A. General requirements. The Commission shall not recommend for approval any subdivision plat which does not provide adequate provision for storm or flood water run-off channels, basins, or improved water drainage systems. The storm water drainage system shall be separate and independent of any sanitary sewer system. A drainage report shall be provided by the owner/developer.
B. Drainage report. The drainage report shall identify the applicable areas of concern and problem areas as listed on the selection matrix contained in the Indiana Handbook for Erosion Control in Developing Areas, October, 1992, as amended, hereinafter referred to as the Erosion Control Handbook. Said reference document can be found at Agricultural Soil Conservation and Stabilization (A.S.C.S.) office and the Whitley County Planning Department.
1. Accommodation of upstream drainage area. A culvert or other drainage facility shall be large enough to accommodate current or existing runoff from the subdivision's entire drainage area, and existing runoff from outside the subdivision. The County Drainage Board or other approved authority shall determine the necessary size of the facility based on the provisions of the required construction standards and specifications assuming conditions of watershed development permitted by the Columbia City Zoning Ordinance, Chapter 8, “The Flood Hazard Overlay District,” and discussed in H-89-2 Model County Subdivision Regulations, T. W. Patterson, Page 49, Paragraph 4.4 (2)(c). Conditions of the watershed which may affect run-off are subsoil type, positive drainage channels, obstructions, and so forth.
2. Description of minor and major drainage systems. The minor system will usually consist of, but not be limited to, storm sewers, drainage ditches, drainage swales, storm inlets or infiltration structures. The minor system shall be designed to handle a 10-year storm. The major system will usually consist of, but is not limited to, roadways, culverts, bridges, and overflow drainage ways. The major system shall be designed to handle a 100-year storm. In the report quantities of water flow shall be noted at each pickup point or culvert. (Reference: Columbia City Zoning Ordinance, 1995, Chapter 8.)
3. The location of existing sub-surface drainage tiles. When developing land for subdivision use, it shall be stated by the owner/developer that existing drainage tiles are viable or non-viable. If they are viable, they may be retained. If they are not viable, they shall be sealed and abandoned or removed. The status of the tiles shall be made a matter of record in the plat file.
4. Lagoons, stormwater ponds, infiltration facilities. Proposals for the inclusion of lagoons, stormwater ponds, or infiltration facilities shall be prepared by a registered professional engineer and shall include data coordinating field tests with design assumptions and estimates of expected annual maintenance costs, if required by the Columbia City Board of Public Works and Safety.
C. Erosion control. Any disturbed or graded area shall be protected from erosion in accordance with the Erosion Control Handbook. This may include de-silting or sediment basins, temporary seeding, mulching, and any other provision necessary to effectively accommodate the increased run-off caused by changed soil and surface conditions during and after development. Areas of concern as listed on the selection matrix contained in the Erosion Control Handbook shall be addressed and control strategies detailed for providing erosion control. Methods selected to control erosion shall be consistent with the Handbook.
D. Retention ponds. The Commission may require retention ponds to regulate the flow of the outfall of storm water. Such ponds shall be protected from erosion in accordance with the Erosion Control Handbook. Such ponds shall be designed and constructed to enable adequate access for maintenance. Retention ponds shall be provided with adequate safeguards against mishaps.
E. Nature of storm water facilities.
1. Location. The applicant may be required by the Commission to carry away by pipe or open ditch any spring or surface water that may exist, either prior to, or as a result of the subdivision. Such drainage facilities shall be located in street/road right-of-way where feasible, or in perpetual, unobstructed easements of appropriate width, and shall be constructed in accordance with the city/county construction standards and specifications.
2. Connection to existing systems. Connection to a state drainage system is allowed only with written approval from the Indiana Department of Transportation. Connections to a county legal drain is allowed only with written approval in accordance with the Indiana Code requirements for legal drains. Connection to a county road ditch is allowed only with written approval of the County Engineer. Connection with city facilities shall require written approval of the Columbia City Board of Public Works and Safety.
3. Accessibility to public storm sewers.
a. When a public storm sewer is accessible, and has the capacity, the applicant shall access the storm water facilities, or if no outlets are adjacent, adequate provision shall be made for the disposal of storm water, subject to the approval of the City/County Engineer or appropriate authority. However, in subdivisions containing lots less than 10,000 square feet in area and in business and industrial districts, underground storm water sewer systems shall be constructed throughout the subdivision and be conducted into an approved outfall. Inspection of the facilities shall be conducted by the City/County Engineer or appropriate authority.
b. Alternative methods of storm drainage may be approved by the City/County Engineer.
4. Effect on downstream drainage areas. The City/County Engineer or appropriate authority shall determine the effect of each proposed subdivision on existing facilities outside the area of the subdivision. County drainage studies, together with such other studies as may be available and appropriate, shall serve as a guide to needed improvements.
Where it is anticipated that the additional flooding, incidental to the development of the subdivision, will overload an existing downstream drainage facility, the Commission may withhold secondary approval of the subdivision until provision (such as a storage facility) has been made by the developer.
No subdivision shall be approved unless adequate drainage from it will be provided to an adequate drainage water course or facility as determined by the City/County Engineer or appropriate authority or an independent, qualified engineering consultant with the cost to be borne by the owner/developer.
5. Areas of poor drainage. Areas which are not in the flood plain but contain soils which are subject to flooding may be approved for subdivision by the Commission, provided that the subdivider fills the affected area of said subdivision to an elevation sufficient to place building sites and streets two feet above ponding levels.
6. Areas of high seasonal water tables. In areas characterized as having a high seasonal water table as determined by the Whitley County Soil and Water Conservation District, lots shall be limited to slab-type construction unless the Commission determines that appropriate engineering techniques will be applied to alleviate the subsurface problem.
7. Floodway areas. If a subdivision of land is proposed within the flood plain, floodways shall be preserved and not diminished in capacity by filling or obstruction, except as approved, in writing, by the Indiana Department of Natural Resources. No residential building site may be located within the floodway (See Chapter 8, “The Flood Hazard Overlay District” of the Zoning Ordinance). (See Figures 8-1, 8-2.)
8. Floodway fringe areas. Where a subdivision is proposed within an area of the flood plain designated as a floodway fringe, the Commission may approve such subdivision provided that: all streets are elevated sufficiently to be above the regulatory flood elevation; all lots for residential usage have a flood protection grade two feet above the regulatory flood elevation; where provided, water and sanitary sewer facilities are constructed to eliminate contamination of, or by, flood water; and, approval to fill the area from the Indiana Department of Natural Resources has been obtained in writing.
9. Flood plain areas. When a subdivision within an area of the flood plain for which floodway and floodway fringe designations have not been made, the Commission shall not approve such subdivision unless all streets are raised sufficiently to be above the regulatory flood elevation; all lots for residential usage have a flood protection grade of two feet above the regulatory flood elevation; where provided, public water and sanitary sewer facilities are constructed to eliminate contamination of, or by, flood water; and, filling to achieve the above will not raise the level of the regulatory flood elevation more than one-tenth of one foot for that reach of the stream. All filling in the flood plain must be approved in writing by the Indiana Department of Natural Resources.
10. Recording of plats in the flood plain and floodway fringe. All final plats having within their boundaries areas whose elevation is below that of the regulatory flood plain shall show and label the regulatory flood boundary and elevation, as of the date the final plat is drawn, on the final plat for recording with the County Recorder.
F. Natural or constructed drainage watercourse. When a subdivision is traversed by a drainage course, drainage way, channel, or stream, a storm water drainage right-of-way shall be provided, granted or dedicated to the city/county conforming substantially to the lines of such watercourse, and of such width as will be adequate for the purpose of both drainage and maintenance of the right-of-way. Wherever possible, it is desirable that the drainage be maintained by an open channel with landscaped banks and adequate width for maximum potential volume of flow. The Whitley County Drainage Board by State Statute requires up to 75 feet on either side of a legal drain. For purposes of this ordinance, a minimum of ten feet of seeded or otherwise stabilized, land shall be planted in the area horizontal to the side-slope of the drainage way. The Drainage Board, which has responsibility for legal drains, shall be consulted in determining other drainage situations.
G. Preservation of low-lying lands. Low-lying lands along watercourses subject to flooding or overflowing during storm periods, whether or not included for dedication, shall be preserved and retained in their natural state as drainage ways, however, any use of these areas shall be governed by the requirements of Chapter 8, “The Flood Hazard Overlay District, of the Columbia City Zoning Ordinance.
H. Drainage of lots and blocks. Lots and blocks shall be so graded as to eliminate depressions that would accumulate storm water. Grades at building sites shall bear such relationship to roadway and curb grades as to prevent flooding during heavy storms of basement windows or floor levels in the absence of basements. Where deemed necessary, the Commission may require the subdivider to submit working drawings showing contours to which property is to be graded to provide for the requirements of this paragraph.
I. Drainage pipe selection. Pipe used for draining shall be of corrugated metal, concrete, or PVC (Poly Vinyl Chloride) of an approved design, size, and strength to meet the requirements of specific conditions which may be encountered. Culverts on existing streets shall be enlarged wherever necessary by reason of diverted or increased concentration of drainage when determined by the City/County Engineer or appropriate authority. Minimum diameters of pipe to be used shall be as follows:
Roadway cross drains 12” minimum
Entrance culverts 12” minimum
Perforated under drains 8” minimum
J. Storm sewers and the rational method. Storm sewers shall be designed by the rational method. The rational method is a means of computing storm drainage flow rates (Q) by use of the formula Q=CIA, where “C” is a coefficient describing the physical drainage area; “I” is the rainfall intensity, and “A” is the area. The rational method is described in Chapter 3 of the “County Storm Drainage Manual” by Christopher B. Burke, Project for Indiana Counties and Cities, School of Engineering, Purdue University, West Lafayette, May 1981, hereinafter referred to as “Drainage Manual.” A copy of the design computation shall be submitted along with the plans for the storm sewers.
The storm sewer plan requires the approval of the City/County Engineer or appropriate authority.
K. Street drainage. All streets/roads abutting or included within the property to be subdivided shall be provided with drainage systems in accordance with the standards in this ordinance. Prior to the construction of street or alley surfaces and pavements, adequate drainage facilities shall be designed by the subdivider, prepared by a registered professional engineer and approved by the Columbia City Board of Public Works and Safety and/or the County Engineer. A storm drainage analysis based upon a ten-year rainfall shall be used as the basis for the drainage system. A copy of the analysis shall be submitted to the Commission and City/County Engineer or appropriate authority along with the drainage facility plans.
L. Shallow swales. Where curbs and gutters are not provided in the street, shallow swales with low points at least 12 inches below the subgrade of the pavement may be required by the Commission and/or the Columbia City Board of Public Works and Safety.
M. As-built plans. Upon completion of the storm sewer improvement, a minimum of two sets of as-built plans and profiles shall be filed with the Commission, or the appropriate authorities.
(1980 Code, Ch. 154, § 4.08) (Ord. 2001-4, passed 3-27-2001)