§ 18.70.500. Minimum stormwater management requirements.

A.

The requirements of this section shall apply to all subdivisions and any development of seven thousand square feet or more within the city planning and platting jurisdiction. The minimum stormwater management requirements shall apply to land development activities that are smaller than the minimum applicable size if such activities are a part of a larger common plan of development, even though multiple separate and distinct land development activities may take place at different times on different schedules. The city commission may, after considering the comments and recommendations of the public works director, grant an exception from the requirements of the minimum stormwater management requirements if it is not feasible due to the natural or existing physical characteristics of the site to meet the applicable standards.

This section shall be applicable to residential subdivisions, except those residential lots, subdivisions and units of subdivision which, on the effective date of this chapter, have infrastructure improvements installed in the subdivision or unit of a subdivision.

B.

The minimum stormwater management requirement is that all applicable developments shall provide management measures necessary to maintain the post development peak discharges for twenty-five year frequency, one hour storm events at a level that is equal to or less than the respective twenty-five year frequency, one hour pre-development peak discharge rate, through stormwater management practices that control the volume, timing, and rate of flows. See Exhibit A, use as reference, for general guidelines.

C.

Stormwater management measures shall be required to satisfy the minimum stormwater management requirements. The stormwater management practices utilized to develop a stormwater management plan shall be implemented according to the following order of preference.

1.

Infiltration of runoff on site;

2.

Off-site stormwater management utilizing an existing playa;

3.

Flow continuation by use of open vegetated swails and natural depressions;

4.

Stormwater retention structures;

5.

Stormwater detention structures.

A combination of successive practices may be used to achieve the applicable minimum stormwater management requirements. The stormwater management plan shall be provided in the Clovis drainage plan and in compliance with the Clovis flood ordinance.

D.

The owner/developer of a subdivision (or a unit of a subdivision) subject to this section shall submit a stormwater management plan at the time of submission of the subdivision plat for preliminary approval (final approval for all residential subdivisions that have received preliminary approval prior to the effective date).

E.

The stormwater management plan for a subdivision may propose compliance in accordance with the requirements of a subsection B above by a subdivision-wide proposal or a lot-control proposal. For new subdivisions or units, it is preferred that a subdivision-wide proposal be submitted.

F.

If a subdivision, after being fully developed, has or will have the potential to create a stormwater impact to downstream properties, the owner/developer must provide on-site stormwater management measures, unless the owner/developer is willing to build a structure to adequately facilitate an off-site stormwater management location (such as the next available playa, without impacting the intervening properties).

G.

If a subdivision is located adjacent to a natural playa that receives runoff from the same water shed as the subdivision, off-site stormwater management utilizing the adjacent playa may be approved.

H.

Whenever off-site stormwater management is proposed, the owner/developer must submit a stormwater control plan demonstrating that: (1) the plan will not impact downstream properties between the subdivision and the receiving property (playa), and (2) the plan will not reduce the original capacity of the receiving property to handle the pre-development runoff from the water shed.

I.

The road system in most areas will be a primary element of the storm drainage collection system of a developed area. Wherever possible, road layouts and grades should be designed to avoid excessive runoff concentration and to minimize the need for storm sewers. Curbed roadways provide drainage outfalls for adjacent properties and site grading generally should provide for runoff from sites toward the roadway. Provisions shall be made in the design of roadways to manage stormwater throughout a subdivision or development. All storm drainage system components must be designed in accordance with the standards of the department of public works manual of construction standards.

J.

Playa stormwater storage shown on the Clovis comprehensive plan and/or the Clovis drainage plan must be accurately defined. The size of the playa may be determined by the designated capacity found in the drainage plan. If a developer wishes to store additional stormwater generated by the subdivision or development, the size of the playa may be increased by the developer if approved by the city.

K.

Existing drainage ways must be continued and be capable of carrying the historic volume of runoff. A drainage way shall be included in the subdivision or development plan if needed to carry stormwater runoff in excess of the event described in subsection B of this section. All drainage ways must be of sufficient width to carry the expected maximum stormwater flow as defined by the Clovis drainage plan and in compliance with the Clovis flood ordinance. An area at least ten feet in width along one side of the channel must be provided in addition to the drainage way channel.

L.

All drainage facilities must meet the standards contained in the department of public works manual of construction standards.

M.

If a stormwater management plan is approved for individual lot(s), a notation of the stormwater control requirement shall be identified on the plat in a manner approved by the city so that the stormwater management control will be identified as a burden on the lot that will run with the title of the property.

(Ord. 1835-2006 § 3(part), 2006).