(A) Performance criteria. Prior to design, applicants are required to consult with the administering authority to determine if they are subject to additional storm water design requirements. Unless judged by the administering authority to be exempt or granted a waiver, the following performance criteria shall be addressed for storm water management at all sites.
(1) All site designs shall establish storm water management practices to control the peak-flow rates of storm water discharge associated with specified design storms, and to reduce the generation of storm water.
(2) These practices should seek to utilize pervious areas for storm water treatment, and to infiltrate storm water runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas, to the maximum extent practical, to provide treatment for both water quality and quantity.
(3) Natural topography and land cover features, such as natural swales, natural depressions, native soil-infiltrating capacity, and natural groundwater recharge areas, shall be preserved and used, to the extent possible, to meet the requirements of this section.
(B) Minimum requirements.
(1) Quantity calculations - estimated.
(a) Design of off-site runoff, on site conveyance network, and street drainage shall meet the minimum requirements set forth in the current edition of the Lowell Town Standards adopted by the Lowell Town Council;
(b) Lot drainage.
1. Minimum lot grades.
a. Primary lot. The PRIMARY LOT is that portion of the lot between the frontage road and the rear face of the residence or building. The minimum grades permissible in the primary lot are as follows:
Type of grade | Recommended | Minimum |
Surface | 2% | 1% |
Lot Line Swale | 2% | 1% |
Cross Lot Swale | 1% | 0.5% |
b. Secondary lot. The SECONDARY LOT is that portion of the lot between the rear property line and the rear face of the residence or building. The minimum grades permissible in the secondary lot are as follows:
Type of grade | Recommended | Minimum |
Surface | 1.5% | 1% |
Lot Line Swale | 1% | 0.5% |
Cross Lot Swale | 1% | 0.5% |
Surface Over Septic Fields | 2% | 1% |
2. Common swales.
a. A
COMMON SWALE is one that serves as a drainage course, carrying the runoff from two or more lots or properties. (Side lot line swales may be excepted from this requirement.)
(2) Quality calculations - actual: storm water quality requirements (treatment of the WQV upon development completion). The WATER QUALITY VOLUME is the storage needed to capture and treat the runoff from the first inch of rainfall. In numerical terms, it is equivalent to an inch of rainfall multiplied by the volumetric runoff coefficient (RV) and the site area.
(a) The following equation is used to calculate WQV (in acre-feet):
WQV = (P) (RV) (A)
where:
WQV = water quality volume (acre-feet)
P = one inch of rainfall
RV = 0.05 + 0.009 (I) where I is the percent impervious cover
A = area in acres
(3) Impact drainage areas - special requirements in protective areas.
(a) The administering authority is authorized, but is not required, to classify certain geographical areas as impact drainage areas, and to enact and promulgate regulations, which are generally applied. In determining impact drainage areas, the administering authority shall consider such factors as topography, soil type, capacity of existing regulated drains, and distance from adequate drainage facilities. In addition to specific impact drainage areas classified by the administering authority, the following areas are hereby designated as impact drainage areas, unless good reason for not including them is presented and approved by the Storm Water Management Board:
1. A floodway, floodway fringe or floodplain boundary as designated by the Indiana Department of Natural Resources.
2. A flood boundary area or floodway as designated by the Federal Emergency Management Agency National Flood Insurance Program.
3. Land within 75 feet of each bank of any open channel, regulated drain.
4. Land within 75 feet of the centerline of any regulated drain tile.
(b) Impervious surfaces shall be kept out of the protective area to the maximum extent practicable.
(c) Where land-disturbing construction activity occurs within a protective area, and where no impervious surface is present, adequate sod or self-sustaining vegetative cover of 70% or greater shall be established and maintained. The adequate sod or self-sustaining vegetative cover shall be sufficient to provide for bank stability, maintenance of fish habitat, and filtering of pollutants from upslope overland flow areas under sheet flow conditions. Non-vegetative materials, such as rock riprap, may be employed on the bank as necessary to prevent erosion, such as on steep slopes or where high velocity flows occur.
Note to users: It is recommended that seeding of non–aggressive vegetative cover be used in the protective areas. Vegetation that is flood- and drought-tolerant, and can provide long-term bank stability because of an extensive root system, is preferable.
(d) Best management practices, such as filter strips, swales, or wet detention basins, that are designed to control pollutants from non-point sources may be located in the protective area.
(e) This paragraph does not apply to:
1. Redevelopment sites;
2. In-fill development less than five acres; or
3. Structures that cross or access surface waters, such as boat landings, bridges and culverts.
(f) Storm water discharges to critical areas with sensitive resources (i.e., navigable waters, receiving waters with approved TMDL limits, recharge areas, water supply reservoirs) may be subject to additional performance criteria, or may need to utilize or restrict certain storm water management practices.
(4) Fueling and vehicle maintenance areas. Special requirements for new retail gasoline outlets, new municipal, state, federal, institutional or commercial refueling areas, or refueling areas that replace their existing tank systems. (Excludes individual or agricultural users.)
(a) Fueling and vehicle maintenance areas shall, to the maximum extent practicable, have BMPs designed, installed and maintained to reduce petroleum within runoff, such that the runoff that enters waters of the state contains no visible petroleum sheen.
(b) Note to users: A combination of the following BMPs may be used:
1. Oil and grease separators;
2. Canopies;
3. Petroleum spill cleanup materials; or
4. Any other structural or nonstructural method of preventing or treating petroleum in runoff.
(5) Alternative requirements. The administrative authority may establish storm water management requirements more stringent than those set forth in this section, if the MS4 Operator determines that an added level of protection is needed to protect sensitive resources.
(Ord. 2006-25, passed 12-28-06; Am. Ord. 2015-21, passed 9-14-15; Am. Ord. 2019-10, passed 5-28-19)