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2. Flood Plain Management The purpose of flood plain management is to: o Protect the publ ic health, safety and general welfare. o Minimize flood losses in areas subject to flood hazards. o Promote the wise use of the flood plain. o Provide for the preservation of floodways and flood plain storage areas in order to protect those downstream from increased flooding. Flood plain controls are critical factors in drainage manage- ment. Successful flood plain controls will preserve a reason- able path for floodwaters by controlling development in flood hazard areas, prevent loss of flood plain storage volume and prevent the introduction of structures, property or land uses into the flood plain which would result in damages. The actual flood plain map is a pictorial representation of the 100-year flood event which is used for control and land planning purposes. Floods of greater magnitude can occur and flooding beyond the extent of the limits shown in the report can also occur due to other factors such as debris blockage at bridges and culverts. Both structural and non-structural methods may be used to alleviate the flood problems. The non-structural measures consist of flood-proofing, building codes, enforcing land use regu- lations, enforcing flood plain zoning, and instituting flood insurance programs. 34 3. Actions by the City of Boulder The City of Boulder has adopted several ordinances to regulate use of the flood plain and to finance improvements for flood control. Flood plain zoning regulations were first adopted in 1969 and strenghtened in 1975. The regulations provide for regulatory floodway along the creek and severely restrict building within its limits. The regulatory floodway is defined as that portion of the 1% (IOO-year) flood plain where flood velocities would exceed two feet per second, where the depth of flow exceeds two feet or the 1 imit of flood plain encroach- ment which would limit the increase in flood depth due to encroachment to one-half foot or less. Non-residential buildings are allowed in the regulatory floodway provided they do not increase flood stages. Buildings are allowed in the portion of the flood plain outside the regulatory floodway provided they are flood-proofed or elevated to two feet or more above the l% (lOO-year) flood level. ,I I I I I I I I I I I I I I I I I I I Flood plain regulations are intended to minimize future escala- tion of the flood hazard. However, regulations provide no protection for existing flood plain development which totals $164 mi II ion dollars (Apri 1 1977) in the 0.2% (500-year) flood plain. The existing development is currently exposed to average damages of over $800,000 annually. With enforcement of existing flood plain regulations, the damage potential will slowly decrease in the future as existing structures are replaced by flood-proofed structures. However, if regulations