(a) The following definition of terms apply to the minimum drainage requirements contained in this title:
(1) "Primary drainage channels or conduits" mean those channels or conduits which have a drainage area of more than 1.0 square miles;
(2) "Minor drainage channels or conduits" mean those channels or conduits having a drainage area of 1.0 square miles or less;
(3) "Inundation" is used to indicate ponded water or water in motion of sufficient depth to damage property due to the mere presence of the water or deposition of silt;
(4) "Flood hazard" means overflow of water having sufficient velocity to transport or deposit debris, to scour the surface soil, or to dislodge or damage buildings, or to cause erosion of the banks of channels;
(5) "Possible flood hazard" means possible extension of areas denoted as subject to "flood hazard" and shall reflect the uncertainty of degree or extent of bank erosion;
(6) "Sheet overflow" means water of minor depth either quiescent or flowing at velocities less than those necessary to produce serious scour;
(7) "Ponding of local storm water" means the standing of water in local depressions. As distinguished from "sheet overflow" this water originates on or in the vicinity of the property and due to the condition of the ground surface is unable to reach a drainage channel or conduit.
(b) Runoff design shall be made for the frequency of occurrence hereinafter stipulated in these standards of modified rational method using basic data in accordance with the requirements set forth in the Standard Specifications. Runoff design shall accommodate the full and future developments within the drainage area. In cases where such drainage areas are underdeveloped fully improved conditions shall be determined for future by conditions as indicated in the general plan of the city for future development and by the zoning ordinance of the jurisdiction within which such areas are located. Any outlet channel required to carry storm water from the proposed subdivision to a defined drainage channel or conduit shall be in accordance with these standards for the ultimate state of development in the drainage area resulting from the particular subdivision.
(c) Drainage channels and conduits directly affecting the proposed subdivision shall have the following minimum capacities:
(1) Primary drainage channels and conduits shall have sufficient capacity to contain a twenty-five-year frequency of occurrence runoff;
(2) Minor drainage channels or conduits shall have sufficient capacity to contain a ten-year frequency of occurrence runoff, including undefined overflow originating within the tract or adjacent thereto.
(d) Storm waters within street areas shall be placed in closed conduits when the maximum depth of in-gutter runoff computed in accordance with the provisions of the supplemental design standards in the specifications exceeds desirable depths in relationship to the velocity, as determined by the city engineer.
(e) Proposed subdivision shall not cause inundation or flood hazard conditions of existing inhabited areas.
(f) Drainage shall be accomplished by gravity without surcharge into catch basins or manholes except by design.
(g) Catch basins shall have inlets of varying lengths so designed that the water is diverted into the catch basin without a reversed direction of the flow of the water. The inlets shall be designed in accordance with Standard Detail No. A-3.
(h) Drainage channels, conduits and appurtenances shall conform in all respects to good engineering practice.
(Ord. 121 § 404, 1967).