§ 16.52.010. Design standards, drainage.

A.

Drainage System Required. A drainage and storm water detention system shall be designed and constructed by the subdivider to provide for the proper drainage of the surface water of the subdivision and the drainage area of which it is a part. A final plat shall not be approved until the subdivider shall submit plans, profiles, and specifications as specified in this section, that have been prepared by a registered professional engineer and approved by the city council, upon the recommendations of the plan commission and city engineer. The city may require retention basins.

B.

Drainage System Plans.

1.

The subdivider shall submit, at the time of filing of a preliminary plat, a preliminary drainage plan or engineering report on the ability of existing watercourse channels, storm sewers, culverts, and other improvements pertaining to drainage or flood control within the subdivision to handle the additional runoff that would be generated by the development of the land within the subdivision. Additional information shall be submitted to adequately indicate that provision has been made for disposal of surface water without any damage to the developed or undeveloped land downstream or below the proposed subdivision. The report shall also include:

a.

Estimates of the quantity of storm water entering the subdivision naturally from areas outside the subdivision;

b.

Quantities of flow at each inlet or culvert.

c.

Location, sizes, and grades of required culverts, storm drainage sewers, and other required appurtenances.

2.

A grading plan for the streets, blocks, and lots shall be submitted by the subdivider for the area within the subdivision.

3.

The design criteria for storm drainage and detention systems shall be based upon information provided by the city engineer. In general, storm sewers and related items shall be designed to contain a minimum of the ten-year storm event underground.

4.

Material and construction specifications for all drainage projects (i.e., pipe, culverts, seed, sod, etc.) shall be in compliance with specifications provided by the city engineer.

C.

Grading. The subdivider shall grade each subdivision in order to establish street, block and lot grades in proper relation to each other and to topography as follows:

1.

The subdivider shall grade the full width of the right-of-way of all proposed streets in accordance with the approved plans.

2.

Block grading shall be completed by one or more of the following methods:

a.

A ridge may be constructed along the rear lot lines that provides for drainage onto the streets;

b.

Parts of all lots may be graded to provide for drainage to the street or to a ditch along the rear lot line;

c.

Draining across rear or side lot lines may be permitted provided that drainage onto adjoining properties is skillfully controlled.

3.

The subdivider shall provide the city engineer with spot elevations on property corners.

D.

Drainage System Requirements. The subdivider shall install all the storm drainage facilities indicated on the plans required in subsection A of this section.

1.

All streets shall be provided with an adequate storm drainage system. The street storm system shall serve as the primary drainage system and shall be designed to carry street, adjacent land, and building storm water drainage. No storm water shall be permitted to be run into the sanitary sewer system within the proposed subdivision.

2.

The design of the off-street drainage system shall include the watershed affecting the subdivision and shall be extended to a watercourse or ditch adequate to receive the storm drainage. When the drainage system is outside of the street right-of-way, the subdivider shall make provisions for dedicating an easement to the city to provide for the future maintenance of said system. Easements shall be a minimum of twenty (20) feet, but the city may require larger easements if more area is needed due to topography, size of watercourse, etc.

3.

Any and all drainage improvements shall be extended to the boundary lines of the tract to be subdivided, unless prevented by topography or other physical conditions, or unless, in the opinion of the city council, upon the recommendation of the plan commission, such extension is not necessary or desirable for the coordination of the layout of the subdivision with the existing layout or the most advantageous future development of adjacent tracts.

4.

All lots shall be provided with a storm sewer lateral unless approved otherwise on a case-by-case basis by the plan commission, based upon a recommendation from the city engineer. The size of the storm lateral pipe shall be a minimum of four-inch nominal diameter for all lots zoned for one and two-family residential structures. The size of the storm lateral pipe for all other zoning districts shall be a size as recommended by the city engineer. In areas where a storm sewer mainline is available in the street, the laterals can be connected directly to the upper quadrant of the storm sewer mainline pipe or connected to inlet structures. In other areas, where a storm sewer mainline is not present in the street, a common collection line located parallel to the curb line shall be installed to direct the water from each lot into a downstream storm sewer manhole or inlet. The design details of the storm sewer laterals, collection pipes, and other related structures shall be included in the overall drainage plan, which is described elsewhere in this chapter.

(Ord. 144-2007; Ord. 3-1998 (part): prior code § 10-3-13)