§ 11-92. Storm drainage systems.

Storm frequencies for use in design should generally be according to AASHTO and FHWA criteria and the minimum frequencies given below of the various classes of roads. No exact criteria for flood frequency of allowable backwater/headwater values can be set which will apply to an entire project or roadway classification. The flow of water in the gutter should be restricted to a depth, and corresponding width, which will not severely obstruct or cause a hazard to traffic. This flow is a function of the quantity of water, the gutter gradient, roughness of the pavement where the flow is contained, and cross section shape of the flow area. The engineer shall provide complete documentation concerning the selection of design frequency and criteria.

(1)

The developer shall install storm drainage facilities, including drains, sewers, catch basins and culverts necessary for the proper drainage of all surface water, and serve the entire drainage area.

(2)

All surface water drainage shall be transported to existing storm sewers, drainage facilities, or natural ditches or streams approved by the County Road Superintendent.

(3)

The developer is responsible for correcting any drainage or flooding problems occurring on adjacent or downhill or downstream property as a result of the development.

(4)

Minimum flood frequency for subdivision and mobile home streets is as follows:

a.

Cross drains:

1.

Class III and IV roads: 25-year flood, unless the adjacent structures in the drainage area are designed to a higher flood frequency.

2.

Class I and II roads: 10-year flood if the drainage area is less than two (2) square miles and the ADT is less than 750. If either is exceeded, use a 25-year flood frequency.

b.

Storm sewers:

1.

Class III and IV roads: 25-year flood unless the connecting system is designed to a higher flood frequency.

2.

Class I and II roads: 10-year flood unless the connecting system is designed to a higher flood frequency.

Note: If local drainage facilities and practices have provided drains of a lesser standard than specified above, special consideration should be given to whether it is realistic to design the proposed system to a higher standard than available outlets.

(5)

The County Road Superintendent shall approve any changes in the storm drainage system.

(6)

The provisions herein are also meant to authorize detention and/or retention ponds when deemed necessary by the County Engineer to address drainage within a land development and on surrounding properties; the quantity and the quality of any runoff from any development shall not be substantially altered from pre-development conditions.

(7)

The County Engineer is hereby authorized to promulgate rules and regulations to further effectuate the goals of this ordinance, subject to approval by the Quorum Court.

(Ord. No. 91-9, Art. 1, § 3.07, 4-11-91; Ord. No. 2006-53, Art. 1, 9-14-06)