(a) All sets of plans which include plans for storm sewers shall include the current Township Storm Sewer Detail Sheets, which shall be considered an inseparable part of the plans when said plans are approved. Plans must be designed in accordance with the current applicable detail sheets and standards noted herein.
(b) A site grading and drainage water plan is required for all developments, except if the building site is a site in a subdivision or other project for which a general site grading plan has been submitted and approved. A separate grading plan or permit will be required for individual building sites, including those in platted subdivisions recorded prior to January 1, 1968. The intent is to require that an enclosed storm drainage system shall be provided for all land development projects. If there are any upstream watershed drainage areas which need to be drained through the site under design consideration, sufficient capacity shall be provided to take fully developed upstream drainage into the system.
(c) Site grading for all building sites shall be reviewed to determine that proposed and/or actual site grading is reasonable, that drainage from land lying upstream is not obstructed and that downstream properties will not be adversely affected by run-off from the property under design consideration. All site grading and drainage needs to meet all current applicable Macomb County stormwater management requirements noted herein. Before a certificate of occupancy for any building is issued, the Township shall approve the final site grading and drainage for each building site. The Township shall require that a survey, drawing and certificate, done by a registered professional engineer or registered land surveyor, be furnished by the developer, indicating that the work has been done in conformity to the approved site grading and drainage plan. It shall be unlawful for any person to interfere with, modify or obstruct the flow of drainage water across any property in any manner different from the approved plan.
During periods of the year when weather conditions make site grading work infeasible, the Building Department may issue a temporary certificate of occupancy subject to the furnishing of a satisfactory bond, letter of credit or cash deposit guaranteeing the completion of the work when weather conditions permit. Such temporary certificate of occupancy shall state the time for final completion, inspection and the date of forfeiture of the guarantee for noncompliance.
Finished easement grades shall be indicated on the plans at each lot or building site corner not adjacent to a street pavement. Permanent finish grade markers consisting of four-inch diameter, 36-inch long concrete encasing a one-half inch diameter steel rod, shall be buried vertically such that the top is at the final finished grade shown on the plan. The builder shall furnish to the Township Building Department a certificate of a registered professional engineer or land surveyor indicating that such markers are correctly in place before issuing a final building certificate of occupancy for a building.
(d) The fall of the land away from the building shall be a minimum of six inches in the first 25 feet (2%). From this elevation, the land shall slope to a drainage water collection swale at a minimum slope of one foot in 100 feet (1%).
(e) The maximum slope of the land for the site, except for transitional terraces between usable site areas, shall be seven feet in 100 feet (7%). The sodded terrace slopes shall be a maximum slope of one foot vertically and four feet horizontally,
(f) Adequate soil erosion and sedimentation control measures shall be specified on the plans, and followed during construction, to conform to the requirements of Act 451 of the Public Act of 1994, entitled Natural Resources and Environmental Protection Act as amended. The Macomb County Public Works Office is the jurisdictional agency responsible for issuing soil erosion permits in Clinton Township.
(g) All buildings having foundation drains shall direct the flow of drainage water from such foundation drains into a storm sewer or a storm drain by means of an underground pipe. Sump pumps shall be used if necessary. No building permit for any building having a basement shall be issued unless the plans for such building indicate a building service sump line connection to a storm sewer, storm drain or road ditch. In no circumstance shall a sump line be connected to the sanitary sewer system.
(h) Drainage water run-off from building service drains and other storm discharge facilities shall be designed so that the discharged water through an impermeable structure, installed and maintained to avoid discharge upon paved surfaces and public rights of way designed for pedestrian and vehicular traffic. Splash blocks or pipes are allowed where the discharge point is at least five feet perpendicularly away from all building walls onto a pervious surface (e.g. grass, pond, bioretention area, etc). Subsection coexists with Section 1470.075(c).
(i) The longitudinal grade of any unpaved drainage swale shall not be less than 1.0 feet per 100 feet (1.0%). Where a site is unable to obtain a fall of 1.0 foot per 100 feet (1.0%) for a longitudinal drainage slope, an acceptable minimum slope will be allowed as determined by the Township Engineer. At no instance will a minimum drainage longitudinal slope be less than 0.3 feet per 100 feet (0.3%). The maximum distance drainage water shall travel in a drainage swale without an intercepting yard catch basin shall be 350 feet. Planned final grade elevations shall be indicated on the plans at a maximum spacing of 50 feet. Drainage swales shall be intercepted by a catch basin on each building site.
(j) Storm water run-off piping systems shall be designed for a ten-year storm by means of the rational method formula Q = CIA, where Q is the peak rate of run-off in cubic feet per second, A is the area in acres, C is the co-efficient of run-off for the drainage area, and I is the average rainfall intensity in inches per hour for a certain time of concentration. The rainfall intensity shall be determined by the formula I = 175/(25+T), where T is the time of concentration equal to the time required for a drop of water to run from the most remote point of the watershed to the point for which run-off is being estimated. The design engineer shall use judgment in arriving at proper imperviousness factors, but in general the following factors are acceptable minimums:
(1) Lawn areas and unimproved natural areas - 0.2
(2) Gravel surfaces - 0.85
(3) Pavement and roof areas - 0.90
(k) Storm water management shall also be designed to the most current requirements of Procedures and Design Standards for Stormwater Management from the Macomb County Public Works Office. A weighted average to determine the overall site’s impervious factor shall be used for stormwater detention calculations.
(l) A storm water pretreatment forebay or structure for each connection to the stormwater system will be required and be sized according to Macomb County stormwater management design standards. The design is subject to approval the Department of Public Services. The pretreatment system shall have a minimum total suspended solids removal rate of 80%.
(m) The developers shall submit a map outlining the various watershed drainage areas, including off-site upstream areas, which drain to each inlet point used for design. The map shall be accompanied by storm sewer design computation. The minimum acceptable size of a storm sewer downstream of any storm water inlet structure is twelve inches in diameter.
(n) For the design of storm sewers, the Manning's formula for pipe sizing with an “N” factor of 0.013 for smooth wall pipe shall be used. Storm sewers shall be designed to provide a minimum velocity, when flowing full, of two and one-half feet per second, if possible. The maximum velocity of storm water flow shall be ten feet per second.
(o) On-site storm sewer shall be a private system to be maintained by the property owner unless it is otherwise determined by the Township Engineer. A recorded Stormwater Maintenance Covenant is required for all developing properties prior to issuance of a Certificate of Occupancy and/or Engineering Plan approval. Any storm sewers requiring easements, shall be agreements solely between private entities with terms and conditions reviewed by Clinton Township. Public storm sewer easements will not be considered in Clinton Township. The minimum acceptable width of private easements for storm sewers shall be 12 feet wide for sewers and 15 inches and under in diameter, 20 feet for sewers over 15 inches in diameter, and 30 feet for sewers over 48 inches in diameter. The sewer shall be placed within the middle third of the above designated easement width. Township Engineer will also consider the depth of the sewer when reviewing the necessary easement width.
(p) Where open drains are proposed for drainage water disposal, the Manning's formula shall be used for determination of flow depth and capacity. When additional permitting agencies are required as part of plan approval, those standards shall apply.
(q) Where possible, a minimum of three feet of cover from the top of the finish road or earth grade to the top of any storm sewer shall be provided. Township Engineer shall consider less cover if existing site conditions warrant a deviation.
(r) The design elevation of the hydraulic gradient profile shall be indicated on the sewer profile view for all proposed storm sewer systems. In some cases, it will be acceptable to allow the hydraulic gradient to be above the top of the sewer pipe, but never less than one foot below an at-grade rim of a storm sewer structure.
(s) Access manholes shall be provided along the storm sewer at every change of pipe size, change of rate of grade, or change of direction. However, the maximum spacing for storm sewer manholes shall be 500 feet.
(t) Catch basins shall not be constructed over a main sewer line to replace manholes in street sewers or trunk sewers outside of streets. Moreover, a manhole normally shall not be used as a storm water inlet structure. However, if a normal manhole location (outside of streets) coincides with a storm water inlet structure location, and at least 75% of the upstream storm water inlet structures are catch basins (with sumps), the manhole may be used as a storm water inlet structure by adding a sump and a catch basin cover on the manhole.
Not more than three upstream catch basins will be allowed to discharge into any catch basin.
Catch basin leads may tap directly into sewers 42 inches and larger. Catch basin sewer leads need not be shown on the plans in profile view.
(u) A prefabricated bar screen shall be installed on the end of all storm sewers 18 inches in diameter and larger which outlet into an open drain. Openings of the bar screen shall be no more than six inches on centers.
(v) In general, pavement-type catch basins shall be located as follows:
(1) At the radius return of street pavement intersections; 150 feet maximum distance of drainage water travel is allowed around a corner without an intercepting catch basin.
(2) At all low points in streets.
(3) At intermediate points along the street or parking areas, such that there is a maximum pavement drainage area per structure as follows:
A. Intercepting road catch basins: 600 lineal feet of road.
B. Low-point catch basins: 0.5 acres
(w) Yard-type catch basins shall be provided at all low points in drainage swales. Intercepting yard-type catch basins, such that not more than 350 feet of swale drainage runs into any one catch basin, other than a low point catch basin where 600 feet of drainage is allowed, shall be provided. In new subdivisions, each lot shall have direct-run lot drainage to a catch basin with an outlet provided in said catch basin for the foundation drain connection. All yard-type catch basins shall be precast concrete with a minimum two-foot diameter. Plastic, fiberglass, corrugated metal, etc. low point structures shall not be permitted.
(x) Improved open drains may be permitted under special circumstances, provided that the Township Engineer has determined that the enclosure of such open drains would require a storm sewer of 60 inches or larger in diameter. When open drains are used, a private or county easement will be required when the drain is being designed to accept flow from more than one source upstream or at the site. If the existing route is currently accepting flow overland or through a pipe an easement may not be required. The design of the open drain shall meet the most current requirements of Procedures and Design Standards for Stormwater Management from the Macomb County Public Works Office.
(y) An extension of the storm sewer system shall be provided to furnish an outlet for foundation drain service pipes for any buildings not otherwise serviced. Such extensions shall have a minimum diameter of eight inches.
(z) If the enclosed sewer pipe system were to fail, an emergency overflow route is required for all developed sites. The emergency overflow route must demonstrate that no buildings would be adversely affected by the storm sewer system failure and an overflow to a public right of way or drain is provided. Emergency overflows to adjacent private properties will require a recorded covenant with that adjoining private property owner.
(aa) Any site improvements to undeveloped property (except individual plot plans), greater than one acre, shall require stormwater to be detained on-site in either a pond or an approvable underground storage system. The storage capacity of such detention systems shall contain a capacity equivalent to the most current design requirements provided in the “Procedures and Design Standards for Stormwater Management” published by the Macomb County Public Works Commissioner (MCPWO Stormwater Management & Design Standards) designed to drain into the detention basin. Discharge from the detention basin shall be at a controlled rate based upon the most current MCPWO Stormwater Management & Design Standards.
(bb) Redeveloped sites will require stormwater detention, following the “Procedures and Design Standards for Stormwater Management” published by the Macomb County Public Works Commissioner (MCPWO Stormwater Management & Design Standards). Stormwater detention with an outlet restriction shall be required for any of the following circumstances:
(1) A net increase in impervious area of the site. The stormwater detention volume shall be calculated using the calculated increase in site imperviousness. The release rate of the detention area must not exceed the pre-existing conditions.
(2) There is limited downstream storm sewer or open drain capacity. If site calculations show that discharge from a newly developed site contribute to downstream storm sewer surcharging and/or flooding, the redeveloped site will need to restrict and detain storm sewer flows to an amount that eliminates downstream surcharging and/or flooding in a ten-year storm event or to a minimum discharge of 0.20 cfs/acre.
(cc) Retention basins may be considered at the discretion of the Township Engineer where no positive outlet is available, and must follow the most current MCPWO Stormwater Management & Design Standards.
(dd) Additional requirements for storm water detention basins are as follows:
(1) The maximum design elevation for storage in the detention basin shall be at least one foot below the low point of the watershed surface area draining into the detention basin.
(2) A detention or retention basin slope cannot be steeper than one foot vertical for every five feet (1:5) horizontal does not need to be fenced. A ten-foot wide maintenance buffer with a maximum side slope of one foot vertical for every ten feet horizontal (1:10) shall be required.
(3) Any side slopes of a detention or retention basin that is between one foot vertical for every 5 feet horizontal (1:5) to one foot vertical for every four feet horizontal (1:4) will require a fence around the entire perimeter of the basin. A ten-foot wide maintenance buffer with a maximum side slope of 1 foot vertical for every ten feet horizontal (1:10) shall be required inside the fenced enclosure. The detention or retention basin shall be completely fenced with a minimum 12-foot wide, double-opening access gate provided with proper locks. The fence shall be six-feet high with a material that is found approvable by the Planning Department, Building Department and Department of Public Services. The bottom of the fence shall be six inches below the ground surface to prevent burrowing by rodents.
(4) The bottom of the basin shall have a minimum grade of 1%. The slope of the gutter line to the outlet shall have a minimum grade of 0.5%.
(5) The entire detention or retention basin area must be sodded or seeded with the turf fully established in accordance with Macomb County Soil Erosion Control requirements before Township approval will be granted.
(6) Rip-rap shall be installed on a geotextile fabric and provided at all pipe entrances to the basin. Sizing of the rip-rap shall be reviewed by the Township Engineer. All pipe entering or leaving the basin shall have either a headwall or flared-end section at the end of the pipe with an erosion control device.
(7) An overflow system shall be provided, which system shall consist of either a pipe having an invert at the design storage level elevation or a concrete spill-way extending from the inside bank slope to the outlet drain.
(8) For basins with pumped outlets, a silt trap and bar screen shall be installed on the inlet pipe to the pump station. The screen clear opening shall be a maximum of two inches.
(9) Pumping stations for dewatering of the detention basins shall include duplicate pumps, with each pump capable of handling the design flow. The controls shall include a lead-pump start and stop, a lag-pump start and stop, an alternator for alternating the lead-lag pump, a high-water alarm system with a light, and a safety all-pumps-off control. An emergency call-out system or other privately monitored emergency system that notifies the property owner(s) must be part of the system design. The control panel, pumps, and wet-well shall be installed inside of the fenced enclosure near the access gate, and the controls shall be installed in a suitable weather-proof and vandal-proof enclosure. The size, make and type of pumps and controls shall be subject to Township approval. Electrical service shall be extended inside the fence with suitable electrical outlets, whether gravity flow or pumps are used for dewatering.
(10) Where the basin abuts residential properties (existing or proposed), a dense hedge shall be planted along the inside perimeter of the fence. Trees may be required by the Township where the basin parallels a roadway and in other instances where improved aesthetics could be achieved without interfering with maintenance.
(11) All detention basins shall be designed so that the entire capacity of the basin can be discharged in 48 hours.
(12) Parking lot detention systems in commercial or industrial areas are not permitted and will only be considered by the Township Engineer on a case by case basis. In no instance will parking lot detention systems be allowed in residentially developed properties. Any parking lot detention area allowed by the Engineer, shall not exceed a depth of 0.5 feet in depth with the storage area not occupying any parking or vehicle storage areas. Parking lot detention areas cannot be placed within an egressible route for ADA facilities.
(13) Enforcement of this section shall be the responsibility of the Township Department of Public Services.
(Ord. 281. Passed 10-2-89; Ord. 481. Passed 10-24-22.)