(a) Generally. As used in this appendix, “ditches” means open watercourses for the purpose of carrying water overland to or in lieu of closed conduits or to other ditches, channels or swales. “Ditches” includes channels and swales.
Ditches shall be shown on the improvement plan as part of the drawings and in profile at the same scale as storm and sanitary sewers.
The plan shall also contain a typical section of the ditch, showing width of bottom, side slopes and type and dimensions of lining.
(b) Design. The design of ditches shall consist of the following:
(1) Hydraulically determining the depth and configuration of ditch necessary to carry the design peak flow at the design velocity. The cross-section of the ditch shall be as shown in the standard drawings.
(2) Determining the type and dimensions of the ditch lining needed to maintain proper erosion control to prevent scour or needed to prevent undesirable sedimentation.
(c) Design Criteria. All ditches shall be designed for the ultimate use of the land and in accordance with the following:
(1) Review information. The information necessary for proper review is the station on the ditch of the point being considered; discharge (Q); velocity (v); coefficient of friction (n); depth (d); and the type, limits and dimensions of ditch lining.
(2) Design sheets. The ditch design sheet recommended by the Village Engineer, or a reasonable fascimile thereof, shall be used in the design and shall accompany the plans submitted for review.
(3) Points of design. Each ditch shall be checked for the information required in division (c)(1) hereof at each point where a concentrated discharge enters the ditch, at each point where the type of ditch lining changes, at each change in grade and at various points throughout its length at a maximum of 400-foot intervals. The entire reach of ditch shall be designed for the total discharge at the lower end of the reach.
(4) Surface run-off. The quantity of surface run-off or discharge shall be computed by the rational formula Q=ciA.
A. Coefficient of run-off (c). A weighted value of c shall be computed for each contributing area using the following values:
0.9 - roof and hard surfaced areas
0.7 - steep grassed areas (4:1 or steeper)
0.4 - for unpaved areas, lawns and yards
B. Intensity of precipitation (I). The intensity of rainfall shall be obtained by use of the rainfall duration-versus-intensity chart D-802 - Area D - Ohio Department of Highways Location and Design Manual. The duration of rainfall shown on the graph is the concentration time or an estimate of the time for the water to flow from the most remote part of the drainage area to the point in the ditch being analyzed. Such time can best be estimated by the use of the overland flow chart found in Volume One of the Date Book for Civil Engineers by Seelye. The minimum time to the first point shall be 15 minutes.
C. Design frequency. The design frequency for depth shall be a ten-year storm and for velocity a two-year storm, except where existing or proposed buildings would be flooded, then in which case a 25 year design frequency shall be used for depth.
(5) Hydraulic design. The ditch will be hydraulically designed by the use of Manning’s formula for open-channel flow. In order to expedite the determination of velocity and depth, the charts contained in the Bureau of Public Roads, Hydraulic Design series No. 3, “Design Charts for Open Channel Flow” may be used.
A. Coefficient of friction (n). The coefficient of friction shall be determined as follows:
n = .015 paved lining of precast concrete riprap
n = .03 bare earth (seeding)
n = .04 sodding of grouted riprap
n = .08 dumped rock channel protection
B. Allowable velocities. The maximum allowable velocities for various linings shall be as follows:
Bare earth (seeding) - to 2.5 feet per second (fps)
Sodding - 2.5 fps to 5.5 fps
Dumped rock channel protection - Over 5.5 fps, or paved lining, precast concrete riprap or grouted riprap
C. Minimum grades or velocity. The minimum grade on any ditch shall be 0.3 percent. On occasion it may be necessary to establish a minimum velocity to preclude any undesirable sedimentation in the ditch. These minimum velocities will be at the discretion of the Village Engineer and will be handled individually.
(d) Grading Plan. The developer shall furnish a grading plan to the Village Engineer unless specifically advised otherwise. If the grading plan is not submitted, the improvement plan review will be delayed and acceptance of the subdivision will be postponed until the grading plan can be reviewed.
(e) Culverts and Storm Sewers.
(1) Generally. Culverts and storm sewers that begin as an open pipe shall be checked for headwater depth. The headwater depth shall be such that no property damage will result at the design storm and all water shall be contained within the established drainage easement.
(2) Inlet and outlet ditches. Inlet and outlet ditches for culverts and storm sewers shall be hydraulically checked, and where, in the opinion of the Village Engineer, excessive velocities exist, erosion control shall be provided. The centerline profile of the existing ditch at the inlet and outlet of a culvert or storm sewer shall be shown at least 100 feet beyond the point of the beginning or end of the work.
(f) Interpretation and Extra Data. The interpretation of this appendix is the sole responsibility of the Village Engineer. The Engineer may, at his or her discretion, require any other data he or she deems necessary for a proper review.
(Ord. 22-1979, passed 9-11-1979)