American Society of Civil Engineers


Comparison and Analysis of Hydrodynamic Models for Restoration Projects: The Case of Pool-Riffle Structures


by M. R. Volkwein, (Student, member ASCE, Senior Undergraduate, Earth Processes & Environmental Flows (EPEF) Research Group, Department of Civil and Environmental Engineering, University of Pittsburgh, Benedum 963, 3700 O’Hara St, Pittsburgh, PA, 15261. E-mail: mrv11@pitt.edu)
Section: Students and New Professionals, pp. 3140-3148, (doi:  http://dx.doi.org/10.1061/41173(414)328)

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Document type: Conference Proceeding Paper
Part of: World Environmental and Water Resources Congress 2011: Bearing Knowledge for Sustainability
Abstract: Naturalization of urbanized streams through the use of pool-riffle structures creates a more hospitable environment and a consistent depth during high discharges while providing self-maintenance of the structure. Whereas during low flow sediment builds up in pools, a pool-riffle structure with sinusoidal narrowing banks allows higher shear stresses to develop in pools during high flows thereby maintaining a pool-riffle structure over time. To design these self-maintaining structures, hydrodynamic models are used to optimize the parameters necessary to facilitate this shear stress reversing process. One-dimensional (1D) models are often favored in place of resource intensive three-dimensional (3D) models. However, the 1D and 3D pool-riffle models do not always agree on the distribution of bed shear stresses. Two-dimensional (2D) models can be used to attempt to validate 1D models and describe their limitations. 1D modeling was completed for four channel designs at eight levels of discharge using HEC-RAS. The design displayed the self-maintenance mechanism for four flow rates where shear stresses in the pools did appear to exceed the stress at the riffles. 2D depth-averaged modeling was done using River2D and initial results show that the mechanism may not be effective. Industry uses 1D modeling most frequently for its cost effectiveness; showing that 1D models may not be sufficient in pool-riffle design could be significant for naturalized channel design.


ASCE Subject Headings:
Hydrodynamics
Restoration
Case studies
Urban areas
Rivers and streams