All secondary drainage channels which are within, or immediately adjacent to, an improvement, development or subdivision, shall be protected and improved by the developer as follows:
A. All land having an elevation below the 50-year maximum flood elevation for the final improved channel shall be dedicated for the purpose of providing drainage, for public park, or drainage and utility easement use.
B. Secondary drainage channels which have a primary function of collecting surface water from adjacent properties or intercepting and diverting side hill drainage shall be improved open channels.
C. Secondary drainage channels which have a primary function of transporting water through the block or collecting water from cross channels and which have a drainage area of less than forty (40) acres shall be improved with closed storm sewers unless special approval has been given by the director for construction of a concrete lined channel; and where the secondary drainage channel has a drainage area of greater than forty (40) acres, an improved open channel or closed storm sewer shall be provided. When the unit to be drained is less than six (6) acres, the director may modify the requirements of the first part of this provision to permit a paved open channel, designed for use as a sidewalk, having a minimum width of four feet (4') and provided with six inch (6") curbs, when designed to drain from the street to a natural stream or improved open channel.
D. Site improvement shall provide for the grading of all building pads to an elevation where all building pads will not be subject to overflow from a regulatory flood and in a manner that will provide for the rapid runoff of stormwater. Manufactured home placement pads shall be elevated to the regulatory flood elevation. All manufactured homes shall be anchored in accordance with requirements outlined in the federal emergency management agency floodplain management regulations, subpart A, section 60.3(b)(8). Substantial improvements to existing structures within the 100-year floodplain will be subject to all regulations and requirements of this chapter. New construction or substantial improvements of residential or nonresidential structures (including manufactured homes) shall have the lowest floor (including basements) elevated to one foot (1') above the level of the regulatory flood. Nonresidential structures and accessory buildings may meet this requirement by floodproofing the structures, including utility and sanitary facilities, up to one foot (1') above the level of the regulatory flood. Mechanical and utility equipment for residential or nonresidential structures shall be designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding. If a nonresidential structure is intended to be floodproofed, a registered professional engineer or architect shall develop and/or review structural design, specifications and plans for the construction, and shall certify that the design and methods of construction are in accordance with the accepted standards of practice for meeting the elevation requirements of this chapter. A record of such certificates which includes the specific elevation (in relation to mean sea level) to which such structures are floodproofed shall be submitted to and maintained by the department of community development.
E. A drainage channel shall not be located in a street easement unless it is placed in an enclosed storm sewer except under the following conditions:
1. Where a paved street surface of at least two (2) lanes is provided on both sides of a paved channel so as to provide access to abutting properties; or
2. Where lots are platted to back up to the street right of way where the drainage channel is located between the rear of the lot line and the paved street, and further provided that at no time in the future shall access be allowed or constructed over the open drainage channel to the rear of a lot so platted. For the purpose of these regulations, a lot which sides to a public street is not considered to back up to the street right of way.
3. When a condition outlined in either subsection E1 or E2 of this section is present, adequate space adjacent to the channel shall be dedicated as right of way to provide for maintenance of the paved drainage channel and its unpaved bank.
F. In single-family residential, duplex or manufactured home developments, site grading shall be carried out in such a manner that surface water from each dwelling lot will flow directly to a storm sewer, improved channel, sodded swale, or paved street without crossing more than four (4) adjacent lots.
G. Surface water collected in streets shall be diverted to storm drains at satisfactory intervals to prevent overflow of six inch (6") high curbs during 25-year frequency rain for the area and grades involved. Drainage area allowed for surface flow on streets at point of diversion shall not exceed twenty (20) acres, regardless of flow.
H. Drainage easement of satisfactory width to provide working room for construction and maintenance shall be provided for all storm sewers with the minimum width being fifteen feet (15').
I. Open channels shall be improved by providing a paved section that will carry the runoff from a rain of 50-year frequency within the lined section and sodded section to carry the additional runoff from a regulatory flood. Whenever an open improved channel is required or authorized for a secondary drainage channel under the provisions of these regulations and the channel crosses residential lots which have been developed under the community unit plan and/or planned unit development or where the channel improvement is to be designed as an area that will be maintained by a property owners' association, the director may modify the requirements of the first part of this provision to permit a channel improvement design in keeping with landscape architectural plans, provided all hydraulic requirements to support the overflow resulting from a regulatory flood rainfall are met in such a manner as to prevent flooding of all building pads. (Ord. 2017, 2014: Ord. 1969, 2011)