General requirements for drainage follow. More specific requirements are per the standards.
(A) Two systems provided. Whenever drainage control measures are proposed or considered, two systems shall be provided, the Minor System and the Major System.
(1) Minor System. The Minor System shall be designed to convey the runoff from the more frequently experienced rainfall events. Generally this system is designed for the storm with the ten-year frequency of recurrence. The system shall consist of swales, inlets, sewers and ditches.
(2) Major System. The Major System shall be designed to convey and manage the runoff from the least frequently experienced rainfall events. This system shall be designed for the storm with the 100-year frequency of recurrence. The system shall consist of swales, inlets, sewers, ditches, and streets. It shall be designed to safely convey and manage the runoff and to minimize property damage.
(B) Pass through runoff.
(1) All drainage plans shall accommodate the runoff that enters the site from other locations in the tributary watershed. The runoff may be diverted around the site or accommodated directly in the design of the site storm runoff control measures. In no event shall off site drainage be blocked or restricted by the proposed development.
(2) When appropriate, and at the request of the City Engineer, the pass through runoff shall be directed through the site detention basins to provide downstream protection from the storms with the more frequent recurrence interval. When this is required the discharge structure and overflow shall be designed to accommodate the pass through runoff.
(C) Exit characteristics.
(1) The characteristics of the runoff exiting a site shall not differ substantially after development from those that existed before development. Any runoff concentrated through the course of development into a sewer, culvert, swale or ditch shall only be discharged into a defined and established drainage course.
(2) It may be necessary to improve the drainage course downstream from a site so that it is capable of conveying the increase runoff from the development. This may be necessary to handle either the rate of discharge or the duration of discharge.
(D) Public and private systems. During the course of the planning and design of the runoff control measures it shall be determined and documented whether the measures are to be public or private.
(1) Public systems. The public system shall be maintained by the city after their acceptance by the city. Generally, public systems shall be those in and/or under public streets, or those conveying the runoff from large areas of the city.
(2) Private systems. The private systems shall be privately maintained. Generally private systems shall be those in and under private streets and private sites. Rear year swales, ditches that convey the runoff from individual sites, or development detention basins constructed as runoff control measure for a development, shall be private systems.
(a) Provisions shall be made for the maintenance of private systems. On an individual site the owner shall maintain the system. In a development, a property owners association, or some other vehicle, shall be established to provide for said maintenance. Documentation of the provisions for maintenance shall be provided to the City Engineer and accepted by him if, in his opinion, they are appropriate.
(b) If the system is not maintained so that it functions in the manner that it was designed and constructed and thereby threatens to affect or damage properties owned by others, or is not in compliance with any agreement between the owner and the city, the Board may, after notice by registered mail to the owner of the property:
1. Cause the necessary repairs to be completed. The cost of said repairs may be assessed to the property owner(s) through the city's assessment process; and/or
2. Levy a fine against the owner of the property of up to $50 for each violation and/or occurrence, each day constituting a separate occurrence. The City Engineer shall provide written notification of the alleged violation and fine to the owner(s) of the property. The notice shall be delivered in person to the owner or his representative, or sent by registered mail. The administration of the procedure shall be through the city's Local Ordinance Violations Bureau. The Board may levy a fine for each and every day that the violation is continued.
(c) Recorded easements shall be provided over all components of public and private systems. The easements shall run to the public and the city for purposes of maintaining the facilities located in said easements. However, the establishment of said easements shall in no manner obligate the city to maintain private systems but shall, in the event of an emergency, allow the city to enter and make temporary emergency repairs to the system. The cost of said emergency repairs may be billed to the entity responsible for the maintenance of the system.
(E) Individual sites.
(1) On individual sites proposed for development the runoff control measures shall specifically provide for adequate surface slopes away from all building structures. They shall also provide for the appropriate elevation of said structure as it may relate to ground water elevations and/or flood elevations from adjacent streams, ponds, detention basins, or street low points.
(2) The location and configuration of downspouts and/or sump pump discharges shall be such that the runoff does not damage or inconvenience adjacent properties. In general, downspouts and sump pump discharge shall be directed towards the front or rear of the site and not at the adjacent site property lines. In no event shall downspouts, sump pumps, footing tiles, or any other surface or ground water source be discharged into the sanitary sewer system.
(F) Controlled discharge required.
(1) The runoff from any combined roof and pavement area over 5,000 square feet, or pavement area alone over 3,500 square feet, shall be controlled and managed in some manner, approved by the City Engineer, before it discharges to the city street or sewer system.
(2) Single and duplex residential construction shall be exempt from the strict requirements of this division. However, the runoff from said construction shall be controlled in a manner that minimized problems to adjacent properties.
(G) Storm sewers, structures, ditches, swales, and culverts. All storm sewers, structures, ditches, swales, and culverts shall be designed and constructed according to the requirements of the standards and sound engineering practice. They shall be designed to safely convey the appropriate designed flows and to minimize maintenance and repair needs.
(H) Retention basins. Because of the predominant soil characteristics in the city, retention basins are not allowed.
(I) Detention basins. Detention basins shall be required for any site proposed for development except individual single and duplex residential construction. The requirements for detention maybe waived by the City Engineer if provisions are made in the overall development for appropriate runoff management.
(1) General. Detention basins shall be designed with a consideration for the welfare of the residents who live in the vicinity and the safety of those who might be attracted to the facility. Basins and their appurtenances shall be designed to require minimum maintenance. Slopes should be flat enough for safe walking and mowing. The areas designed for detention basins shall be designed to be used for other purposes such as recreation, man-made wetlands, open space, or other uses. The use of fences shall be kept to a minimum. The designer is encouraged to make the facility as aesthetically pleasing as possible. Slopes should vary. Straight lines should be avoided. Long sweeping curves should be used to make the facility appear natural and part of the overall landscape. Basins should be landscaped with tress and shrubs appropriate to that location.
(2) Storage volume and discharge rate. Detention basins shall provide a storage volume adequate to contain the runoff from the developed site that results from a storm event with a 100-year frequency of recurrence. The discharge rate through the discharge control structure shall not exceed the runoff rate from the undeveloped site that results from a storm with a two-year frequency of recurrence.
(3) Dry bottom basins. Dry bottom basins shall be designed with adequate bottom slopes to minimize standing water after the stored runoff has been discharged. Underdrains may be required to provide additional drainage, particularly in the vicinity of the discharge control structure.
(4) Wet bottom basins.
(a) Wet bottom basins shall be designed to provide a permanent water depth adequate to retard weed growth and to sustain aquatic life. They shall incorporate provisions for walkways around the perimeter of the pool to allow for recreational use and for access for weed control and emergency response. The ground slopes below pool level shall be sufficiently flat to allow an individual who falls in to recover and walk from the water without great difficulty.
(b) The design of this type of basin shall consider the need for shoreline bank protection from wave action and the need for a supplemental water supply for use during periods of low rainfall. Wet bottom basins generally present more difficult maintenance requirements than do the dry bottom basins.
(c) These requirements include, but are not limited to, weed control, algae control possible wildlife management, erosion control at the shore line, and maintenance of the supplemental water supply equipment. The developer shall make adequate provision for these items.
(5) Paved area basins. Paved areas such as parking lots may be used for detention basins where appropriate. The basins shall be designed so that the maximum stored water depth is not likely to cause damage to vehicles or adjacent property. Generally, the basin(s) should be located in the more remote areas of the lot and/or in the service drives if possible.
(6) Underground basins. Underground detention basins are permitted but should be used only when no other options are available. Underground basins shall be designed using vaults, pipe networks, or other means that allow access for inspection, cleaning, and/or maintenance. Storage of runoff in the voids of aggregate beds shall be avoided.
(7) Discharge control structure and overflow. Discharge control structures shall be designed to be safe, simple, and easily maintained. Their design shall be such that they are not subject to clogging with debris. They shall not rely on manual operation of valves or gates. Wherever possible they shall be designed to provide storage from the runoff generated by storm events with the greater frequencies of recurrence, as well as the major storms.
(J) Renovation of existing developed sites. There are certain sites in the city that were developed without providing appropriate drainage control measures. If any renovations or additions that require a building permit are proposed for these locations the applicant shall also provide reasonable drainage control measures appropriate for the site.
(K) Erosion and siltation. Wherever possible, drainage control measures shall be designed to help control erosion and situation. Pass through runoff shall be diverted around the site to the greatest extent practical. Detention basins shall be undercut to provide sediment traps during the construction phase of the development. After the development is completed, the basins shall be cleaned and the ground surfaces brought to final grade.
(Ord. 26-2008, passed 7-14-08)