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When a retention basin is utilized to handle storm water runoff in a residential subdivision, the following design standards shall be applicable unless otherwise approved by the City Engineer:
(A) The minimum storage volume shall be computed by estimating the area under a hydrograph of a 100 year storm of two hour duration (1.22 inches per hour) as shown in division (J) of this section. In addition, the greater of either one foot of freeboard or 25% additional basin capacity shall be provided in the facility.
(B) Maximum basin depth shall not exceed three and one-half feet unless otherwise approved by the City Engineer. If additional depth is approved, the facility shall be enclosed with a six-foot high masonry block fence and 16-foot wide wood gate with lock.
(C) Maximum side slope shall be four to one unless otherwise approved by the City Engineer.
(D) An acceptable method of transporting water from the street into the basin shall be provided so as to preserve the integrity of the basin walls and floor.
(E) Daily nuisance water from lawn watering, car washing, and the like, shall be intercepted by dry wells prior to reaching the earthen floor of the retention basin and disposed of by utilization of a percolation field.
(F) All residential streets shall be designed to carry the runoff from a 10-year two-hour storm between the curbs. In cases where the peak flows from the design storm exceeds the street capacity, storm sewers of sufficient size to carry the excess must be installed. The minimum pipe size for underground storm drainage shall be 18-inches or as approved by the City Engineer. The peak flow from a 50-year storm must be carried within the cross-section between buildings (front yards and street) for subdivisions served by retention basins.
(G) The floor elevations of all habitable space shall be above flood levels equivalent to a 100-year storm.
(H) All streets shall have vertical curb with minimum longitudinal slope as shown in the table below, designed in accordance with accepted City of Yuma Construction Standards.
Straight (400 foot radius and over) curb
Curved (less than 400 foot radius) curb
Valley gutter flowline
(I) Each retention basin shall be constructed so that storm water will not stand after termination of a storm event for longer than five days in the valley or 36 hours on the mesa. Basin drainage shall be accomplished by infiltration or by controlled flow into an existing facility suitable to receive, transport and dispose of storm water. When controlled flow is proposed, the owner/developer and the city shall obtain approval from the owner of the existing facility prior to formulating final drainage plans for the retention basin. Final drainage plans shall be subject to the review and approval of the City Engineer.
(J) (1) The owner of the property on which the retention basin is to be located shall grant a right to use said property for drainage purposes. Such grant shall be made by means of a document which shall be approved by the City Attorney and recorded in the office of the County Recorder and which shall contain the following:
(a) A legal description of the property to be used for storage purposes.
(b) A legal description of the property which is permitted to drain to the basin.
(c) A statement that the owner is responsible for construction and maintenance of the basin in accordance with standards established by the City Engineer.
(d) A statement that no habitable structure(s) may be constructed within the basin.
(e) A statement that the property shall be used for storm water storage so long as it is required for such purpose in the opinion of the City Engineer.
(f) Such other provisions as are deemed by the City Attorney to be necessary and proper to effectuate the purposes of this chapter.
(2) In lieu of the requirements contained in this division, the owner may dedicate the property to be used for storm water retention to the city for drainage and for public use. Such dedication shall become effective only upon acceptance of the basin by the City Engineer. As conditions precedent to acceptance of dedication, the owner/developer shall include landscaping (grass and trees), an irrigation system of the flood and/or sprinkler type, and lighting as specified in approved city standards.
(K) Retention basin volume.
(L) A retention basin, to become dedicated to the city, shall be located adjacent to arterial streets (mile and half-mile streets) and the geometries of the basin shall be coordinated with the City Engineer.
(M) With approval of the City Engineer, a retention basin may be located on other streets which allow a direct storm sewer route to an arterial street. Additionally, properly designed and sized inlets, manholes, storm sewer lines and all other appurtenances shall be constructed to a point where the storm sewer may be connected to a future storm main on an arterial street.
('80 Code, § 31-147) (Ord. 1670, passed 10-12-77; Ord. 1836, passed 6- 20-79; Ord. O2021-021, passed 8-4-2021) Penalty, see § 193-99