(A) A storm water sewer or a surface drainage system adequate to serve the area being subdivided shall be provided to accommodate a 50-year storm. The Indiana Department of Transportation for crossings of state-maintained facilities or U.S. Corps of Engineers for the crossings of "blue water" streams may require accommodation of greater than the 50-year storm. Any storm water retention or detention facilities shall be designed to accommodate the difference between the 5-year storm without the proposed development and the 50-year storm with the proposed development. Such system shall be in accordance with plans and specifications approved by the County Drainage Board prior to primary plat approval. The flow in any drainage structure shall not exceed 90% of the structure capacity, except for basin discharge pipes that can be 100% of capacity.
(B) (1) Wherever curbs and gutters are provided or when the Area Plan Commission and the County Surveyor determine the natural surface drainage to be inadequate, the subdivider shall construct a storm water sewer system with catch basins appropriately spaced along the streets in the subdivision. Valley gutters extending across the street surface shall not be used.
(2) Wherever curbs and gutters are provided within a development, stormwater flow in the gutterline shall not exceed 600 lineal feet. In cases of excessive lengths of drainage, an inlet should be installed to intercept the water and direct the water through a structure. In design of the subdivision, provisions shall be made to prohibit the drainage of stormwater across intersections. Positive drainage shall be achieved and no standing water shall be allowed. The minimum gutter grade shall not be less than 0.65%. Side drains from the gutter (or curb spill-outs) are prohibited.
(C) A natural surface drainage system shall be permitted when curbs and gutters are not provided and the natural drainage will, in the opinion of the County Surveyor, adequately drain the storm water from the subdivision. The drainage ways should be shallow swales sowed in grass rather than deep, open ditches and have a minimum grade of 1% unless lined with a concrete ribbon. Roadside drainage shall not be disrupted by private driveways. The subdivider shall install a suitable pipe in accordance with the county's Driveway Culvert Ordinance.
(D) In the design of a storm water sewer system for a subdivision, the present and future expected run-off from the larger drainage area should be considered. For this reason, it may be desirable that larger sewers than those needed to service the immediate subdivision be installed.
(E) All pipes shall conform to American Society of Testing Materials Standards Specifications in Section 7, 8 and 9 and Design Criteria shall conform to the County Storm Drainage Manual to insure maximum hydraulic efficiency.
(F) All drainage structures shall be designed and shown on the Street Construction Plans with a detail sheet showing the size and type of structures to be used, including drop structures, culverts, street inlets, manholes, beehives and area drains. These shall be constructed in accordance with the plans and specifications on file as well as the manufacturers specifications. Adequate grade and drainage structure friction coefficients shall be obtained and indicated on supporting drainage calculations for the type of structure used. The flow in any drainage structure shall not exceed 90% of the structure capacity, except for basic discharge pipes that can be 100% of capacity. All drainage structures shall have junction boxes at major changes in grade or direction that are accessible for maintenance and repair of the structure.
(G) Drainage swales flatter than 1% grade shall use either 16-inch wide, six-inch thick, concave, reinforced, concrete ribbons or 16-inch wide, six-inch thick, reinforced, concrete flat ribbons with three feet of sod on each side. Drainage swales greater than 8% shall have appropriate, permanent erosion control measures.
(BC Ord. 2006-05, passed 3-20-06; Am. BC Ord. 2021-08, passed 1-11- 21; Am. BC Ord. 2021-09, passed 1-11-21; Am. BC Ord. 2021-10, passed 1-11-21)