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examine the potential effects of those changes. To evaluate the effects of the regrading and the construction of the levee around much of the state park subsequent to. the 1984 flood event, the CWCB contracted with IF, Sato & Associates, study contractor for the 1992 FIS revisions, to modify the computer model of the Colorado River floodplain that they assembled for those 1992 revisions. Sato & Associates modified the FEMA analysis to take account of the levee system constructed at the state park and the levee system at the Pepsi-Cola plant in 1991. In Sato's modified analysis, performed for the CWCB, it was assumed that the regrading and the levee construction would prevent floodwaters from entering the state park and that the changes would remain intact even with significant erosive forces. The CWCB analysis has determined that flood depths would increase approximately 2 feet. The velocities in the river channel during a 100-year flood would experience a substantial increase (an average increase from 6 feet per second to 12 feet per second). Table 4 below shows these changes in flood stage and velocity for six cross-sections from the downstream face of the Redlands Parkway bridge over the river upstream to the Pepsi-Cola levee. In light of these predicted changes, any assumptions about the levees withstanding erosive forces must be subject to serious scrutiny. TABLE 4 FLOOD DEPTHS AND VELOCITIES FOR CONNECTED LAKES AND DUKE LAKE (With and Without Levees) 1 OO-yr. EI. 100-yr. EI. 100-yr. Vel. lro,.-. Vii Location Cross-Section Levee EI. W/O Levee WI Levee W/O Levee WI Levee D/S Redlands Pkwy. W N.A. 4533.3 4533.3 7.2 fps 7,2 fps West end of Connected Lakes State Park X ? 4535.9 4535.9 5.3 fps 5.9 fps Middle of Park Y 4540.8 4537,0 4537.8 6.5 fps 13.0 fps Middle Duke Lake Z 4540.4 4540.7 4542.3 8.5 fps 9.2 fps East end Park AA 4542.5 4543.4 4545.4 3.7 fps 6.6 fps Pepsi-Cola Levee BB 4557.0 4547,6 4549.8 10.2 fps 11.0 fps Note: Velocities greater than 7.0 fps will cause major erosion problems and streambank instability. The profile sheet for the Connected Lakes and Duke Lake, which is included at the end of this section, shows the levee around a portion of the State Park, as it exists today. It also shows the currently effective 100-year flood elevation from the FIS without incorporating the effects of the 1991 levees on those elevations. Subsection 5.3 Flood Risk During a 50-year and a 100-year flood there would be a problem at Connected Lakes and Duke Lake. If the existing levee were not modified and reinforced with riprap on the river face, there would severe erosion to the levee protecting the Connected Lakes. There would also be failure with overflows into Duke Lake. There would be a direct connection between the lakes and the .13.2