Section 1: Purpose, Authority, and Jurisdiction

9/6/2002

SECTION 1: PURPOSE, AUTHORITY, AND JURISDICTION

§ 1.1 Need for stormwater ordinance. It is hereby found and declared that in order to make adequate provisions to protect the life, liberty, and property of the residents of (www.t2s2.org) from encroachment, damage, or destruction from stormwater runoff attributable to the development or change in use of adjacent or other properties within the corporate limits and extraterritorial jurisdiction of the City of (www.t2s2.org), that there exists the necessity for setting forth certain procedures and standards to be followed in the management, conveyance, and control of stormwater runoff attributable, directly or indirectly, to the change in use of, development of, or subdivision of, by either platting or metes-and-bounds, property within the administrative jurisdictions of the City of (www.t2s2.org).

§ 1.2 Intent of rules and regulations. These rules and regulations are intended to serve the following purposes:

(1)  To assist orderly, economic, efficient, and coordinated development of storm conveyance and management systems within (www.t2s2.org) and its planning area;

(2)  To promote the health, safety, and general welfare of the residents of (www.t2s2.org) and the area;

(3)  To ensure the conformance of stormwater management and conveyance system plans with the public improvement plans of (www.t2s2.org);

(4)  To secure equitable handling of all stormwater management and conveyance system plans by providing uniform procedures and standards for observance by all parties.

§ 1.3 Stormwater plans to be submitted to City Engineer. Any person or persons, business, corporation, partnership, or entity intending to develop, subdivide, improve, modify, or change the use of a tract of land within the territorial jurisdiction of the City of (www.t2s2.org), shall submit detailed plans, including calculations, computer printouts, references, and any other pertinent information used in the determination of the design of the stormwater management and conveyance system, to the City Engineer for approval.

§ 1.4 Approved plans required to proceed. No person or persons, business, corporation, partnership, or entity, shall proceed with the development, subdivision, improvement, modification, or change in the use of a tract of land within the territorial jurisdiction of the City of (www.t2s2.org) without the stormwater management and conveyance system being approved by the City Engineer or the appropriate Boards, Committees, and City Council of the City of (www.t2s2.org).

SECTION 2: DEFINITIONS

§ 2.1 General semantics and syntax. As used in these rules and regulations, words in the present tense include the future; words in the singular include the plural; the word “may” is permissive; the word “should” is strongly recommended, but not required; the word “shall” is mandatory and not directory.

§ 2.2 Specific words and phrases defined. Certain words in these regulations are defined for the purpose hereof as follows:

2.2.1  Catch basin. A type of drop inlet where the outlet is above the floor, thus providing a space on the inlet floor for the collection of trash, debris, and other solid or semi-solid objects.

2.2.2  City. The City of (www.t2s2.org) and its boards, commissions, legislative bodies, and staff.

2.2.3  City Engineer. The City Engineer of (www.t2s2.org) or his/her authorized representative.

2.2.4  Conveyance System. An element or device whose primary function is the transportation of fluid. Pipes, storm sewers, drop inlets, ponds, culverts, ditches, swales, creeks, draws, sloughs, ravines, lakes, and gullies are examples of conveyance systems.

2.2.5  Conduit. Any closed device for conveying a liquid.

2.2.6  Design Storm. The hydrologic event for which storm runoff will be calculated.

(a)  Design Storm Return Period. The average return period for a storm of a given magnitude. For computations prescribed by these regulations, the design storm return period shall be 25 years.

(b)  Design Storm Duration. The maximum duration of the design storm. For those computations requiring a design storm duration, said duration shall be 6 hours.

2.2.7  Detention Facility. A basin, facility, or structure whose purpose is to hold water for a limited amount of time, and to discharge that water at a steady rate. (see Rate of Discharge)

2.2.8  Detention Pond. Also known as a dry pond. See Detention Facility.

2.2.9  Drainage Area. See Watershed.

2.2.10  Drainage Basin. See Watershed.

2.2.11  Drainage Channel. A linear depression, draw, gully, ravine, or similar type of topographic feature of the ground surface whose primary purpose is the conveyance of surface water.

2.2.12  Drop Inlet. A subterranean structure with an opening at or near the top for intercepting surface water flow.

(a) Curb Inlet. A drop inlet in which the opening is located in one or more of the sides of the inlet structure. For streets, these inlets are generally located behind the curb with the opening in the curb.

(b) Grated Inlet. A drop inlet in which the opening is located in the top. Typically, this opening is covered with a grate. For streets, these inlets are typically located in front of the curb, with the opening in the pavement itself.

(c) Combination Inlet. A drop inlet with openings in one or more sides and all or part of the top.

2.2.13  Flow Rate, Q. The volume of fluid passing a given point for a specified unit of time. Typically expressed in cubic feet per second (CFS).

2.2.14  Freeboard. The difference in elevation between the water surface in a calm, steady state and a point of reference, such as the top of an embankment.

2.2.15  Inlet. A point of entry for flow. For a drop inlet, the inlet is typically the opening where surface water enters.

2.2.16  Intensity, I. The intensity of a hydrologic event of a given duration and return period, expressed in units of length per unit time, typically inches per hour (in/hr). Typically, the event duration used for determining I is TC. (See Time of Concentration and Design Storm)

2.2.17  Invert. The bottom, or flow line, of a drop inlet, conduit, or culvert.

2.2.18  Outlet. A point of discharge of flow. An outlet may be either surface or subterranean, physical or theoretical.

2.2.19  Rate of Discharge. The flow rate at which water is released from a detention facility or other element of a stormwater conveyance system.

2.2.20  Reach. The maximum amount of distance traveled by a water droplet to travel from the most hydraulically remote point in the watershed boundary to the watershed outlet.

2.2.21  Retention Facility. A basin, facility, or structure whose purpose is to retain and hold water indefinitely.

2.2.22  Retention Pond. Also known as a wet pond. See Retention Facility.

2.2.23  Runoff Coefficient. A coefficient used to describe the perviousness of the surface over which the hydrologic event is occur. Paved areas have higher runoff coefficients than unpaved areas.

2.2.24  Swale. A shallow drainage channel.

2.2.25  Territorial Jurisdiction. All of the geographic area within the corporate limits of the City of (www.t2s2.org) and the geographic area lying in unincorporated Collin County over which some of the laws, regulations, and authority of the City of (www.t2s2.org) apply.

2.2.26  Time of concentration, TC. The maximum amount of time required for a water droplet to travel from the most hydraulically remote point in the watershed boundary to the watershed outlet.

2.2.27  Watershed. A contiguous geographic area in which all surface runoff travels to the same point.

SECTION 3: PROCEDURAL REQUIREMENTS

§ 3.1 Submittal to City Engineer. All stormwater management plans shall be submitted to the City Engineer for review and approval. The City Engineer, at City Engineer’s discretion, may request supporting documents, and said requested shall expediently be submitted to the City Engineer for review.

§ 3.2 Responsibility of City Engineer. The City Engineer shall review a submittal with the utmost professional objectivity and thoroughness, and shall be completed in a timely manner. Upon completion of the review, the City Engineer shall notify the Submitter, in writing, the results of the review, including possible violations of federal, state, county, and local ordinances, as well all comments and concerns, based on reasonable engineering knowledge and experience, regarding the proposed stormwater management plan.

§ 3.3 Appeal of City Engineer’s denial. A submitter has the right to appeal a denial of a stormwater management plan by the City Engineer to all appropriate boards and bodies of the City of (www.t2s2.org). A request must be made in writing to the City Engineer and the lowest board, body, or agency of the City of (www.t2s2.org) with jurisdiction. All avenues of appeal must be exhausted before an appeal can be made to the next higher board, body, or agency.

§ 3.4 Response of City Engineer to appeal. Upon the receipt of a written request for an appeal, the City Engineer shall prepare a report to the board, body, or agency with the appropriate jurisdiction to hear the appeal detailing the denial. A copy of this report will also be made available to the Appellant.

§ 3.5 Board, Body, or Agency may grant appeal. The lowest board, body, or agency with the City of (www.t2s2.org) with jurisdiction may, at its discretion, approved a storm management plan denied by the City Engineer.

§ 3.6 Appellant’s rights if appeal denied. If an Appellant’s appeal is not successful, Appellant has the right to appeal to then next higher body, board, or agency of the City of (www.t2s2.org).

§ 3.7 Approved storm drainage plan required for modifications. No person or persons, business, corporation, partnership, or entity, shall proceed with the development, subdivision, improvement, modification, or change in the use of a tract of land within the territorial jurisdiction of the City of (www.t2s2.org) without a stormwater management plan approved by the City Engineer or having been successfully appealed to a body, board, or agency of the City of (www.t2s2.org) having appropriate jurisdiction.

§ 3.8 Approved stormwater management plan to be filed with City. A complete copy of an approved stormwater management plan, including all plans, drawings, calculations, specifications, and other pertinent documents, shall be filed with the City Clerk of the City of (www.t2s2.org) for placement among the public records of the City of (www.t2s2.org). Extra copies shall be provided to the City Engineer, the Public Works Director, the Planning Commission, and any local, county, state, or federal agencies with a vested interest or jurisdiction.

SECTION 4: GENERAL GUIDELINES

§ 4.1 Stormwater management systems shall conform to all regulations. All stormwater management systems shall be designed in accordance with the design parameters established in these and all other applicable local, state, and federal regulations.

§ 4.2 Conformance to natural contours. Where practicable, all development and modifications to land use shall conform to the natural contours of the land and natural and preexisting man-made drainage ways shall remain undisturbed.

§ 4.3 New property boundaries to conform with drainage ways. Where practicable, lot boundaries shall be made to coincide with natural and preexisting man-made drainage ways within subdivisions to avoid the creation of lots that can be built upon only by altering such drainage ways.

§ 4.4 Developments must drain properly. All developments and land use modifications shall be provided with a drainage system that is adequate to prevent the undue retention of surface water on the site. Surface water shall not be considered unduly retained if:

(1)  The retention results from a technique, practice, or device deliberately installed as part of an approved sedimentation or storm water runoff control plan; or

(2)  The retention is not substantially different in location or degree than that experienced by the site prior to modification, provided that such retention does not pose a danger to health or safety.

§ 4.5 Diversion of flow prohibited. The diversion of surface water flow into a sanitary sewer or another watershed is hereby prohibited.

§ 4.6 Drainage systems to be coordinated. Whenever practicable, the drainage system of a site to which modifications have been made shall coordinate and be connected to the drainage systems or drainage ways on surrounding properties or streets.

§ 4.7 Adjacent properties shall not be impacted. All modifications shall be constructed and maintained so that adjacent, nearby, or downstream or upstream properties are not unreasonable burdened with surface waters as a result of such modifications. Specifically,

(1)  No modification to a site or property may be constructed or maintained so that such modification unreasonably impedes the natural flow of water from higher adjacent properties across the property that has been modified, thereby unreasonably causing substantial damage or potential damage to such higher adjacent properties; and

(2)  No modification may be constructed or maintained so that surface waters from such development are unreasonably collected and channeled onto lower adjacent properties at such locations or at such velocities or volumes as to cause substantial damage to such lower adjacent properties.

§ 4.8 Plan submittal requirements. The following information is required on all stormwater management and drainage plan submittals:

4.8.1  Drainage Areas. Drainage areas must be identified for both the pre- and post-modification conditions. For each drainage area, the following information must be provided for both the before and after conditions, unless otherwise noted:

(a)  Drainage area boundaries;

(b)  Design storm flow rates;

(c)  Drainage area in acres;

(d)  Time of concentration;

(e)  Points of concentration;

(f)  Reach;

(g)  Runoff coefficients;

(h)  Detention requirement;

(i)  Soil losses;

(j)  Contours of a sufficient precision to be able to calculate flow rates with reasonable accuracy.

4.8.2  Channels, swales, and ditches. Channels, swales, and ditches must be identified for both the pre- and post-modification conditions. Unless otherwise noted, the following channel, swale, and ditch information must be provided for the before and/or after conditions, where applicable:

(a)  Channel, swale, and ditch locations;

(b)  Direction of flows and flow rates;

(c)  Average, minimum, and maximum flow velocities;

(d)  Average, minimum, and maximum flow depths;

(e)  Flow line profile (channel and ditches only);

(f)  Flow line elevations at changes in grade (swales only);

(g)  A sufficient number of cross-sections to provide for a reasonably accurate determination of the water surface profile;