(A) The City of Washington shall require a drainage review.
(B) All development shall comply with the requirements of the checklist set forth herein prior to the issuance of a building permit under Chapter 153 of the Washington Code of Ordinances.
(1) Drainage review requirements. New residential subdivisions, commercial developments over 0.25 acre, and all industrial developments shall conform with the drainage review requirements.
(2) Exempt from drainage review requirements. Individual new residential structures to be constructed on lots situated within existing platted additions and/or subdivisions, or on implanted tracts shall be exempt from the drainage review requirements.
(3) Individual commercial developments exempt from drainage review requirements. Individual commercial developments on tracts less than or equal to 0.25 acre shall be exempt from the drainage review requirements.
(4) Information required by City Engineer. Depending on the nature, complexity and location of the project, and the flood prone sensitivity of the project area, more or less information and data may be required by the City Engineer.
(5) Minimum requirements. Drainage plans must include at a minimum:
(a) One copy of a certified site plan, and in some incidents due to complexity may need to be signed by a P.E. or a P.L.S. showing the following items for the subject tract:
1. Site boundaries including bearings and lengths of property lines, total area of tract, north arrow and scale;
2. Names and record deed information for owner of the subject tract and for all adjoiners to the subject tract;
3. Recorded and/or platted utility easements;
4. Spot elevations and existing contour lines at - foot intervals, and reference bench marks. Existing contour lines at two-foot intervals may be used for project sites determined to have an excessive degree of relief. The City Engineer shall be consulted with for this determination;
5. Adjoining highways, county roads, city streets and alleys, including names, right-of-way widths, pavement widths and type of surface;
6. Locations of all existing on-site and off-site utilities;
7. Existing drainage pattern including existing storm sewers, manholes, inlets, ditches, swales, ponds and lakes;
8. Locations and dimensions of all existing building structures, driveways and parking areas;
9. Locations and descriptions of vegetative cover such as grass, brush, weeds and trees; and
10. Predominate soil types and descriptions as shown in the Natural Resources Conservation Service county soil survey;
(b) Narrative describing existing land use of proposed site and adjoining properties;
(c) One copy of a certified site plan showing the following items for the proposed development of the subject tract:
1. Finish floor elevations, curb and pavement elevations, contour lines, storm sewer manholes and inlet grates and invert elevations;
2. Locations and dimensions of proposed building structures, pavement, vegetative areas, utilities, storm sewers, manholes, inlets, ditches, swales, ponds and lakes;
3. Location, dimensions and details of proposed stormwater detention facility;
4. All proposed demolition;
5. Proposed erosion control features shall be shown on the erosion and sediment control plan required herein;
6. Existing impervious area.
A. The designer shall show on the site plan, in tabular form, the total existing or preconstruction impervious area, in square feet, that exists on the site in its present or preconstruction or predevelopment condition; and
B. When paved areas and other materials exist that are less than 100% impervious, the designer may propose reductions to the impervious area based upon values for C from the rational method, as presented in the HERPICC Stormwater Drainage Manual, July 1994. The utility will make the final determination in all matters regarding calculations of the impervious area.
7. Proposed impervious area. The designer shall show on the site plan, in tabular form, the proposed post construction impervious area in square feet for the site in its proposed post-construction or post-development condition.
(d) Narrative describing the proposed land use of the site and a description of the proposed drainage system and detention facility.
(e) Drainage design calculations prepared and certified by an indiana registered professional engineer or land surveyor utilizing the following criteria:
1. Calculation of the undeveloped 10-year frequency storm peak flow rate from the subject tract.
2. Calculation of the developed 25-year frequency storm peak flow rate from the subject tract.
3. Calculations and details for detaining a developed 25-year frequency storm peak flow rate to an undeveloped 10-year frequency storm peak flow rate.
4. For projects located in the flood prone sensitive areas, increased developed storm frequencies may be required. The City Engineer shall be consulted with for this determination.
5. All methods and calculations shall be in accordance with acceptable standards as outlined in the HERPICC Stormwater Drainage Manual published by the Purdue Research Foundation, West Lafayette, Indiana.
6. The Board reserves the right to require additional stormwater storage volume if the capacity of the receiving downstream channel or storm sewer system is limited or inadequate.
(6) Stormwater storage methods.
(a) The required stormwater storage volume must be detained onsite by the provisions of appropriate wet or dry bottom reservoirs, by underground tanks or pipes, by storage on flat roofs, parking areas, lawns or other acceptable techniques.
(b) Measures, which retard the rate of overland flow and the velocity in runoff channels, shall also be used to partially control runoff rates.
(7) Stormwater release rate.
(a) The allowable release rate shall be the undeveloped 10-year frequency storm peak rate unless the City Engineer determines that the capacity of the receiving downstream channel or storm sewer system requires a lower rate.
(b) The stormwater release rate shall not result in storage duration in excess of 48 hours unless additional storms occur within the period.
(c) The utility will make the final determination in all matters regarding allowable release rates.
(8) General detention basin design requirements.
(a) The maximum planned depth of stormwater stored (without a permanent pool) shall not exceed 4 feet unless a 6-foot high fence protects the basin.
(b) All stormwater detention facilities shall be separated by not less than 25 feet from any occupied building or structure.
(c) Safety screens having a maximum opening of 4 inches shall be provided for any pipe or opening to prevent children or large animals from crawling into the structures.
(d) Danger signs shall be mounted at appropriate locations to warn of deep water, possible flood conditions during storm periods and other dangers that exist. Fencing shall be provided if deemed necessary by the Board.
(e) Outlet control structures shall be designed to operate as simply as possible and shall require little or no maintenance and/or attention for proper operation. They shall limit discharges into existing or planned downstream channels or conduits so as not to exceed the stormwater release rate.
(f) Emergency overflow facilities such as a weir or spillway shall be provided in case the normal discharge devices become totally or partially inoperative. The overflow facility shall be of a design that its operation is automatic and does not require manual attention. The overflow facility shall be designed to handle a 25-year storm event.
(g) Grass or other suitable vegetative cover shall be provided throughout the entire detention storage basin area. Grass shall be cut regularly during the growing season as required to maintain the facility in a nuisance free condition.
(h) Debris and trash removal and other necessary maintenance shall be performed on a regular basis to assure continued operation in conformance to design.
(i) No detention facility or other water storage area, permanent or temporary, shall be constructed under or within 10 feet of any utility pole or high voltage electric line. Likewise, poles or high voltage electric lines shall not be placed within 10 feet of any detention facility or other water storage facility.
(j) Detention facilities must maintain setbacks from private and public water supply facilities as prescribed by Indiana State Board of Health and the Recommended Standards for Water Works by the Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers.
(9) Dry bottom facility design requirements. Detention facilities, which will not contain a permanent pool of water, shall comply with the following requirements:
(a) Provisions shall be incorporated into facilities for complete interior drainage of dry bottom facilities, including the provisions of natural grades to outlet structures, longitudinal and transverse grades to perimeter drainage facility, paved gutters, or the installation of subsurface drains;
(b) The detention facility shall, whenever possible, be designed to serve as a secondary or multipurpose function; and
(c) In excavated detention facilities, side slopes of 3:1 or flatter shall be provided for stability, in the event of valley storage, natural slopes maybe considered stable.
(10) Wet bottom facility design requirements.
(a) Where part of a detention facility will contain a permanent pool of water, all the items required for general and dry bottom detention storage shall apply except that the system of drains required to maintain a dry bottom facility will not be required. A controlled positive outlet will be required to maintain the design water level in the wet bottom facility and provide required detention storage above the design level.
(b) However, the following additional conditions shall apply:
1. Facilities designed with permanent pools or containing permanent lakes shall have a water area of at least 1/2 acre. If fish are to be used to keep the pond clean, a minimum depth of approximately 10 feet shall be maintained over at least 25% of the pond area. The remaining lake shall have no extensive shallow areas, except as required by division (B)(3) above.
2. In excavated lakes, the underwater side slopes in the lake shall be stable. In event of valley storage, natural slopes may be considered stable.
3. A safety ledge 4 to 6 feet width is required and shall be installed in all lakes approximately 30 to 36 inches below the permanent water level. In addition, a similar maintenance ledge 12 to 18 inches above the permanent water line shall be provided. The slope between the 2 ledges shall be stable and of a material such as stone or riprap which will prevent erosion due to wave action.
4. A safety ramp exit from the lake will be required in all cases and shall have a minimum width of 20 feet and exit slope of 6 horizontal to 1 vertical (6:1). The ramp shall be of a material that will prevent its deterioration due to vehicle use or wave action.
5. Periodic maintenance is required in lakes to control weed and larval growth. The facility shall also be designed to provide for the easy removal of sediment, which will accumulate during periods of reservoir operation. A means of maintaining the designed water level of the lake during prolonged periods of dry weather is also required.
6. For emergency use, facility cleaning or shoreline maintenance, additional facilities may have to be provided or plans prepared for auxiliary equipment to permit emptying and drainage.
7. Aeration facilities to prevent pond stagnation shall be provided, if required by the utility. Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Board.
(11) Roof top storage. Detention storage requirements may be met in total or in part by detention on flat roofs. Details of the design to be included in the building permit application shall include the depth and volume of storage, details of outlet devices and down drains, elevations of emergency overflow provisions and certification of the structural portion of the building design plans by a professional engineer or architect.
(12) Parking lot storage. Paved parking lots may be designed to provide temporary detention storage of stormwaters on all or a portion of their surfaces. Outlets will be designed so as empty the stored waters slowly. Depths of storage shall be limited to a maximum of 8 inches in vehicle parking areas so as to limit damage to parked vehicles and so that access to parked vehicles is not impaired. The utility may require implementation of best management practices and/or construction of best available treatment technologies to reduce stormwater pollution from parking lots.
(13) Underground tanks or pipes. Detention storage requirements may be met in total or in part by detention in underground tank(s) or in a network of underground pipes. Tanks must be of reinforced concrete construction unless otherwise approved by the utility. Pipes must be reinforced concrete or dual wall (corrugated exterior/smooth interior) high-density polyethylene (HPDE) materials unless otherwise approved by the utility. Details of the underground storage system and the outlet or release structure(s) to be included in the building permit application.
(14) Retention basins. Retention basins (no outlet) are considered a last resort system. The utility may require the construction of a suitable outlet to prevent the use of retention basins. Retention basins will not be considered unless infiltration wells, dry wells, or other sub-surface absorption system are proposed in conjunction with the retention well.
(15) Facility financial responsibilities. The construction cost of stormwater control systems and required facilities shall be accepted as part of the cost of land development.
(16) Facility maintenance responsibilities. Maintenance of detention/retention facilities during construction and thereafter shall be the responsibility of the land developer/owner. Assignment of responsibility for maintaining facilities serving more than 1 lot or holding shall be documented by appropriate covenants to property deeds, unless responsibility is formally accepted by a public body, and shall be determined before the final drainage plans are approved.
(17) Inspections. All public and privately-owned detention storage facilities may be inspected by representatives of the utility at the city's discretion.
(18) Corrective measures. If deficiencies are found by the inspector, the owner of the detention/retention facility will be required to take the necessary measures to correct these deficiencies. If the owner fails to do so, the city will undertake the work and collect the cost of maintenance or repair from the owner using lien rights if necessary.
(19) Joint development of control systems. Stormwater control systems may be planned and constructed jointly by 2 or more developers as long as compliance with this chapter is maintained.
(20) Installation of erosion control systems. Runoff and erosion control systems in accordance with division (B)(16) above shall be installed. The city will require an erosion control plan to be submitted as part of the construction plans and specifications. Detention/retention basins shall be designed with an additional 6% of available capacity to allow for sediment accumulation resulting from development and to permit the pond to function for reasonable periods between cleanings. Basins should be designed to collect sediment and debris in specific locations so that removal costs are kept to a minimum.
(21) Detention facilities in floodplains; off-site drainage provisions. When the allowable runoff is released in an area that is susceptible to flooding, the developer may be required to construct appropriate storm drains through the area to avert increased flood hazard caused by the concentration of allowable runoff at 1 point instead of the natural overland distribution. The requirement of off site drains shall be at the discretion of the utility.
(22) As-built plans. Whenever the utility has agreed to consider accepting facilities constructed by developers, a professionally prepared (by professional engineer or registered land surveyor) and certified “As Built” set of prints or plans shall be submitted to the Board for review.
(Ord. 15-2004, passed 9-13-2004; Am. Ord. 21-2018, passed 11-13-2018)