This section prescribes general requirements to be followed in layout of the subdivision or development and subsequent design and construction. More specific requirements are in subsequent sections of Code.
(A) General drainage. Design requirements pertaining to drainage systems other than detention or retention facilities are in subsequent sections of Code. The following requirements shall be considered and addressed in initial planning stages in addition to those of Municipal Code addressing development in areas prone to flooding:
(1) No tract or portion of a tract shall be approved for development if it is subject to periodic flooding such that lots or pavements and other infrastructure are periodically inundated. This extends to jurisdictional and municipal-jurisdictional drainageways and base flood areas.
(2) All inhabitable shelters including basements shall be a minimum of one foot above jurisdictional and municipal-jurisdictional drainageway flood elevations (the base flood elevation at the 100-year event) in the vicinity of the subdivision or development regardless of whether said flood elevations extend into the tract, and a minimum of one foot above water surfaces associated with a 100-year event occurring in conduits and drainageways. All
driving surfaces including private parking lots, shall also be a minimum of two feet above jurisdictional flood elevations.
(3) Dedicated streets and other public accessways shall remain passable to vehicles such that no greater than nine inches of depth of flow at the 100-year storm event shall be allowed to discharge via public accessways as mentioned and said depth shall not remain for more than two hours.
(4) All areas and features requiring state, federal, or other local review and approval shall be identified prior to the preliminary plat approval process.
(5) Storm runoff from areas upstream and downstream of the subdivision or development must be accommodated by systems proposed, in accordance with requirements of this code. In general, runoff from upstream shall be passed through unimpeded in terms of backwater and storage. Storage utilized by constrictions downstream shall remain. Future development upstream and downstream, private or public (by the city), that is pending at the time of the subdivision or development approval process initiation shall be accommodated in design.
(6) For all drainage design the most conservative interpretations will be made, including but not limited to: accounting for conduit systems for pending or existing upstream development such that the most conservative discharges reach the subdivision or development being considered and accounting for existing and future backwater effects downstream. The city reserves the right to require application of the most conservative interpretations in terms of drainage design for the subdivision or development being considered. The city also reserves the right to require drainage calculations extending beyond the subdivision or development being considered and impacting the same.
(7) Underground, or buried, conduit systems shall remain generally perpendicular at street crossings to facilitate future maintenance.
(8) All single family residential roof and foundation drains, including sump pits and pumps, shall be discharged to the front and rear of lots and not to side lot lines. Roof and foundation drains, including sump pits and pumps, shall drain to daylight with the opening at least 15 feet from the foundation and at least 5 feet before the right-of-way or sidewalk.
(9) All multi-family, commercial, and industrial roof and foundation drains not utilizing sump pits and pumps shall be discharged, via buried conduit, into underground conduit systems including storm sewers and culverts and not above or across ground surfaces in any fashion.
(10) The city has no maintenance responsibility for, nor any responsibility to, remediate backups in above ground or buried conduits from their taps to sewer conduits to their connections at the buildings draining storm runoff via roof drains or sump pit drains that might occur due to high water surfaces in City owned and maintained conduits and drainageways.
(11) All developments’ roof and parking area runoff must pass through detention systems, on-site within a particular lot or through a common detention area, before exiting the tract boundaries.
(12) All commercial and industrial tracts’ roof and parking area runoff served by a common detention or retention area for a particular subdivision shall pass through buried conduit within the tract before entering into the public storm sewer system at an inlet or manhole.
(13) Sinkholes shall not be utilized for receiving new storm sewer system discharges.
(14) Swales and grading. Runoff from lots shall be directed to piping or drainage swales so that adjoining lots or properties are not impacted by the runoff. Yard swales or grading will not be maintained, re-graded or re-established by the city.
(B) Treatment of detention or retention facilities. These facilities require additional planning. Design requirements for these are in subsequent sections of Code. The following requirements shall be considered and addressed in initial planning stages:
(1) Additional definition of detention facilities is required as even inlet intakes can serve to detain flows. For the purpose of design and definition in this Code, inlet and culvert intakes and conduits within public areas will not be considered as contributing to detention volume unless included in the designated easement for the detention and/or retention facility which shall include all surface area inundated at the peak water surface at the 100-year event for the individual system(s).
(2) Detention or retention facilities shall not be located in the path of an existing ditch, stream, jurisdictional and municipal-jurisdictional drainageways, or base flood areas so as to create higher backwater and reduce storage for incoming discharges. Side-channel facilities are discouraged, but when necessary, the same backwater and loss of storage criteria for jurisdictional and municipal-jurisdictional drainageways shall apply.
(3) Existing ponds and lakes can be utilized as detention facilities with drainage calculations that show there is sufficient storage above normal pool elevations for those that are not located in the path of an existing ditch, stream, jurisdictional and municipal-jurisdictional drainageways, or base flood areas. For those existing ponds and lakes that are located as such, no additional water surface increase will be allowed above existing normal pool elevations and additional excavation will be required to limit the described increase. The developer may be required to reconfigure existing storage and outlet configurations depending on the needs of the subdivision.
(4) All facilities requiring permitting by the IDNR shall be designed prior to submittal to the IDNR. The developer may obtain classification by the IDNR prior to design, but this will not be considered final until design plans are submitted to the IDNR. All submittals to the IDNR and other agencies involved shall be copied to the city.
(5) The city will not undertake the maintenance of detention or retention facilities.
(6) Underground detention systems are allowed for developments. However, public drainage systems including drainageways with surface discharges, but primarily conduits within right-of-way and easement, shall only discharge to or pass discharges through detention or retention facilities that are of an open basin design, i.e. earthen slopes accessible by vehicles, and not of an underground type. This is due to the potential high costs for emergency maintenance or expansion.
(7) All detention or retention areas shall be included in easement so as to allow emergency and general access by the city, to reserve the right of the city to expand or make improvements to the facility, and to reserve the right to discharge additional runoff into said facility. Notwithstanding anything contained herein, the owner of the land involved is first responsible for maintenance and improvements to the facility.
(8) Access shall be provided to the outlet or pumping station area of the facility via easements and an access road, as prescribed in the city construction details. This reservation may also be used by the city for electrical distribution to any pumping station and for all other utilities.
(9) Detention or retention facilities shall be designed for the entire tract being platted. In the event that phased construction and platting will occur, a separate design just for the tracts being platted shall be required. The developer may construct and/or plat the full facilities with initial phases, however, the outlet design shall coincide with the separate design requirements.
(10) Storm water discharges from commercial, industrial, and multi-family lots or tracts will be treated differently than for those that are strictly single-family due to their potential magnitude and impact on surface flows within street and backlot areas. When said discharges enter into a public conduit system, with or without detention on the lot(s) or tract(s) themselves, said conduit system shall be designed to accommodate the 100-year event discharge from said lot(s) or tract(s) with the same freeboard and capacity requirements as for the same system normally designed to accommodate the 10-year event discharges. All conduit serving the described land use shall be designed to accommodate the 100-year event. Drainage calculations, primarily hydraulic grade lines, shall be provided that show what will occur in conduits and connected inlets that enter into the described 100-year system(s) serving single-family land use at coincident 100-year events in both systems.
(11) Outlets from detention systems on individual lots or development tracts that are not for public use and those that serve only a few lots within an entire development (public) must be connected to appropriately sized public conduit that extends to each lot being served. Outlets from described systems must connect to the public system via buried conduit. When outlets from development tract detention systems are connected to existing public systems that were not designed to accommodate lower frequency events, release of discharges from said tract at all storm frequencies shall not exceed those of pre-development conditions at the 10-year frequency.
(12) Parking lot and roof top detention systems will not be allowed except in business areas where buildings are in close proximity to each other as deemed such by the City.
(13) Pre-development discharges from the subdivision or development shall remain unchanged or reduced in terms of type and quantity of flow and/or velocity at every point of discharge along the boundary of the tract including existing sheet flow conditions at all storm event frequencies. Detention facilities shall be installed to effect this. Note the exception to this is that buried conduit connections to existing public systems from detention system outlets of development tracts shall discharge only pre-development flows at the ten-year frequency.
(14) Discharge from a tract cannot exit the boundary, travel in public ROW and drainage systems, and then be routed back into onsite detention or detention serving several lots of the tract unless the described system is part of a new development meeting other Code requirements.
(15) Proposed detention and retention facilities including outlet structures shall be constructed before any proposed grading begins.
(16) In the event that downstream roadways, right-of-way, properties, conduit systems, or combinations of the aforementioned are at such an elevation such that pre-development discharges to said areas cause periodic inundation such that roadway and continuous access are disrupted periodically or there is inundation of conduit systems adversely affecting downstream properties, the City will require the developer to secure easements and/or additional measures to effect minimum downward slope requirements of this Code from the outlet points of the proposed subdivision or development.
(C) Treatment at development boundaries. The following requirements shall be considered and addressed in initial planning stages.
(1) At all locations along development boundaries where areas drain into the development, an area around the drainage structure, culvert or inlet, equal to at least 1% of the intercepted drainage area shall be set-aside and placed in drainage and utility easement.
(2) The drainage structure within the set-aside area noted in division (C)(1) of this section shall be positioned at the downstream end of the set-aside area.
(3) In the event of phased construction and platting where drainage systems discharge off of development boundaries, tailwater within the downstream drainageways shall be considered in the design of the immediate systems. In the event that tailwater is not considered in the design, subsequent connected drainage systems shall be designed such that their water surface at discharge points is equal to depths calculated with immediate development.
(Ord. 1069, passed 7-20-1998; Am. Ord. 1696, passed 3-21-2016) Penalty, see § 34-1-12