(a) This drainage policy, control guidelines and criteria do not provide solutions to all drainage problems, nor is the engineer restricted to these designs or procedures exclusively. Although the policies as stated will hold true for most development work, the City realizes that there may be individual projects involving special or unusual drainage design problems. Exceptions may be granted by the Public Service Director to the policies and criteria in such cases when engineering study(s) justify modification.
(b) Experience has shown that most of the more serious flooding situations are "created". Development can lead to ever increasing flooding problems unless well-conceived, cooperative stormwater drainage and flood control programs are undertaken throughout the entire watershed. For this reason, the general policy of the City of Grandview Heights shall be:
(1) Land uses and developments which increase runoff rate or volume shall control the discharge rate of runoff prior to its release to off-site land.
(2) It is the responsibility of the property owner to not change or alter any drainage course, ditch, flood routing path or drainage system on his property that will damage or cause flooding to adjacent, upstream or downstream property owners.
(3) All stormwater drainage systems, including conveyances, within a development shall be designed to have capacity and depth, including sufficient invert elevations to permit future connections, to serve that total tributary area at the design storm frequency, and based on the rate of single family, residential runoff.. The system for the upstream tributary area must be extended through the development.
(4) All proposed development with a runoff rate greater than that which the downstream system has capacity for, or will be designed for, will be required to control the rate of stormwater discharge.
(5) All developments having existing controls located downstream from the site will be required to control the flow rate of stormwater discharge to that rate which existed prior to development.
(6) All information necessary shall be submitted to the City to determine how stormwater runoff should be controlled within the development prior to its release to downstream properties. The tributary area and the upstream watersheds should be determined using natural land divides unless man-made alterations are approved by the City Engineer as the basis for watershed delineations.
The Stormwater Management Policy applies to all land developments not specifically exempted or granted a waiver as provided under the appropriate section of this Policy.
(c) Adequate Drainage Outlet. Surface water runoff from a development shall be drained off site to an adequate drainage outlet. The location of the outlet shall be approved by the City Engineer and may consist of a ditch, stream, storm sewer, or approved detention basin having sufficient capacity to accommodate the surface water runoff in an engineered manner.
(Ord. 09-04. Passed 2-16-09.)