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§ 11.05.040.040 GENERAL DESIGN REQUIREMENTS.
   (A)   All required stormwater retention/detention facilities must be constructed and in operation prior to paving and building construction, unless otherwise approved by the Department of Public Works.
   (B)   The capacity of the downstream drainage course is required to be evaluated for a minimum distance of one-fourth mile from the point of discharge of the development.
      (1)   The downstream conveyance system must be adequately sized to handle off-site peak flows conveyed through the development plus the on-site developed peak flow discharged to the drainage course from the controlling ten-year storm.
      (2)   This system should be shown on the drainage layout.
      (3)   The size of the controlled outlet shall be calculated for the total drainage basin when the total run-offs from both off-site and on-site areas are combined.
   (C)   The limits of the FEMA mapped 100-year floodplain shall be required to be delineated on the final plat, as well as the engineering drawings for plat construction.
   (D)   Arrows indicating drainage direction in all public and private property shall be shown on the construction drawings for all hydraulic conveyance systems.
   (E)   (1)   A topographical map sufficient in area to show all areas draining onto the proposed land development must be submitted and show enough of abutting downstream properties to indicate natural or human-made drainage course into which the proposed land development is to drain.
      (2)   The direction of flow, acreage of areas contributing drainage to the development, the outline of the development and location of intermittent streams or drainage courses which are within the site boundaries shall be indicated on this map.
   (F)   Surface water entering the subject property shall be received at the naturally occurring location, and surface water exiting the subject property shall be discharged at the natural location, with adequate energy dissipaters within the subject property to eliminate the potential for detriment to the existing downstream infrastructure.
(Prior Code, § 11.05.040.040) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)
§ 11.05.040.050 STORM SEWER SYSTEM; MINIMUM REQUIREMENTS.
   (A)   Manhole spacing. The maximum spacing between storm manholes shall be 500 feet.
   (B)   Minimum pipe size.
      (1)   The minimum diameter of any storm drain pipe shall be 12 inches, except that a maximum length of 60 lineal feet of eight-inch diameter pipe may be used between inlets and manholes.
      (2)   The minimum size of any storm drain culvert is 12 inches.
   (C)   Storm drain manhole ring and cover.
      (1)   The storm drain manhole ring and cover shall be East Jordan Iron Works Model 3 772Z 1 or an approved equal.
      (2)   The cover shall be marked “storm.”
   (D)   Curbs and gutters or swales.
      (1)   Streets and roads shall be designed to ensure proper drainage and curbs and gutters or swales shall be required in all subdivisions.
      (2)   Curbs and gutters of adjoining properties shall be extended to match any new curb and gutter. Gutter, ditch and swale flow line grades shall be greater than 0.5%.
   (E)   Culverts and drainage facilities. Culverts of adequate size shall be provided and installed by the developer where drainage channels intersect any street right-of-way or easement. All culverts shall extend at least the width of the base of the fill.
      (1)   The amount of backfill to be placed over the culvert and a culvert’s capacity shall be determined by a licensed professional engineer.
      (2)   This shall include arrangements for driveway culverts. Culverts larger than 24 inches shall have flared ends.
   (F)   Drain inlet frame and grate. The curb inlet frame and grate shall be Olympic SM 49, East Jordan Iron Works combination of product numbers 7222Ml or 7222M3 (Herringbone grate) or an approved equal.
   (G)   “Beehive” area drain frame and grate. The beehive area drain frame and grate shall be Neenah Foundry Model R-2560-D6 “beehive grate with frame,” East Jordan Iron Works 1205-2 or an approved equal.
   (H)   “Drive over” area drain frame and grate. The drive over area drain frame and grate shall be Neenah Foundry Model R-2556-A Type C frame with Type G grate, East Jordan Iron Works Model 1848-G or an approved equal.
   (I)   Sump requirements for catch basins and manholes. A 18-inch sump is required for catch basins and drain inlets. A 24-inch sump is required for storm drain manholes.
(Prior Code, § 11.05.040.050) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)
§ 11.05.040.060 FLOW CONTROL AND RETENTION/DETENTION POND DESIGN REQUIREMENTS.
   (A)   This section outlines the requirements for sizing flow control facilities. The flow control standards are based on the Stormwater Management Manual for Eastern Washington and the Spokane County Stormwater Manual.
      (1)   Standard flow control facilities are detention, retention (natural depressions) and infiltration facility.
      (2)   Any other facility is considered a non-standard system and shall be evaluated individually by the City PWD.
      (3)   Flow control facilities are necessary to mitigate potential adverse impacts on down-gradient properties due to the increase in stormwater run-off caused by land development.
   (B)   (1)   The peak rate of stormwater run-off from any proposed land development to any natural or constructed point of discharge downstream shall not exceed the pre-development peak rate of run-off.
      (2)   The post development volume of run-off can exceed the pre-development volume of run-off when the required down-gradient analysis demonstrates that there will be no adverse impacts on down gradient properties or existing natural and constructed conveyance systems.
(Prior Code, § 11.05.040.060) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)
§ 11.05.040.070 DETENTION FACILITIES MINIMUM REQUIREMENTS.
   (A)   Facility volume.
      (1)   The CN method requires the selection of, or the input of, a rainfall distribution and the precipitation associated with a design storm.
      (2)   The NRCS Type I 24-hour ten- and 100-year storm events are the design storms to be used for all flow control facilities that use a surface discharge.
      (3)   Detention ponds shall be sized using one of the following methods:
         (a)   Sized to contain the difference between the post development and the pre-development 24-hour storm events; or
         (b)   Post development level pool routing method with a draw down time of 72 hours.
   (B)   Setbacks. When a detention facility is proposed upslope of developed property or at the top of a slope inclined 15 % or greater, the minimum setback from the slope must be greater than or equal to 50 feet or as determined by a licensed engineer with geotechnical experience.
   (C)   Release point.
      (1)   Generally.
         (a)   Stormwater run-off from a developed site shall leave the site in the same manner and location as it did in the pre-developed condition.
         (b)   The distance between the outlet structure and the inlet into the detention facility shall be maximized.
      (2)   Outflow control structures.
         (a)   Control structures are manhole or catch basins with a restrictor device used for controlling outflow from a facility to meet a desired standard.
            1.   Outflow structures are required for all stormwater detention facilities.
            2.   The restrictor device is usually multiple orifices, consisting of two or more orifices and/or a weir section sized to meet performance requirements.
         (b)   1.   Run-off shall enter the detention facility through a conveyance system separate from the control and outflow conveyance system.
            2.   The distance between the inlet and outlet shall be maximized to reduce sediment from accumulating in the outflow structure. The types of outflow control structures are listed below.
               a.   Multiple orifice restrictors.
                  i.   In most cases, control structure need only two orifices: one at the bottom and one near the tip of the riser;
                  ii.   Minimum orifice diameter is three inches; and
                  iii.   Orifice shall be constructed on a tee section or on a baffle.
               b.   Risers and weir restrictor.
                  i.   Properly designed weirs maybe used as flow restrictors. However, they must be designed to provide for primary overflow of the developed 100-year peak flow discharging to the detention facility; and
                  ii.   The combined orifice and riser (or weir) overflow may be used to meet flow requirements. However, the design must still provide for primary overflow of the developed 100-year peak assuming all orifices are plugged.
               c.   Outflow control structure minimum requirements. The following minimum access requirements shall be met. Additional requirements are specified in Appendix A.
                  i.   An access road to the control structure is required for inspection and maintenance; and
                  ii.   Manhole and catch basin lids for control structure shall be locking and rim elevation shall match proposed finish grade.
(Prior Code, § 11.05.040.070) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)
STREETS AND TRANSPORTATION
§ 11.05.050.010 OVERVIEW.
   (A)   Purpose.
      (1)   It is the purpose of this section to establish minimum standards for public and private transportation facilities for vehicles, public transit, pedestrians and bicycles, hereafter constructed or improved as a condition of city approval of a development, or a transportation project constructed by the city. These standards are intended to implement city’s growth policy and to minimize total costs over the life of the transportation system.
      (2)   Implementing these standards requires balancing of several policy concerns, including, but not limited to:
         (a)   Providing a safe and efficient transportation system;
         (b)   Implementing the complete streets policy;
         (c)   Discouraging excessive speed; and
         (d)   Requiring no more right-of-way than necessary.
   (B)   Definitions. Words and phrases in these standards have the same general meaning as those contained in the city subdivision regulations, the zoning ordinance of the city and the MPWSS. If terms are conflicting or unclear, the PWD will clarify the meaning and intent.
   (C)   Functional classifications; purpose. The purpose of a functional classification system for city roads is to define varying levels and types of transportation infrastructure, and to provide for the safe and efficient movement of people and goods, while at the same time preserving residential areas and maintaining the economic vitality of commercial and industrial areas. The system classifies transportation facilities as either urban or rural roads. Within urban roads, they are further divided into arterials, collectors or local roads.
   (D)   Functional classifications; urban roads. Urban roads are classified as outlined below.
      (1)   Major arterial. The basic element of the city’s road system. All other functional classifications supplement the major arterial network. Access to a major arterial is generally limited to intersections with other major arterials or to the interstate system. Direct access is minimal and controlled. The purpose of a major arterial is to serve the major centers of activity, the highest traffic volume corridors and the longest trip distances in an urbanized area. This classification of roads carries a high proportion of the total traffic within an urban area. The intended function is to provide for the expedient movement of traffic. Posted speed limits on major arterials typically range from 35 mph to 70 mph and typically carry greater than 15,000 vehicles per day.
      (2)   Minor arterial. Interconnects with and augments the major arterial system. It also provides access to lower classifications of roads on the system and may allow for traffic to directly access destinations. They provide for movement within sub-areas of the city, whose boundaries are largely defined by the major arterial road system. They serve through traffic, while at the same time provide direct access for commercial, industrial, office and multi-family development but, generally, not for single-family residential properties. The purpose of this classification of road is to increase traffic mobility by connecting to both the major arterial system and also providing access to adjacent land uses. Posted speed limits on minor arterials typically range from 25 mph to 55 mph and can carry between 5,000 and 15,000 vehicles per day.
      (3)   Major collector. Provides for land access and traffic circulation within and between residential neighborhoods, and commercial and industrial areas. It provides for the equal priority of the movement of traffic, coupled with access to residential, business and industrial areas. A collector roadway may at times traverse residential neighborhoods. Posted speed limits on collectors typically range from 25 mph to 45 mph and can carry between 3,500 and 5,000 vehicles per day.
      (4)   Minor collector. Provides for land access and traffic circulation within and between residential neighborhoods, and commercial and industrial areas. Future growth of the city outside the subdivision will have limited use of the roadway. It provides for the equal priority of the movement of traffic, coupled with access to residential, business and industrial areas. Posted speed limits on collectors typically range from 25 mph to 45 mph and can carry between 1,500 and 3,500 vehicles per day.
      (5)   Local. Comprises all facilities not included in the higher systems. Its primary purpose is to permit direct access to abutting lands and connections to higher systems. Usually through-traffic movements are intentionally discouraged. Posted speed limits on local roads typically range from 20 mph to 30 mph and designed for less than 1,500 vehicles per day.
(Prior Code, § 11.05.050.010) (Ord. 2019-9, passed 9-3-2019; Ord. 2021-15, passed 12-20-2021)
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