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Chapter 13.04

STORMWATER DRAINAGE CONTROL

Sections:
13.04.005    Purpose.
13.04.010    Policy.
13.04.015    Storage and controlled release of stormwater runoff.
13.04.020    Controlled release rate required.
13.04.025    The boards' rights to discretionary decisions.
13.04.030    Record of board decisions.
13.04.035    Special or emergency decisions.
13.04.037    Petition filing fee.
13.04.040    Conflicting ordinances.
13.04.045    Compliance with other ordinances.
13.04.050    Notification of the floodplain management ordinance.
13.04.055    Definitions.
13.04.060    Prior approval required for projects.
13.04.065    Exemptions from plan approval.
13.04.070    Exemptions are subject to statutes and regulations.
13.04.075    Plan approval required to start construction.
13.04.080    Plan approval required to record a plat.
13.04.085    Request by applicant for plan review and approval.
13.04.090    Board approval of drainage plan recorded.
13.04.095    Conditions of drainage plan approval.
13.04.100    Conditions of plan approval remaining in force.
13.04.105    Enforcement of drainage plan approval.
13.04.110    Remedies for violations of the terms of plan approval.
13.04.115    The board and the commissioners may act together.
13.04.120    APC site improvement permits conditioned.
13.04.125    Building permits conditioned.
13.04.130    Phased development of large projects allowed.
13.04.135    Drainage plan--General requirements by policy.
13.04.140    Information submittal and review schedule.
13.04.145    Detailed final drainage plan required.
13.04.150    Preliminary drainage plan allowed.
13.04.155    Approval of preliminary drainage plan limited.
13.04.160    Contents of preliminary drainage plan.
13.04.165    Contents of the final drainage plan.
13.04.170    Final drainage plan layout.
13.04.175    Submittal of a written drainage design report.
13.04.180    Typical cross sections of the drainage facilities.
13.04.185    A site plan required.
13.04.190    Timely review by board of final drainage plan.
13.04.195    Final drainage plan approval.
13.04.200    Recording, storing, and viewing of final approval.
13.04.205    Determination of runoff quantities.
13.04.210    Amount of runoff to be accommodated by various parts ofhe drainage system.
13.04.215    Storm sewer design standards.
13.04.220    Storm sewer--Manning Equation.
13.04.225    Minimum pipe sizing.
13.04.230    Storm sewer grade.
13.04.235    Alignment.
13.04.240    Manholes.
13.04.245    Pipe easements.
13.04.250    Inlets.
13.04.255    Workmanship.
13.04.260    Materials.
13.04.265    Material specifications.
13.04.270    Minimum cover over storm sewer pipe and culverts.
13.04.275    Integrity of the storm sewer system.
13.04.280    Attachments and references in Section 13.04.505.
13.04.285    Materials and methods other than included herein.
13.04.290    Installation of nonconforming materials shall constitute a misrepresentation.
13.04.295    Culverts, bridges, pipes, and other structures in, near, or crossing regulated drains.
13.04.300    Inspection of storm sewer system installation.
13.04.305    Open channel design standards.
13.04.310    Open channel--Manning's equation.
13.04.315    Channel cross section and grade.
13.04.320    Maintenance of designed ditch grade and condition.
13.04.325    Period ditch inspections.
13.04.330    Ditch condition responsibility of property owner.
13.04.335    Order to remove obstruction or restore condition.
13.04.340    Remedy for improper or untimely repairs.
13.04.345    Waterway stabilization and cover.
13.04.350    Grass mix matched to site conditions.
13.04.355    Timely channel seeding.
13.04.360    Erosion control by percentage of grade.
13.04.365    Low flow troughs in wide bottom channels.
13.04.370    Trickle troughs in wet bottom channels.
13.04.375    Vee-shaped channels.
13.04.380    Concrete channel liners to have under-baffles.
13.04.385    Open channel side slopes.
13.04.390    Channel stability.
13.04.395    Channel easements.
13.04.400    Structures appurtenant to drainage channels.
13.04.405    Stormwater detention.
13.04.410    Acceptable detention methods.
13.04.415    Design storm.
13.04.420    Allowable release rate.
13.04.425    Upstream flow through drainage system.
13.04.430    Determination of storage volume--Rational method.
13.04.435    Determination of storage volume--Other methods.
13.04.440    General detention/retention basin design requirements.
13.04.445    Rooftop stormwater storage.
13.04.450    Parking lot stormwater storage.
13.04.455    Financial responsibility for facility construction.
13.04.460    Responsibility for drainage facility maintenance.
13.04.465    Joint development of control systems.
13.04.470    Installation of control systems.
13.04.475    Certified "as-built" plans required.
13.04.480    Changes in plan.
13.04.485    Determination of impacted drainage areas.
13.04.490    Other requirements.
13.04.495    Disclaimer of liability.
13.04.500    Corrective action.
13.04.505    Attachments and reference material.

Section 13.04.005    Purpose.

    A.    To Reduce or Prevent Flood Hazard. To reduce the hazard to public health and safety caused by excessive stormwater runoff which may result when land use changes from agricultural and other nonurban land uses to more urbanized land uses.
    B.    To Reduce or Prevent Flood Damage. To reduce or prevent damage to public and private property, including existing streams, drainage channels, and stormwater drainage facilities which may be caused by excessive stormwater runoff resulting during and after land development.
    C.    To Protect and Conserve Resources. To protect and conserve water and land resources by implementing beneficial design features and conservation techniques.
    D.    To Promote Economic Development. To promote orderly economic development and resource use. (Ord. dated 10/31/94 § 100)


Section 13.04.010    Policy.
    A.    Drainage Plan Required. It is the policy of the board of county commissioners of Vanderburgh County, Indiana, hereinafter referred to as the commissioners, that an engineered drainage plan be submitted to the Vanderburgh County drainage board, hereinafter referred to as the drainage board, for any new development, redevelopment, new construction, addition to existing construction, or other land disturbing activity located within the commissioners' and/or the drainage board's jurisdiction which shall result in the addition of impervious surfaces exceeding a total of ten thousand (10,000) square feet.
    B.    Subject Development Defined as Project. Any new development, redevelopment, new construction, additional construction, or other land disturbing activity which shall result in the addition of impervious surfaces totaling over ten thousand (10,000) square feet, hereinafter shall be called a project.
    C.    Drainage Plan Submittal. The engineered drainage plan for a project shall be submitted, in triplicate, to the Vanderburgh County surveyor, Room 325 Civic Center Complex, 1 Martin Luther King Blvd., Evansville, IN 47708, no later than two full weeks prior to the drainage board meeting at which the engineered drainage plan is to be presented.
    D.    Drainage Plan Review Route. The Vanderburgh County surveyor, hereinafter referred to as the surveyor, will determine the route of review, in accordance with this chapter, for an engineered drainage plan, hereinafter referred to as the drainage plan submitted for a project. (Ord. dated 10/31/94 § 200)


Section 13.04.015    Storage and controlled release of stormwater runoff.
    A.    It is the policy of the drainage board that the drainage plan for certain projects shall include provisions for the storage and controlled release of excess stormwater runoff, unless such controlled release specifically is waived due to the direct discharge of stormwater into a major waterway such as Pigeon Creek, or the Ohio River; or into a secondary waterway at a point of study where direct discharge has been determined to be of benefit to the tributary watersheds, and tributary waterways.
    B.    Projects which shall be subject to the requirement for storage and controlled release of excess stormwater runoff include: 1.    Major Subdivisions. All new major subdivisions as defined in Title 16 of this code, which major subdivisions are shown to discharge an amount of stormwater in addition to that which is discharged prior to new development.
2.    Minor Subdivisions—C-0 Through M-3. All new minor subdivisions as defined in Title 16 of this code, which minor subdivisions are zoned for commercial use, or for industrial use.
3.    Certain Residential Parcels. Any new "parcelization" as defined in Title 16 of this code, on which parcel residential development will disturb five acres or more of land surface, and/or add a total of one acre or more of impervious surfaces.
4.    All Commercial and Industrial parcels. All "parcelizations" as defined in Title 16 of this code, which parcels are zoned for commercial use, or are zoned for industrial use.
5.    Certain Other Projects. Any project for which the drainage board, the commissioners, or the Vanderburgh County surveyor shall require or recommend storage and controlled release of stormwater runoff due to the project's location within:
a.    The East Side Urban Drainage Watershed;
b.    The watershed of a regulated drain;
c.    An impacted drainage area;
d.    The North U.S. 41 Industrial Corridor. 6.    Impacted drainage area defined. An impacted drainage area is an area defined, declared, and mapped by the drainage board which area is unlikely to be easily drained because of one or more factors including but not limited to history of flooding, soil type, topography, land use, lack of adequate drainage outlet, location in a floodplain, location within seventy-five (75) feet either side of a regulated drain, or location within a watershed of an overburdened waterway, drain or system of drains. (Ord. dated 10/31/94 § 201) a. Being the Boundary of Lands lying generally within one and one half mile either side of North U.S. Highway 41 and draining into the Pond Flat System of Regulated Drains of Vanderburgh County, Indiana; and more particularly described as follows: 1.    Beginning on the South Line of Section Six (6), Township Five (5) South, Range Ten (10) West at a point approximately Six Hundred Seventy (670.0) feet East of the Southwest Corner thereof and in the intersection of Inglefield Road and Darmstadt Road;
2.    Thence Northwardly along Darmstadt Road approximately Two Thousand (2,000.0) feet to its intersection with Princeton Road;
3.    Thence continuing Northwardly along Princeton Road to the Vanderburgh/Gibson County Line and the North Line of Section Nineteen (19), Township Four (4) South, Range Ten (10) West at a point approximately Fifteen Hundred Fifty (1,550.0) feet East of the Northwest Corner thereof;
4.    Thence East and along said County Line to its intersection with Old State Road on the North Line of Section Twenty-one (21), Township Four (4) South, Range Ten (10) West a point approximately Twenty-three Hundred (2,300.0) feet West of the Northeast Corner thereof;
5.    Thence Southwardly and Southwestwardly along Old State Road to its intersection with Inglefield Road and the South Line of Section Five (5), Township Five (5) South, Range Ten (10) West at a point approximately Fourteen Hundred (1,400.0) feet West of the Southeast Corner thereof.
6.    Thence West along Inglefield Road and the Point of Beginning; and containing lands draining into the Pond Flat System of Regulated Drains in Vanderburgh County, Indiana which lands are experiencing rapid industrial and commercial development causing accelerated and greater cumulative storm water runoff into said Regulated Drains.
i. Projects as defined in Section 13.04.010 of the Vanderburgh County Code and subject to the requirement for storage and controlled released of storm water as defined in Sections 13.04.015 (B) 1-5 of the Vanderburgh County Code, and which Projects lie within or partially within the boundaries of the North U.S. Highway 41 Industrial Corridor Impacted Drainage Area as declared herein by the Vanderburgh County Drainage Board on November 23, 1998, shall be limited to a post development controlled peak release rate of storm water runoff during a one hundred (100) year return period storm to a rate equal to or less than the peak release rate during a ten (10) year return period storm from the same land area prior to its development.
ii. Projects exempted from the requirements of this Section include projects which have had final drainage plan approval prior to December 1, 1998.
iii. A project for which the primary plat and development plans have expired unimplemented with the Area Plan Commission (APC) by virtue of APC’s codes, requirements and policies, and which project requires newly initiated submittal of plats and development plans through APC’s procedures shall be considered a new project subject to the requirements of this Section.  (Amended 11/30/98) b.  The boundary description of the designated Impacted Drainage Area in the rapidly developing unincorporated eastern part of Vanderburgh County, Indiana, is as follows: 1.  Beginning at the intersection of Burkhardt Road and Russell Lloyd Expressway;
2.  Thence North along the centerline of Burkhardt Road to its intersection with Old Boonville Highway;
3.  Thence Northeasterly along the centerline of Old Boonville Highway to its intersection with Telephone Road;
4.  Thence East along the centerline of Telephone Road to the Warrick County line;
5.  Thence South along said County line to the center of said Lloyd Expressway;
6.  Thence West along the center of said Lloyd Expressway to its intersection with Burkhardt Road at the Point of Beginning; and containing lands draining into the Eastside Urban System of Regulated Drains in Vanderburgh County, Indiana, which lands are experiencing rapid industrial and commercial development causing accelerated and greater cumulative storm water runoff into said Regulated Drains.
i.  Projects as defined in Section 13.04.010 of the Vanderburgh County Code and subject to the requirement for storage and controlled release of storm water as defined in Sections 13.04.015(b)1-5 of the Vanderburgh County Code, and which Projects lie within or partially within the boundaries of the unincorporated eastern part of Vanderburgh County Impacted Drainage Area as declared herein by the Vanderburgh  County Drainage Board on the 20th day May, 2002, shall be limited to a post development controlled peak release rate of storm water runoff during a one hundred (100) year return period storm to a rate equal to or less than the peak release rate during a ten (10) year return period storm from the same land area prior to its development.
ii.  Projects exempted from the requirements of this Section shall include all subdivisions recorded prior to adoption of this Ordinance CO.05.02.006 and commercial and industrial projects which have had final drainage plan approval prior to June 1, 2002.
iii.  A project for which the primary plat and development plans have expired unimplemented with the Area Plan Commission (APC) by virtue of APC's codes, requirements and policies, and which project requires newly initiated submittal of plats and development plans through APC's procedures shall be considered a new project subject to the requirements of this Section. (Amended 5/20/02)
(13.04.015, Amended, 05/20/2002; Manual, Amended, 12/10/1998)


Section 13.04.020    Controlled release rate required.
    Projects required to store excess stormwater runoff shall be required to release the stored stormwater at a controlled release rate equal to or less than that established in this section.
    A.    Release Rate Established. The post development controlled peak release rate of stormwater runoff during a twenty-five (25) year return period storm from a project required to detain excess stormwater runoff shall not exceed the peak release rate during a ten (10) year return period storm from the same land area prior to its development.
    B.    Storage and Release Rate Calculations. 1.    The predevelopment release rates and post development storage rates and controlled release rates of stormwater runoff shall be calculated using the methods, factors, and charted data specified by, supplied as a part of, attached to, or referenced by this chapter.
2.    Methods, factors, and data other than those referred to in subsection (B)(1) of this section shall have prior approval of the drainage board before submittal as a part of a proposed drainage plan.     C.    Storage Calculation Form Provided. 1.    Form 800, which shall be used to determine storage volumes, is provided in Section 13.04.505, at the end of this chapter.
2.    Form 800 shall be completed and submitted with the drainage plan, using the rainfall data and runoff coefficients contained in Section 13.04.205 of this chapter, and/or addenda hereto. (Ord. dated 10/31/94 § 202)


Section 13.04.025    The boards' rights to discretionary decisions.
    Because topography, soil types, field conditions, and the availability and adequacy of outlets for stormwater runoff vary with almost every site, the requirements for stormwater drainage tend to be a unique matter for each project; therefore, the drainage board and the county commissioners retain the right to make discretionary decisions on an individual basis.
    A.    Discretionary Decisions. Discretionary decisions may include, but shall not be limited to, the exemption of certain projects from the requirements to detain excess stormwater runoff, in part or totally, and other decisions within the parameters of this chapter, based upon the purpose and the policy of this chapter as stated in Sections 13.04.005 and 13.04.010.
    B.    Technical Advisors to the Boards. The drainage board and the county commissioners shall authorize and empower certain technical advisors including: 1.    The Vanderburgh County surveyor;
2.    The Vanderburgh County highway engineer;
3.    The Vanderburgh County soil and water conservation district.     C.    Technical Advisors' Powers. The drainage board and the county commissioners shall empower their technical advisors as follows: 1.    To make reviews of submitted plans and supporting data;
2.    To make recommendations to the drainage board and the county commissioners with regard to such reviews; and to make other reports when so ordered by the boards;
3.    To make periodic inspections before, during, and after completion of a project; and to report findings to the drainage board and the county commissioners;
4.    To act on behalf of the drainage board and the county commissioners when so authorized, or by ordinance.     The drainage board encourages and advises anyone with an interest in a project to contact the technical advisors named above at the earliest possible time during the planning stage of the project. (Ord. dated 10/31/94 § 203)


Section 13.04.030    Record of board decisions.
    A.    Decisions by the drainage board and the county commissioners with regard to this chapter shall be made only during regular or special meetings of the drainage board, or during regular or special meetings of the county commissioners.
    B.    Records of actions taken by the drainage board, and/or the county commissioners with regard to this chapter shall be made.in the appropriate edition of the minutes of each board's meetings. (Ord. dated 10/31/94 § 204)


Section 13.04.035    Special or emergency decisions.
    A.    In special or emergency circumstances where actions must be taken quickly in order to enforce the purposes, the policies, or other requirements of this chapter, the drainage board, the county commissioners, or their duly authorized representatives may make decisions, or take actions outside of board meetings.
    B.    Special or emergency decisions and actions of the drainage board, the county commissioners, and/or their authorized representatives shall be recorded in the appropriate edition of the minutes of each board's meetings. (Ord. dated 10/31/94 § 205)


Section 13.04.037    Petition filing fee.
    A.    That I.C. 36-9-27.4-1, et seq. governs what action the drainage board may take with respect to petitions filed with the drainage board concerning the removal of an  obstruction from a drain or natural surface watercourse.
    B.    That pursuant to I.C. 36-9-27.4-11, a $100.00 filing fee shall be paid to county by a Petitioner who files a petition with the drainage board seeking the removal of an obstruction under I.C. 36-9-27.4-1, et seq.  Such filing fee shall be submitted to the drainage board located in Room 305, Civic Center Complex in Evansville, Indiana at the time of the filing of the Petition.

(04/07/1997, Added, 04/07/1997)


Section 13.04.040    Conflicting ordinances.
    The provisions of this chapter shall be deemed as additional requirements to minimum standards required by other ordinances of Vanderburgh County, Indiana; and in the case of conflicting requirements, the most restrictive requirements shall apply. (Ord. dated 10/31/94 § 300)


Section 13.04.045    Compliance with other ordinances.
    In addition to the requirements of this chapter, compliance with the requirements set forth in other applicable ordinances with respect to submission and approval of preliminary and final subdivision plats, improvement plans, building and zoning permits, inspections, appeals, variances, and similar matters; and compliance with applicable state and federal laws and regulations shall be required. (Ord. dated 10/31/94 § 400)



Section 13.04.050    Notification of the floodplain management ordinance.
    The Floodplain Management Ordinance of Vanderburgh County, Indiana contains certain requirements applicable to projects subject to this chapter. (Ord. dated 10/31/94 § 401)


Section 13.04.055    Definitions.
    As used in this chapter:
    "Applicant" means the person, persons, partnership, corporation, or other private entity, their heirs or assigns who shall apply to the board for drainage plan approval.
    "Board" or "drainage board" means the Vanderburgh County drainage board; except where "boards" refers to both boards.
    "County commissioners" or "commissioners" means the board of county commissioners of Vanderburgh County, Indiana.
    "Detention basin" means a facility constructed to restrict the flow of stormwater to a prescribed maximum rate, and to detain concurrently the excess waters that accumulate behind the controlling outlet.
    "Drainage area" or "watershed area" means the land area which stormwater is collected from, conveyed through, and/or carried off from by a drainage system.
    "Dry bottom detention basin" or "dry basin" means a basin designed to drain completely dry after providing its planned stormwater storage function.
    "Duration" or "storm duration" means the time period, given in hours or minutes, of a rainfall event.
    "Engineer" or "county engineer" means the Vanderburgh County highway engineer, or duly appointed representative(s).
    "Flood elevation" means the vertical limits of elevation at all locations delineating the maximum level of high waters for a flood of a given return period.
    "Floodplain" means the area adjoining a river or stream which has been or may be covered by flood- waters; and comprising the regulatory floodway and floodway fringe.
    "Floodway" or "regulatory floodway" means the channel of a river or stream plus those portions of the floodplain adjoining the channel which are required to efficiently carry and discharge the peak flow of the one hundred (100) year flood.
    "Outfall" or "outlet" means the point or structure at which the stormwater discharges from the system or a part thereof.
    "Peak flow" means the maximum rate of flow of water at a given point in the system from a predetermined storm.
    "Project" means any new development, redevelopment, new construction, reconstruction, or land disturbing activity which creates an additional ten thousand (10,000) square feet of impervious surface, or disturbs five acres or more of land surface, and is regulated by this drainage chapter.
    "Rainfall intensity" means the cumulative depth of rainfall occurring over a given duration expressed in inches per hour.
    "Regulated drain" or "legal drain" means a drain maintained by the county surveyor and the drainage board under Indiana Drainage Code, IC 36-9-27.
    "Release rate" means the amount of stormwater let go from a given land area or release point in cubic feet per second.
    "Retention basin" or "wet bottom retention basin" means a basin designed to hold a permanent pool of water after providing its planned detention of stormwater runoff.
    "Return period" means the average interval of time within which a given rainfall event will be equaled or exceeded once; expressed in years. Expressed as a percentage of chance, a one hundred (100) year return period storm has a one percent chance of occurring in any one-year period.
    "Runoff coefficient" or "C-factor" means a decimal fraction relating the amount of rain which runs off a parcel of land to the total amount of rain falling. So expressed as a percentage, a C-factor of .25 means that twenty-five (25) percent of the rain falling on a parcel of land can be expected to discharge from that parcel of land.
    "Stormwater drainage facility" means any single part or any combination of parts of a system designed and/or constructed to gather, convey, store and discharge rainfall.
    "Stormwater drainage system" means a complete combination of facilities designed and constructed to gather, convey, store, and discharge rainfall in an orderly fashion.
    "Surveyor" or "county surveyor" means the Vanderburgh County surveyor, or duly appointed representative.
    "SWCD" means the Vanderburgh County soil and water conservation district.
    "Tributary" as an adjective means contributing stormwater from upstream land areas into the storm drainage system.
    "Tributary" as a noun means a stream, waterway, channel, or other conduit of stormwater contributing upstream drainage into the drainage system of a project. (Ord. dated 10/31/94 § 500)



Section 13.04.060    Prior approval required for projects.
    No person, partnership, corporation, or other private entity shall undertake or accomplish a project without prior drainage board approval of a final drainage plan as defined and required by this chapter. (Ord. dated 10/31/94 § 601)


Section 13.04.065    Exemptions from plan approval.
    The approval of a final drainage plan shall not be required by the provisions of this chapter for the following:
    A.    Excavation of cemetery graves;
    B.    Ordinary cultivation or use of agricultural land including tilling, terracing, construction of drains, and construction of tool storage or harvest storage facilities, all so long as such activities do not adversely affect drainage facilities, and so long as such activity shall not change land contours greater than two feet in elevation;
    C.    The planting or tilling of gardens, shrubs, trees, or other common agricultural or landscaping activities so long as such activities do not reduce the conveying or holding capacity of waterways, ponds, and basins; nor interfere with the proper operation and maintenance of regulated, public, or private drainage facilities;
    D.    Filling and grading a basement site after demolition of a structure, to conform to the adjacent terrain;
    E.    A fill less than one foot in depth placed on natural terrain with a slope flatter than four percent, not intended to support a structure, and which does not exceed one thousand (1,000) cubic yards per acre, and does not obstruct the existing drainage pattern;
    F.    Construction of permitted structures within the limits of a project with an approved drainage plan, so long as the construction fully complies with, and does not alter or the approved drainage plan for that project or adversely affect the project's storm drainage system. (Ord. dated 10/31/94 § 602)


Section 13.04.070    Exemptions are subject to statutes and regulations.
    The above exemptions are subject to statutory provisions with regard to regulated drains, and applicable local, state, or federal laws, ordinances, and regulations. (Ord. dated 10/31/94 § 603)


Section 13.04.075    Plan approval required to start construction.
    Final drainage plan approval shall be obtained before physical activity is undertaken to construct the project with the exception of such testing as typically is required to determine procedures or materials to be used. (Ord. dated 10/31/94 § 604)


Section 13.04.080    Plan approval required to record a plat.
    Final drainage plan approval shall be obtained prior to the recording of a plat of a major subdivision, as defined and required by Title 16. (Ord. dated 10/31/94 § 605)


Section 13.04.085    Request by applicant for plan review and approval.
    A.    All requests for drainage plan approval shall be made by the applicant to the drainage board through the county surveyor's office by the presentation to the surveyor of the drainage plan and the supporting data, all in triplicate, by the close of the business day two full weeks prior to the meeting at which approval of the drainage plan shall be sought.
    B.    The three copies of drainage plans and supporting data, shall be distributed by the surveyor as follows: 1.    To the surveyor's drainage plan records;
2.    To the county engineer;
3.    To the soil and water conservation district. (Ord. dated 10/31/94 § 606)

Section 13.04.090    Board approval of drainage plan recorded.
    Drainage plan approval, or disapproval of a drainage plan shall be expressed in a regular meeting or special meeting of the drainage board, and such approval or disapproval shall be recorded in the minutes of the board's meeting. (Ord. dated 10/31/94 § 607)


Section 13.04.095    Conditions of drainage plan approval.
    In order for an applicant to obtain approval of a final drainage plan, the following requirements must be met:
    A.    The applicant shall be eligible under the terms of this chapter to apply for and obtain drainage plan approval.
    B.    The drainage plan and supporting submittals required by this chapter shall have been prepared and submitted in a timely and proper manner in accordance with the provisions of this chapter.
    C.    The drainage plan and supporting submittals shall reflect compliance with the requirements of this chapter, and compliance with any conditions of approval applied to the plan by the drainage board.
    D.    The submitted data shall be gathered, analyzed, assembled into the drainage plan and supporting submittals; and shall be certified, and presented to the drainage board all by a civil engineer or land surveyor regularly engaged in stormwater drainage design, and registered to practice in the state of Indiana.
    E.    An easement has been dedicated to house any off-site drainage facilities if such facilities are required to serve the project's stormwater drainage system.
    F.    The person, persons, partnership, corporation, or other entity to whom approval of the drainage plan is granted must be the person, persons, partnership, corporation, or entity who will be responsible for accomplishing the project for which the drainage plan is developed. (Ord. dated 10/31/94 § 608)


Section 13.04.100    Conditions of plan approval remaining in force.
    A.    In order for the approval of the final drainage plan to remain in force, the following conditions shall be met: 1.    The applicant shall notify the surveyor and the APC site review committee prior to making any modification of the approved drainage plan.
2.    The applicant shall obtain approval of the drainage plan when making a major modification of the plan.     B.    Materials Change Constitutes Major Modification. A change from the materials designated in the approved drainage plan shall constitute a major modification requiring approval by the board.
    C.    Detailed "As-Built" Plans Required. The applicant shall agree to submit, and shall submit within thirty (30) days of completion of the drainage facilities of a project, two complete sets of as-built plans to the surveyor which shall show every detail of the finished installation of all storm water drainage facilities for the completed project.
    D.    Final Inspection After Delivery of "As-Builts." The final inspection of the drainage facilities shall be made only subsequent to the delivery by the surveyor of one set of the as-built plans to the county engineer; and shall be based upon said as-built plans. 1.    The applicant shall install and maintain the street system and the storm drainage system until the project has been completed, or until maintenance of such systems is assumed by others.
2.    The applicant shall agree to remove, and shall remove sediment from, or repair erosion damages to all property where such damage has been caused by the project.
3.    The applicant shall allow the drainage board, or agents of the drainage board, to enter the project to verify compliance with this chapter or to bring the project into compliance with this chapter.
4.    The applicant shall develop methods of maintenance for all drainage facilities, and shall have printed clearly on the plat, and/or other documents of record for the project, the developed methods of maintenance. (Ord. dated 10/31/94 § 609)


Section 13.04.105    Enforcement of drainage plan approval.
    A.    The board shall make inspections, or shall order inspections to be made of a project site to ensure compliance with the requirements of this chapter, and other terms and/or conditions attached to the approval of a drainage plan and/or a street plan.
    B.    The board may deny, withdraw, or suspend approval of a drainage plan if the board determines that: 1.    The requirements of this chapter are not met in full;
2.    Other terms and/or conditions of the approval of a final drainage plan and/or a street plan are violated;
3.    A drainage plan or a street plan or an attached submittal contains a false statement or a misrepresentation;
4.    Some part of a drainage plan or a street plan is not executed in good faith, or is not executed in accordance with the various plans approved by the boards;
5.    A project is undertaken without an approved final drainage plan;
6.    An alteration or a modification is made to a drainage system prior to the completion of a project, which alteration or modification is not documented to or authorized by the board and/or their appointed representative in accordance with the requirements of this chapter. (Ord. dated 10/31/94 § 610)


Section 13.04.110    Remedies for violations of the terms of plan approval.
    The drainage board will take such actions as the  board deems necessary and legal to remedy a violation of the terms and/or conditions of plan approval, or will take such actions as the board deems necessary and legal to bring a project determined not to be in compliance with the requirements of this chapter into such compliance; and such actions of the board may include, but are not limited to:
    A.    Levying a Fine for Violations. Levying a fine equal to not more than one hundred dollars ($100.00) per day per violation determined to exist after thirty (30) days beyond the date on which a notice of the violation was sent by registered mail to the last known address of the party determined by the drainage board to be the party responsible for the violation of the terms and/or conditions of plan approval, and/or to be the party responsible for the condition of the drainage system which is not in accordance with the requirements of this chapter.
    B.    The Fine Shall be Levied Against the Violator. A fine as described in subsection A of this section shall be levied against the party determined by the board to have violated the terms and/or conditions of plan approval, or against the party determined by the board to be the party to have caused the condition of the drainage system which is not in accordance with the requirements of this chapter.
    C.    Disposition of Moneys Collected From Fines. 1.    Moneys collected from fines assessed against properties within residential subdivisions using the Plan "B" method of maintenance as defined in Section 13.04.460 shall be deposited into the Plan "B" repair account created by this chapter and described in said Section 13.04.460.
2.    Moneys collected from fines assessed against properties in projects which are not residential subdivisions using the abovesaid Plan "B" shall be deposited into the general storm drainage account which account is created and described by said Section 13.04.460.     D.    Correcting Violations by Contractual Services. 1.    The drainage board also may contract for work to be accomplished to bring a project, or a part thereof, into compliance with the requirements of this chapter, and/or the terms and conditions of plan approval; and the board shall bill the cost of such work to the property owner upon whose property the work is accomplished.
2.    If the cost of such work as is described in subsection (D)(1) of this section is levied against a property owner, but is not paid by said property owner within ninety (90) days of date of the mailing of the bill, the board shall pay the contractor who accomplished the work from funds as follows: a.    For properties in subdivisions using Plan "B" method of maintenance the payments shall be made from the Plan "B" repair account.
b.    For properties other than those in subdivisions using Plan "B" method of maintenance, the payments shall be made from the general storm drainage account.     E.    The Board May Apply a Tax Lien to Collect Payment. If the board contracts for work to correct a violation as described in subsection D of this section, and the owner of the property upon which the work is accomplished fails to pay for the costs of the work as billed by the board within ninety (90) days of the mailing date of the bill, the board shall apply a tax lien in an amount equal to the cost of the work against the subject property.
    F.    Disposition of Moneys Collected for Contractual Works. All moneys collected from property owners for works contracted by the board to correct violations, whether said monies are collected directly from the property owners or collected through tax liens, shall be deposited into the same repair accounts from which the moneys to pay the costs of the works were withdrawn originally. (Ord. dated 10/31/94 § 611)



Section 13.04.115    The board and the commissioners may act together.
    In the levying of a fine, and/or in the contracting for work to correct violations as described in Section 13.04.110, the drainage board and the county  commissioners may take the actions described in Section 13.04.110 either separately or together, as is recommended to be appropriate by the legal council to the boards. (Ord. dated 10/31/94 § 612)


Section 13.04.120    APC site improvement permits conditioned.
    The area plan commission shall not issue an improvement permit on a project requiring final drainage plan approval until such approval has been expressed by the board. (Ord. dated 10/31/94 § 613)


Section 13.04.125    Building permits conditioned.
    The Vanderburgh County building commissioner shall not allow construction of buildings, or other impervious structures or facilities to commence at the site of a project requiring final drainage plan approval until:
    A.    Such approval has been expressed by the drainage board;
    B.    And all storm drainage facilities are constructed. (Ord. dated 10/31/94 § 614)


Section 13.04.130    Phased development of large projects allowed.
    Large projects may be divided into phases for the purpose of constructing drainage facilities and obtaining permits in accordance with the requirements of this chapter. (Ord. dated 10/31/94 § 615)


Section 13.04.135    Drainage plan--General requirements by policy.
    A.    Unless a project has been exempted from the requirement to submit a drainage plan, the applicant shall provide a detailed drainage plan and supporting submittals in accordance with the provisions of this chapter.
    B.    Unless a project subject to the requirement to detain excess stormwater runoff has been exempted from that requirement, the drainage plan and supporting submittals shall demonstrate clearly that the post development peak rate of stormwater runoff during a twenty-five (25) year return period storm is controlled sufficiently so that it shall not exceed the peak runoff rate from the same project site in its pre-development condition during a ten (10) year return period storm,
    C.    The required computations shall be made using only the methods, factors, charts, and data specified by or supplied within this chapter, or approved for use by the drainage board.
    D.    The critical storm durations used in the submitted computations to design detention storage shall be those durations which require the greatest detention storage.
    E.    Computations for land areas of two hundred (200) acres or less shall be made either by the Rational Method using the runoff coefficients and rainfall data given in this chapter; or by hydrographic techniques, or computer storm drainage modeling methods approved by the drainage board.
    F.    For land areas larger than two hundred (200) acres, hydrographic techniques and computer storm drainage modeling methods approved by the board shall be used.
    G.    All calculations submitted to determine stormwater runoff and storage volumes shall be made by hydrographic techniques and computer modeling methods granted prior approval of the drainage board upon the recommendation of the county surveyor, and/or the county engineer.
    H.    Form 800 as referenced hereinabove shall be the form used for charting and submitting storage volumes when using the Rational Method.
    I.    The HERPIC County Storm Drainage Manual, September 1994 Edition, and the hydrographic techniques and modeling methods contained therein are approved by the board for use in determining stormwater runoff and storage. (Ord. dated 10/31/94 § 701)


Section 13.04.140    Information submittal and review schedule.
    The required drainage plan and supporting data shall be submitted and reviewed by a schedule as follows:
    A.    Regular Drainage Board Meetings. The Vanderburgh County drainage board generally meets on the fourth Monday of each month, unless an official holiday coincides with the fourth Monday, in which case the board generally meets on the Tuesday immediately following the official holiday.
    B.    Special Drainage Board Meetings. 1.    Special meetings of the board outside the regular and advertised annual schedule of board meetings may be requested of the board, or may be called by the board.
2.    Special meetings shall be granted, called, announced, advertised, and held at the discretion of the board and/or the commissioners.
3.    The Vanderburgh County auditor shall provide a schedule of all drainage board meeting dates and times.     C.    Plan Submittal Deadline. 1.    For a drainage plan to be reviewed by the board's technical advisors prior to the regular monthly meeting, and to receive recommendations to the board at that meeting, the drainage plan and supporting data must be submitted in triplicate to the surveyor by the close of business day two full weeks prior to the meeting at which plan approval shall be sought.
2.    Drainage plans and data not submitted two weeks prior to the meeting, as stated above, may be viewed by the board at its discretion; but are liable to come before the board without a positive recommendation, should the technical advisors lack sufficient review time.
3.    Drainage plans will be reviewed by the advisors in the same chronological order in which the plans are received.
4.    The drainage board requires a printed agenda from the auditor submitted no later than noon of the Thursday immediately preceding the drainage board meeting.     D.    Late Submittals Omitted From Agenda. Any plan, or request submitted to the surveyor later than Noon on the Thursday immediately preceding the Board meeting will not appear on the agenda, and may be heard by the drainage board only at its discretion.
    E.    Notification of Insufficiency. Notification of the insufficiency of a drainage plan or other insufficiency of submittal may be issued by the surveyor, or by other technical advisors to the board with explanation of the insufficiency provided to the applicant.
    F.    Viewing of Plan Guaranteed. In the absence of a notification of insufficiency as described in subsection E of this section, any plan timely submitted shall be viewed by the board at its regular monthly meeting, or at a special meeting called for that purpose.
    G.    Additional Time Required for Review—Delayed Review. If additional review time is required beyond that time described above, the applicant will be notified by the authorized representative of the board requiring the additional time with an explanation for the postponement of the presentation of the drainage plan to the board.
    H.    Review Delay for Additional Information. If additional information beyond that submitted with the drainage plan is required by the board or by one or more of the technical advisors the person(s) requiring the additional information shall notify the applicant in a timely fashion as to the information needed and the reason for the additional information.
    I.    Applicant May Protest Delay; or Appeal "Insufficiency." The applicant may protest postponement of presentation of the drainage plan or appeal the notification of insufficiency, by requesting to be put on the agenda at or before noon of the abovesaid Thursday agenda deadline; and then appearing before the drainage board. (Ord. dated 10/31/94 § 702)


Section 13.04.145    Detailed final drainage plan required.
    A comprehensive final drainage plan shall be submitted for each project subject to the provisions of this chapter. The final drainage plan shall be designed to convey stormwater runoff in a safe and orderly fashion and to detain the increased storm water runoff where detention is required. (Ord. dated 10/31/94 § 703)



Section 13.04.150    Preliminary drainage plan allowed.
    Presentation of a preliminary form of the final drainage plan may be allowed when the applicant is in need of approval of a preliminary drainage plan to satisfy certain requirements of the area plan commission (APC), and it can be shown that the complexity of the project prohibits the submittal of the final drainage plan within the time limits set by the APC for plan submittals. (Ord. dated 10/31/94 § 704)


Section 13.04.155    Approval of preliminary drainage plan limited.
    A.    Approval of a preliminary form of the final drainage plan shall not constitute, nor be interpreted as, final approval of the final drainage plan for a project as required herein.
    B.    Permits not Issued on Preliminary Approval. The area plan commission shall not issue a site improvement permit, nor shall the building commissioner issue a building permit, nor shall the owner or developer of a project start construction of a project subject to the requirements of this chapter until the board approves the final drainage plan for the project. (Ord. dated 10/31/94 § 705)


Section 13.04.160    Contents of preliminary drainage plan.
    A.    The contents of the preliminary drainage plan shall include a map based on the most current county planimetric maps, or a topographic map prepared from a more recent aerial photo reconnaissance that provides more accurate data, complete with contour lines, and showing the following: 1.    The extent and area of each watershed affecting the design of the drainage facilities for the project;
2.    The soil types based on the most current information available from the SWCD;
3.    Zone "A" floodplain based on the current FIRM panels;
4.    The existing man-made and natural waterways, ponds, basins, pipes, culverts, and other drainage facilities or features within or affecting the project;
5.    The preliminary layout and design of the streets, and all stormwater drainage facilities, including depressed pavements used to convey or temporarily store overflow from the heavier storms, and all outlets for the storm water drainage facilities;
6.    The existing streams, floodways, and floodplains to be maintained, and new channels to be constructed, their locations, cross sections, profiles, and materials used;
7.    The proposed culverts and bridges to be built, with the specific materials to be used, elevations, waterway openings, and the basis of their design;
8.    Existing detention basins or ponds within the project, or outside the project but affecting it, to be maintained, enlarged, or otherwise altered, together with any new basins or ponds to be built; and their basis of design;
9.    The estimated depth and amount of storage required of the basins and ponds, and their available freeboards;
10.    The estimated location and percentage of impervious surface existing and expected to be constructed at completion of the project;
11.    Any interim plan which is to be incorporated into the project pending its completion according to the final drainage plan.     B.    Notations and Explanations on the Preliminary Plan. All notations necessary to indicate the existing conditions, and the proposed functions of the various features shown thereon; and shall include the following.
    C.    Geographic Orientation Required. A north arrow, scale, location insert, and other information necessary for geographic clarification shall be included on a preliminary plan.
    D.    Data Required to Accompany Preliminary Plan. Descriptive data sufficient to support the feasibility of the preliminary drainage plan with regard to the requirements of this chapter, including calculations of the predevelopment and post development runoff rates using rainfall data supplied herein shall accompany a preliminary drainage plan.
    E.    Recommendation of Preliminary Plans Restricted. No preliminary drainage plan shall be recommended to the drainage board by their technical advisors unless the preliminary drainage plan shall be a workable plan according to the same criteria as, and capable of being incorporated into, a final drainage plan.
    F.    Determination of Sufficiency. The drainage board shall decide the sufficiency of the preliminary drainage plan, and any conditions or additional requirements to be applied to the preliminary drainage plan. (Ord. dated 10/31/94 § 706)


Section 13.04.165    Contents of the final drainage plan.
    The contents of the final drainage plan shall include all the items listed above for a preliminary drainage plan, plus:
    A.    Soils Map. A soils map indicating soils names and their hydrologic classification must be provided for a proposed project.
    B.    Location and Topographic Map. In addition, a location and topographic map must be provided showing the land to be developed, and such adjoining land whose location and topography may affect or be affected by the layout or drainage of the project.
    C.    Contour Intervals. 1.    The contour intervals shown on the topographic map shall be two and one-half feet for slopes less than four percent; and five feet for slopes four percent or greater; or best available;
2.    The location of streams and other stormwater conveyance channels, both natural and man-made; and the vertical and horizontal limits of the one hundred (100) year floodplain, according to FIRM panels, and/or the building commissioner; all properly identified;
3.    The normal shoreline of lakes, ponds, swamps, and basins, their floodplains, and lines of inflow and outflow;
4.    The location of exiting regulated drains, farm drains, inlets and outfalls;
5.    Storm, sanitary, and combined sewers, and outfalls;
6.    Wells, septic tank systems, and outfalls, if any;
7.    Seeps, springs, sinkholes, caves, shafts, faults, or other such geological features visible, or of record;
8.    The limits of the entire proposed project and the limits of the expected extent of land disturbance required to accomplish the project;
9.    The location of the streets, lot lines, and easements;
10.    A scale, preferably one inch equals fifty (50) feet;
11.    An arrow indicating North.     D.    On-Site Bench Mark Required. A bench mark determined by "Mean Sea Level Datum 1929," is required to be located within the project limits. (Ord. dated 10/31/94 § 707)


Section 13.04.170    Final drainage plan layout.
    A.    In addition to the requirements listed for a preliminary drainage plan, the final drainage plan shall depict the following: 1.    The extent and area of each watershed tributary to the drainage facilities within the project;
2.    The final layout and design of proposed storm sewers, their inlet and outfall locations and elevations, the receiving streams or channels; all with the basis of their design;
3.    The location and design of the proposed street system, including depressed pavements used to convey or detain overflow from storm sewers and over-the-curb runoff resulting from heavier rainstorms, and the outlets for such overflows; all with their designed elevations;
4.    The locations, cross sections, and profiles of existing streams, floodways, and floodplains to be maintained, and the same for all new channels to be constructed;
5.    The materials, elevations, waterway openings, size, and basis for design of the proposed culverts and bridges;
6.    Existing ponds and basins to be altered, enlarged, filled, or maintained; and new ponds, basins, swales, to be built, and the basis of their design;
7.    The location and percentage of impervious surfaces existing and expected to be constructed;
8.    The material types sizes slopes grades and other details of all the stormwater drainage facilities;
9.    The estimated depth and amount of storage required in the new ponds or basins, the freeboard above the normal pool and highwater pool of wet basins, and details of the emergency overflows from the basins;
10.    For all controlled release basins, a plot or tabulation of the storage volumes with corresponding water surface elevations, and a plot or tabulation of the basin outflow rates for those water surface elevations;
11.    The location of any applicable "impacted drainage areas" or other areas designated to remain totally undisturbed, natural, or for common and/or recreational use.     B.    Protection of Structures From One Hundred Year Flooding. All structures to be occupied as residences or businesses shall have finished floor elevations two feet above the high water calculated to occur during a one hundred (100) year return period storm for the subject building site; and the required floor elevations shall be depicted on the plan drawings for such affected sites. (Ord. dated 10/31/94 § 708)


Section 13.04.175    Submittal of a written drainage design report.
    The final drainage plan shall be accompanied by a written report containing the following:
    A.    Any significant stormwater drainage problems existing or anticipated to be associated with the project;
    B.    The analysis procedure used to identify and evaluate the drainage problems associated with the project;
    C.    Any assumptions or special conditions associated with the use of the procedures, especially hydrologic or hydraulic methods, used to identify and evaluate drainage problems associated with the project;
    D.    The proposed design of the drainage control system;
    E.    The results of the analysis of the proposed drainage control system showing that it does solve the project's identified and anticipated drainage problems;
    F.    A detailed description, depiction, and log of all hydrologic and hydraulic calculations or modeling, and the results obtained thereby; together with the input and output files for all computer runs;
    G.    Maps showing individual drainage areas within the project subdivided for use in the analysis thereof. (Ord. dated 10/31/94 § 709)


Section 13.04.180    Typical cross sections of the drainage facilities.
    One or more typical cross sections must be provided for each existing and proposed channel, basin, pond, or other open drainage facility, which cross sections:
    A.    Must show the elevation of the existing land immediately adjacent to all drainage facilities;
    B.    Must show the high water elevations adjacent to all waterways and impoundments as expected from the one hundred (100) year storm in relationship to permanent structures (Ord. dated 10/31/94 § 710)


Section 13.04.185    A site plan required.
    A site plan must be provided, drawn to scale, showing the overall site dimensions with existing and proposed drainage facilities, streets, parking lots, buildings and other existing or proposed improvements. (Ord. dated 10/31/94 § 711)


Section 13.04.190    Timely review by board of final drainage plan.
    The drainage board's consideration of the final drainage plan will not be continued greater than two consecutive regular meetings, including the first hearing of the final drainage plan, without due cause shown, such as insufficiency of plan, conflict between plans, or other discrepancy, omission, or defect of the plan(s), or unless the applicant consents to a continuance. (Ord. dated 10/31/94 § 712)


Section 13.04.195    Final drainage plan approval.
    Any drainage plan in compliance with the requirements of this chapter and with conditions and requirements applied by the drainage board shall be approved by the drainage board. (Ord. dated 10/31/94 § 713)


Section 13.04.200    Recording, storing, and viewing of final approval.
    A.    Drainage plan approval shall be recorded in the minutes of the meeting at which the approval occurs.
    B.    The drainage board's minutes are kept by the Vanderburgh County auditor, and may be viewed at the auditor's office. (Ord. dated 10/31/94 § 714)


Section 13.04.205    Determination of runoff quantities.
    A.    Computing Rates of Stormwater Runoff. The stormwater runoff quantities shall be computed for the area of the project, plus the area of the watershed flowing into the project. The quantity of runoff which is generated as the result of a given rainfall intensity may be calculated as follows in this section.
    B.    The Rational Method. 1.    For areas up to and including two hundred (200) acres, the Rational Method may be used, providing the runoff coefficients and rainfall data given in this chapter are employed.
2.    In the Rational Method, the peak rate of runoff, "Q," in cubic feet per second (cfs) is computed as: Q  =  C I A
a.    Where: "C," or the runoff coefficient, is the ratio of peak runoff rate to average rainfall rate over the entire watershed during the time of concentration.
b.    Where: "I" = the rainfall intensity in inches per hour.
c.    Where: "A" = the tributary drainage area in acres. 3.    Guidance to selection of the runoff coefficient "C" is provided by Table 13.04.205-A and Table 13.04.205-B, which show values for different types of surface characteristics.
4.    The composite "C" value used for a drainage area with various surface types shall be the weighted average value for the total area calculated from a breakdown of individual areas having different surface types.
Table 13.04.205-A

UNDEVELOPED RUNOFF
COEFFICIENTS (Cu)

Surface Type—Woodland, Turfed Meadows, Rough Pasture, Fallow Brush.

    Slope:
    Less than 2%     C    =    0.12
    2% to 5%            C    =    0.24
    5+% to 10%        C    =    0.36
    Over 10%           C    =    0.48

Surface Type—Cultivated Fields.

    Slope:
    Less than 2%     C    =    0.20
    2% to 5%            C    =    0.35
    5+% to 10%        C    =    0.50
    Over 10%           C    =    0.65


Table 13.04.205-B

DEVELOPED RUNOFF
COEFFICIENTS (Cd)

Surface Type—Pavement, Rooftop, Other Impervious Surfaces:

    Slope:
    Less than 2%     C    =    0.92
    2% to 5%            C    =    0.94
    5+% to 10%        C    =    0.96
    Over 10%           C    =    0.98

Surface Type—Lawns with Turf.

    Slope:
    Less than 2%      C    =    0.15
    2% to 5%             C    =    0.25
    5+% to 10%        C    =    0.40
    Over 10%            C    =    0.55

Surface Type—All Water Surfaces, Basins, Ponds and Lakes.

                C     =     1.00

    C.    Determination of Rainfall Intensity. 1.    "I" or rainfall intensity shall be determined from data interpolated from the weather bureau rainfall frequency curves, which data is shown in Table 13.04.205-C.
2.    When using the Rational Method, the storm duration is equal to the "time of concentration" (tc), which is the travel time from the most hydraulically distant point to contribute to the point under consideration.
3.    The travel time to a given location shall be the sum of the overland flow time, the gutter flow time, and the sewer flow time.
4.    The time of concentration (tc) at the point under consideration is the longest travel time when all paths are considered.
5.    In terms of sewer design practice, the inlet time for each sub-basin must be compared to the travel time from all upstream sub-basins, and the longer time selected as the local time of concentration.
6.    The flow time in the storm sewers may be estimated by the distance in feet divided by the velocity of flow in feet per second (fps).
7.    The velocity shall be determined by the Manning Formula.
8.    Inlet time is the combined time required for the runoff to reach the inlet of the storm sewer.
9.    Inlet time includes overland flow time, and flow time through established surface drainage channels, and sheet flow across such areas as lawns, fields, and parking lots.
10.    Commonly used formulas employed in the determination of the overland flow time are Ragan (1972), Kerby (1959), Federal Aviation Agency, and Izzard (1946.)     D.    Rates for Acreage in Excess of Two Hundred Acres. 1.    The runoff rate for areas in excess of two hundred (200) acres shall be determined by hydrologic methods and computer modeling which have received prior approval of the drainage board.
2.    Hydrologic methods and computer modeling methods which receive board approval will be attached to the ordinance codified in this chapter as addenda.
     Table 13.04.205-C
    RAINFALL INTENSITY-DURATION-FREQUENCY
    TABLE FOR EVANSVILLE
    Intensity in Inches Per Hour

                    Storm Return Period in Years
Storm Duration    5        10        25        50        100
5 minutes        6.063        6.625        7.208        7.936        8.469
10 minutes        4.863        5.380        5.925        6.616        7.126
15 minutes        4.029        4.515        5.033        5.697        6.194
30 minutes        2.837        3.226        3.646        4.194        4.608
60 minutes        1.549        1.819        2.078        2.412        2.663
2 hours            1.053        1.230        1.400        1.620        1.785
3 hours            0.774        0.899        1.019        1.175        1.291
4 hours            0.632        0.736        0.836        0.965        1.062
5 hours            0.524        0.606        0.684        0.785        0.861
6 hours            0.453        0.522        0.589        0.676        0.741
7 hours            0.399        0.459        0.516        0.591        0.647
8 hours            0.358        0.412        0.463        0.530        0.581
9 hours            0.323        0.370        0.415        0.472        0.516
10 hours        0.297        0.339        0.379        0.431        0.470
11 hours        0.276        0.314        0.351        0.399        0.435
12 hours        0.259        0.296        0.331        0.376        0.410
13 hours        0.245        0.280        0.314        0.357        0.390
14 hours        0.233        0.267        0.299        0.341        0.372
15 hours        0.220        0.252        0.281        0.320        0.349
16 hours        0.209        0.238        0.266        0.302        0.329
17 hours        0.198        0.225        0.251        0.284        0.310
18 hours        0.189        0.215        0.240        0.272        0.296
19 hours        0.181        0.206        0.299        0.260        0.282
20 hours        0.175        0.199        0.222        0.251        0.273
21 hours        0.169        0.193        0.215        0.244        0.266
22 hours        0.164        0.187        0.208        0.236        0.257
23 hours        0.160        0.181        0.202        0.229        0.250
24 hours        0.154        0.174        0.194        0.219        0.239
24 hours        0.149        0.168        0.187        0.212        0.230
26 hours        0.143        0.162        0.180        0.204        0.221
27 hours        0.139        0.156        0.174        0.196        0.212
28 hours        0.135        0.152        0.169        0.190        0.206
29 hours        0.132        0.149        0.165        0.186        0.201
30 hours        0.129        0.145        0.161        0.182        0.197
31 hours        0.126        0.142        0.158        0.178        0.193
32 hours        0.122        0.138        0.153        0.173        0.188
33 hours        0.119        0.135        0.149        0.168        0.183
34 hours        0.116        0.131        0.146        0.164        0.178
35 hours        0.113         0.128        0.142        0.160        0.174
36 hours        0.111        0.125        0.139        0.157        0.171

    Table 13.04.205-D

    HUFF CURVE COORDINATES
    Percent Precipitation Values
    Evansville Station
    Four Quartiles
                               
                                                   10% Probability                 

    Storm Time         Qt. 1    Qt. 2    Qt. 3    Qt.4
    0%            00.00    00.00    00.00    00.00
    10%            45.44    15.56    13.64    17.14
    20%            69.63    32.50    23.62    28.75
    30%            79.14    60.00    30.83    37.50
    40%            86.09    77.27    40.00    43.40
    50%            89.09    88.72    53.85    50.00
    60%            92.85    93.94    77.62    55.17
    70%            95.00    95.77    90.33    62.55
    80%            96.97    97.50    96.30    83.33
    90%            98.78    98.98    98.78    96.92
    100%            100.00    100.00    100.00    100.00




    20% Probability

    10%            36.67    12.28    10.00    13.23
    20%            60.00    27.27    18.67    23.38
    30%            71.15    49.40    28.86    30.41
    40%            78.57    69.38    35.19    37.61
    50%            85.19    82.31    48.08    44.12
    60%            88.57    89.38    70.38    51.43
    70%            92.35    93.29    87.82    60.00
    80%            95.23    96.12    94.49    79.05
    90%            97.96    98.40    98.09    95.00

    30% Probability
    10%            30.00    9.86    8.00    10.00
    20%            52.80    22.98    16.36    20.00
    30%            66.67    42.77    24.00    26.79
    40%            74.19    62.50    32.00    33.67
    50%            80.00    77.14    44.44    40.44
    60%            85.45    85.00    67.34    47.65
    70%            85.45    85.00    67.34    47.65
    80%            89.39    90.73    84.21    57.14
    90%            93.55    94.73    92.50    75.83

    40% Probability

                Qt. 1    Qt. 2    Qt. 3    Qt.4
    10%            27.00    8.00    6.45    8.00
    20%            48.48    20.00    13.08    16.64
    30%            60.74    37.20    20.29    23.75
    40%            69.83    57.93    28.81    30.00<