3.6 - Drainage
A. General Drainage Requirements
B. Nature of Storm Water Facilities
The Subdivider may be required by the Plan Commission to carry away, by pipe or open ditch, any spring or surface water that may exist, either previously to, or as a result of the Subdivision. Such drainage facilities shall be located in the Street Right-of-Way or in perpetual, unobstructed easements of appropriate width, and shall be constructed in accordance with the Town of Plainfield construction standards and specifications. Whenever a change of land use occurs, concentrated storm water discharge to adjacent areas shall not be permitted unless the discharge is conveyed through a suitable drainage feature to: (i) an approved outlet within the Right-of-Way; (ii) an existing drainage easement; (iii) a defined drainageway as approved by the Town Engineer; or (iv) an open ditch which appears as a dashed or solid blue line on the 7.5 Minute Series Topographic Quadrangle Map as published by the United States Geological Survey. The drainage feature used to convey the site discharge to the approved outlet shall be located in the Right-of-Way or easement of appropriate width.
2. Public Storm Sewers
With the exception of storm water conveyance along non-residential Local Streets within the I-2, I-3 and I-4 Districts, all storm water conveyance within or parallel to and adjacent to the public Right-of-Way shall be fully contained in storm sewers with an adequate and approved outlet. Residential Subdivisions containing Lots of less than 15,000 square feet and Non-Residential Subdivisions shall be provided with storm sewers to convey all on-site drainage. However, on-site drainage swales with required conveyance capacity of less than five (5) cubic feet per second under the ten (10) year post-development design storm may be allowed.
3. Accommodation of Upstream Drainage Areas
A culvert, storm sewer, open ditch, or other drainage facility shall, in each case, be large enough to convey potential runoff from its entire upstream drainage area, whether inside or outside the Subdivision. The minimum conveyance provided for upstream, off-site drainage areas shall be the runoff resulting from the one-hundred (100) year storm over the present state of upstream, off-site drainage areas. The conveyance provided for upstream waters may be decreased to the extent that hydrograph routing and detention on land controlled by the Subdivider and dedicated to the Town of Plainfield as a drainage easement allows for decreased capacity; provided, that the runoff resulting from the one-hundred (100) year storm is staged less than one (1) foot above the stage on the natural drainage way at the interface of the development with the upstream drainage area. Culvert capacities for conveyance under interior Local, Collector, and Arterial Streets without roadway overtopping shall be the runoff resulting from the twenty-five (25) year, fifty (50) year, and one-hundred (100) year storms respectively over off-site areas in present state and on-site areas in post development state. Driveway culvert capacities shall be the capacities required for the Street classification to which the Driveway connects. Greater culvert capacity shall be required to protect the finished floor elevation of Buildings from the post-development one-hundred (100) year storm when, in the opinion of the design engineer or the Town Engineer, the finished floor elevation is threatened. It is recommended that drainage of loading docks or other building features which are proposed at an elevation lower than adjacent roadways be considered with respect to culvert drainage impacts.
4. Effect on Downstream Drainage Areas
The release rate of storm water from development, redevelopment and new construction shall not exceed the storm water runoff rate from the land in its present state of development.
5. Areas of Poor Drainage
Areas which are not in the floodplain, but which contain soils subject to flooding, may be approved for Subdivision by the Plan Commission, provided that the Subdivider fills the affected areas of said Subdivision to an elevaton sufficient to place Building sites and Streets two (2) feet above the ponding levels.
6. Areas of High Seasonal Water Tables
In areas characterized by soils having a high seasonal water table as determined by the Hendricks County Soil and Water Conservation District, Lots shall be limited to slab type construction unless the Plan Commission determines that appropriate engineering techniques will be applied to alleviate the subsurface problem.
7. Special Flood Hazard Areas
If any portion of a proposed Subdivision lies within the flooodplain the Subdivision shall comply with Plainfield Ordinance No. 1-96, "Management of the Floodplain and Other Areas of Special Flood Hazard of the Town of Plainfield."
C. Dedication of Drainage Easements
D. Connection to Town Drainage Utilities
Whenever practical, all Subdivisions within the Town of Plainfield shall connect to drainage utilities provided by the Town of Plainfield. In those instances where the Plan Commission determines that connection to Town of Plainfield drainage utilities would pose an unusual or unnecessary hardship at the time of development, the Plan Commission may make a recommendation to the Town Council to approve a connection to another public or semi-public drainage utility, provided, however, that all drainage facilities are installed to Town of Plainfield standards or alternative standards approved by the Town Engineer, and, provision is made in the design and layout of the drainage facilities for connection to the Town of Plainfield drainage utilities at such time as the Town of Plainfield extends drainage utility facilities to the Subdivision.
E. Maintenance Responsibility for Detention / Retention Facilities
The Subdivider shall be responsible for the maintenance of all detention and retention facilities during construction. After construction, the owner of the real estate shall be responsible for the maintenance of all detention and retention facilities. Assignment of the responsibility for maintaining a detention or retention facility which serves more than one Lot or land holding shall be permitted only where:
Amended: Ord. No. 4-2000