The profile of Portola Parkway varies approximately 2 feet above and below the adjacent land. Consequently, minor ponding may occur where Portola Parkway is high and sheet flow across Portola Parkway will occur at low points. It should be noted that depths along Portola Parkway are less than 1 foot (figure 26). Figure 27 shows lines of arrival times for the basin study. It is concluded that Portola Parkway is essentially unaffected by a hypothetical failure of the LO2P3O Temporary Retarding Basin.
Application 5: Two-Dimensional Floodflows Around a Large Obstruction
In another temporary detention basin site, floodflows (from a dam-break) would pond upstream of a landfill site, and then split, when waters are deep enough, to flow on either side of the landfill. An additional complication is a railroad berm located downstream of the landfill, which forms a channel for floodflows. The study site (see figure 28) is bounded on the north by a temporary berm approximately 300 feet north of the Union Pacific Railroad, bounded on the east by Milliken Avenue, bounded on the south by the Union Pacific Railroad and bounded on the west by Haven Avenue.
A 200-foot grid control volume discretization was constructed as depicted in figure 29. In each grid, an area-averaged ground elevation was estimated based on the topographic map. A Manning's roughness coefficient of n = 0.030 was used throughout the study.
From figure 30 it is seen that flood plain spreads out laterally and flows around the landfill. The flow ponds up around the landfill; along the north side of the landfill, the water ponds as high as 9.2 feet, and along the east and west sides of the landfill, the water ponds up to 5.1 feet high. As the flow travels south, it ponds up to a depth of 4.8