Broadview Heights City Zoning Code
CHAPTER 1286
DETENTION AND RETENTION BASIN DESIGN
§ 1286.01 COMPLIANCE REQUIRED.
All detention and retention basins constructed in the city shall be constructed in conformance with the provisions of this chapter.
(Ord. 1-91, passed 1-7-1991)
§ 1286.02 FINDINGS AND GENERAL STANDARDS.
(A) The prevention of accelerated flooding and stream channel erosion in conjunction with urban development requires control of the discharge rate and volume of runoff prior to its release to off-site land. The purpose of this chapter is to: permit development without increasing the flooding of other lands, and
provide a basis for design of storm drainage systems on lands above or below undeveloped areas which will preserve the rights and options of both contributing and receiving property owners and assure the long-term adequacy of storm drainage systems.
(B) Accelerated channel erosion as well as increased flooding damage, could be controlled if the predevelopment hydrograph could be maintained. It is usually not practical, however, to retain the predevelopment rate of infiltration when a large part of the watershed is covered with impervious surfaces. The concept of reducing peak flows below those of predevelopment storms was developed as an alternative to maintaining the predevelopment hydrograph. The logic of this concept is to compensate for the increased erosiveness of:
(1) Increased volume of runoff due to loss infiltration;
(2) More frequent occurrences of the same flow. For example, a subdivision may have the peak flow of a predevelopment five-year storm occur once a year after development is complete; and
(3) Less sediment in the runoff water because the watershed is paved with nonerosive surfaces or good grass cover.
(C) The two-step standard requires that:
(1) The peak rates of runoff from an area after development shall be no greater than the peak rates of runoff from the same area before development for all 24-hour storms from one- to 100-year frequency. Designing for the one-, two-, five-, ten-, 25-, 50-, and 100-year storms is considered adequate to meet the requirement. Storm water requirements must be met at each point storm water is discharged from a development area;
(2) If the volume of runoff from an area after development will be greater than the volume of runoff from the same area before development, it shall be compensated by reducing the peak rate of runoff from the critical storm and all more frequent storms occurring on the development area to the peak rate of runoff from a one-year frequency, 24-hour storm occurring on the same area under predevelopment conditions. Storms of less frequent occurrence (longer return periods) than the critical storm up to the 100-year storm, shall have peak runoff rates no greater than the peak runoff rates from equivalent size storms under predevelopment conditions.
(D) The critical storm for a specific development area is determined as follows:
(1) Determine the total volume of runoff from a one-year frequency, 24-hour storm, occurring on the development area before and after development;
(2) From the volumes determined in division (D)(1) hereof, determine the percent of increase in volume of runoff due to development, and, using this percentage, select the 24-hour critical storm from this table:
If the Percentage of Increase in Volume Runoff Is: | The 24 Hour “Critical Storm” for Discharge Limitation Will Be: | |
Equal to or greater than | and less than | |
If the Percentage of Increase in Volume Runoff Is: | The 24 Hour “Critical Storm” for Discharge Limitation Will Be: | |
Equal to or greater than | and less than | |
0 | 10 | 1 year |
10 | 20 | 2 year |
20 | 50 | 5 year |
50 | 100 | 10 year |
100 | 250 | 25 year |
250 | 500 | 50 year |
500 | – | 100 year |
(E) The standard set forth in division (D) hereof basically requires peak flow to be reduced in proportion to increased runoff volume. If runoff volume is not increased, peak flows are only required to match predevelopment peak runoff rates for equivalent size storms for all storms from one-year to 100-year storms. This criterion is designed to require more control when the change in the runoff pattern caused by development is more drastic. The quantity and cost of preventative control features will need to be in proportion to the level of increase in runoff caused by the change in land use; a fair and equitable criterion.
(F) Concern is frequently expressed in regard to the extremes of the accelerated storm water control standard; the one- and the 100-year frequency storms. Justification for using the one-year storm is based on the erosivity of stream flow and on what is known as the “routing problem”. Small or frequent storms are very erosive because they occur so often. Damage doesn’t have time to heal before the next storm comes. Bankfull channel flow is essentially the most erodible state of stream flow on the channel itself. Any increase spills out over the floodplain with very little increase in the velocity of channel flow. Any flow less than bankfull generally has a corresponding decrease in velocity, and, therefore, causes less erosion damage to the channel. Where there is a significant increase in runoff volume, it is very important to have the runoff occur at something less than bankfull flow, especially in watersheds approaching complete development. Longer duration of bankfull flow than that which occurred under predevelopment conditions, can have disastrous effects on the stream channel and resulting sediment pollution. Since channels generally size themselves for about a one and one-half to a two-year frequency storm runoff event, the one-year storm was chosen as the control storm to prevent significant channel erosion.
(G) The “routing problem” is the problem of channel flow downstream from numerous smaller watersheds. As runoff from the smaller watersheds is altered, the effect on channel flow somewhere downstream, where all of the watersheds come together, can be favorable or adverse. Ideally, the entire large watershed should be hydraulically planned and the level of control of each sub-watershed should be based on the accumulative effects downstream. Since experience has proven the near impossibility, politically, of realizing that degree of organizational control, the one-year outlet rate is further justified in order to minimize adverse effects on the “routing problem” when compensation is necessary to control increased flow volumes.
(H) Many people suppose that runoff peaks and volumes do not increase from the large or infrequent storm because the ground is saturated by these storms and most of the rainfall will run off whether the land is used for forest land, cropland or urban purposes. Urbanization can, in fact, cause an increase in both peak and volume of runoff. Most of the increase may be in the early part of such a storm and perhaps the 25- or 50-year storm control may adequately address the situation. There are many variables which affect the storm water runoff pattern, including soil type, slope, kind of cover, percent of impervious cover, kind of disturbance and compaction. The 100-year storm needs to be examined in a development situation to determine its specific effect. Emergency flow areas and emergency outlets from structural work need to account for such storms if basements are not to be full of water and structures are not to fail. The additional control necessary for the 100-year frequency storm is not a highly significant factor in storm water management for accelerated runoff control.
(I) In addition to controlling channel erosion, this standard should make long range planning for storm water management easier. Storm sewers and stream channels can be designed in accordance with existing runoff conditions knowing that upstream runoff rates cannot be increased. This standard would also prevent an increase in flood levels and frequencies below future developments and, in many cases, reduce development costs because of reduced storm sewer size, particularly where multiple use detention facilities can be utilized in designated open space.
(J) A uniform procedure for determining runoff would be helpful in designing to meet this standard. The U.S. Soil Conservation Service procedures in Technical Release No. 55, 1986 edition, are recommended. These procedures consider watershed area, watershed shape, change in land use, soil type, hydrologic condition, impervious area, modification of hydraulic channels, increased intensity of rainfall near the middle of a storm, initial abstraction (surface storage, interception and infiltration prior to runoff), and decreased infiltration as a storm progresses.
(Ord. 1-91, passed 1-7-1991)
§ 1286.03 DEFINITIONS.
As used in this chapter.
“Channel.” Means a natural or artificial watercourse, which continuously or periodically contains moving water or which forms a connecting link between two bodies of water. It has a definite bed and banks which confine the water. “Channel flow” means the water flowing within the limits of the defined channel.
“Detention/Retention Basin Manual.” Means the technical design manual prepared by the Engineer of the City of Broadview Heights.
“Developer.” Means any person who acts in his or her own behalf or as the agent of an owner of property and who engages in the alteration of land or vegetation in preparation for or in connection with construction activity.
“Development.” Means any alteration of land or vegetation in preparation for or in connection with construction activity.
“Drainageway.” Means a route or course along which water moves or may move to drain an area.
“Emergency flow way.” Means the flow routes and drainageway necessary to convey the 100-year storm through a development.
“Emergency spillway.” Means a spillway that must be included in all retention/detention basin designs, SCS Methods must be utilized in its design. Design frequency of 100 years must be used.
“Erosion control.” Refers to requirements documented in the Ohio Department of Natural Resources Division of Soil and Water Conservation “Urban Sediment Pollution Abatement Rules”.
“Fence.” Means an enclosure that is required around all storm water facilities as required by the Planning Commission.
“Flood.” Means the temporary inundation of any land not normally covered by water due to heavy rainfall or runoff or due to a temporary rise in the level of rivers, streams, watercourses, or lakes.
(1) “Average annual flood.” Means a flood equal to the mean of discharges of all the maximum annual floods during the period of record.
(2) “Regional flood.” Means the name applied to the 100-year flood in floodplain information reports. The 100-year flood has a 1% probability of being equaled or exceeded in a period of 100 years.
(3) “Maximum probable flood.” Means the largest flood discharge believed possible considering the meteorologic conditions and snow cover on the watershed.
“Floodway.” Means the channel of the watercourse and those portions of the adjoining floodplain which are used to convey the regional flood.
“Grassed waterway.” Means a broad and shallow natural course or constructed channel covered with erosion-resistant grasses or similar herbaceous cover and used to conduct surface water.
“Hydrologic and hydraulic study.” Means engineering study utilizing SCS TR 55, 1986 edition, to determine rates, volumes, and distribution of storm runoff, and its collection, storage, and conveyance.
“Runoff.” Means the portion of rainfall, melted snow or irrigation water that flows across the ground surface and eventually is returned to streams.
(1) “Accelerated runoff.” Means increased runoff due to less permeable surface area primarily caused by urbanization.
(2) “Peak rate of runoff.” Means the maximum rate of runoff for any storm.
(3) “Runoff volume.” Means the total quantity or volume of runoff during a specified time period. It may be expressed in acre-feet, in inches-depth of the drainage area, or in other units of volume.
“Storage.” Means the control, retention, or detention of runoff.
(1) “Detention storage.” Means storm runoff collected and stored for a short period of time and then released at a controlled rate. (Dry pond)
(2) “Retention storage.” Means storm runoff collected and stored for a short period of time and which is released at a controlled rate, leaving a minimum pool of water in the facility. This facility is often associated with water-related or aesthetic uses. (Wet pond)
“Storage facility.” Means any facility used to store, retain or detain storm runoff, which shall include, but not be limited to, retention and detention storage facilities, underground pipe, rooftop or parking lot storage, basins, depressions and pools.
“Storm drainage system.” Means the surface and subsurface system for the removal of water from the land, including both the natural elements of streams, gullies, ravines, marshes, swales and ponds, whether of an intermittent or continuous nature, and human-made elements which include conduits and appurtenant features, culverts, ditches, channels, storage facilities, streets, and the storm sewer system.
(1) “Initial drainage system.” Means that part of the storm drainage system which is used regularly for collecting, transporting, and disposing of storm runoff, snow melt, and miscellaneous minor flows. The initial system is also termed the “convenience system”, the “minor system”, or the “storm sewer system”, and may include many features ranging from curbs and gutters to storm sewer pipes and open drainageways.
(2) “Major drainage system.” Means that storm drainage system which carries the runoff from a storm having a frequency of occurrence of once in 100 years. The major system will function whether or not it has been planned and designed and whether or not improvements are situated wisely with respect to it. The major system is also termed the “emergency flow way”. The major system usually includes many features such as streets, ravines, and major drainage channels. Storm sewer systems may reduce the flow in many parts of the major system by storing and transporting water underground.
“Storm frequency.” Means the average period of time in which a storm of a given duration and intensity can be expected to be equaled or exceeded.
“Stream.” Means a course of running water usually flowing in a particular direction in a definite channel and discharging into some other stream or body of water.
“Watercourse.” Means a channel in which a flow of water occurs either continuously or intermittently in a definite direction. The term applies in either natural or artificially constructed channels.
(Ord. 1-91, passed 1-7-1991)
§ 1286.04 DETENTION/RETENTION BASIN MANUAL.
The Detention/Retention Basin Manual is hereby adopted by the city, and the policies, standards, specifications, and provisions contained therein shall apply to the development of all subdivisions in the city.
(Ord. 1-91, passed 1-7-1991)
§ 1286.05 HYDROLOGIC AND HYDRAULIC STUDIES.
(A) A hydrologic and hydraulic study of each subdivision or development shall be submitted as part of the construction drawings.
(B) These studies will be used to establish the adequacy of the drainage system of the development site. As part of these studies, the adequacy of the storm drainage facility necessary to carry the runoff from the initial storm design shall be shown. Also the flow routes and drainageways necessary to convey the 100-year storm (the emergency flow way) through the development shall be shown. All necessary easements shall be shown.
(C) These studies will also be used to establish the adequacy of the drainage system of the proposed development to receive and convey initial and major storms from dominant (upstream) property.
(D) These studies will also be used to establish the adequacy of the drainage system of the proposed development so as not to create or worsen drainage problems downstream. As part of these studies, storage facilities will be located and identified by type.
(E) Along with the above, a construction site erosion control plan shall be submitted along with the other reports with all Planning Commission submittals. Guidelines are outlined in Exhibit “E” attached to original Ordinance 1-91, passed January 7, 1991.
(Ord. 1-91, passed 1-7-1991)
§ 1286.06 STORM WATER RUNOFF LIMITATIONS.
(A) If the hydrologic and hydraulic studies reveal that the proposed development or subdivision would not increase the total volume of runoff, the peak rate of runoff after development for all return periods of storms up to 100 years shall equal the pre-developed peak for all storm frequencies.
(B) If the hydrologic and hydraulic studies reveal that the total volume of runoff is increased, the peak rate of runoff from the critical storm, after development, shall not exceed the predevelopment peak rate of runoff from a one-year frequency storm for a 24-hour period. The critical storm shall be determined in accordance with the Detention/Retention Basin Manual and the peak rate of runoff for each storm of greater or lesser frequency shall be determined in accordance therewith. However, the peak rate of runoff after development may not exceed the peak rate of runoff before development.
(Ord. 1-91, passed 1-7-1991)
§ 1286.07 SUBDIVISION OR DEVELOPMENT DRAINAGE SYSTEM.
(A) Storm drainage facilities for the subdivision or development shall be designed to accommodate runoff from the 100-year storm. Site design and grading plans shall provide emergency drainageways to avoid damage to a structure and to avoid endangering public safety, which emergency drainageways shall be designed to accommodate runoff from the 100-year storm frequency.
(B) If the collector facilities cannot be located in street rights-of-way, then they shall be located adjacent to side or rear lot lines where easements shall be provided to and along the facilities.
(C) All storm water flow from the proposed subdivision or development, including flows from upstream areas passing through, and further including increased flow attributable to changes in time of concentration or changes in the former runoff factor (imperviousness), shall be conveyed to the proper outlet for the entire tributary area via a natural channel or pipe/culvert either or both of which shall be improved so as to be of adequate capacity.
(D) “Emergency flow way” means the flow routes and drainageway necessary to convey the 100-year storm through a development.
(E) These requirements must be met at each point storm water is discharged from a development area.
(F) In the event that retention or detention structures exceed specified sizes, required inspection and permits from the Ohio Department of Natural Resources Division of Water are required.
(G) In some cases, the City Engineer may require the submittal of additional information (HEC-1 or HEC-2) on the existing and proposed drainage system and the effects on existing drainage or natural waterways.
(Ord. 1-91, passed 1-7-1991; Ord. 15-16, passed 2-22-2016; Ord. 07-2021, passed 2-1-2021)
§ 1286.08 EASEMENTS AND ACCESS.
Access to flood control or storm drainage facilities for emergency, inspection, maintenance and improvement purposes, shall be provided as follows.
(A) Access to flood control or storm drainage ditches, channels, and storage facilities, shall be by means of easements. Such easements shall be not less than 15 feet in width, exclusive of the width of the ditch, channel, or other facility it is to serve, and an easement of this type shall be provided on one side of a flood control or storm drainage ditch, channel, or similar type facility.
(B) Access along flood control or storm drainage ditches and channels shall be by means of easements. Such easement shall be not less than 15 feet in width, exclusive of the width of the ditch, channel, or other facility it is to serve, and an easement of this type shall be provided on both sides of a flood control or storm drainage ditch, channel, or similar facility.
(C) Access along the initial drainage system shall be by means of easements. Such easements shall be not less than 15 feet in width, with a minimum of five feet in width on each side of the centerline.
(D) Access around storage facilities shall be a 25-foot easement in the case of detention (dry) basins, and a 25-foot easement with a 25-foot level beach in the case of retention (wet) basins, measured from the top of the bank, and shall include the storage facility itself.
(E) Easements for the emergency flow ways shall be a minimum of 15 feet in width or larger if required.
(F) Flood control or storm drainage easements containing underground facilities shall have a minimum width of 15 feet.
(G) Those lots crossed by an easement are restricted against the planting within said easement of trees, shrubbery or plantings with woody growth characteristics, and against the construction therein of buildings, accessory buildings, fences, walls or any other obstructions to the free flow of storm water, and are also restricted against changing of the final grade from that described by the approved grading plan.
(Ord. 1-91, passed 1-7-1991)
§ 1286.09 MAINTENANCE.
(A) Any portion of the drainage system, including on-site and off-site storage facilities, that is constructed by the developer will be continuously maintained by the owner or subsequent owners through a homeowners association in title of the affected lands unless it is officially accepted by the city for maintenance. The developer shall cause the maintenance obligation to be inserted in the chain of title to the affected lands as a covenant running with the land in favor of the city. Detention and retention basins shall only be installed in common areas and shall be maintained by all owners or subsequent homeowners through a homeowners association in title on the affected areas with the cost of said maintenance done by all owners in the subdivision equally. In the event of a failure of the homeowners association, all homeowners within the subdivision shall be responsible for the cost of said maintenance equally.
(B) The need for maintenance can be minimized by designing low maintenance facilities. There are many design options which can result in nearly maintenance-free storm water control. Low maintenance is a priority in the design of all facilities.
(C) Multi-use facilities incorporating assets such as aesthetics and recreation can be incorporated with the design of these facilities.
(D) All facilities must be inspected and maintained by the homeowners association twice yearly on May 1 and again on November 1 and periodically throughout the year to ensure that the facilities are operational.
(Ord. 1-91, passed 1-7-1991; Ord. 30-2021, passed 6-7-2021)
§ 1286.10 URBAN SEDIMENT ABATEMENT RULES.
The provisions of the Ohio Department of Natural Resources, Division of Soil and Water Conservation, “Urban Sediment Abatement Rules” (O.A.C. 1501:15-1-01 through 1501:15-1-06) shall be complied with in this chapter.
(Ord. 1-91, passed 1-7-1991)
§ 1286.11 OHIO DAM SAFETY LAWS.
The provisions of the Ohio Department of Natural Resources (Ohio Dam Safety Laws (July 1, 1987) shall be complied with in this chapter.
(Ord. 1-91, passed 1-7-1991)
§ 1286.12 SOILS MAP.
A soils map, at a scale of one inch equals 200 feet, shall be submitted for review, as follows:
(A) Contours shall be at two-foot intervals;
(B) All soil types shall be noted along with all ground cover and woodlands and all other ground conditions;
(C) The total drainage area tributary to the proposed project, including the project, shall be noted. (Before and after development conditions must be noted);
(D) A legend must be provided noting the soils, area in acres, and soil groups before and after development;
(E) A copy of the U.S. Department of Agriculture SCS Soil Survey of Cuyahoga County, Ohio, 1980, showing the entire drainage area and sub-area, shall accompany the soils map; and
(F) All existing drainage facilities must be noted, i.e., storm sewer culverts, lakes and swamps, and the like.
(Ord. 1-91, passed 1-7-1991)
§ 1286.13 DRAINAGE AREA MAP.
A drainage area map shall be submitted for review, before and after development, as follows:
(A) An aerial photograph with a scale of one inch equals 100 feet must be supplied with the entire drainage area and all sub-areas noted, along with all existing land use conditions. Contours shall be at a minimum of two-foot intervals.
(B) All existing drainage facilities must be noted along with all necessary field data.
(C) All natural waterways must be noted and cross-sections of all waterways must be submitted along with any other data to sufficiently determine the exact time of concentration or travel time.
(D) All existing and proposed modifications to the drainage system must be noted.
(E) A complete storm sewer design, noting all proposed storm sewers, culverts and other storm water management facilities, must be submitted.
(F) The emergency flow way must be shown on this plan, i.e., the flow route for a 100-year storm conveyed through the proposed project.
(Ord. 1-91, passed 1-7-1991)
§ 1286.14 SOIL CONSERVATION SERVICE, TECHNICAL RELEASE NO. 55, JUNE 1986, URBAN HYDROLOGY FOR SMALL WATERSHEDS.
(A) All appropriate procedures must be utilized in the design of any storm water facility, as follows:
(1) Using a Type II rainfall distribution and North Royalton rainfall data;
(2) Using a runoff curve summary showing pre-development and post- development conditions;
(3) Using runoff calculations;
(4) Using travel time and time of concentration calculations;
(5) Using calculations on peak discharge and discharge volume;
(6) Using pre-hydrographs and post-hydrographs; or
(7) Using storage volume requirements.
(B) All storms must then be routed through the proposed drainage facility. SCS TR 20, or any other method approved by the City Engineer, may be used to perform this routing procedure.
(C) SCS emergency spillway design calculations must be submitted for a 100-year storm.
(D) Any additional information required by the City Engineer must be submitted at this time.
(E) All City Engineer’s outlet details must be used.
(F) The TR 55 computer programs may be utilized in this process.
(Ord. 1-91, passed 1-7-1991)