engaging the public and stakeholders, addressing water quality regulations, and mitigating issues related to stormwater runoff and flooding. In this study, 124 urban WMPs across the United States were reviewed to characterize historic approaches and identify emerging trends in watershed planning. Planning methods and tools were qualitatively evaluated, followed by statistical analyses of a subset of 63 WMPs to identify relationships between planning factors. Plans developed by a municipality or consultant were associated with more occurrences of hydrologic modeling and site‐specific recommendations, and fewer occurrences of characterizing social watershed factors, than plans authored by agencies, organizations, or universities. WMPs in the past decade exhibited greater frequency in the use of pollutant load models and spatially explicit hydrologic and hydraulic models. Project prioritization was found to increasingly focus on feasibility to implement proposed strategies. More recent plans additionally exhibited greater consideration for water quality, ecological health, and public participation. Innovation in planning methods and consideration of future watershed conditions are primary areas that were found to be deficient in the study WMPs, although analysis methods and tools continue to improve in the wake of advancing technology and data availability. Research Impact Statement: Methodologies for the development of Watershed Management Plans (WMPs) in urban areas are being responsive to changes in policy and technology. [ABSTRACT FROM AUTHOR]

Highlights • MECOR thermal hydraulic model was developed for AP1000. • A double ended cold leg (DECL) break simulated. • Input model verified against WCOBRA-TRAC results. • Calculations are extended to analyze the behaviour of ADS and IRWST. • Concluded that the calculated PCT is well below the safety criteria of 1477 K. Abstract The AP1000 is currently an advanced pressurized water reactor with emergency core cooling systems (ECCS) completely dependent on natural circulation. It is under construction in the USA and has been commissioned in China and is being considered by several countries to use this advanced technology for a power source. With this objective in mind, a representative MELCOR model (for the AP1000) has been developed to better understand the thermal hydraulics involved and to assess the performance of the safety systems for a design basis accident such as large break LOCA (LBLOCA) with availability of the safety systems. The results from these calculations were compared to those obtained using WCOBRA-TRAC, developed by Westinghouse Electric Company, which are reported in the AP1000 European Design Control Document. MELCOR was selected for the design assessment activities specifically because of its capabilities to model severe accident scenarios and features such as containment behaviour. It is one of the system thermal hydraulic codes, which are recommended for severe accident analysis in light water reactors. The aim of the current study is to assess the thermal hydraulic models and correlations in MELCOR against a specific code developed for a design basis accident such as a LBLOCA. This exercise will validate the input model for a LBLOCA and then use the input model for station blackout studies and the impact on the containment. A double ended cold leg (DELC) break in the loop containing the Core Makeup Tanks (CMT) is considered for this study. The calculated break flow, peak cladding temperature, accumulator, and CMT injection flow rates are compared to those reported. These calculated results are found to be satisfactory according to ECCS acceptance criteria for the temperature and hydrogen generation. This study has been further extended to analyse the containment behaviour during the accident. The calculations for the transient were extended to observe the behaviour of the Automatic Depressurization System (ADS) and IRWST injection capabilities which can effectively avoid core uncovery for a longer duration of the time. These systems can only work when the reactor system is depressurized. MELCOR calculated a PCT value (occurs just after the break) as 1242 K while the total hydrogen produced was calculated to be 2.216 kg which is only 0.61% of the total potential hydrogen production from oxidation. [ABSTRACT FROM AUTHOR]

This article describes how a sustainable watershed-level planning approach is used to develop a flood-mitigation and stormwater management plan for an 11 km2 watershed in southeastern Pennsylvania, USA. West Ambler is an Environmental Justice (EJ) community located in the downstream portion of the watershed with socioeconomically vulnerable residents facing unequal distribution of environmental risks. This study uses a methodological framework based on the three dimensions of EJ (i.e., Distribution, Procedure/Participation, and Recognition) to address watershed concerns while managing risks within the EJ community. Although the project is scientifically grounded by a GIS-based watershed assessment and hydrologic and hydraulic modeling, all project components are influenced by one or more EJ dimensions, with an emphasis on community engagement and multi-municipal collaboration. Flood-mitigation suggestions are based on the evaluation of hundreds of stormwater management facilities throughout the watershed. This article explains the process of using an EJ framework in watershed-wide planning and management. [ABSTRACT FROM AUTHOR]

• Three deterministic abutment scour prediction models were assessed. • Statistically assessment was performed in terms of accuracy and conservatism. • Vertical wall and spill through abutments are examined separately. • Proposed method allows for choosing the scour prediction method based on the desired level of conservatism and accuracy. More than 80 percent of the bridges in the United States are built over waterways. The support systems of the structures crossing waterways are subjected to scour during their service life owing to the flowing water-induced bed shear stresses, resulting in scour. Work herein is focused on characterizing the error associated with three abutment scour prediction models included in the Hydraulic Engineering Circular No. 18. An abutment scour database is utilized to quantify the predicted versus the measured scour depth relationship. Abutment scour prediction models are assessed in terms of two statistical parameters, termed herein Mean Absolute Percentage Error (MAPE, as a measure of accuracy of the prediction), and Level of conservatism , (defined as percentage of cases for which the predicted scour exceeded the measured scour.) For scour associated with vertical wall and spill through abutments, responses to long abutment, and intermediate abutment are examined separately. For vertical wall abutments, conservatism ranged from 4.76% to 100%, and MAPE ranged from 44% to 201%. For spill through abutments, conservatism ranged from 0% to 100%, and MAPE ranged from 10.3% to 347%. Comprehension of the accuracy and conservatism of the deterministic models considered herein contributes to understanding the limitation of the scour depth prediction models. [ABSTRACT FROM AUTHOR]

In 2008 flooding occurred over a majority of Iowa, damaging homes, displacing residents, and taking lives. Estimated damages to the state totaled $10 billion. One of the city affected by the flood was Waverly City, USA which is the Cedar River flow in side of it. One-dimensional/two-dimensional (1D/2D)-Mike Flood hydrodynamic model and 1D-HecRAS hydraulic model were developed for flood analyses in Waverly City. For developing both models, channel geometry was obtained from bathymetric surveys and combined with surface topography obtained from Light Detection and Ranging surveys. Roughness parameters were estimated using land use data from the National Land Cover Dataset and aerial photos. Calibration of roughness on floodplain and channels represents an important issue to determine flood inundation area. Both models were calibrated and validated with 2008 flood. The riverbed was validated with high water levels measured after flood. The floodplain was validated with photos, which was taken during flood from airplane. After calibration and validation, results were compared to choose the best one. Return period flood discharge were calculated and run with best inundation model for determine flood inundation maps. These maps can be used by residents and planners in Waverly City to help make informed decisions about potential risk from floods. [ABSTRACT FROM AUTHOR]

A recently developed watershed-scale hydraulic model (De-facto Reuse Incidence in our Nation's Consumptive Supply [DRINCS]) was applied to estimate municipal wastewater treatment plant (WWTP) contribution to downstream water treatment plant (WTP) influent flow. Using DRINCS and geocoded data for 14,651 WWTPs and 1,320 WTPs, the occurrence of treated municipal wastewater in drinking water supplies is geographically widespread, and its magnitude depends largely on the flow condition and size of the source river. Under average streamflow conditions in this study, the median contribution of wastewater flow to drinking water supplies was approximately 1% and increased to as much as 100% under low-flow conditions (modeled by Q95). Wastewater contributions to nutrient and emerging contaminant loading were estimated and geospatially compared with the findings of the US Environmental Protection Agency's Unregulated Contaminant Monitoring Rule and Long Term 2 Enhanced Surface Water Treatment Rule. In turn, this analysis offers important insights into the treatment challenges facing treatment facilities across the United States. [ABSTRACT FROM AUTHOR]

This study modelled flood losses (economic damages) along the Middle Mississippi River (MMR) (1) using current US government estimates of flow frequencies and (2) using frequencies based on the original, unaltered discharge measurements. The official flood frequencies were quantified in the Upper Mississippi River System Flow Frequency Study (UMRSFFS), but as a last step in that study, early discharges along the MMR were reduced by up to 54% to reflect a purported bias in early measurements. Subsequently, early discharge measurements were rigorously tested, and no such bias was found. Here, flood damages were quantified using a combination of one-dimensional hydraulic modelling and flood-loss modelling. For all recurrence intervals, damages were much less using the UMRSFFS flow frequencies compared with the frequencies based on the original discharge measurements, with differences ranging up to 79% (100-year event) and $2.9bn (200-year event). Annualized losses in the study area based on the UMRSFFS frequencies were just $41.6m versus $125.6m using the raw frequencies (an underestimation of 67%). These totals do not include flood losses elsewhere along the MMR, including in metropolitan St Louis. In summary, a seemingly small methodological adjustment - in this case, a single hidden adjustment, not documented anywhere within the UMRSFFS - can have dramatic societal impacts in terms of underestimation of flood probabilities and flood risk. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: One-dimensional hydraulic modeling and flood-loss modeling were used to test the effectiveness of levee setbacks for flood-loss reduction along the Middle Mississippi River (MMR). Four levee scenarios were assessed: (1) the present-day levee configuration, (2) a 1000m levee setback, (3) a 1500m levee setback, and (4) an optimized setback configuration. Flood losses were estimated using FEMA’s Hazus-MH (Hazards US Multi-Hazard) loss-estimation software on a structure-by-structure basis for a range of floods from the 2- to the 500-year events. These flood-loss estimates were combined with a levee-reliability model to calculate probability-weighted damage estimates. In the simplest case, the levee setback scenarios tested here reduced flood losses compared to current conditions for large, infrequent flooding events but increased flood losses for smaller, more frequent flood events. These increases occurred because levee protection was removed for some of the existing structures. When combined with buyouts of unprotected structures, levee setbacks reduced flood losses for all recurrence intervals. The “optimized” levee setback scenario, involving a levee configuration manually planned to protect existing high-value infrastructure, reduced damages with or without buyouts. This research shows that levee setbacks in combination with buyouts are an economically viable approach for flood-risk reduction along the study reach and likely elsewhere where levees are widely employed for flood control. Designing a levee setback around existing high-value infrastructure can maximize the benefit of the setback while simultaneously minimizing the costs. The optimized levee setback scenario analyzed here produced payback periods (costs divided by benefits) of less than 12years. With many aging levees failing current inspections across the US, and flood losses spiraling up over time, levee setbacks are a viable solution for reducing flood exposure and flood levels. [Copyright &y& Elsevier]

This study presents a new Monte Carlo-based flood inundation modelling framework for estimating probability weighted flood risk using a computationally efficient graphics processing unit ( GPU) two dimensional ( 2D) hydraulic model. The 2D flood model is programmed in the GPU framework providing a unique ability to run numerous simulations in a short period of time, permitting the integration of 2D hydraulic modelling into Monte Carlo analysis. The framework operates by performing many 2D flood simulations of randomly sampled input parameters to develop a spatially varied flood hazard map. The probabilistic framework is demonstrated using a 1% annual probability flood event and simulating 1000 different flood simulations by randomly selected peak flows of the Swannanoa River in Buncombe County, USA. The results, in general, display benefits of probabilistic flood risk approach compared with a single simulation approach. The latter approach underestimated 28% of flood risk relative to the former. As the number of simulations increased from 1 to 1000, areas identified as low danger and judgment zone increased by 87.4% and 36.8% respectively, whereas the high danger zone increased by 9.3%. In conclusion, the new Monte Carlo flood risk modelling framework has the ability to provide improved accuracy of flood risk and greater insight into the spatial distribution of flood risk. [ABSTRACT FROM AUTHOR]

Design discharge at a location of interest is conventionally determined using flood frequency analysis, precipitation frequency analysis, or national flood frequency equations. However, none of these three methods can be used to estimate the design discharge for ungauged watershed where high flows are from overflows of the watershed's bordering stream(s), such as the Hartsville Coulee watershed located in northwestern Minnesota. The historical high flows in the Hartsville Coulee were from the overflows of the Red River of the North (RRN). The objective of this study was to set up and use a HEC-RAS hydrodynamic model to determine the maximum overflow rate from RRN into the Hartsville Coulee in 1997, when the record flooding occurred. The model was calibrated using the observed daily streamflows at four US Geological Survey (USGS) gauging stations along RRN. The breach, over which the floodwater was spilled into the Hartsville Coulee in 1997, was defined using the topographic data surveyed by US Army Corps of Engineers (USACE). The results indicated that the maximum overflow rate was likely between 250 and 310 m3 s-1. The computed overflow rate in this study was well compatible with the value estimated by USGS based on a field reconnaissance as well as the value estimated by USACE using Manning equation. In generalization, the HEC-RAS hydrodynamic module can be used to estimate design discharges for overflow-receiving drainage areas such as the Hartsville Coulee watershed. [ABSTRACT FROM AUTHOR]

Large-scale culvert replacement programs could benefit migratory fish populations by reconnecting reproductive and foraging habitats in fragmented watersheds. The objectives of this study were to: (1) identify stream and culvert characteristics contributing to fish passage barriers within an Appalachian watershed, U.S.A.; (2) quantify the total amount of Brook trout ( Salvelinus fontinalis) reproductive habitat isolated above culverts; and (3) use an ecological currency to identify culvert replacement priorities and stream mitigation credit opportunities. We surveyed 120 state-owned culverts and used a fish passage assessment filter to determine the “passability” of each culvert. We then constructed a geographic information system stream network model to quantify the amount of trout reproductive habitat isolated by culverts. Ninety-seven percent of surveyed culverts were classified as obstacles or complete barriers to trout dispersal. Culvert impassability was higher in small streams with slopes exceeding 3–5%, suggesting a direct relationship between slope and impassability. Thirty-three percent of Brook trout reproductive habitat, representing over 200 km of stream, was isolated by culverts. This is a conservative estimate, because we did not survey privately or federally owned culverts. The top 20 prioritized culverts accounted for nearly half of the habitat loss. Our results indicate that standard culvert designs placed in streams with slopes exceeding 5% consistently produce trout dispersal barriers and should be avoided during new road construction. The process developed here provides an efficient method for identifying culvert replacement priorities and may be used to maximize watershed scale benefits of stream restoration. [ABSTRACT FROM AUTHOR]

Intense rainfall over coastal areas characterized by significant urban development, predominantly clay soils, and flat slopes can cause significant flooding problems. Extreme floods in coastal areas occur when storm-water systems lose capacity due to high levels in receiving streams. The Texas Medical Center is located near downtown in Houston, Texas, and extensive flooding during Tropical Storm Allison in June of 2001 crippled many of the facilities with approximately $1.5 billion in damages. In order to better understand dynamic responses and to design abatements to the existing infrastructure, the performance of the storm-water pipe systems under extreme receiving water conditions in a highly urbanized area was quantified by using an integrated model. A hydrologic/hydraulic model was created based on the storm water management model with NEXRAD radar rainfall and hydrographs generated from Hydrologic Engineering Center’s hydrologic modeling system. The model was accurately calibrated against historic storm events. The simulated double-peaked hydrographs explained that the significant backwater effects in Harris Gully worsened the flooding situation within streets by limiting storm-water outflow and overland flow. The analysis evaluated the existing storm-water system to identify potential pathways for overland flow and pipe flow to the receiving bayou, and proposed mitigation alternatives by incorporating additional major sewers to bypass the main culverts in the Harris Gully area in order to provide significant flood relief. [ABSTRACT FROM AUTHOR]

Evaluation of flood risk in an interior watershed (one protected from flooding by a levee) requires application of watershed, channel, statistical, and economic models in an integrated, coordinated manner. The Strong Ranch Slough and Chicken Ranch Slough watershed in Sacramento, California is such a watershed. We describe herein how we used standard-of-practice models within a coincident-frequency analysis framework to evaluate existing flood damage potential and flood damage potential with a variety of proposed damage-reduction measures. [ABSTRACT FROM AUTHOR]

As a part of a study examining alternatives for flow augmentation for fall run Chinook salmon migration on the Cosumnes River, California, two models were constructed to simulate channel flow combined with seepage losses. The first model is a numerical, one-dimensional diffusion wave approximation of the St. Venant equations coupled to a seepage routine that uses either a Green and Ampt infiltration routine or a head-based seepage routine that can handle seepage to or from the channel. The second model uses an analytical solution to the diffusion wave approximation of the St. Venant equations and also incorporates the Green and Ampt method to represent losses due to seepage for the simulation of flow over a dry riverbed. The two models are used to simulate low flow periods in the Michigan Bar to McConnell reach of the Cosumnes River in order to determine flows associated with a minimum depth necessary for fall run Chinook salmon migration. These computed flows were compared against historical data in order to determine volumes of flow augmentation for the time period October through December which corresponds to the spawning period of fall run Chinook salmon. Computed flow augmentation volumes were compared with available reservoir storage in the watershed in order to determine if such flow augmentation would be possible. Both models proved capable of simulating low flow periods on the Cosumnes River. During dry years, the computed flow augmentation volumes represent a significant percentage of the available reservoir storage, indicating that augmentation flows may not always be possible for the entire time period from this source alone. [ABSTRACT FROM AUTHOR]

This paper describes a simple analytical model for assessing meander bend migration rates. The new model is innovative in that it can be applied directly using output data from one-dimensional hydraulic models. The method is designed as a first approximation that can be applied rapidly to large reaches of river systems, and should not be considered as a replacement for more detailed bank stability assessments. The model is based on a conversion factor for one-dimensional shear stress. Comparison of the conversion factor with existing data sets is presented. Converted shear stresses are translated to bank erosion volumes, which in turn are related to meander bend migration rates, using bank geometry and an appropriate sediment transport law. Results are presented for an evaluation of meander bend migration rates for a restoration feasibility study for a project on the Williamson River, Oregon. [ABSTRACT FROM AUTHOR]

Hydrological GIS preprocessing tools are used to spatially relate different datasets for producing topologically connected watersheds and deriving attributes for model parameterization. Obtaining such information requires disparate data-sources from various websites with lengthy processing requirements. This research describes the development of HMS-PrePro, an open-source GIS preprocessing tool that was developed for the U.S. Army Corps of Engineers' (USACE) Hydrologic Engineering Center's Hydraulic Modeling System (HEC-HMS) software. HMS-PrePro provides data as a service by connecting to Esri's Living Atlas web service and extracting authoritative hydrological datasets for any watershed of interest in the contiguous United States. The datasets are saved to a local geodatabase, and spatial operations are executed to automatically delineate the watershed, derive topological connections, and estimate several common hydrologic parameters. An output basin text file is produced in HEC-HMS format for rapid model initialization. • A GIS tool rapidly preprocesses basin files for HEC-HMS hydrological modeling. • The tool can streamline common geospatial steps for other hydrological applications. • The Living Atlas map service provides authoritative data in a useful GIS format. • Improved accessibility to data services enhances standard GIS-based hydrology. [ABSTRACT FROM AUTHOR]

The severity and frequency of extreme flood events are increasing worldwide. Advanced mathematical modelsare commonly used to predict flood events and reduce the impacts on urbanized areas. Technological improvementshave recently led to the spread of heterogeneous networks of low-cost sensors used to measure hydrologicalvariables, such as water level or precipitation, in a more distributed way. Moreover, the growing availability ofqualitative flow information, retrieved for example from social media, is opening more opportunities to complementstandard sources of information from in-situ or remote sensors that can be used to improve hydrological andflood predictions. However, only a few studies assessed the usefulness of assimilating qualitative flow observationswithin hydrological and/or hydraulic model for improving flood predictions.This study aims at proposing novel approaches for assimilating qualitative flow observations in hydrologic routingmodel and assessing their usefulness for improving flood estimation. The case study is based on five different riversin the USA where a three-parameter Muskingum model is used to propagate streamflow. Qualitative flow observations,generated synthetically from observed flow measurements, are converted into fuzzy observations using mainflow characteristic for defining fuzzy classes. An innovative fuzzy error corrector method, adapted from a controlsystem application of robot navigation, is used in this study to assimilate the qualitative flow observations. Thisstudy demonstrates the usefulness of assimilating qualitative flow observations for improving flood predictions. Inparticular, the proposed output updating method is found not sensitive to biased qualitative observations and thedefinition of fuzzy sets used to represent qualitative observations. [ABSTRACT FROM AUTHOR]

The article reports on the merger between MWH Soft Inc. and Wallingford Software Ltd. It states that the two companies provide hydraulic modeling software designed for water and wastewater utilities throughout the world. Moreover, a full suite of software products equipped for hydrology will be produced by the combined company.