A. No land shall be developed and no form and function shall be permitted that results in water runoff causing flooding, erosion, or deposit of minerals on adjacent properties. Such runoff shall be properly channeled into a storm drain, watercourse, ponding area, or other public facilities subject to the review and approval of the City Engineer and in accordance with storm drainage plans as may be established by the City.
B. In the case of all residential subdivisions of three (3) or more lots, business and industrial developments, the drainage plans with appropriate spot site elevations shall be submitted to the City Engineer for review and the final drainage plan shall be subject to written approval. In the case of such uses, no modifications in grade and drainage flow through fill, erection of retaining walls or other such actions shall be permitted until such plans have been reviewed and received written approval from the City Engineer.
C. The following standards shall apply to all development and activity that necessitates the grading, stripping, cutting, filling, or exposure of soils.
1. General Standards:
a. The development shall conform to the natural limitations presented by topography and soil so as to create the least potential for soil erosion.
b. 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.
c. 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.
d. The drainage system shall be constructed and operational as quickly as possible during construction.
e. Whenever possible, natural vegetation shall be retained and protected.
f. Where the topsoil is removed, sufficient arable soil shall be set aside for respreading over the developed area. The soil shall be restored to a depth of four inches (4") and shall be of a quality at least equal to the soil quality prior to development.
g. When soil is exposed, the exposure shall be for the shortest feasible period of time. No exposure shall be planned to exceed sixty (60) days. Said time period shall be extended only if the City Engineer is satisfied that adequate measures have been established and will remain in place.
h. The natural drainage system shall be used as far as is feasible for the storage and flow of runoff. Stormwater drainage shall be discharged to marshlands, swamps, retention basins or other treatment facilities. Diversion of stormwater to marshlands or swamps shall be considered for existing or planned surface drainage. Marshlands and swamps used for stormwater 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.
2. Exposed Slopes: The following control measures shall be taken to control erosion during any activity where soils are exposed:
a. No slope should be steeper in grade than four feet (4') horizontal to one foot (1') vertical (4:1).
b. Exposed slopes steeper in grade than ten feet (10') horizontal to one foot (1') vertical (10:1) should be contour plowed to minimize direct runoff of water.
c. 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.
d. 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.
e. Exposed slopes shall be protected by whatever means will effectively prevent erosion considering the degree of slope, soil 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.
f. 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. (Ord. 10-003, 1-19-2010, eff. 7-1-2010)
3. Design Standards:
a. Manmade Waterways:
(1) The natural aboveground drainage system shall be utilized to the extent possible to dispose of runoff. Storm sewers are only to be used where it can be demonstrated that the use of the aboveground natural drainage system will not adequately dispose of runoff. Aboveground runoff disposal waterways may be constructed to augment the natural drainage system. To the extent possible, the natural and constructed waterways shall be coordinated with an open space trail system. (Ord. 10-003, 1-19-2010, eff. 7-1-2010; amd. 2017 Code)
(2) The widths of a constructed waterway shall be sufficiently large to adequately channel runoff from a ten inch (10") storm. Adequacy shall be determined by the expected runoff when full development of the drainage area is reached.
(3) No fences or structures shall be constructed across the waterway that will reduce or restrict the flow of water.
(4) The banks of the waterway shall be protected with a permanent turf vegetation.
(5) The banks of the waterway shall not exceed five feet (5') horizontal to one foot (1') vertical (5:1) in gradient.
(6) The gradient of the waterway bed shall not exceed a grade that will result in a velocity that will cause erosion of the banks of the waterway.
(7) The bed of the waterway shall be protected with turf, sod, or concrete. If turf or sod will not function properly, riprap may be used. Riprap shall consist of quarried limestone, fieldstone (if random riprap is used) or construction materials, provided said construction materials are limited to asphalt cement and concrete. The riprap shall be no smaller than two inches (2") square nor larger than two feet (2') square. Construction materials shall be used only in those areas where the waterway is not used as part of a recreation trail system.
(8) If the flow velocity in the waterway is such that erosion of the turf sidewall will occur and said velocity cannot be decreased via velocity control structures, then other materials may replace turf on the sidewalls. Either gravel or riprap may be allowed to prevent erosion at these points.
b. Water Velocity:
(1) The flow velocity of runoff in waterways shall be controlled to a velocity that will minimize erosion of the waterway.
(2) Flow velocity shall be controlled through the installation of diversions, berms, slope drains, and other similarly effective velocity control structures.
c. Sediment Control:
(1) To prevent sedimentation of waterways, pervious and impervious sediment traps and other sediment control structures shall be incorporated throughout the contributing watershed.
(2) 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 may serve as temporary sediment control features during the construction stage of a development.
(3) Permanent impervious sediment control structures consist of sediment basins (debris basins, silt basins, or silt traps) and shall be utilized to remove sediment from runoff prior to its disposal in any permanent body of water.
d. Maintenance Of Erosion Control System:
(1) The erosion and velocity control structures shall be maintained in a condition that will ensure continuous functioning according to the provisions of this title.
(2) Sediment basins shall be maintained as the need occurs to ensure continuous desilting action.
(3) 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.
(4) Prior to the approval of any development, the developer shall make provision for continued maintenance of the erosion and sediment control system.
D. The top of any exterior foundation shall extend above the elevation of the street, gutter or inlet of an approved drainage device a minimum of twelve inches (12") plus two percent (2%). Exceptions to this standard may be approved by the City Engineer when it can be demonstrated that required drainage to the point of discharge and away from the structure is provided at all locations on the site. (Ord. 10-003, 1-19-2010, eff. 7-1-2010)