Chapter 13.35
STORMWATER MANAGEMENT

Sections:

13.35.010    Applicability.

13.35.020    Waiver – Exemptions – Mitigations.

13.35.030    Performance criteria for stormwater management.

13.35.040    Requirements for stormwater management plan approval.

13.35.050    Construction inspection.

13.35.060    Maintenance and repair of stormwater facilities.

13.35.010 Applicability.

(a) Except as provided in TMC 13.35.020(d), unless an exception is granted pursuant to TMC 13.30.080(d), this chapter shall apply to the following:

(1) All requests for approval of subdivision plats and site plans pertaining to land development activities that are greater than or equal to one acre of land, including projects that cause a land disturbance less than one acre that are part of a larger common plan of development or sale; or

(2) Land disturbance activities that are less than one acre but located in an impacted watershed as determined by the director based upon an engineering study. (Ord. 19625 § 11, 8-23-11.)

13.35.020 Waiver – Exemptions – Mitigations.

(a) The director may grant a waiver for one or more stormwater management requirements if the standard can be met in any of the following ways:

(1) Discharging the stormwater runoff to an existing stormwater management facility, whether public or private, that is an off-site facility designed, adequately sized, constructed and maintained to provide a level of stormwater control that is equal to or greater than that which would be afforded by on-site practices and there is an entity responsible for long-term operation and maintenance of the stormwater practice, provided the developer produces a written agreement permitting the discharge of stormwater runoff and long-term operation and maintenance to the existing stormwater management facility.

(2) Engineering studies determine that installing a stormwater management facility in order to meet the stormwater management standards will cause adverse impact to water quality, or cause a negative impact to a downstream channel.

(3) For redevelopment, engineering studies demonstrate there is no net increase in stormwater runoff from current conditions.

(b) Acceptable mitigation measures may be required in order to prevent deterioration of existing culverts, bridges, dams, and other structures, degradation of biological functions or habitat, accelerated stream bank or stream bed erosion or siltation, and increased threat of flood damage to public health, life, and property. Such mitigation measures may include, but are not limited to:

(1) The purchase and donation of privately owned lands, or the granting of an easement to be dedicated for preservation or reforestation.

(2) The creation of a stormwater management facility or other drainage improvement on previously developed properties, public or private, that currently lack stormwater management facilities.

(3) Granting an easement or dedicating land to the city to be used for the construction of an off-site stormwater management facility. Such easement shall be granted prior to issuance of any building permit.

(c) A request for waiver shall not be granted without an engineering study shown in drainage plans submitted for new development or redevelopment that creates additional impervious surfaces establishing the adequacy of downstream or shared off-site stormwater management facilities which offer equivalent or greater protection than the standard(s) for which a waiver is requested.

(d) Site plans for single-family and two-family dwellings on individual lots are exempt from this chapter unless they are located in an area which drains to an impacted waterway as deemed by the director based on an engineering study. (Ord. 19625 § 12, 8-23-11.)

13.35.030 Performance criteria for stormwater management.

All subdivision plats and site plans shall meet the following requirements for stormwater management:

(a) Designs shall establish stormwater management practices to control peak flow rates of discharge according to the storm drainage design criteria. These practices should utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots, storage areas, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity.

(b) All stormwater runoff generated from new developments shall not discharge directly into a jurisdictional wetland or local water body without adequate treatment as specified in the post construction stormwater quality policy. Where such discharges are proposed, they shall meet all applicable local, state and federal requirements, permits, plans and programs. The owner is responsible for complying with all local state and federal permits that are applicable to the site.

(c) BMPs shall be designed to promote infiltration to the maximum extent possible through the use of structural and nonstructural methods.

(d) For new development and redevelopment, structural stormwater treatment practices shall meet the following performance standards:

(1) Stormwater runoff shall be treated for water quality prior to discharge from the development site.

(2) Designed according to the City of Topeka Design Criteria and Drafting Standards.

(3) Reduce the discharge of the total maximum daily load (TMDL) regulated pollutants to an associated stream and/or lake as identified in the Post Construction Stormwater Quality Policy set forth by the director.

(4) Reduce the discharge of principal pollutants of concern as identified in the Post Construction Stormwater Quality Policy set forth by the director. (Ord. 19625 § 13, 8-23-11.)

    Cross References: Department of public works, TMC 2.25.170.

13.35.040 Requirements for stormwater management plan approval.

(a) No application for subdivision plats or site plans to which this chapter applies shall be approved unless the application includes a stormwater management plan detailing in concept how runoff and associated water quality impacts resulting from development will be controlled or managed.

(b) Stormwater Management Concept. The stormwater management concept plan shall include the following information to evaluate the environmental characteristics of the project site, the potential impacts of all proposed development of the site, both present and future, on the water resources, and the effectiveness and acceptability of the measures proposed for managing stormwater generated at the project site:

(1) A map (or maps) indicating the location of existing and proposed buildings, roads, parking areas, utilities, structural stormwater management and sediment control facilities. The map(s) will also clearly show proposed land use with tabulation of the percentage of surface area to be adapted to various uses, drainage patterns, locations of utilities, roads and easements, and the limits of clearing and grading. A written description of the site plan and justification of proposed changes in natural conditions may also be required.

(2) A plan designed by qualified personnel showing that the proposed stormwater management measures are capable of controlling runoff from the site in compliance with this chapter and the specifications of the storm drainage design criteria. A written or graphic inventory of the natural resources at the site and surrounding area as it exists prior to the commencement of the project and a description of the watershed and its relation to the project site. This description shall address soil conditions, forest cover, topography, wetlands, native vegetative areas on the site, and environmentally sensitive features that provide particular opportunities or constraints for development.

(3) A written description of the individual(s) responsible for maintenance of the proposed plan.

(4) A written description of the maintenance that shall be performed by the responsible party.

(5) The director may also require a concept plan to address the maximum development potential of a site under existing zoning, regardless of whether the applicant presently intends to develop the site to its maximum potential.

(c) Final Stormwater Management Plan Requirements. After review of the stormwater management concept plan, and modifications to that plan as deemed necessary by the director, a final stormwater management plan shall be submitted for approval. The final stormwater management plan, in addition to the information from the concept plan, shall include the following:

(1) Contact Information. The name, address, and telephone number of all persons having a legal interest in the property and the tax reference number and parcel number of the property or properties affected.

(2) Topographic Base Map. A one inch equals 200 feet topographic base map of the site which extends a minimum of 100 feet beyond the limits of the proposed development and indicates existing surface water drainage including streams, ponds, culverts, ditches, and wetlands; current land use including all existing structures; locations of utilities, roads, and easements; and significant natural and manmade features not otherwise shown.

(3) Calculations. Hydrologic and hydraulic design calculations for the pre-development and post-development conditions for the design storms specified in the storm drainage design criteria. Such calculations shall include (i) description of the design storm frequency, intensity and duration, (ii) time of concentration, (iii) soil curve numbers or runoff coefficients, (iv) peak runoff rates and total runoff volumes for each watershed area, (v) infiltration rates, where applicable, (vi) culvert capacities, (vii) flow velocities, (viii) data on the increase in rate and volume of runoff for the design storms referenced in the storm drainage design criteria, and (ix) documentation of sources for all computation methods and field test results.

(4) Soils Information. If a stormwater management control measure depends on the hydrologic properties of soils (e.g., infiltration basins), then a soils report shall be submitted. The soils report shall be based on on-site boring logs or soil pit profiles. The number and location of required soil borings or soil pits shall be determined based on the need to determine the suitability and distribution of soil types present at the location of the control measure.

(5) Maintenance and Repair. The design and planning of all stormwater management facilities shall include detailed maintenance and repair procedures to ensure their continued function, as well as the individual(s) responsible for such maintenance. The applicant shall identify the parts or components of a stormwater management facility that need to be maintained and the equipment, skills or training necessary. Provisions for the periodic review and evaluation of the effectiveness of the maintenance program and the need for revisions or additional maintenance procedures shall be included.

(6) Landscaping. The applicant shall present a detailed plan for management of vegetation at the site after construction is finished, including responsibility for the maintenance of vegetation at the site and the practices employed to ensure that adequate vegetative cover is preserved. These provisions shall be prepared by qualified personnel.

(7) Easements. The applicant shall provide access to the city for all stormwater treatment facilities or easements at the site for the purpose of inspection and repair by securing all the necessary easements needed on a permanent basis. These easements will be shown on the recorded plat or granted by separate instrument and shall run with the land.

(8) Erosion and Sediment Control Plans for Construction of Stormwater Management Measures. The applicant shall prepare an erosion and sediment control plan or submit a SWPPP for all construction activities related to implementing any on-site stormwater management practices.

(9) Other Environmental Permits. The applicant shall assure that all other applicable environmental permits have been acquired for the site prior to approval of the final stormwater design plan.

(10) Requirement for Stabilization. Banks of all streams, channels, ditches and other earthen stormwater conveyances shall be left in a stabilized condition upon completion of the new development or redevelopment. No actively eroding, bare or unstable vertical banks shall remain after completion of construction.

(11) All stormwater facilities and systems, including those designed and constructed for water quality treatment, downstream channel stabilization, and peak discharge control shall be designed, constructed and maintained in accordance with the criteria, standards, and specifications presented in this chapter, or other professionally accepted manual for stormwater quality management. The standards for water quality treatment, downstream channel stabilization and peak discharge analysis and control shall be achieved through the use of one or more stormwater quality management facilities that are designed and constructed in accordance with the design criteria, guidance, and specifications provided in a professionally accepted manual for stormwater quality or other acceptable professional methods. Methods, designs or technologies for stormwater quality management facilities that are not provided in any stormwater quality manual may be submitted for approval if it is proven that such methods, designs or technologies will meet or exceed the stormwater treatment standards set forth in this chapter. (Ord. 19625 § 14, 8-23-11.)

    Cross References: Department of public works, TMC 2.25.170.

13.35.050 Construction inspection.

(a) The director shall have the right to perform inspections during the construction of the stormwater management system.

(b) As Built Plans. All applicants shall submit actual “as built” plans for any stormwater management practices located on site after final construction is completed. The plan shall identify the final design specifications for all stormwater management facilities and shall be certified by qualified personnel. (Ord. 19625 § 15, 8-23-11.)

13.35.060 Maintenance and repair of stormwater facilities.

(a) Stormwater Management Easement. Prior to the approval of subdivision or site plan applications pertaining to land development activities described in TMC 13.35.010(a), the owner of the site shall provide for access to the facility at reasonable times for periodic inspection by the city, or its contractor or agent, and shall require the property owner to ensure that the facility is maintained in proper working condition to meet design standards and any other provisions established by this chapter. The stormwater management easement shall be shown on the recorded plat or granted by separate, recorded instrument.

(b) Inspection of Stormwater Facilities. The director shall have the ability to conduct inspections of the stormwater facilities. Inspections may include, but are not limited to: reviewing maintenance and repair records; sampling discharges, surface water, groundwater, and material or water in drainage control facilities; and evaluating the condition of drainage control facilities and other stormwater treatment practices.

(c) Failure to Maintain Practices. If a responsible party fails or refuses to meet the requirements set forth in the stormwater management plan, the city, after reasonable notice, may pursue enforcement of the plan or the provisions of this chapter. (Ord. 19625 § 16, 8-23-11.)

    Cross References: Department of public works, TMC 2.25.170.