(A) The design and construction of the storm sewers and appurtenances shall be the responsibility of the subdivider and reviewed for acceptance by the Village Engineer. The Rational Method as described in the most recent version of the state’s Department of Transportation Drainage Manual shall be used to design the municipal storm drainage system of the subdivision.
(B) Minimum capacity of storm sewers shall be adequate to carry a ten-year storm under gravity flow conditions.
(C) Storm sewer inlets shall be placed such that runoff encroaches on no more than one-half the pavement width for the ten-year design storm.
(D) Culverts carrying flow under a roads shall be designed based on the street classification.
Classification | Design Storm Event | Freeboard (Pavement Low Point to High Water) |
Arterial | 50-year | 3 feet |
Collector | 25-year | 2 feet |
Local street | 25-year | 1 feet |
(E) The minimum design velocity for a storm sewer shall be two and one-half feet per second. The maximum design velocity for a storm sewer shall be eight feet per second.
(F) A concrete flared end section or cast-in-place headwall is required for all culverts and storm sewer outlets.
(G) All field tile found during construction shall be left in a functional condition and incorporated into the new drainage system.
(H) Storm sewers and appurtenances shall be installed in accordance with the latest edition of the Standard Specifications for Water and Sewer Construction in Illinois. Connection of new storm sewers to the existing system shall not be made until approved by the Village Engineer.
(I) Storm sewers located under streets shall be reinforced concrete with bell and spigot or tongue and groove joints. Storm sewers not located under streets may be PVC or other materials approved by the Village Engineer.
(J) Storm sewer manholes and inlets shall be precast concrete components or monolith concrete. Bases shall be cast in place concrete or precast concrete.
(K) Storm sewers shall be not smaller than 12-inch diameter and be installed on granular cradle bedding.
(L) All storm sewers and appurtenances located below or within two feet of street surfaces, sidewalks, curbs and gutters shall be backfilled with select granular backfill and mechanically compacted to a minimum of 95% SPD in minimum 12-inch loose lifts.
(M) All storm sewers shall be lamped for straightness and visually inspected. All tests shall be done by the subdivider’s engineer or by an independent testing company under the supervision of the subdivider’s engineer. All test results shall be documented and submitted to the Village Engineer for review.
(N) (1) All areas of development must provide an overland flow path that will pass the 100-year flood flow (including off-site tributary flow) without damage to structures or property. If the drainage area is less than 20 acres, the storm sewer pipe and inlet may be sized for the 100-year flow instead of providing an overland flow path.
(2) The overland flow path shall be protected from any development, such as fencing, landscaping, storage sheds or other obstructions which could impair its function by impeding flow. This protection shall be established through a properly recorded covenant running with the land, restricting the use of the overland flow path area.
(3) Structures adjacent to an overland flow path shall have the following lowest opening elevation for the following tributary areas:
(a) One-half foot above the BFE for tributary areas of 20 acres or less; and
(b) One foot above the BFE for tributary areas of 20 acres or greater.
(O) If the proposed activity involves a channel modification, it shall be demonstrated that:
(1) There are no practicable alternatives to the activity that would accomplish its purpose with less impact to the natural conditions of the body of water affected. Possible alternatives include levees, bank stabilization, flood-proofing of existing structures, removal of structures from the floodplain, clearing the channel, high flow channel or the establishment of a stream side buffer strip or green belt. Channel modification is acceptable if the purpose is to restore natural conditions and improve water quality and fish and wildlife habitat;
(2) Water quality, habitat and other natural functions would be improved by the modification and no significant habitat area may be destroyed, or the impacts are offset by the replacement of an equivalent degree of natural resource values;
(3) Migration of fish and other aquatic organisms will not be adversely impacted, sediment bedload transport (a critical component of stream geomorphology and function) will not be impaired, temporary or permanent accumulation of sediment will not result and increases in stream water temperatures will not occur; and
(4) The activity has been planned and designed to maintain the carrying capacity of an altered or relocated watercourse and will be constructed in a way which will minimize its adverse impacts on the natural conditions of the body of water affected, consistent with the following criteria.
(a) The physical characteristics of the modified channel shall match as closely as possible to those of the existing channel in length, cross-section, slope and sinuosity. If the existing channel has been previously modified, restoration of more natural physical conditions should be incorporated into a channel modification design, where practical.
(b) Hydraulically effective transitions shall be provided at both the upstream and downstream ends of the project, designed such that they will prevent erosion.
(c) One-sided construction of a channel shall be used when feasible. For example, removal of streamside (riparian) vegetation should be limited to one side of the channel, where possible, to preserve the shading and stabilization effects of the vegetation.
(d) Clearing of stabilization vegetation shall be limited to that which is essential for construction of the channel.
(e) Channel banks shall be constructed with a side slope no steeper than 3:1 horizontal to vertical, wherever practicable.
(f) All disturbed areas associated with the modifications shall be seeded or otherwise stabilized as soon as possible upon completion of construction to control erosion during normal and flood flows. An erosion blanket or an equivalent material shall be required to stabilize disturbed channel banks prior to establishment of the vegetative cover. Permanent stabilization shall be installed as soon as practical, but not later than ten days after the channel construction is complete.
(g) Temporary erosion control shall be installed prior to excavation associated with a channel modification and must be maintained throughout the construction period. The temporary erosion control shall be removed upon written notification from the (enforcement officer).
(h) If the existing channel contains considerable bottom diversity such as deep pools, riffles and other similar features, such features shall be provided in the new channel. Spawning and nesting areas and flow characteristics compatible with fish habitat shall also be established, where appropriate.
(i) New or relocated channels should be built in the dry. All items of construction, including vegetation, should be completed prior to diversion of water into the new channel.
(j) There shall be no increases in stage or velocity as the channel enters or leaves the project or unless necessitated by a public flood control project.
(k) Unless the modification is for a public flood control project, there shall be no reduction in the volume of flood water storage outside the floodway as a result of the modification (i.e., no floodplain fill).
(l) A channel maintenance easement is required along all channels draining 100 acres or more. The minimum width of the maintenance easement shall be 25 feet centered on the channel or the distance between the tops of banks plus 20 feet, whichever is greater.
(Ord. 16-102, passed 4-4-2016)