The following standards shall apply to all development and activity that necessitates the grading, stripping, cutting, filling or exposure of soils.
(A) General standards.
(1) The development shall conform to the natural limitations presented by topography and soil so as to create the least potential for soil erosion.
(2) Erosion and siltation control measures shall be coordinated with the different stages of development. Appropriate control measures shall be installed prior to development when necessary to control erosion.
(3) Land shall be developed in increments of workable size such that adequate erosion and siltation controls can be provided as construction progresses. The smallest practical area of land shall be exposed at any one period of time.
(4) The drainage system shall be constructed and operational as quickly as possible during construction.
(5) Whenever possible, natural vegetation shall be retained and protected.
(6) If it is necessary to remove top soil from a site being graded or excavated, sufficient top soil shall be hauled back upon completion of the activity to cover the area to a depth of four inches. The top soils hauled in and spread on the disturbed area shall be of a quality at least equal to the top soil removed from the site.
(7) When soil is exposed, the exposure shall be for the shortest feasible period of time. No exposure shall be planned to exceed 60 days. Said time period shall be extended only if the Planning Department is satisfied that adequate measures have been established and will remain in place.
(8) The natural drainage system shall be used as far as is feasible for the storage and flow of runoff. Storm water drainage shall be discharged to marshlands, swamps, retention basins or other treatment facilities. Diversion of storm water to marshlands or swamps shall be considered for existing or planned surface drainage. Marshlands and swamps used for storm water shall provide for natural or artificial water level control. Temporary storage areas or retention basins scattered throughout developed areas shall be encouraged to reduce peak flows, erosion damage and construction costs.
(B) Exposed slopes. The following control measures shall be taken to control erosion during construction.
(1) No exposed slope should be steeper in grade than five feet horizontal to one foot vertical.
(2) Exposed slopes steeper in grade than ten feet horizontal to one foot vertical should be contour plowed to minimize direct runoff of water.
(3) At the foot of each exposed slope, a channel and berm should be constructed to control runoff. The channelized water should be diverted to a sedimentation basin (debris basin, silt basin or silt trap) before being allowed to enter the natural drainage system.
(4) Along the top of each exposed slope, a berm should be constructed to prevent runoff from flowing over the edge of the slope. Where runoff collecting behind said berm cannot be diverted elsewhere and must be directed down the slope, appropriate measures shall be taken to prevent erosion. Such measures should consist of either an asphalt paved flow apron and drop chute laid down the slope or a flexible slope drain. At the base of the slope drain or flow apron, a gravel energy dissipator should be installed to prevent erosion at the discharge end.
(5) Exposed slopes shall be protected by whatever means will effectively prevent erosion considering the degree of slope, soils material, and expected length of exposure. Slope protection shall consist of mulch, sheets of plastic, burlap or jute netting, sod blankets, fast growing grasses or temporary seedings of annual grasses. Mulch consists of hay, straw, wood chips, corn stalks, bark or other protective material. Mulch should be anchored to slopes with liquid asphalt, stakes and netting or should be worked into the soil to provide additional slope stability.
(6) Control measures, other than those specifically stated above, may be used in place of the above measures if it can be demonstrated that they will as effectively protect exposed slopes.
(C) Design standards. When constructed facilities are used for storm water management, they must be designed and installed consistent with the field office technical guide of the local soil and water conservation districts.
(1) Waterways.
(a) The use of the natural above ground drainage system to dispose of runoff should be strongly encouraged. Storm sewers should only be used where it can be demonstrated that the use of the above ground natural drainage system will not adequately dispose of runoff. Above ground runoff disposal waterways may be constructed to augment the natural drainage system. To the extent possible, the natural and constructed waterways should be coordinated with an open space trail system.
(b) The widths of a constructed waterway shall be sufficiently large to adequately channel runoff from a ten-inch storm. Adequacy shall be determined by the expected runoff when full development of the drainage area is reached.
(c) No fences or structures shall be constructed across the waterway that will reduce or restrict the flow of water.
(d) The banks of the waterway shall be protected with a permanent turf vegetation.
(e) The banks of the waterway shall not exceed five feet horizontal to one foot vertical in gradient.
(f) The gradient of the waterway bed should not exceed a grade that will result in a velocity that will cause erosion of the banks of the waterway.
(g) The bed to the waterway shall be protected with turf, sod or concrete. If turf or sod will not function properly, rip rap may be used. Rip rap shall consist of quarried limestone, fieldstone (if random rip rap is used) or construction materials; provided, said construction materials are limited to asphalt cement and concrete. The rip rap shall be no smaller than two inches square nor no larger than two feet square. Construction materials shall be used only in those areas where the waterway is not used as part of a recreation trail system.
(h) If the flow velocity in the waterway is such that erosion of the turf side-wall will occur and said velocity cannot be decreased via velocity control structures, then other materials may replace turf on the sidewalls. Either gravel or rip rap would be allowed to prevent erosion at these points.
(2) Water velocity.
(a) The flow velocity of runoff in waterways shall be controlled to a velocity that will minimize erosion of the waterway.
(b) Flow velocity should be controlled through the installation of diversions, berms, slope drains and other similarly effective velocity control structures.
(3) Sediment control.
(a) To prevent sedimentation of waterways, pervious and impervious sediment traps and other sediment control structures shall be incorporated throughout the contributing watershed.
(b) Temporary pervious sediment traps could consist of a construction of bales of hay with a low spillway embankment section of sand and gravel that permits a slow movement of water while filtering sediment. Such structures should serve as temporary sediment control features during the construction stage of a development.
(c) Permanent impervious sediment control structures consist of sediment basins (debris basins, desilting basins or silt traps) and shall be utilized to remove sediment from runoff prior to its disposal in any permanent body of water.
(d) New constructed storm water outfalls to public waters must provide for filtering or settling of suspended solids and skimming of surface debris before discharge.
(4) Maintenance of erosion control system.
(a) The erosion and velocity control structures shall be maintained in a condition that will ensure continuous functioning according to the provisions of this chapter.
(b) Sediment basins shall be maintained as the need occurs to ensure continuous desilting action.
(c) The areas utilized for runoff waterways and sediment basins shall not be allowed to exist in an unsightly condition. The banks of the sediment basins and waterways shall be landscaped.
(d) Prior to the approval of any plat for development, the developer shall make provision for continued maintenance on the erosion and sediment control system.
(Ord. 18-4, passed 6-19-2018)