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REQUIREMENTS AND STANDARDS
§ 160.20 REQUIREMENT FOR CONTROLS OF RUNOFF FROM PROJECTS UNDER CONSTRUCTION/NEW CONSTRUCTION.
   (A)   The following Best Management Practices which address the problem of urban runoff shall apply to all projects undergoing construction in the city. The Best Management Practices list set forth below is required by the city. The requirements set forth below shall apply at the time of demolition of an existing structure or commencement of construction and until receipt of a certificate of occupancy:
      (1)   Runoff sediment and construction waste from construction sites and parking areas shall not leave the site;
      (2)   Any sediments or other materials which are tracked off the site shall be removed the same day as they are tracked off the site. Where determined by the Stormwater Manager or his or her designated representative, a temporary sediment barrier shall be installed;
      (3)   On an emergency basis only, plastic covering may be utilized to prevent erosion of an otherwise unprotected area, along with runoff devices to intercept and safely convey the runoff;
      (4)   Excavated soil shall be located on the site in a manner that eliminates the possibility of sediments running into the street or adjoining properties. Soil piles shall be covered until the soil is either used or removed. A plastic or micro-mesh fabric should be used;
      (5)   No washing of construction or other industrial vehicles shall be allowed adjacent to a construction site. No runoff from wash vehicles on a construction site is allowed to leave the site;
      (6)   Drainage controls shall be utilized as needed, depending on the extent of proposed grading and topography of the site, including but not limited to the following:
         (a)   Detention ponds, sediment ponds or infiltration pits;
         (b)   Dikes, filter berms, silt fences or ditches;
         (c)   Down drains, chutes or flumes.
   (B)   Observe basic principles such as:
      (1)   Preserve existing vegetation as much as possible;
      (2)   Mulch or seed bare soil immediately for the best and cheapest erosion protection;
      (3)   Use silt fences, brush barriers, or other approaches to pond and filter sediment from runoff;
      (4)   Install silt check dams made of rock, brush or other products to prevent ditch erosion and remove sediment;
      (5)   Protect inlets and outlets; and
      (6)   Settle out soil particles in sediment traps and basins.
   (C)   The Stormwater Management Plan shall contain, but not be limited to, the following information unless specifically excluded by the Stormwater Manager.
      (1)   A topographic map of the project site and adjacent areas, of suitable scale and contour interval, which shall define the location of streams, the extent of flood plains and calculated high water elevations, the shoreline of lakes, ponds, swamps and detention basins including their inflow and outflow structures, if any.
      (2)   The location and flow line elevation of all existing sanitary, storm or combined sewers.
      (3)   Detailed determination of runoff anticipated for the entire project site following development indicating design volumes and rates of proposed runoff for each portion of the watershed tributary to the storm drainage system, the calculations used to determine said runoff volumes and rates and restatement of the criteria which have been used by the project engineer throughout calculations.
      (4)   A layout of the proposed stormwater management system including the location and size of all drainage structures, storm sewers, channels and channel sections, detention basins, and analyses regarding the effect said improvements will have upon the receiving channel and its high water elevation.
      (5)   The slope, type, and size of all existing and proposed storm sewers and other waterways impacting or impacted by the proposed development on the site.
      (6)   For all detention basins, a plot of tabulation of storage volumes with corresponding water surface elevations and of the basin outflow rates for those water surface elevations
      (7)   For all detention basins, design hydrographs of inflow and outflow for the 25 year, 24-hour events for the site under existing and developed conditions.
      (8)   A profile and one or more cross sections of all existing and proposed channels or other open drainage facilities, showing existing conditions and the proposed changes thereto, conditions called for by these regulations and the relationship of structures, streets and other utilities to such channels.
(Ord. 2803, passed 12-10-2012) Penalty, see § 160.99
§ 160.21 DESIGN CRITERIA.
   The following rules shall govern the design of improvements with respect to managing stormwater runoff:
   (A)   Methods of determining stormwater runoff rate and volume. The volume of required stormwater storage and runoff shall be calculated on the basis of the runoff from a 25-year frequency storm with 24-hour duration. The calculations can be made in accordance with the instantaneous runoff factor method, the rational method or other methods that may be deemed appropriate by the Stormwater Manager.
   (B)   Release rate.
      (1)   All developments undertaken as outlined in that chapter shall be done in such a way as to insure that stormwater falling on a given site shall be absorbed or detained on site to the extent that the controlled release rate of stormwater runoff from all developments shall not exceed the pre-development stormwater runoff rate. The rate at which stormwater runoff is delivered to a designated stormwater storage area shall be unrestricted.
      (2)   In the event that the Stormwater Manager determines that the natural downstream channel or storm sewer system is inadequate to accommodate the release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the downstream channel or storm sewer system.
   (C)   Development design.
      (1)   Where it can be demonstrated by the developer that a higher storm water release rate will not be contrary to the purpose and intent of this chapter and where such proposed release rate will not adversely affect properties in the downstream portion of the watershed, the Stormwater Manager may permit such release to be used as deemed appropriate.
      (2)   Streets, blocks, lots, parks and other public grounds shall be located and laid out in such a manner as to minimize the velocity of overland flow and allow maximum opportunity for infiltration of stormwater into the ground and to preserve and utilize existing and planned streams, channels and detention basins and include whenever possible, streams and floodplain within parks and other public grounds.
   (D)   Excess stormwater passage.
      (1)   An excess stormwater passage shall be provided for all stormwater areas. Such passage shall have the capacity to convey through the proposed development the excess stormwater. The capacity for a passage shall be such that it will be able to transport the peak rate of run-off from a 100-year, 24-hour return frequency storm.
      (2)   There shall be no buildings or structures constructed within excess storm water passage, however, parking lots, playgrounds and park areas, which shall not impair or endanger the water holding capability of a development, shall be considered compatible uses.
      (3)   Appropriate land planning shall be undertaken to preserve the existing natural drainage of a proposed development as part of the excess stormwater passage.
      (4)   Open channels shall be protected from erosion by appropriate vegetative covers, lining or other treatment and earthen channel side slopes shall be no steeper than two to one. Open channels with lining shall have a maximum gradient on side slopes of 67% and channel side slopes steeper than 67% shall be designed as structural retaining walls.
   (E)   Stormwater storage/detention areas. The increased stormwater runoff resulting from the proposed development may be accommodated by the provision of appropriate detention facilities including wet or dry bottom reservoirs, flat roofs, parking lots or streets. Storage areas shall be designed, if possible to provide secondary purposes for recreation, open spaces, parking lot or other types of use that will not be adversely affected by intermittent flooding. The following shall govern the design of detention facilities:
      (1)   Storage volume.
         (a)   All stormwater storage areas must be designed to contain and safely pass stormwater runoff. The combined capacity of these storage areas shall be sufficient to contain the storm from the development. The detention facility must be designed for periodic maintenance and energy dissipaters shall be provided at points necessary.
         (b)   The ponding of stormwater runoff shall not exceed a depth of one foot on a pedestrian mall area or 1-1/2 feet maximum in parking lots. Where these areas are used for ponding the maximum depth should occur in the most remote and least used areas.
         (c)   The drainage and grading design shall be prepared to insure that in a 100-year storm the depth of water run-off in any street, alley, or pedestrian mall will not exceed the level of the first floor of any building.
         (d)   For wet pond storage areas when calculating the storage capacity, only the volume available to store excess stormwater shall be considered. Permanent water storage does not constitute control of excess storm runoff.
      (2)   Release rate. At no time during the design storm shall the stormwater runoff release rate exceed the allowable release rate as set forth in division (B) of this section.
      (3)   Release velocity. Detention facilities shall release stormwater at a non-erosive velocity. The protected channel receiving the detention discharge shall incorporate features to reduce velocity to non-erosive levels at the point where such discharge enters the unprotected channel. If release is into a subsurface conduit the energy gradient in the receiving facility shall not be increased beyond the slope of the conduit.
      (4)   Spillway.
         (a)   Overflow for each stormwater storage area shall be provided in the event of a storm in excess of the design capacity occurs. Such overflows shall be constructed to function without specific attention and shall become part of the excess stormwater passage.
         (b)   Emergency spillways shall be provided to permit the safe passage of runoff generated from a 100-year, 24-hour storm, or greater if required by state law.
         (c)   Where rooftop storage or excess stormwater is provided, the building shall be provided with adequate structural design to insure that roof failure does not occur. Overflow areas shall be provided so that the weight of stored stormwater will not exceed the structural capacity of the roof.
      (5)   Freeboard. Detention facilities shall have adequate capacity to contain storage volume of tributary stormwater runoff with at least one foot of freeboard above the water surface of flow in the emergency spillway in a 100-year, 24-hour storm or as required by state law.
   (F)   Sinkholes and subterranean water channels.
      (1)   The use of sinkholes or subterranean water channels for direct drainage of excess stormwater shall not be permitted although they may be used to drain a stormwater storage area. The introductions of any foreign matter or the filling, clogging or interfering with the natural drainage capabilities of the sinkholes shall not be permitted.
      (2)   Sinkholes shall not be altered in any way which would negatively affect the drainage capabilities of the sinkhole. Development within the 100-year floodplain of a sinkhole shall not be permitted.
(Ord. 2809, passed 12-10-2012) Penalty, see § 160.99
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