A. Irrigation Ditches:
1. All existing irrigation ditches located on the site or straddling a site property boundary shall be piped with a sufficient size pipe and shall be coordinated with water user.
2. Property owners are responsible for the protection of irrigation ditches per the relevant sections of this chapter.
3. Discharges to private ditches require written approval from the ditch owners and design shall comply with the terms of approvals and the stormwater design standards and regulations and the land disturbance permit.
4. Piping of ditches and modification to the diversion boxes require documented coordination with ditch owners or representative but are not required to receive written approval of ditch owners. Design and coordination requirements shall comply with the stormwater design standards and regulations and the land disturbance permit documents.
B. Stormwater Design And BMP Manuals:
1. Adoption: The municipality adopts as its stormwater design and best management practices (BMP) manuals the following publications, which are incorporated by reference in this chapter as if fully set out herein:
a. "Mapleton City Corporation Stormwater Design Standards And Regulations".
b. "Mapleton City Corporation Stormwater Master Plan".
c. "Mapleton City Stormwater Management Plan" (Mapleton public works department).
2. Inclusions; Updates: These manuals include a list of acceptable BMPs and include specific design performance criteria and operation and maintenance requirements for each stormwater practice. The manuals may be updated and expanded from time to time, at the discretion of the governing body of the city, upon the recommendation of the city engineer, based on improvements in engineering, science, monitory and local maintenance experience. Stormwater facilities that are designed, constructed and maintained in accordance with these BMP criteria will be presumed to meet the minimum water quality performance standards.
C. General Performance Criteria For Stormwater Management: Unless granted a waiver or judged by the city engineer or designee to be exempt, the following postconstruction performance criteria shall be addressed for stormwater management at all sites:
1. Design of storm drain systems in boundaries and discharges into a Mapleton City Corporation storm drain system requires direct supervision of a Utah registered professional engineer, and shall carry the seal of the same supervising professional engineer.
2. All site designs shall control the peak flow rates of stormwater discharge associated with design storms specified in this chapter or in the BMP manual and reduce the generation of postconstruction stormwater runoff to preconstruction levels. These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity.
3. To protect stream channels from degradation, specific channel protection criteria shall be provided as prescribed in the BMP manual.
4. Stormwater discharges to critical areas with sensitive resources (i.e., cold water fisheries, swimming beaches, recharge areas, water supply reservoirs) may be subject to additional performance criteria, or may need to utilize or restrict certain stormwater management practices.
5. Stormwater discharges from "hot spots" may require the application of specific structural BMPs and pollution prevention practices.
6. Prior to or during the site design process, applicants for land disturbance permits shall consult with the city engineer or designee to determine if they are subject to additional stormwater design requirements.
7. The calculations for determining peak flows as found in the BMP manual shall be used for sizing all stormwater facilities.
D. Minimum Control Requirements:
1. Stormwater discharge during all construction activities shall comply with the terms of the land disturbance permit, the stormwater design standards and regulations, and/or requirements set forth by the building code, and the state of Utah UPDES requirements.
2. Stormwater designs shall meet the multistage storm frequency storage requirements as identified in the BMP manual unless the city engineer or designee has granted the applicant a full or partial waiver for a particular BMP under this section.
3. Runoff rates from one lot to another may not exceed preexisting conditions or in such a manner that may unreasonably and unnecessarily cause more harm than formerly.
4. If hydrologic or topographic conditions warrant greater control than that provided by the minimum control requirements, the city engineer or designee may impose any and all additional requirements deemed necessary to control the volume, timing, and rate of runoff.
E. Stormwater Management Plan Requirements: Property owners are responsible to manage stormwater runoff and sediment whether in conduit systems or on the surface that traverse or originate on their property, unless this responsibility is relinquished through the terms and conditions of an easement. The stormwater management plan shall include sufficient information to allow the city engineer or designee to evaluate the environmental characteristics of the project site, the potential impacts of all proposed development of the site, both present and future, on the water resources, and the effectiveness and acceptability of the measures proposed for managing stormwater generated at the project site. To accomplish this goal the stormwater management plan shall include the following:
1. Topographic Base Map: A one inch equals five hundred feet (1" = 500') topographic base map of the site which extends a minimum of one thousand feet (1,000') beyond the limits of the proposed development and indicates:
a. Existing surface water drainage including streams, ponds, culverts, ditches, sinkholes, wetlands; and the type, size, elevation, etc., of nearest upstream and downstream drainage structures;
b. Current land use including all existing structures, locations of utilities, roads, and easements;
c. All other existing significant natural and artificial features;
d. Proposed land use with tabulation of the percentage of surface area to be adapted to various uses; drainage patterns; locations of utilities, roads and easements; the limits of clearing and grading;
e. Proposed structural BMPs;
f. A written description of the site plan and justification of proposed changes in natural conditions may also be required.
2. Calculations: Hydrologic and hydraulic design calculations for the predevelopment and postdevelopment conditions for the design storms specified in the BMP manual. These calculations must show that the proposed stormwater management measures are capable of controlling runoff from the site in compliance with this chapter and the guidelines of the BMP manual. Such calculations shall include:
a. A description of the design storm frequency, duration, and intensity where applicable;
b. Time of concentration;
c. Soil curve numbers or runoff coefficients including assumed soil moisture conditions;
d. Peak runoff rates and total runoff volumes for each watershed area;
e. Infiltration rates, where applicable;
f. Culvert, stormwater sewer, ditch and/or other stormwater conveyance capacities;
g. Flow velocities;
h. Data on the increase in rate and volume of runoff for the design storms referenced in the BMP manual; and
i. Documentation of sources for all computation methods and field test results.
3. Soils Information: If a stormwater management control measure depends on the hydrologic properties of soils (e.g., infiltration basins), then a soils report shall be submitted. The soils report shall be based on on-site boring logs or soil pit profiles and soil survey reports. The number and location of required soil borings or soil pits shall be determined based on what is needed to determine the suitability and distribution of soil types present at the location of the control measure.
4. Maintenance And Repair Plan: The design and planning of all stormwater management facilities shall include detailed maintenance and repair procedures to ensure their continued performance. These plans will identify the parts or components of a stormwater management facility that need to be maintained and the equipment and skills or training necessary. Provisions for the periodic review and evaluation of the effectiveness of the maintenance program and the need for revisions or additional maintenance procedures shall be included in the plan. A permanent elevation bench mark shall be identified in the plans to assist in the periodic inspection of the facility.
5. Landscaping Plan: The applicant must present a detailed plan for management of vegetation at the site after construction is finished, including who will be responsible for the maintenance of vegetation at the site and what practices will be employed to ensure that adequate vegetative cover is preserved. Where it is required by the BMP, this plan must be prepared by a registered landscape architect licensed in Utah.
F. Maintenance Easements: The applicant must ensure access to the site for the purpose of inspection and repair by securing all the maintenance easements needed. These easements must be binding on the current property owner and all subsequent owners of the property and must be properly recorded in the land record.
G. Maintenance Agreement: The owner of property to be served by an on site stormwater management facility must execute an inspection and maintenance agreement that shall operate as a deed restriction binding on the current property owner and all subsequent property owners. The maintenance agreement shall:
1. Assign responsibility for the maintenance and repair of the stormwater facility to the owner of the property upon which the facility is located and be recorded as such on the plat for the property by appropriate notation.
2. Provide for a periodic inspection by the property owner for the purpose of documenting maintenance and repair needs and ensure compliance with the purpose and requirements of this chapter. The property owner will arrange for this inspection to be conducted by a registered professional engineer licensed to practice in the state of Utah who will submit a sealed report of the inspection to the city engineer or designee. It shall also grant permission to the city to enter the property at reasonable times and to inspect the stormwater facility to ensure that it is being properly maintained.
3. Provide that the minimum maintenance and repair needs include, but are not limited to: the removal of silt, litter and other debris, the cutting of grass, grass cuttings and vegetation removal, and the replacement of landscape vegetation, in detention and retention basins, and inlets and drainage pipes and any other stormwater facilities. It shall also provide that the property owner shall be responsible for additional maintenance and repair needs consistent with the needs and standards outlined in the BMP manual.
4. Provide that maintenance needs must be addressed in a timely manner, on a schedule to be determined by the city engineer or designee.
5. Provide that if the property is not maintained or repaired within the prescribed schedule, the city engineer or designee shall perform the maintenance and repair at its expense, and bill the same to the property owner. The maintenance agreement shall also provide that the city engineer's cost of performing the maintenance shall be a lien against the property.
H. Dedication: The municipality shall have the discretion to accept the dedication of any existing or future stormwater management facility, provided such facility meets the requirements of this chapter, and includes adequate and perpetual access and sufficient areas, by easement or otherwise, for inspection and regular maintenance. Any stormwater facility accepted by the municipality must also meet the municipality's construction standards and any other standards and specifications that apply to the particular stormwater facility in question.
I. Sediment And Erosion Control Plans: The applicant must prepare a sediment and erosion control plan for all construction activities that complies with this subsection.
1. The sediment and erosion control plan shall accurately describe the potential for soil erosion and sedimentation problems resulting from land disturbing activity and shall explain and illustrate the measures that are to be taken to control these problems. The length and complexity of the plan is to be commensurate with the size of the project, severity of the site condition, and potential for off site damage. The plan shall be sealed by a registered professional engineer licensed in the state of Utah. The plan shall also conform to the requirements found in the BMP manual, and shall include at least the following:
a. Brief description of the intended project and proposed land disturbing activity including number of units and structures to be constructed and infrastructure required.
b. A topographic map with contour intervals of five feet (5') or less showing present conditions and proposed contours resulting from land disturbing activity.
c. All existing drainageways, including intermittent and wet weather. Include any designated floodways or floodplains.
d. A general description of existing land covers. Individual trees and shrubs do not need to be identified.
e. Stands of existing trees as they are to be preserved upon project completion, specifying their general location on the property. Differentiation shall be made between existing trees to be preserved, trees to be removed and proposed planted trees. Tree protection measures must be identified, and the diameter of the area involved must also be identified on the plan and shown to scale. Information shall be supplied concerning the proposed destruction of exceptional and historic trees in setbacks and buffer strips, where they exist. Complete landscape plans may be submitted separately. The plan must include the sequence of implementation for tree protection measures.
f. Approximate limits of proposed clearing, grading and filling.
g. Approximate flows of existing stormwater leaving any portion of the site.
h. A general description of existing soil types and characteristics and any anticipated soil erosion and sedimentation problems resulting from existing characteristics.
i. Location, size and layout of proposed stormwater and sedimentation control improvements.
j. Proposed drainage network.
k. Proposed drain tile or waterway sizes.
l. Approximate flows leaving site after construction and incorporating water runoff mitigation measures. The evaluation must include projected effects on property adjoining the site and on existing drainage facilities and systems. The plan must address the adequacy of outfalls from the development: when water is concentrated, what is the capacity of waterways, if any, accepting stormwater off site; and what measures, including infiltration, sheeting into buffers, etc., are going to be used to prevent the scouring of waterways and drainage areas off site, etc.
m. The projected sequence of work represented by the grading, drainage and sedimentation and erosion control plans as related to other major items of construction, beginning with the initiation of excavation and including the construction of any sediment basins or retention facilities or any other structural BMPs.
n. Specific remediation measures to prevent erosion and sedimentation runoff. Plans shall include detailed drawings of all control measures used; stabilization measures including vegetation and nonvegetation measures, both temporary and permanent, will be detailed. Detailed construction notes and a maintenance schedule shall be included for all control measures in the plan.
o. Specific details for the construction of rock pads, wash down pads, and settling basins for controlling erosion; road access points; eliminating or keeping soil, sediment, and debris on streets and public ways at a level acceptable to the city engineer or designee. Soil, sediment, and debris brought onto streets and public ways must be removed by the end of the workday by machine, broom or shovel to the satisfaction of the city engineer or designee. Failure to remove the sediment, soil or debris shall be deemed a violation of this chapter.
p. Proposed structures; location (to the extent possible) and identification of any proposed additional buildings, structures or development on the site.
q. A description of on site measures to be taken to recharge surface water into the groundwater system through infiltration. (Ord. 2012-02, 2-21-2012, eff. 3-18-2012)
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