(A) Roadside ditches are required for all existing or proposed roads that will not have curbs and gutters.
(B) Roadside ditches shall be located so as to provide a shoulder width as dictated by the road classification and sound engineering design. In no case shall the shoulder width be less than seven feet.
(C) Ditch slopes greater than or equal to 1% and less than 3% grade shall be sodded. Ditch slopes greater than or equal to 3% grade shall protected with riprap.
(D) The ditches shall not be filled in by the property owner without installing storm sewers at any time in the future. The covenants shall specifically prohibit this.
(E) General Guidelines for Ditch Cross-sections:
(1) Traversable ditch cross sections are defined in Figures 10, 11, and 12. Two curves are shown on each figure. The area below the lower curve represents ditch cross sections that can be traversed by a vehicle containing unrestrained occupants and, thus, has a Severity Index of 1.0.
(2) The upper curve is for ditch cross sections that have a Severity Index of 1.6, and thus, vehicle occupants must be restrained in order to safely traverse the ditch. The use of Severity Index = 1.6 may be necessary because of right-of-way restrictions or to avoid nominal changes to existing ditches. In addition, the following items shall, be considered.
(3) Slopes of 3:1 shall be used only where site conditions do not permit the use of flatter slopes;
(4) Embankment surfaces must be uniform to permit traversability of a 3:1 slope. Vehicle rollover can be expected if the embankment is soft or rutted; and
(5) Foreslopes steeper than 4:1 are not desirable because their use severely limits the range of backslopes producing a safe ditch configuration.
(F) Ditches In Fill Sections On Reconstruction Projects.
(1) If any part of the backslope of the ditch section falls within the Clear Zone then the slopes shall be evaluated in accordance with Figures 10, 11, and 12. Existing ditch combinations that fall on or below the 1.6 Severity Index may remain. Areas with ditch slope combinations that fall above the 1.6 Severity Index curve shall be evaluated for cost and accident history before deciding to make an improvement. If improvement is warranted, the slope combination should preferably fall below the SI = 1.0 curve, but at least below the SI = 1.6 curve.
(2) If the ditch falls outside the Clear Zone, traversability may not be considered.
(G) Ditches In Fill Sections On New Facilities. If the ditch falls within the Clear Zone, the Designer shall select a front slope, backslope, and ditch width that will fall within the 1.0 Severity Index curve on Figures 10, 11, and 12.
(H) Ditches In Cut Sections On Reconstruction Projects. Additional right-of-way shall be obtained, if practical, when the ditch cross section can be made traversable by flattening the slopes or by moving the ditch farther from the road. Other means of making the ditch traversable, which shall be evaluated, are as follows:
(1) Use of a pipe in the ditch;
(2) Raising the grade of the ditch; and
(3) Placing 4" rip rap in the ditch to change ditch contour, and such that the projection of any one piece of rip rap does not exceed 2" above surrounding area.
(I) Ditches In Cut Sections On New Facilities. The desirable section is shown in Figures 10, 11, and 12. For minimum ditch sections, provide a section which falls on or below the 1.6 Severity Index curves on Figures 10, 11, and 12.
(Ord. 1999-06, passed 6-8-99)
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