COHSTREX Project Overview


Long-term goals

The long-term goals of this research are to combine state-of-the-art remote sensing and in situ measurements with advanced numerical modeling (a) to characterize coherent structures in river and estuarine flows and (b) to determine the extent to which their remotely sensed signatures can be used to initialize and guide predictive models.

Objectives

Coherent structures are generated by the interaction of the flow with bathymetric and coastline features. These coherent structures produce surface signatures that can be detected and quantified using remote sensing techniques. Furthermore, a number of relationships between coherent structures and flow characteristics have been suggested that have the potential to allow flow parameters (e.g. mean velocity, bottom roughness, shear, and turbidity) to be inferred from remote measurements. The objectives are to test the following four hypotheses:

  1. Flow parameters can be inferred from remotely sensed signatures of coherent structures.
  2. Numerical models can be constrained with these inferred parameters.
  3. The effect of stratification on the strength of coherent structures can be used to detect the presence or absence of stratification and the location of the fresh/salt water interface.
  4. Numerical and field experiments can be used together to predict, interpret, characterize, and understand coherent structures.

Approach

The key to this project is an interactive process that blends sophisticated remote sensing, in-situ measurements, and numerical simulation. Our approach is to conduct closely coupled field and numerical model experiments to test the hypotheses listed above. The plan includes two major field experiments with both in situ and remote sensing measurements - the first occurred in Year 2 (2006) and the second is planned for Year 4. A preliminary experiment was conducted in Year 1 (2005) to aid in the design of the major field efforts.

The research involves four main areas - (1) in situ measurements, (2) remote sensing, (3) modeling, and (4) physics and classification of coherent structures. The in situ field measurements will be used to characterize the overall flow field to investigate the generation of coherent structures at specific sites, and initially, to provide boundary inputs for the numerical models. The surface signatures of coherent structures in the same region will be detected using remote sensing techniques and compared with the in situ and model results. The numerical models will serve three roles, viz., (1) precursor simulations in which existing bathymetry and assumed regional forcing will allow us to guide the measurement plans, (2) detailed simulations of both the region and specific local areas for comparison to field-determined coherent structures, and (3) simulations to aid in characterizing the mechanisms by which observed coherent structures are formed, to evaluate the sensitivity of these generation mechanisms to variations in forcing, and to predict the surface signature that such structures generate.

Results from the in situ field observations, remote sensing, and numerical model runs will be synthesized into a classification scheme that includes all observed coherent structures. Predictive scaling relationships will be developed in order to generalize the results from this study to other systems. The result of this integrated approach will be a thorough investigation of the mechanisms and evolution of coherent structures in rivers and estuaries in order to link their surface expressions to subsurface flow features.

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