The stormwater management requirements established by this Article are intended to reduce urban runoff and mitigate the effects of new development, redevelopment, or infill development on the existing drainage system by ensuring the preservation of permeable surfaces and requiring the installation of stormwater Best Management Practices (BMPs) to slow surface flow of stormwater runoff and promote filtration, plant uptake, absorption and infiltration into sub-soils to reduce subsidence rates.

(1)

No building permit or certificate of occupancy may be issued for any lot or use subject to the requirements of this Article unless all the requirements of this Article have been met. Failure to implement the stormwater management plan, or to maintain the lot or use in conformance with the stormwater management plan, is cause for revocation of the certificate of occupancy and/or the application of fines and penalties, as established in this Ordinance. In addition, all landscape is subject to periodic inspection.

(2)

Prior to the issuance of a certificate of occupancy, any development that requires a stormwater management plan shall have a landscape architect and/or civil engineer licensed in Louisiana certify with signature and seal in an affidavit that the stormwater management measures have been installed in accordance with all approved plans and specifications.

With the understanding that landscaping is critical to proper stormwater management, it is highly recommended that both this and the previous chapter, Article IX: Landscaping Regulations, be read in their entirety before beginning any site planning so that landscaping design measures are incorporated into stormwater management in the most efficient and cost effective manner possible.

(a)

Applicability:

(1)

In order to comply with federal, state, and local regulations for urban stormwater management, a stormwater management plan shall be submitted as part of any new development, including redevelopment, of a site of seven thousand (7,000) square feet or more of impervious surface, or any new development, including redevelopment, or a site of one (1) acre or more in size.

(2)

Single-family and multi-family dwellings of five (5) units or less do not require submittal of a stormwater management plan, but shall comply with all other applicable federal, state and local stormwater ordinances.

(b)

Stormwater Plan Submission and Approval: Three (3) sets of each plan must be submitted to the Director of the Department of Inspections and Code Enforcement. The Director shall approve each plan in consultation with a landscape architect and/or civil engineer licensed in the State of Louisiana prior to issuance of the building permit.

(1)

In addition to meeting the requirements herein, each plan must include any criteria that may be required by the Director of the Department of Planning. If disapproved, justification must be given to the applicant.

(2)

All reviewed plans will be returned to the designer marked "approved" or "approved as noted" or "denied." Rejected plans may be returned to the department for re-evaluation once noted corrections are made.

(3)

A copy of each approved plan will be archived to ensure that it was implemented as permitted and maintained as required.

(4)

For new developments that require final action by the City Council, the applicable stormwater plan must be approved by the Department of Planning prior to Council action. If changes occur to the plan after approval, the changes must not compromise the original plan.

(c)

Content of Stormwater Management Plan: Stormwater management plans shall be prepared by a landscape architect and/or civil engineer licensed in Louisiana. A stormwater management plan, including the pre-development runoff rate and the post-development runoff rate, shall contain the following information:

(1)

The location of the property and adjacent developments and infrastructure.

(2)

Existing site conditions, including a description and map of land cover, contours, soil types, and estimated pollutant load.

(3)

Description and development plan of the proposed development, including land cover, contours, and empirically expected pollutant load.

(4)

All storm drainage systems, including existing and proposed drain lines, culverts, catch basins, headwalls, hydrants, manholes, and temporary and permanent stormwater Best Management Practices (BMPs).

(5)

All pertinent calculations and specifications used in the design and construction of the permanent stormwater BMPs to retain, detain, or filter the first one (1) inch of stormwater runoff during each rain event. Safeguards to prevent short-circuiting of permanent stormwater BMPs shall be designed into the system. Capacities of BMPs shall show surface and sub-surface volumes (in aggregate, chambers, cisterns, etc.) in gallons.

(6)

Plan implementation, including BMP installation methods, phases, and timelines for installation and maintenance of BMPs.

(7)

A plan showing site sub-catchment areas, retention BMP areas and capacities, detention BMP areas and capacities, conveyance BMPs, and stormwater runoff treatment train of BMPs in which runoff is filtered through a series of BMPs before entering the City drainage system (surface or sub-surface).

(8)

Description of how the proposed drainage and temporary and permanent stormwater BMPs will be maintained.

(9)

The estimated cost of proposed drainage and temporary and permanent stormwater BMPs.

(d)

Alternative Compliance:

(1)

The standards contained in this Article are intended to encourage development which is economically viable and environmentally sensitive. The standards are not intended to be so specific as to inhibit creative development. Project conditions associated with individual sites may justify approval of alternative methods of compliance with the landscape standards. Conditions may arise where normal compliance is impractical or impossible, or where maximum achievement of the City's objectives can only be obtained through alternative compliance.

(2)

Requests for alternative compliance will be accepted for any permit application to which the requirements of this Article apply, when one (1) or more of the following conditions are met:

a.

Topography, soil, vegetation, drainage, or other site conditions are such that full compliance is impractical.

b.

Improved environmental quality would result from the alternative compliance provisions of this Article.

c.

Spatial limitations, irregularly shaped lot, or unusual servitude requirements may justify alternative compliance.

d.

Public safety considerations make alternative compliance necessary.

(3)

A request for alternative compliance must be submitted to the Director of the Department of Planning when the landscape plan is submitted.

a.

The Director of the Department of Planning, in consultation with the Director of the Inspections and Code Enforcement department, may not reduce the requirements of this Article by more than fifty (50) percent.

b.

Requests for alternative compliance must be accompanied by sufficient written explanation and landscape plan drawings to allow appropriate evaluation and decision by the Director of the Department of Planning in consultation with the Director of the Department of Inspections and Code Enforcement.

c.

Upon review of the request, a determination will be made by the Director of Planning, who shall inform the applicant, by letter, of the determination.

(a)

Stormwater Management Measures:

(1)

Effective on-site stormwater management is supported by a combination of stormwater BMPs, as outlined in (1)d(b), guided by the following strategies:

a.

First, create conditions that allow detention and infiltration of stormwater runoff on-site through the use of pervious paving, open vegetated areas, green roofs, blue roofs, and other methods that allow water to permeate back into the ground.

b.

Next, additional stormwater runoff should be detained, stored, infiltrated, and/or filtered through the use of BMPs.

c.

Finally, runoff in excess of the first one (1) inch shall exit the site through surface or subsurface drainage.

(2)

Infiltration practices shall be utilized to reduce runoff volume increases, stabilize subsoils, and recharge shallow groundwater.

(3)

Best Management Practices (BMP) shall be employed to minimize pollutants in stormwater runoff prior to discharge into a separate storm drainage system or water body.

(4)

All stormwater management facilities shall be designed to provide an emergency overflow system, and incorporate measures to provide a non-erosive velocity of flow along its length and at any outfall.

(5)

The designed release rate of any stormwater structure shall be modified if any increase in flooding or stream channel erosion would result at a downstream dam, highway, structure, or normal point of restricted stream flow.

(b)

Stormwater Best Management Practices: Stormwater Best Management Practices (BMP) minimize runoff, increase infiltration, recharge groundwater, and improve water quality. In order to accomplish the performance standard required by this section, stormwater BMPs shall be used. Stormwater BMPs shall be designed as described in Bayou Land RC&D's "Stormwater BMP Guidance Tool." Alternate BMPs may be considered but shall be approved as part of the stormwater management plan. The following list of stormwater BMPs are not prescriptive, but provide guidance for establishing a site-specific stormwater management regime, and include, but are not limited to:

(1)

Bioswales: Bioswales are vegetated swales planted with native plants or ornamental grasses. They transport water, allow some to infiltrate, and can be designed as a landscape feature. Bioswales are not grassed but are planted with a variety of wetland plant species that flower, fruit, and have ornamental qualities.

(2)

Circular Depressions: Circular grassed depressions are similar to rain groves, but are smaller and contain only grass within the depressions. It is preferable to use multiple circular grassed depressions. Circular grassed depressions should be six (6) inches deep and range in diameter from thirty-six (36) inches to seventy-two (72) inches.

(3)

Constructed Wetlands: Constructed wetlands, such as wet ponds, are commonly used on large development projects such as golf courses, shopping centers, business parks, and industrial sites. These wetlands shall be designed as part of an integrated drainage system, built around lakes and ponds that may include detention areas, retention areas, irrigation ponds, or low-lying areas that collect and store stormwater.

(4)

Detention/Retention Basins: Wet retention basins are constructed, naturalistic ponds with a permanent or seasonal pool of water (also called a "wet pool" or "dead storage"). Aquascape facilities, such as artificial lakes, are a form of wet pool facility that can incorporate innovative design elements to allow them to function as a stormwater treatment facility in addition to a water feature.

Dry extended detention (ED) basins are basins whose outlets have been designed to drain from a full condition within thirty-six (36) to forty-eight (48) hours to allow sediment particles and associated pollutants to settle and be removed. Dry ED basins to not have a permanent pool and are designed to drain completely between storm events. The slopes, bottom, and forebay of dry ED basins should be vegetated.

(5)

Disconnected Roof Tops, Recycling, and Irrigation: A disconnected rooftop is one where stormwater falling on a building roof is captured and prevented from being added to stormwater runoff from a construction site. Since the water is relatively clean, it can be reused for certain domestic use or recycled through an irrigation system for evaporative disposal or to feed moisture to landscape beds, lawns, and tree stands.

(6)

Ditch Gardens: Louisiana ditch gardens are a variant of a bioswale that increases water quality. These are constructed by designing long thin but shallow depressions that can be planted with Louisiana wetland plants that trap sediments, infiltrate water, and clean water of pollutants.

(7)

Flow Diffusers: Flow diffusers consist of several design features that can accept channelized flow and convert it to sheet flow to disengage the erosive power of running water. Examples of flow diffusers include turf grass panels, vegetative meadows, shallow stone filtration trenches, or basins reinforced with very low earth berms.

(8)

French Drains, Infiltration Trenches, and Dry Wells: Infiltration trenches are excavated into the ground either horizontally or vertically and filled with stone aggregate to capture and allow exfiltration of stormwater runoff into the surrounding soils from the bottom and sides of the trench or well. Pollutant removal is achieved by filtration of the runoff through the stone aggregate and soil, as well as biological and chemical activity within the soil. This is called a French drain in Louisiana, and can be fitted with an outflow if soil types warrant such treatment.

(9)

Grassed Swales: Grassed swales are designed conveyance devices used to transport water over the surface of the ground to a point of disposal that may be a catch basin, ditch, water body, or a stormwater BMP that will filter, infiltrate, evaporate, and clean the water of TSS, solid waste, and other pollutants. Swales are often appropriate along property lines, public streets, and around buildings.

[(10)]

Habitat Preservation and Protection Areas: Habitat Protection Areas (HPA) are large tree protection areas in which a complete habitat of plants, soils, water regimes, animal life, and nutrients work together to produce clean air, pure water, rich soils, and a population of animal life living and growing off of the biological productivity and diversity.

[(11)]

Permeable Pavers, Porous Surfaces, Grass Paving, and Structural Soils: Porous paving reduces site runoff and allows the infiltration of stormwater. Structural soils are designed to bear the weight of heavy construction such as parking lots, terraces, and courtyard, but also provide void space for tree roots and stormwater infiltration.

[(12)]

Planted Stormwater Buffers: Planted stormwater buffers can absorb stormwater falling on development sites. Planted buffers can improve internal drainage and be linked for maximum stormwater collection during rainfall events. Buffers can be built for stormwater management along roadways, at property edges, parallel to walkways, driveways, structures, and almost any place on a development site in which open space can be found that can be planted.

[(13)]

Preserved Forest Floors: Rain falling on the tree canopy is managed as soon as raindrops fall on leaves and continues until the roots uptake the water hours after the storm event. This preserves trees and manages stormwater, as well as preserves natural habitat and remnant forest stands on development sites.

[(14)]

Preserved Wetlands: Wetlands are characterized as vegetated parcels of land that have standing water for part of the year. Wetlands are also delineated according to existing vegetation and soil types. The Army Corps of Engineers designate a wetland as any low area meeting certain jurisdictional requirements of water, soil, and vegetation. Wetlands within cities are often low areas that trap and hold rainfall and release it at very slow rates of water flow.

(15)

Rain Gardens: Rain gardens are small shallow depressions planted with a variety of native or ornamental plants that can treat small amounts of runoff to improve water quality. Rain gardens are generally small collections of water loving plants planted on a low site area that naturally collects rainfall.

(16)

Rain Groves: Rain groves are miniature forests that provide multiple services. They provide habitat for birds and other fauna that live close to developed areas. A rain grove will intercept runoff to provide a suitable habitat to grow a variety of wetland trees and shrubs.

(17)

Rooftop Runoff Management: Rooftop runoff management captures stormwater through a variety of techniques, including green roofs, blue roofs, cisterns, and rain barrels.

(18)

Sand Filters: Sand filters are depressions, trenches, barriers, or sand lens constructed of porous mineral matter that improve groundwater recharge to filter, clean, and trap waterborne pollutants.

(19)

Stream Bank or Riparian Buffers: A stream bank buffer is a protected area along a water body, such as a stream, bayou, pond, or lake, where development is restricted or prohibited. They can vary in width from twenty (20) feet to two hundred fifty (250) feet. The widths of the buffer zone is dependent upon the size of the stream, its drainage load, and overflow characteristics, although other factors such as slope, soils, and amount of vegetation are considered.

(20)

Tree Protection Areas: Tree Protection Areas (TPA) are small Habitat Preservation Areas (HPA) that are set aside as an area around the trunk of a tree to be preserved on a development site. The purpose of the TPA is to protect the critical root zone (CRZ) of the tree and to prevent damage or interference during construction. This area is established in relation to the tree size, diameter of the crown, diameter of the tree at DBH, and location of feeder roots where most of the water and plant nutrients are absorbed.

(21)

Cisterns and Underground Stormwater Chambers: Aboveground stormwater cisterns and underground stormwater chambers are effective long-term stormwater management systems. They are primarily used for landscape irrigation with grey water, or to temporarily store and release at a predictable rate of stormwater flow.