City of Maryville, MO Storm Water Concept and Preliminary Development Plans

In developing plans for a residential/commercial subdivision, individual lots in a residential/commercial subdivision development shall not be considered to be separate land-disturbing activities and shall not require individual storm water management permits. Instead, the residential/commercial subdivision development, as a whole, shall be considered to be a single land-disturbing activity. Hydrologic parameters that reflect the ultimate subdivision development shall be used in all engineering calculations. Individual lot development with new dwellings or any structure which has more than fifty percent (50%) added to existing square footage shall require submittal of topographical maps with before and after elevations for the entire perimeter of the lot.

If individual lots or sections in a residential/commercial subdivision are being developed by different property owners, all land-disturbing activities related to the residential/commercial subdivision shall be covered by the approved storm water management plan for the residential/commercial subdivision. Individual lot owners or developers shall sign a certificate of compliance that all activities on that lot will be carried out in accordance with the approved storm water management plan for the residential/commercial subdivision. (See Exhibits A and B of Ord. No. 5430 which are on file in the City offices).

Residential/commercial subdivisions which were approved for construction by the City Council prior to the effective date of these regulations are exempt from these requirements. Development of new phases of existing subdivisions which were not previously approved shall comply with the provisions of these regulations.

For residential land-disturbing activities involving less than one (1) acre of actual land disturbance which are not part of a larger common plan of development or sale, the person responsible for the land-disturbing activity shall submit a simplified storm water management plan to the Public Works Department meeting the requirements listed below. This plan does not require approval by the municipality and does not require preparation of certification by the designers specified in Section 560.160 of Article II. All commercial developments regardless of size must conform to Article II, Sections 560.070 through 560.160, unless a waiver is granted by the municipality.

A narrative description of the storm water management facilities to be used.

A general description of topographic and soil conditions of the development site.

A general description of adjacent property and a description of existing structures, buildings, and other fixed improvements located on surrounding properties.

A sketch plan to accompany the narrative which shall contain:

A site location drawing of the proposed project, indicating the location of the proposed project in relation to roadways, jurisdictional boundaries, streams and rivers;

The boundary lines of the site on which the work is to be performed;

All areas within the site which will be included in the land-disturbing activities shall be identified and the total disturbed area calculated;

A topographic map of the site;

Anticipated starting and completion dates of the various stages of land-disturbing activities and the expected date the final stabilization will be completed; and

The location of temporary and permanent vegetative and structural storm water management control measures.

Storm water management plans shall contain certification by the person responsible for the land-disturbing activity that the land-disturbing activity will be accomplished pursuant to the plan. (See Exhibit C of Ord. No. 5430 which is on file in the City offices.)

Storm water management plans shall contain certification by the person responsible for the land-disturbing activity of the right of the municipality to conduct on-site inspections. (See Exhibit D of Ord. No. 5430 which is on file in the City offices.)

The municipality reserves the right to require storm water management preparation as in Article II, Section 560.130, as recommended by the Director of Public Works.

For residential land-disturbing activities disturbing greater than or equal to one (1) acre or less than one (1) acre if part of a common development plan of one (1) acre or more and all commercial land-disturbing activities, the requirements of Article II, Sections 560.070 through 560.160, shall apply.

Section 560.070 Storm Water Concept and Storm Water Management Plan.

[R.O. 2008 §560.070; Ord. No. 5430 §1, 6-25-1996]

A storm water concept plan for development shall be submitted for review by the Public Works Department prior to submission of the storm water management plan and construction plans for the entire development, or any portion thereof. The storm water concept plan must identify the location and type of facilities to be constructed in sufficient detail to accurately estimate construction costs and enable the Public Works Department to determine if a storm water management plan is needed. If they determine a final storm water management plan is not needed, the storm water concept plan then becomes the storm water management plan for this development.

All preliminary plats of the development shall be consistent with the storm water concept plan required in Subsection (A), above.

Upon approval of the concept plan by the Director of Public Works, the applicant shall submit a final storm water management plan (as part of the construction plans) to the City Council for review and approval.

Should any storm water management plan involve any storm water management facilities or land to be dedicated to public use, the same information shall also be submitted for review to the department having jurisdiction over the land or other appropriate departments or agencies prior to submission to the City Council for review and approval. The final storm water management plan shall serve as the basis for all subsequent construction.

If disapproved by the City Council, the storm water management plan may be reviewed with the designer, where it will either be changed, modified or resubmitted. If rejected, changes, additional analysis or other information needed to approve the next submittal of the concept plan shall be identified by the City Council. After the receipt of the revised storm water management plan, the City Council shall issue a decision approving, rejecting or conditionally approving the plan with modification.

Section 560.080 Permit Requirements.

[R.O. 2008 §560.080; Ord. No. 5430 §1, 6-25-1996]

No final occupancy permit shall be issued without the following:

Recorded easement for storm water management facilities.

Receipt of an as-built plan which includes a certification of the storm drainage system.

No site grading permit shall be issued or modified without the following:

Right of entry for emergency maintenance if necessary. (See Exhibit E & F of this Ord. No. 5430 which are on file in the City offices.)

Right of entry for inspections. (See Exhibits E & F of this Ord. No. 5430 which are on file in the City offices.)

Any off-site easement needed.

An approved storm water concept plan or storm water management plan, as appropriate.

An approved storm water ownership and maintenance plan.

The approved storm water management plan shall contain certification by the applicant that all land clearing, construction, development and drainage will be done according to the storm water management plan or previously approved revisions. Any and all site grading permits may be revoked at any time if the construction of storm water management facilities is not in strict accordance with approved plans. (See Exhibit C of this Ord. No. 5430 which is on file in the City offices.)

In addition to the plans and permits required from the municipality, applicants shall obtain all State and Federal permits required for the proposed development.

Section 560.090 Fees.

[R.O. 2008 §560.090; Ord. No. 5430 §1, 6-25-1996]

A list of fees for plan review and other fees associated with this Chapter can be obtained from the Public Works Department.

Section 560.100 Permit Suspension and Revocation.

[R.O. 2008 §560.100; Ord. No. 5430 §1, 6-25-1996]

A site grading permit may be suspended or revoked if one (1) or more of the following violations have been committed:

Violation(s) of the conditions of the storm water management plan as approved;

Construction not in accordance with the approved plans;

Non-compliance with correction notice(s). (See Exhibit G of this Ord. No. 5430 which is on file in the City offices) or stop work order(s), (see Exhibit H of this Ord. No. 5430 which is on file in the City offices); or

The existence of an immediate danger in a downstream area in the judgment of the Director of Public Works or his/her designee.

If one (1) or more of these conditions are found, a written notice of violation(s) shall be served upon the owner or authorized representative and an immediate stop work order may be issued. The notice shall set forth the measures necessary to achieve compliance with the plan. Correction of these violations must be started immediately or the owner shall be deemed in violation of this Chapter.

Section 560.110 Minimum Runoff Control Requirements.

[R.O. 2008 §560.110; Ord. No. 5430 §1, 6-25-1996]

The minimum storm water control requirements shall provide management measures necessary to accomplish the following:

Install storm water management facilities to limit the 2-year and 10-year developed peak discharge rates to pre-developed peak discharge rates. The design of these facilities shall be based on procedures contained in the Storm Water Management Design Guide or procedures approved by the Director of Public Works. The 2-year and 10-year design storms cover the range of normal flooding. Structures must be analyzed for both. The 25-year storms are commonly used for structures under roadways.

The requirements or portions thereof, of Subsection (A)(1) above, may be waived by the City Council if it can be shown by the detailed engineering calculations and analysis which are acceptable to the municipality that one (1) of the following exists:

The installation of storm water management facilities would have insignificant effects on reducing downstream flood peaks;

Storm water management facilities are not needed to protect downstream developments and the downstream drainage system has sufficient capacity to receive any increase in runoff for the design storm;

It is not necessary to install storm water management facilities to control developed peak discharge rates at the exit to a proposed development and installing such facilities would increase flood peaks at some downstream locations; or

The Public Works Department determines that storm water management facilities are not needed to control developed peak discharge rates and installing such facilities would not be in the best interest of the municipality.

The requirements or portions thereof, of Subsection (A)(1) above, may not be waived if the municipality determines that not controlling downstream flood peaks would increase known flooding problems, or exceed the capacity of the downstream drainage system.

A waiver shall only be granted after a written request is submitted to the City Manager through the Public Works Department by the applicant containing descriptions, drawings, and any other information that is necessary to evaluate the proposed land disturbing activity. A separate written waiver request shall be required if there are subsequent additions, extensions, or modifications which would alter the approved storm water runoff characteristics to a land disturbing activity receiving a waiver. The municipality will conduct a review of the request for a waiver.

Discharge velocities shall be reduced to provide a non-erosive velocity flow from a structure, channel or other control measure or the velocity of the 10-year design storm runoff in the receiving waterway prior to the land disturbing activity, whichever is greater.

For all storm water management facilities, a hydrologic-hydraulic study shall be done showing how the drainage system will function with and without the proposed facilities. For such studies the following land use conditions shall be used. Existing land use data shall be taken from the most recent aerial photography and field checked and updated.

For the design of the facility outlet structure, use developed land use conditions for the area within the proposed development and existing land use conditions for upstream areas draining to the facility.

For any analysis of flood flows downstream from the proposed facility, use existing land use conditions for all downstream areas.

All storm water management facilities emergency spillways shall be checked using the 100-year storm and routing flows through the facility and emergency spillways. For this analysis, developed land use conditions shall be used for all areas within the analysis.

If accepted for municipal maintenance, the effects of existing upstream detention facilities can be considered in the hydrologic-hydraulic study.

Section 560.120 Storm Water Management Facilities.

[R.O. 2008 §560.120; Ord. No. 5430 §1, 6-25-1996]

Storm water management facilities may include both structural and non-structural elements. Natural swales and other natural runoff conduits shall be retained where practicable.

When additional storm water management facilities are required to satisfy the minimum control requirements, the following measures are examples of what may be used:

Storm water detention structures (dry basins);

Storm water retention structures (wet ponds — minimum depth six (6) feet);

Facilities designed to encourage overland flow, slow velocities of flow and flow through buffer zones;

Infiltration practices.

Where detention and retention structures are used, designs which consolidate these facilities into a limited number of large structures will be preferred over designs which utilize a large number of small structures.

Storm water management plans can be rejected by the municipality if they incorporate structures and facilities that will demand considerable maintenance, will be difficult to maintain or utilize numerous small structures if other alternatives are physically possible.

The drainage system and all storm water management structures within the municipality (including both public and private portions) will be designed to the same engineering and technical criteria and standards. The municipality's review will be the same whether the portion of the drainage system will be under public or private control or ownership.

All storm water management measures shall be designed in accordance with the design criteria contained in the Storm Water Management Design Guide using procedures contained in this manual or procedures approved by the municipality.

Section 560.130 Plan Requirements.

[R.O. 2008 §560.130; Ord. No. 5430 §1, 6-25-1996]

Storm water management plans shall include as a minimum the following:

A vicinity map indicating a north arrow, scale, boundary lines of the site and other information necessary to locate the development site.

The existing and proposed topography of the development site.

Physical improvements on the site, including present development and proposed development.

Location, dimensions, elevations and characteristics of all storm water management facilities.

All areas within the site which will be included in the land disturbing activities shall be identified and the total disturbed area calculated.

The location of temporary and permanent vegetative and structural storm water management control measures.

An anticipated starting and completion date of the various stages of land disturbing activities and the expected date the final stabilization will be completed.

A determination that no occupied first (1st) floor elevation of any structure is below the 100-year plus one (1) foot flood elevation.

At the direction of the Director of Public Works, for all portions of the drainage system which are expected to carry between fifty (50) and one hundred fifty (150) cfs for the 100-year storm, the 100-year plus one (1) foot flood elevation analysis, the Public Works Department will determine that one (1) of the following conditions may exist:

The estimated runoff would create a hazard for adjacent property or residents.

The flood limits would be of such magnitude that adjacent residents should be informed of these limits.

10.

For all portions of the drainage system which are expected to carry one hundred fifty (150) cfs or more for the 100-year storm, the 100-year plus one (1) foot flood elevation analysis shall be done and flood limits shall be shown on the storm water management plans.

11.

Storm water management plans shall include designation of all easements needed for inspection and maintenance of the drainage system and storm water management facilities. As a minimum, easements shall have the following characteristics:

Provide adequate access to all portions of the drainage system and structures.

Provide sufficient land area for maintenance equipment and personnel to adequately and efficiently maintain the system with a minimum of ten (10) feet along both sides of all drainage ways, streams, channels, etc., and around the perimeter of all detention and retention facilities or sufficient land area for equipment access for maintenance of all storm water management facilities. The distance shall be measured from the top of the bank or toe of the dam whichever is applicable.

Restriction on easements shall include prohibiting all fences and structures which would interfere with access to the easement areas and/or the maintenance function of the drainage system.

12.

To improve the aesthetic aspects of the drainage system, a landscape plan for all portions of the drainage system shall be part of the storm water management plan. This landscape plan shall address the following:

Tree saving and planting plan.

Types of vegetation that will be used for stream bank stabilization, erosion control, sediment control, aesthetics and water quality improvement.

Any special requirements related to the landscaping of the drainage system and efforts necessary to preserve the natural aspects of the drainage system.

13.

To improve the water quality aspects of the drainage system, the storm water management plan shall include best management practices to control the water quality of the runoff during the land disturbing activities and during the life of the development. This requirement is in addition to the requirements of the Missouri Department of Natural Resources Storm Water Pollution Prevention Permit.

14.

The storm water management plans shall include all engineering calculations needed to design the system and associated structures including pre- and post-development velocities, peak rates of discharge and inflow and outflow hydrographies of storm water runoff at all existing and proposed points of discharge from the site.

15.

Description of site conditions around points of all surface water discharge including vegetation and method of flow conveyance from the land disturbing activity.

16.

Construction and design details for structural controls.

17.

The expected timing of flood peaks through the downstream drainage system shall be assessed when planning the use of detention facilities.

18.

In determining downstream effects from storm water management structures and the development, hydrologic-hydraulic engineering studies shall extend downstream to a point where the proposed development represents less than ten percent (10%) of the total watershed.

19.

All storm water management facilities and all major portions of the conveyance system through the proposed development (i.e., channels, culverts) shall be analyzed, using the design and 100-year storms for design conditions and operating conditions which can reasonably be expected during the life of the facility. The results of the analysis shall be included in the hydrologic-hydraulic study.

20.

If the storm water management plan and/or design report indicates that there may be a drainage or flooding problem at the exit to the proposed development or at any location between the exit point and the ten percent (10%) downstream point, the Director of Public Works may require:

Water surface profiles plotted for the conditions of pre- and post-development for the 100-year design storm;

Elevations of all structures potentially damaged by the 10- and/or 100-year flows.

21.

All storm water management plans submitted for approval shall contain certification by the person responsible for the land disturbing activity that the land disturbing activity will be accomplished pursuant to the approved plan and that responsible personnel will be assigned to the project. (See Exhibit C of this Ord. No. 5430 which is on file in the City offices).

22.

All storm water management plans shall contain certification, by the person responsible for the land disturbing activity, of the right of the Municipality to conduct on-site inspections. (See Exhibit D of this Ord. No. 5430 which is on file in the City offices).

23.

No storm water management plan shall be considered approved without the inclusion of an approval signature and date on the plans by the Director of Public Works or his/her designee. The approval on the plans is solely an acknowledgement of satisfactory compliance with the requirements of these regulations. The approval does not constitute a representation or warranty to the applicant or any other person concerning the safety, appropriateness or effectiveness of any provision or omission from the storm water management plan.

24.

Approved storm water management plans remain valid for five (5) years from the date of approval. Extensions or renewals of the plan approvals may be granted by the City Manager upon written request by the person responsible for land disturbing activity.

Section 560.140 Plan Hydrologic Criteria.

[R.O. 2008 §560.140; Ord. No. 5430 §1, 6-25-1996]

The hydrologic criteria to be used for the storm water concept and storm water management plans shall be as follows:

25-year design storm for all cross-drain culverts and drainage designs.

10-year design storm for all interior culverts and drainage designs.

2- and 10-year design storms for all detention and retention basins using procedures contained in the Storm Water Management Design Guide or approved by the Public Works Department.

All drainage designs shall be checked using the 100-year storm for analysis of local flooding and possible flood hazards to adjacent structures and/or property.

All hydrologic analysis will be based on land use conditions specified in Section 560.110(B).

For the design of storage facilities, a secondary outlet device or emergency spillway shall be provided to discharge the excess runoff in such a way that no danger of loss of life or facility failure is created. The size of the outlet device or emergency spillway shall be designed to pass the 100-year storm as a minimum requirement.

Section 560.150 Plan Water Quality Criteria.

[R.O. 2008 §560.150; Ord. No. 5430 §1, 6-25-1996]

Following are the criteria related to using storm water management facilities for water quality purposes:

Ponds, lakes and reservoirs.

When the land disturbing activity consists of the construction of a pond, lake or reservoir which is singly built and not part of a permitted land disturbing activity, the following procedures will apply:

(1)

A storm water management plan will not be required if the pond, lake or reservoir is permitted under the State Dams and Reservoirs Safety Act or has received a Certificate of Exemption from the State Dams and Reservoirs Safety Act. Best management practices should be used to minimize the impact of erosion and sediment.

(2)

A storm water management plan will be required for the construction of all ponds, lakes or reservoirs not meeting the conditions in (1) above that otherwise meet the size requirement for storm water management plan approval.

When ponds are used for water quality protection, the ponds shall be designed as both quantity and quality control structures. Sediment storage volume shall be calculated considering the clean out and maintenance schedules specified by the designer during the land disturbing activity. Sediment storage volumes may be predicted by the Universal Soil Loss Equation or other methods acceptable to the Director of Public Works.

Storm water runoff and drainage to a single outlet from land disturbing activities which disturb ten (10) acres or more shall be controlled during the land disturbing activity by a sediment basin where sufficient space and other factors allow these controls to be used until the final inspection. The sediment basin shall be designed and constructed to accommodate the anticipated sediment loading from the land disturbing activity and meet a removal efficiency of eighty percent (80%) suspended solids or 0.5 ML/L peak set table solids concentration, whichever is less. The outfall device or system design shall take into account the total drainage area flowing through the disturbed area draining to the basin.

Other practices may be acceptable to the municipality if they achieve an equivalent removal efficiency of eighty percent (80%) for suspended solids or 0.5 ML/L peak set table solids concentration, whichever is less. The efficiency shall be calculated for disturbed conditions for the 10-year twenty-four (24) hour design storm event.

Permanent water quality ponds having a permanent pool shall be designed to store and release the first (1st) one-half (½) inch of runoff from the site over a twenty-four (24) hour period. The storage volume shall be designed to accommodate, at least, one-half (½) inch of runoff from the entire site.

Permanent water quality ponds, not having a permanent pool, shall be designed to release the first (1st) inch of runoff from the site over a twenty-four (24) hour period.

The use of measures other than ponds to achieve water quality improvement are recommended on sites containing less than ten (10) disturbed acres.

Infiltration practices.

Permanent infiltration practices, when used, shall be designed to accept, at a minimum, the first (1st) inch of runoff from all impervious areas.

Area drainage to infiltration practices must be established and vegetative filters established prior to runoff entering the system. Infiltration practices shall not be used if a suspended solids filter system does not accompany the practice. If vegetation is the intended filter, there shall be at least a twenty (20) feet width of vegetative filter prior to storm water runoff entering the infiltration practice.

The bottom of the infiltration practice shall be at least two (2) feet above the seasonal high water table, whether perched or regional, determined by direct piezometer measurements which can be demonstrated to be representative of the maximum height of the water table on an annual basis during years of normal precipitation or by the depth in the soil at which mottling first occurs.

The infiltration practice shall be designed to completely drain of water within seventy-two (72) hours.

Soils must have adequate permeability to allow water to infiltrate. Infiltration practices are limited to soils having an infiltration rate of at least 0.30 inches per hour. Initial consideration will be based on a review of the appropriate soil survey, and the survey may serve as a basis for rejection. On-site soil borings and textural classifications must be accomplished to verify the actual site and seals on high water table conditions when infiltration is to be utilized.

Infiltration practice greater than three (3) feet deep shall be located at least ten (10) feet from basement walls.

Infiltration practices designed to handle runoff from impervious parking areas shall be a minimum of one hundred fifty (150) feet from any public or private water supply well.

The design of infiltration practice shall provide an overflow system with measures to provide a non-erosive velocity of flow along its length and at the outfall.

The slope of the bottom of the infiltration practice shall not exceed five percent (5%). Also, the practice shall not be installed in fill material, as piping along the fill/natural ground interface may cause slope failure.

An infiltration practice shall not be installed on or atop a slope whose natural angle of incline exceeds twenty percent (20%).

Clean outs will be provided, at a minimum, every one hundred (100) feet along the infiltration practice to allow for access and maintenance.

Section 560.160 Professional Registration Requirements.

[R.O. 2008 §560.160; Ord. No. 5430 §1, 6-25-1996]

Storm water concept and storm water management plans and design reports that are incidental to the overall or ongoing site design shall be prepared, certified, and stamped/sealed by a qualified registered Missouri professional engineer, land surveyor, or landscape architect using acceptable engineering standards and practices. All other storm water concept, and storm water management plans and design reports shall be prepared, certified and stamped/sealed by a qualified registered Missouri professional engineer using acceptable engineering standards and practices.

The engineer, surveyor or landscape architect shall perform services only in areas of his/her competence and shall undertake to perform engineering or land surveying assignments only when qualified by education and/or experience in the specific technical field. In addition, the engineer, surveyor or landscape architect must verify that the plans have been designed in accordance with this Chapter and the standards and criteria stated or referred to in this Chapter.