Model Geometry

Bathymetry Data

The model grid was developed based on detailed cross sections for the Columbia River and the Willamette River provided by the ACOE (Knutson, 2000).  To develop the model grid, cross sections were used from RM 145 (Bonneville Dam) to RM 53.8 (Beaver Army Terminal) in the Columbia River and from RM 0 to RM 24 (Oregon City Falls) in the Willamette River, as shown in Figure 1. Figure 2 shows two example cross sections in the Willamette River provided by ACOE. These cross-sections were transformed from the UNET format to a format compatible with CE-QUAL-W2.

Bathymetry data in the Willamette River between RM 24 and just below the Oregon City Falls (RM 26.5) were obtained from a survey work done in 1999 by the ACOE using a sound transponder and Global Positioning System (GPS).  The bathymetry data for the last 0.3 miles between the ACOE data set and the Oregon City Falls were obtained by digitizing bathymetric estimates on the USGS quadrangle map.  The data sets provided x, y, and z coordinates that were combined and used in SURFER, a 3-D mapping program, to develop the model grid between RM 24 and the Oregon City Falls. Figure 3 shows the location of the data provided by the ACOE and the USGS map.

Cross-sections of the Willamette River between the Oregon City Falls (RM 26.8) and Canby Ferry (RM 35) were provided by Portland General Electric (PGE, 1998). The cross-sections were based on a survey done by the National Oceanic and Atmospheric Administration (NOAA) on October 25, 1997.  Figure 4 shows the extent of the cross sections available for this reach of the river. Figure 5 shows a sample cross-section at RM 29.6.

Bathymetry data from RM 0.0 to RM 1.2 in the Clackamas River and the cove (an abandoned gravel pit) connected to the Clackamas River was obtained from survey work requested by Pacific Water Resources (Savage, 2000). Part of the Clackamas River (1 mile) and the cove are modeled given that both are tidally influenced. The head of tide in the Clackamas River ends above the entrance of the cove (Kyle, 2000).  The bathymetry data were combined with elevation data from the USGS Digital Elevation Model to extract model cross-sections for CE-QUAL-W2.  Figure 6 shows contour plots of the data used to generate the grid for the model.

Model Grid Development

Using the river cross-sections and the bathymetric contour plots discussed above, the model grid was developed for 4 water bodies.  Figure 7 shows a layout of the model grid over the region.  A total of 16 branches make up the 4 water bodies in the model.  The Willamette River above the Oregon City Falls is modeled as one branch within a waterbody.  The second Waterbody consists of two branches, the first is the mainstem of the Willamette River and the second is Multnomah Channel.  The Columbia River represents a third waterbody with 11 branches.  The first branch is the main channel of the Columbia River and the remaining 10 branches are at tributary inflows or side channels around islands in the river.  The fourth waterbody represents the lowest reach of the Clackamas River and a gravel pit cove on the side, both of which are tidally influenced.  Segment size was based on the spacing of the cross-sections in the bathymetry data when using UNET data.  Layer thickness in the model is 2 meters throughout.  Table 1 provides the model grid specifications and boundary conditions for each branch.
 

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