For the purpose of this subchapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
DETENTION FACILITY. Any structure which is designed to collect and store surface water for subsequent gradual discharge.
DRAINAGE FACILITY. Any component of the drainage system. The total drainage system consists of two distinct components, the minor system and the major system. Both systems must be jointly planned and properly engineered.
(1) MAJOR DRAINAGE SYSTEM. The system that conveys the runoff when the capacity of the minor system is exceeded or inoperable due to temporary blockage. The MAJOR SYSTEM consists of major channels, large conduits and impoundments, as well as the less obvious watercourses inundated during surcharging and overflow from the minor system. The objective in MAJOR SYSTEM planning and design is to eliminate property damage and loss of life during major storm events. The peak design storm return period for the MAJOR SYSTEM is 100 years.
(2) MINOR DRAINAGE SYSTEM. The initial stormwater collection network which conveys the runoff from relatively frequent rainfall events. Elements of the MINOR SYSTEM include yard swales, street or roadway curbs and gutters, and storm sewers or open ditches, which collect and concentrate local storm runoff. The MINOR SYSTEM may be thought of as the drainage system which handles the local storm runoff generated within the confines of a subdivision or a neighborhood. It is not practical or economical to size the MINOR SYSTEM components for major or infrequent storm events. The objective in MINOR SYSTEM planning and design is to provide for convenience, eliminate nuisance ponding of water and frequently occurring minor flood damage, and to minimize street maintenance efforts. The design storm return period for the MINOR SYSTEM is ten years.
EXCESS STORMWATER RUNOFF. The portion of the stormwater which exceeds the safe storm drainage capacity of storm sewers or natural drainage channels serving a specific watershed.
FLOODPLAIN. The general floodplain area is the portion of the flood hazard area subject to periodic flooding and delineated by the latest revision of the flood hazard boundary maps prepared by the Federal Emergency Management Agency and designated as the 100-year floodplain boundary. Where no map exist, boundaries of FLOODPLAIN AREA may be determined by hydrologic calculation acceptable to FEMA. In calculating the boundaries of the FLOODPLAIN, the regulatory flood shall be
a 100-year frequency flood, and it shall be assumed that the entire drainage area contributing stormwater runoff which is deposited in the channel location in question will be developed as the city zoning and subdivision regulations suggest.
FLOODWAY. The portion of the flood hazard determined by the hydraulic calculations as the stream channel and overbank areas which are capable of conveying the regulatory flood discharge, a 100-year frequency flood discharge, keeping it within designated heights and velocities. The FLOODWAY is intended to be kept free of encroachment to carry the deeper fast moving water, and to serve as the primary drainage way for conveyance of flood water. The designated height for determining the FLOODWAY boundaries is one foot increase of the 100-year flood elevations.
100-YEAR 24-HOUR FREQUENCY RAINFALL. A precipitation event of 24-hours duration, having a 1% chance of occurring in any one year.
PROTECTED CHANNEL. A channel which receives stormwater discharge and which is paved, rip-rapped or otherwise improved by addition of human-made materials so as to reduce the potential for erosion.
SAFE STORM DRAINAGE CAPACITY. The quantity of stormwater runoff that can be transported by a channel or conduit without having the water surface rise above the top of the channel or conduit plus any designated freeboard.
STORMWATER CHANNEL. A natural or human-made open watercourse with definite bed and banks which periodically or continuously contains moving water, or which forms a connecting link between two bodies of water.
STORMWATER RUNOFF. Water that results from precipitation which is not absorbed by the soil or vegetation or evaporated and which flows over the ground surface or is collected in channels or conduits.
STORMWATER RUNOFF RELEASE RATE. The rate of which stormwater runoff is released from dominant to servient land.
(Ord. 980.2-9-94, passed 8-24-1994; Ord. 2023-022, passed 6-26-2023)