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4-22 East Salt Creek near the central facilities site at the mouth of Munger Canyon is deeply incised. The main channel is approxi- mately 15 to 20 feet wide and 6 to 10 feet deep, with a smaller low flow channel included. Streambed slopes range from approxi- mately 0.6 percent in the upstream reaches to over 3 percent in the reaches downstream of the road crossing. The channel geometry is shown in plan on Figure 4.3-45, 100-Year Floodplain Boundary; channel slopes are shown on Figure 9.3-35, East Salt Creek Water Surface Profiles. It is planned to construct a culvert sufficient to pass the 100- year discharge at the Munger Canyon/East Salt Creek road cross- ing. This will require a minimum of a 16' 7" by 10' 7" corrugated steel plate arch culvert or the hydraulic equivalent. The road crossing also marks the location of a hydraulic boundary between super-critical flow conditions on the downstream and subcritical on the upstream side. 4.3.4.3 100-Year Floodplain Boundary • Downstream of the road crossing, the channel is deeply incised into the alluvium and the lOD-year flood flows are contained within the channel as shown on Figure 4.3-45, 100-Year Floodplain Boundary. Upstream of the Munger Canyon road crossing, 100-year flows are generally contained within the incised channel. However, there is the possibility of flood flows breaking out of the channel approximately 2,200 feet upstream of the road. If this should occur, flood waters may flow overland across the floodplain and reenter the main channel near the road crossing. These flows would be very shallow, with depths generally less than one foot and no greater than two feet. Velocities would be low, with a maximum of two feet per second. This area of possible overland flow is shown crosshatched in Figure 4.3-45. • Major facilities in the valley are planned to be constructed out of the floodplain and higher than the potential 100-year