14 Oct 2020

Red River Structure Physical Model Study

Abstract: A proposed Red River Structure (RRS), intended to function as one of three gated structures comprising the Fargo-Moorhead Metropolitan Area Flood Risk Management Project, was tested in a general physical model. A 1:40 Froude-scale was applied to model the structure, engineered channels, existing bathymetry/topography in the Red River and overbank areas, and the proposed Southern Embankment. The physical model was used to ensure that the RRS could pass at least 104,300 cfs during the Probable Maximum Flood while maintaining a maximum pool water surface elevation of 923.5 ft. The physical model was also utilized to optimize the approach structure, stilling basin, retaining walls, and erosion protection designs. The physical modeling effort resulted in an optimized stilling basin wall, retaining wall, and end sill geometry/configuration where erosive conditions were not observed outside and adjacent to the stilling basin. Properly designed riprap (St. Paul District’s R470 gradation) proved to be successful in protecting the proposed RRS from potential scour downstream. The modified approach wall design proved to be successful in creating safe approach flow conditions as well as acceptable flow separation patterns. It is recommended that Alternative 3 be the design used going forward.

28 Apr 2020

PUBLICATION NOTICE: Lower Columbia River Adaptive Hydraulics (AdH) Model: Development, Water Surface Elevation Validation, and Sea Level Rise Analysis

Abstract: A numerical model of the Lower Columbia River, validated to water surface elevations, has been generated using the Adaptive Hydraulics (AdH) code. The model boundary conditions include an ocean tidal boundary and five inflows: the Lewis, Cowlitz, Willamette, and Sandy Rivers, and the Columbia River at Bonneville Lock and Dam. The model, which spans approximately 146 river miles, accurately reproduces water surface elevations measured in the field at several locations along the model domain. An examination of the AdH model’s Friction Library was also conducted. The Friction Library was used in this application to estimate the effects of pile dikes. Rather than model individual piles in the model mesh, the piles were modeled using the Friction Library’s submerged vegetation material type. Through testing of this application, it was determined that the Friction Library approach, which enhances model run time and efficiency, can accurately reproduce the global effects of pile dike fields. Additionally, the validated model was used to analyze three sea level rise (SLR) scenarios, which correspond to predicted SLR at Astoria, OR, at 50, 75, and 100 years from the present (0.5 meter [m], 1.0 m, and 1.5 m, respectively).

27 Apr 2020

PUBLICATION NOTICE: Investigation into Laboratory Bathymetric Measurement Techniques

ABSTRACT: There is no universally accepted way to accurately and efficiently measure bathymetry in laboratory hydraulic models. Remote sensing techniques can measure bathymetry without making contact with the model, and some remote sensing techniques can measure the bathymetry in laboratory models without draining the water. The four categories of remote sensing technology investigated in this report are echo sounding technology, laser technology, image processing technology, and radar technology. The technology of each category has strengths and limitations, but can be used in the laboratory to measure bathymetry. Echo sounding technology works well in environments with suspended sediment, but the accuracy is reduced by large beam footprints. Laser technology does not perform as well with suspended sediment but can provide high-accuracy bathymetric measurements. Stereophotography, discussed in the image processing technology section, requires optically clear water and can provide very accurate bathymetric mapping. Radar technology can be very helpful when sub-bottom stratigraphy is important. Technology from each of the categories has been scaled for field application to measure bathymetry and submerged coastal structures.