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Seattle, WA, United States

Nelson A.,Northwest Hydraulic Consultants Inc. | Dube K.,Watershed GeoDynamics
Earth Surface Processes and Landforms | Year: 2016

We exploit a natural experiment caused by an extreme flood (~500year recurrence interval) and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley-scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form. Sediment slug movement is a crucial process that shapes gravel-bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport. Further, increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility, channel width, and alluvial bar dominance. Pre- and post-flood LiDAR and aerial photographs bracketing the 2007 flood on the Chehalis River in south-western Washington State, USA, document the channel response with high spatial and temporal definition. The sediment slug behaved as a Gilbert Wave, with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters' reaches and reaches where confined valleys enter into broad alluvial valleys. Differences between the valley form of two separate sub-basins impacted by the pulse highlight the important role channel and channel-floodplain connectivity play in governing downstream movement of sediment slug material. Finally, channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form. Specifically, the channel widened, lateral channel mobility increased, and the proportion of the active channel covered by bars increased in all reaches in the study area. The response scaled tightly with the relative amount of bed material sediment transport through individual reaches, indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network. © 2016 John Wiley & Sons, Ltd. Source

Axworthy D.H.,Northwest Hydraulic Consultants Inc.
BHR Group - 12th International Conference on Pressure Surges | Year: 2016

Surge alleviation strategies are descnbcd I) to prevent over-pressurization of two large diameter transmission mains sith little allowance for surge following turbine load rejection and closure of pressure reducing valves, and 2) to prevent column separation in a third transmission main after pump power failure The sometimes competing priorities of each surge control device were accommodated for the proposed bi-dwectional operation of the transmission mains. The results of the transient analyses show both the inability of the existing surge control devices and the effectiveness of the additionally proposed surge protection measures to control pressure surges to acceptable levels in the transmission mains. © BHR Group 2015. Source

Rosenberg E.A.,University of Washington | Keys P.W.,University of Washington | Booth D.B.,University of Washington | Hartley D.,Northwest Hydraulic Consultants Inc. | And 3 more authors.
Climatic Change | Year: 2010

The design of stormwater infrastructure is based on an underlying assumption that the probability distribution of precipitation extremes is statistically stationary. This assumption is called into question by climate change, resulting in uncertainty about the future performance of systems constructed under this paradigm. We therefore examined both historical precipitation records and simulations of future rainfall to evaluate past and prospective changes in the probability distributions of precipitation extremes across Washington State. Our historical analyses were based on hourly precipitation records for the time period 1949-2007 from weather stations in and near the state's three major metropolitan areas: the Puget Sound region, Vancouver (WA), and Spokane. Changes in future precipitation were evaluated using two runs of the Weather Research and Forecast (WRF) regional climate model (RCM) for the time periods 1970-2000 and 2020-2050, dynamically downscaled from the ECHAM5 and CCSM3 global climate models. Bias-corrected and statistically downscaled hourly precipitation sequences were then used as input to the HSPF hydrologic model to simulate streamflow in two urban watersheds in central Puget Sound. Few statistically significant changes were observed in the historical records, with the possible exception of the Puget Sound region. Although RCM simulations generally predict increases in extreme rainfall magnitudes, the range of these projections is too large at present to provide a basis for engineering design, and can only be narrowed through consideration of a larger sample of simulated climate data. Nonetheless, the evidence suggests that drainage infrastructure designed using mid-20th century rainfall records may be subject to a future rainfall regime that differs from current design standards. © 2010 Springer Science+Business Media B.V. Source

Haltas I.,Northwest Hydraulic Consultants Inc. | Kavvas M.L.,University of California at Davis
Journal of Hydrologic Engineering | Year: 2010

There is a strong analogy between fractal geometries and scale invariant processes. Fractal geometries are self-similar at different scales. Similar to fractal geometriessolutions of scale invariant processes at different space-time scales are self-similar. This unique property of scale-invariant processes can be employed to find the solution of the processes at a much larger or smaller space-time scale based on the solution calculated on the original scale. Herewe investigate scale invariance properties of hydrologic processes as initial-boundary value problems in one-parameter Lie group of point transformations framework. Scaling (stretching) transformation has unique importance among other Lie group of point transformationsas it leads to the scale invariance or scale dependence of a process. Scale invariance of a process allows using the same mathematical model for the process at different scales and facilitates finding the solution at any scale using the solution at the original scale. In this studythe process parameters and source/sink terms are regarded as state variables of some (secondary) processes that underlie or couple with the original process. Then under the scaling transformationsthe invariance conditions for the resulting system of processes at time-space scales that are different from the original time-space scales are investigated. The conditions to be satisfied by the form of a governing equation and its parametersas well as the initial and boundary conditions of the processare established in order for the process to be scale invariant. Alsothe self-similarity of the solution of an invariant process is demonstrated by various numerical example problems. © 2011 ASCE. Source

Papanicolaou A.N.,University of Iowa | Elhakeem M.,Abu Dhabi University | Wardman B.,Northwest Hydraulic Consultants Inc.
Journal of Hydraulic Engineering | Year: 2010

The predictive capability of a two-dimensional (2D)-hydrodynamic model, the finite-element surface water modeling system (FESWMS), to describe adequately the flow characteristics around emergent bendway weir structures was evaluated. To examine FESWMS predictive capability, a sensitivity analysis was performed to identify the flow conditions and locations within the modeled reach, where FESWMS inputs for Manning's n and eddy viscosity must be spatially distributed for to better represent the river bed flow roughness characteristics and regions where the flow is highly turbulent in nature. The sensitivity analysis showed that high flow conditions masked the impact of Manning's n and eddy viscosity on the model outputs. Therefore, the model was calibrated under low flow conditions when the structures were emergent and had the largest impact on the flow pattern and model inputs. Detailed field measurements were performed under low flow conditions at the Raccoon River, Iowa for model calibration and verification. The model predictions were examined for both spatially averaged and distributed Manning's n and eddy viscosity model input values within the study reach for an array of emergent structures. Spatially averaged model inputs for Manning's n and eddy viscosity provided satisfactory flow depth predictions but poor velocity predictions. Estimated errors in the predicted values were less than 10% for flow depth and about 60% for flow velocity. Distributed Manning's n and eddy viscosity model inputs, on the contrary, provided both satisfactory flow depth and velocity predictions. Further, distributed inputs were able to mimic closely the recirculation flow pattern in the wake region behind the bendway weir structures. Estimated errors in the predicted values were less than 10 and 25% for flow depth and velocity, respectively. Overall, in the case of distributed model inputs, FESWMS provided satisfactory results and allowed a closed depiction of the flow patterns around the emergent bendway weirs. These findings suggest that 2D models with spatially distributed values for Manning's n and eddy viscosity can adequately replicate the velocity vector field around emergent structures and can be valuable tools to river managers, except in cases when detailed three-dimensional flow patterns are needed. The study was limited to the examined low flow conditions, and more field data, especially under high flow conditions, are necessary to generalize the findings of this study regarding the model prediction capabilities. © 2011 ASCE. Source

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