A. The stormwater collection system shall be designed either:
1. To pass a minimum of the runoff from a ten percent (10%) chance storm in a pipe network together with an overland flow path with capacities so that the combination of the two will pass the runoff from a one percent (1%) chance storm under ultimate urbanized conditions.
2. Or, to pass the entire runoff from a one percent (1%) chance storm in the pipe network. Should the entire runoff from a one percent (1%) chance storm be conveyed in an enclosed drainage network, grading shall be designed to convey the runoff from the one percent (1%) chance storm overland in the event of inlet or storm sewer blockage or bypass.
3. In either case, an overland drainage easement shall be required for overland flows. No overland flows shall be allowed to adversely affect structures.
4. In areas where overland flows may cause problems, the city manager may require that the entire runoff from the one percent (1%) chance storm shall be conveyed through an enclosed drainage network.
5. In areas where ultimate urbanized flows are not planned for conveyance to a regional detention facility, the city manager may reduce the capacity requirement to the existing condition flows.
B. The overland flow portion of the collection system shall be confined to dedicated rights of way, or drainage easements to assure the stormwater can pass through the development without inundating the lowest level of any building, dwelling, or structure. All drainage easements shall be shown on the plat.
C. The distance between inlets, as well as the distance to the first inlet on a street shall be determined by the lesser of the following:
1. For the one percent (1%) chance storm, water depth shall not exceed the top of curb, or
2. Six hundred feet (600').
D. At sump locations, the water depth shall not exceed six inches (6") above the top of curb, or twelve inches (12") above the top of grate, whichever is less, for the one percent (1%) chance storm. Where sump collection systems are used, an overflow route shall be provided in the event of a complete blockage of the inlet of pipe. If the inlets and pipe are sized for the one percent (1%) chance storm, a sod overflow can be used. If a ten percent (10%) chance storm inlet and pipe system is designed, the overflow area shall be concrete lined. When a sod overflow structure is constructed, it shall be lined with Bermuda grass or approved equal and shall contain energy dissipaters, if required at the outflow point.
E. Driveway approaches shall be designed and constructed so that the runoff from the one percent (1%) chance storm shall not leave the roadway except in locations where the driveway is designed as part of the drainage system.
F. Runoff from areas greater than one-half (1/2) acre outside the roadway of arterial and collector streets shall be collected before it reaches the roadway. In no circumstance shall concentrated flows be allowed to discharge into arterial streets. Parking lots shall have internal drainage systems so as to reduce concentrated flow onto streets. This requirement shall not apply to residential lots used as single-family residences. The city manager may approve sheet flows to the subject streets when connecting to an underground storm sewer system is not economical. In sheet flow instances, the developer must prove no adverse impact to the traveling public, and that the street drainage system is capable of conveying the increased flows.
G. Site grading shall provide surface water drainage directly into a storm sewer, natural drainage course, improved channel, or paved street without crossing more than four (4) adjacent lots.
H. No inlets shall be designed for placement within driveways or entries unless individually approved by the city manager.
I. Drainage or utility easements of satisfactory width to provide working room for construction and maintenance shall be provided for all stormwater collection systems. In no case shall the total easement width be less than fifteen feet (15').
J. All improved open drainage courses shall be maintained by the owner of the land upon which they are located and by the person or entity actually occupying the land upon which the improved open drainage courses are located. Maintenance called for by this section shall be performed as often as necessary to keep the drainage course free of debris and any wild growth above the height of eighteen inches (18") above the finished grade of the improved drainage course. Maintenance as necessary to keep sedimentation from exceeding twelve inches (12") in depth above the finished grade will also be performed. In the event that a person or entity charged with the maintenance of an improved open drainage course allows sedimentation in excess of the limits prescribed above, or allows wild growth or debris in excess of the limits prescribed above, to accumulate within the improved open drainage course, and the premises upon which the sedimentation, wild growth, or debris is allowed to accumulate is hereby expressly declared to be a nuisance. In addition to any other remedies available to the city, such nuisances may be abated in the manner provided under this code for any other nuisance. (Ord. 1969, 2011)