Abstract: Session F 1:50 pm (Back to Session F)
Hydraulic Consideration of Stream Restoration Using the Corridor Model and SRH-2D
Anthony (Tony) Osei
In Protocol 1 and 3 stream restoration projects where extensive channel and floodplain grading may be required, it is beneficial to have a sense of how much floodplain grading is adequate to create a stable stream. In the design process, after the stream geomorphic ratios are computed to set the stream planform, floodplain and stream grading requirements are examined. At RES, our approach is to use the Corridor Model within AutoCAD Civil 3D to grade the floodplain without the channel. A preliminary 1-dimensional hydraulics model (HEC-RAS) is setup to model the graded floodplain. The 1-D model provides the initial downstream boundary conditions for a preliminary 2-dimensional model. Also, the 1-D model reveals to the designer the vulnerabilities in the stream system relative to shear stresses and the potential for degradation in the proposed restoration reach but the one-dimensional model does not tell the whole story. To compensate, the2-dimensional model is setup using the water surface elevation computed by the 1-D model. Next, the 2-D model is utilized to yield the full hydrodynamic effects and the pattern of flow is observed as it proceeds through riffles, pools and at bends while eddy currents, shear stresses and velocities at certain locations of interest are examined. Designers use this information to tweak the preliminary design. Further grading is usually required in the floodplain and minor or major alterations of the stream planform could be made to create a more stable system. In the next iteration of grading, the stream is imbedded in the floodplain. At this point in the design process, the proposed stream structures required for bed or bank stabilization are known and the preliminary HEC RAS model is revised based on the updated surface from the Corridor Model, which creates a detailed hydraulics 1-D model. This 1-D model is calibrated to match real life stream behavior as much as possible. The water surface from the refined 1-D model is then used to re-run the 2-D model. This refined 2-D model provides better visual information on shear stresses and velocities at points of interests within the restored stream system.