(A) 
Applicability. The storage and controlled release rate of excess stormwater runoff shall be required for any redevelopment or other new construction located within the City of Angola city limits if soil disturbance greater than or equal to one acre is proposed and operations that result in the land disturbance of less than one acre of total land area that are part of a larger common plan of development or sale.
(B) 
Exemptions for Detention Requirements. Detention will not be required for the following:
(1) 
Land alterations for the construction, enlargement, or location (on a permanent foundation) of a one-family dwelling, two-family dwelling, or accessory structure appurtenant to either a one- or two- family dwelling; notwithstanding the requirements for an individual lot plot plan permit in this chapter.
(2) 
Land-disturbing activities where there will be no additional impervious surfaces associated with the final completed project, including, but not limited to, ditch construction/reconstruction and utility installation/maintenance activities.
(3) 
Notwithstanding the provisions of AMC § 13.15.510, those site developments where the stormwater management system has been designed such that:
(a) 
After combining flows from both the off-site and on-site drainage areas, there will be no increase in the total peak discharge from the developing site during the two-, 10-, and 100-year storm events; and
(b) 
The volume of runoff for each project site outlet has not been increased for the two-, 10- and 100-year storm events; and
(c) 
The flow width and velocity at the property boundary line of each subbasin is less than or equal to that flow width and velocity which existed prior to the development for the two-, 10-, and 100-year storm events.
(Ord. 1751-2024)
(A) 
Detention Policy. It is recognized that most streams and drainage channels serving the City of Angola do not have sufficient capacity to receive and convey stormwater runoff resulting from continued urbanization. Accordingly, except for situations provided in AMC § 13.15.500(B), the storage and controlled release of excess stormwater runoff shall be required for all developments and redevelopments located within the City of Angola.
(Ord. 1751-2024)
(A) 
General Requirements.
(1) 
Storage Volume.
(a) 
Storage volumes shall be computed using a computer model that can generate hydrographs based on time of concentration and curve number calculation.
(b) 
Storm durations shall be used that maximize the peak flow for the pre-developed condition and maximize detention storage volume for the post-developed condition.
(c) 
When determining curve numbers for post-developed conditions, the initially determined hydrologic soil group for disturbed areas should be changed to the next less infiltrating capacity category (i.e., A to B, B to C and C to D).
(B) 
General Release Rates.
(1) 
All detention facilities shall meet the minimum requirements of detaining the post-developed 100-year storm and releasing the runoff at the pre-developed 10-year peak storm release rate. Likewise, the post-developed 10-year peak storm shall be detained and released at the pre-developed two-year peak storm release rate.
(2) 
In no instance shall the post-developed runoff exceed the pre-developed runoff in the two-year, 10-year, or 100-year peak design storms.
(3) 
If the downstream receiving channel or pipe is inadequate to accommodate the post-developed flow, then the release rate must be further reduced.
(4) 
The minimum allowable orifice size is four inches.
(5) 
For sites where the pre-developed area has more than one outlet, the release rate should be computed based on pre-developed discharge to each outlet point. The computed release rate for each outlet point shall not be exceeded at the respective outlet point even if the post-developed conditions would involve a different arrangement of outlet points.
(C) 
Management of Off-Site Runoff.
(1) 
Runoff from all upstream tributary areas (off-site land areas) may be bypassed around the detention/retention facility without attenuation. Such runoff may also be bypassed through the detention/retention facility without attenuation; provided, that a separate outlet system or channel is incorporated for the safe passage of such flows, i.e., not through the primary outlet of a detention facility. Unless the facility is being designed as a regional detention facility, the primary outlet structure shall be sized and the invert elevation of the emergency overflow weir determined according to the on-site runoff only. Once the size and location of primary outlet structure and the invert elevation of the emergency overflow weir are determined by considering on-site runoff, the 100-year pond elevation is determined by routing the entire inflow, on-site and off-site, through the facility.
(2) 
The detention facility shall be designed in such a manner that a minimum of 90 percent of the maximum volume of water stored and subsequently released at the design release rate shall not result in a storage duration in excess of 48 hours from the start of the storm unless additional storms occur within the period. In other words, the design shall ensure that a minimum 90 percent of the original detention capacity is restored within 48 hours from the start of the design 100-year storm.
(3) 
An emergency overflow/spillway shall be designed for the release of exceptional storm runoff or in emergency conditions should the normal discharge devices become totally or partially inoperative. The overflow facility shall be of such design that its operation is automatic and does not require manual attention. At a minimum, emergency spillways shall be capable of handling 125 percent of the peak inflow into the facility resulting from the 100-year storm event from the entire contributing watershed in the post-developed condition.
(4) 
Note that the efficiency of the detention/retention facility controlling the on-site runoff may be severely affected if the off-site area is considerably larger than the on-site area. As a general guidance, on-line detention may not be effective in controlling on-site runoff where the ratio of off-site area to on-site area is larger than 5:1. Additional detention (above and beyond that required for on-site area) may be required by the City of Angola when the ratio of off-site area to on-site area is larger than 5:1.
(D) 
Downstream Restrictions.
(1) 
In the event the downstream receiving channel or storm sewer system is inadequate to accommodate the post-developed release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the receiving downstream channel or storm sewer system. Additional detention, as determined by the City of Angola, shall be required to store that portion of the runoff exceeding the capacity of the receiving sewers or watercourses. When such downstream restrictions are suspected, the City of Angola may require additional analysis to determine the receiving system's limiting downstream capacity.
(2) 
If the proposed development makes up only a portion of the undeveloped watershed upstream of the limiting restriction, the allowable release rate for the development shall be in direct proportion to the ratio of its drainage area to the drainage area of the entire watershed upstream of the restriction.
(E) 
Acceptable Outlet and Adjoining Property Impacts Policies.
(1) 
Design and construction of the stormwater facility shall provide for the discharge of the stormwater runoff from off-site land areas as well as the stormwater from the area being developed (on-site land areas) to be acceptable outlet(s) (as determined by the City of Angola) having capacity to receive upstream (off-site) and on-site drainage. The flow path from the development outfall(s) to a regulated drain or natural watercourse (as determined by the City of Angola) shall be provided on an exhibit that includes topographic information. Any existing field tile encountered during the construction shall also be incorporated into the proposed stormwater drainage system or tied to an acceptable outlet.
(2) 
Where the outfall from the stormwater drainage system of any development flows through real estate owned by others prior to reaching a regulated drain or watercourse, no acceptance shall be granted for such drainage system until all owners of real estate crossed by the outfall consent in writing to the use of their real estate through a recorded easement. In addition, no activities conducted as part of the development shall be allowed to obstruct the free flow of floodwaters from an upstream property. If an adequate outlet is not located on site, then off-site drainage improvements may be required. Those improvements may include, but are not limited to, extending storm sewers, clearing, dredging and/or removal of obstructions to open drains or natural watercourses, and the removal or replacement of undersized culvert pipes as required by the City of Angola.
(Ord. 1751-2024)
The calculation methods as well as the type, sizing, and placement of all stormwater facilities shall meet the design criteria, standards, and specifications outlined in the City of Angola Stormwater Technical Standards Manual. The methods and procedures in the City of Angola Stormwater Technical Standards Manual are consistent with the policies stated above.
(Ord. 1751-2024)
(A) 
Inspection by the City of Angola.
(1) 
After the issuance of the site improvement permit by the City of Angola and the commencement of construction activities, the City of Angola has the authority to conduct inspections of the work being done to ensure full compliance with the provisions of this chapter, City of Angola Stormwater Technical Standards Manual, CSGP, and conditions of the approved permit.
(2) 
The City of Angola has the authority to perform or require inspections of all public or privately owned stormwater facilities and BMPs.
(B) 
Owner Operation and Maintenance.
(1) 
An operation and maintenance manual (O&M manual) shall be prepared and submitted for approval in accordance with AMC § 13.15.330 and must include the information in the City of Angola Stormwater Technical Standards Manual.
(2) 
Following construction completion, the operation, maintenance, and inspection of stormwater quantity measure(s) shall be the long-term responsibility of the owner of the stormwater quantity measure(s).
(3) 
Stormwater quantity facilities shall be maintained in good condition, in accordance with operation and maintenance manual approved under the site improvement permit, and shall not be subsequently altered, revised, or replaced without the approval of the City of Angola.
(4) 
The owner of stormwater quantity facilities shall be responsible for inspections that evaluate physical conditions, available storage capacity, and the operational condition of the stormwater quantity measure in accordance with the operation and maintenance manual. The owner must conduct necessary inspections at least once per year. The inspections shall follow the operation and maintenance procedures listed in the Indiana Stormwater Quality Manual and/or the approved O&M manual. Inspection requirements of the O&M manual shall not be altered without approval from the City of Angola.
(5) 
If deficiencies are found during an inspection by the City of Angola, the owner of the facility will be notified by City of Angola and will be required to take all necessary measures to correct such deficiencies. If the owner fails to correct the deficiencies within the allowed time period, as specified in the notification letter, the City of Angola will undertake the work and collect from the owner using lien rights, if necessary.
(C) 
Assignment of responsibility for maintaining facilities serving more than one lot or holding shall be documented, unless responsibility is formally accepted by a public body, and determined before the final site improvement permit is approved.
(D) 
Inspection reports and documentation records must be maintained by the owner for a period of five years and produced upon request by City of Angola personnel within 48 hours of the request.
(Ord. 1751-2024)