A drainage 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. The subdivision shall be graded as shown on the approved improvement plan.
(a) Drainage Plan. As part of the required improvement plans, a plot plan showing by the use of arrows how the subdivider proposes to surface drain each lot shall be submitted to and approved by the City Engineer.
(b) Grading Requirements. No grading, sidewalk, pavement construction, or installation of utilities shall be permitted in any proposed street until the improvement plans have been approved. 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) Street grading plan. A grading plan shall be prepared for the streets along with street improvement details. The grading of the roadway shall extend the full width of the right-of-way. The strips between the pavement and the right-of-way shall be at a grade of not less than 3% and not more than 4% upward from the curb to the sidewalk or property line.
(2) Lot grading. Lots shall be graded so that water drains away from each building at a minimum grade of 2% for a distance of 10 feet. Surface drainage swales shall have a minimum grade of 1% and shall be designed so that surface water will drain into a driveway, street gutter, storm sewer, drain inlet, or natural drainageway.
(3) Topsoil. If the process of grading or regrading any land area within a subdivision results in the removal of topsoil, the topsoil shall not be removed from the subdivision site or used as fill, but shall be conserved or stockpiled and shall be used as loam or top dressing for lawns, private property, or areas within the public right-of-way, i.e., devil strips or street lawns within the Subdivision. The procedures required herein may be performed after the construction of the required public improvements or structures upon public improvements or structures upon private lots has been substantially completed, but shall be completed before the initial occupancy of any dwellings.
(4) Trees. As many trees as possible shall be retained, and the grading shall be adjusted to the existing grade at the trees.
(c) Drainage System Requirements. The design criteria for the drainage systems shall be based on the standards of the City Engineer.
(1) Road drainage system. The road storm drainage system shall serve as the local drainage system. It shall be designed to carry roadway, adjacent land and house storm water drainage. Storm sewers shall drain into natural waterways as soon as possible.
(2) Off-road drainage system. The design of the off-road drainage system shall provide for the watershed affecting the allotment and shall be extended to a watercourse or storm sewer adequate to receive the storm drainage.
A. Storm drainage facilities constructed by the subdivider shall be provided with an easement which provides access not less than 20 feet in width for maintenance equipment to all sections.
B. Easements for drainage facilities shall be not less than 20 feet in width. Where the watercourse is large, easement widths shall be increased as determined by the City Engineer. Where watercourses cross platted lots diagonally, the subdivider may straighten the courses where practicable and shall substantially follow sublot lines. Easements shall be shown on the record plat and shall cover all existing or reconstructed watercourses.
C. All storm drainage courses shall be enclosed with approved pipe.
(d) Protection of Drainage Systems. The subdivider shall adequately protect all roadways and watercourses to the satisfaction of the City Engineer. All land where the vegetation has been injured or destroyed or which is in need of protection to prevent erosion, deposits in the drainage facilities, or unsightly conditions shall be restored and protected as directed by the City Engineer. In all cases, any drainage facility within the subdivision shall be in a stable condition and free from erosion, sedimentation, and debris.
(e) Pipe System. The pipe sizes shall be based on drainage calculations and approved by the City Engineer.
(Ord. 2007-222. Passed 1-10-08.)