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/ .01- .:;- ! FUTURE COMMUNITY DEVELOPMENT DRAf1~ Future Flood Depths and Velocities 'two concerns with future community development in the basin arc its potential to cause flood damage by an increase j,n IOO-year water surface elevations and/or G~eatio~ of hazardous flood velocities. An increase in flood depth over the existi ng profile wi 11 generally I . inundate additional areas and cause the flood bOVV\(lane.~) to expand. In general, water flowing at a rate of 7 feet per second or greater will cause severe erosion of streambanks and is capable of transporting large rocks. Fill around bridge abutments and some streambanks may be eroded and large amounts of gravel, sand, and silt. may be transported by water flowing at a rate from 5 to 7 feet per second" Water flowing at about 2 feet per second or less may deposit sand ,. silt, and other debris. An increase in flood depth and/or velocity from development can be due to an increase in 100-year runoff by creation of mo:re impervious areas and more significantly, encroachment into the floodplain itself. When J encroachments onto the natural floodplain arc allowed, such as with artificial fill, the flood carrying capaeity is reduced. The depth of water I or the flo~r velocity in the remaining floodplain area must normally increase in order to convey the same magnitude of flood, and thus the flood hazard to areas near the encroachment may he increased. The impact of encroach- ment and increased runoff due to development can be mitigated by use of sound floodplain management regulations. Floodplain Management Regulations I While the need to minimize property damage due to flooding has been recognized by city and county planners, tho city's current zoning regul'.Itions I (Reference - ) do not address or provide <111Y guidullce reg;trdillg the ['[ood h,1z<1nl.