Performance Assessment and Improvement of Hydrodynamic Mathematical Models via Field Observations and Controlled Laboratory Experiments
* What primary physical processes represent the most difficulty for numerical modeling of complex river hydrodynamics on a wide rage of spatial and temporal scales?
* How well do existing multi-dimensional numerical modeling methods (e.g., TrimR2D, 2.5DRiemann, RiCOM) represent such physical processes?
+ What are the implications of model limitations?
+ How can the associated difficulties be overcome?
* Can existing numerical models achieve high quality predictive outcomes based on comparison with field and controlled experimental laboratory observations?
* What are the most appropriate guidelines for selecting the best numerical model (i.e., best practices) for river hydrodynamics and flood prediction applications based upon comparison with physical observations?
Need and Benefit
Flows in rivers encompass a wide range of temporal and spatial scales and are sufficiently complicated that testing of models in the field is at best, difficult. However, specific scales can be isolated with controlled laboratory experiments that can then provide the necessary data for testing various aspects of existing numerical models for river hydrodynamics.
Although there are many different models presently available both within and outside of Reclamation (TrimR2D, 2.5DRiemann, RiCOM, MIKE21, HEC-RAS, FLUENT, FLOW3D, etc.), they are either proprietary, limited in dimensional representation, obviously in error, or in some cases applied in a manner that is technically incorrect. Reclamation managers face many problems including on-the-ground Environmental Assessments (EAs) and Environmental Impact Statements (EISs), optimization of operations, flood inundation, and river restoration as a few examples where high quality prediction methods are critical to successful management or operational decisions. This proposal intends to improve the level of confidence in existing two-dimensional (2D) models (e.g., TrimR2D, Riemann, and RiCOM) for modeling of multi-dimensional river hydrodynamics via detailed comparison with field observations and controlled laboratory experiments.
If the models prove to compare well with such experimental data, then they provide a means to predict the consequences of specific flood discharges on broad range of given river topography, as well as interpret the flood history from the patterns of erosion and deposition left by ancient floods. By achieving these specific objectives, the models will provide Reclamation with powerful, quantitative, and predictive methods to analyze flows far in excess of discharges commonly observed in river systems controlled by dams throughout the Western United States. Furthermore, they will allow for predicting consequences of modified operations without risky field experimentation that could cause permanent changes in geomorphology or detrimentally affect river ecology. The data obtained from careful experiments stand on their own, providing a means to test more sophisticated models as they become available in the future.
Paramount to comparison of model results with experimental data is the development of improved laboratory measurement techniques including Particle Image Velocimetry (PIV). Present capabilities are limited to point measurement techniques (e.g., Acoustic Doppler Velocimeter) that--although providing a time series of three-dimensional (3D) velocity components at a single point--cannot provide a spatial snap-shot of flow fields and so have limited capability when attempting to understand how and why numerical models may poorly represent the physics of certain flow regimes. The benefits from development of PIV capabilities will immediately carry over to other projects that require a full-field perspective in drawing technically correct conclusions about hydraulic performance. A few examples of this include:
* Silvery Minnow egg transport and deposition (Application for Middle Rio Grande Silvery Minnow Restoration)
* San Joaquin River Restoration involving a multitude of questions regarding hydrodynamics and water quality
* Stilling basin pressure fluctuations and slab hydraulic uplift
* Fish screen hydrodynamics
* Erosion potential
* Sediment transport
The ability to quantitatively measure spatial flow structures in these cases will open the door to new management and design approaches and ultimately improved management decisions and design performance.
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