Stormwater Manual - Pima County Flood Control District

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1.4 General Criteria for New Development 1.4.1 Watershed Studies Watershed studies are necessary to evaluate the impacts of a given development on the public drainage system and to define the post-development floodplain. The criteria for conducting watershed studies are given in Chapter 3. The LFUCG has a program for inventorying the stormwater system, collecting physical and chemical data describing the waters, and developing watershed models. The program also includes collecting information on the physical nature of the stream or channel, detail of the natural vegetation in the floodplain, the riparian vegetation, the nature and extent of any unique features like wetlands, and the biological community in the water. In watersheds where the models are completed, the LFUCG shall define the post development floodplain and set the other stormwater criteria for the development. In areas where the models are not completed, the LFUCG may require the Developer to conduct the study. 1.4.2 Regional Stormwater Management The LFUCG shall require regional stormwater management facilities when practicable. This is more cost effective than requiring each small development project to construct its own stormwater facilities. In addition, the long-term maintenance requirements will be less because there will be fewer of these small facilities to maintain. The LFUCG may require two or more developers to jointly fund the construction of a common water quality and/or water quantity practice by requiring cooperation between the developers or using a fee-in-lieu of constructing stormwater BMPs as defined later in this chapter. 1.4.3 Existing Stormwater Master Plans Expansion Area 2 The regional stormwater master plan for Expansion Area 2 is contained in a report prepared by Commonwealth Technology, Inc. entitled “Preliminary Engineering Report – Stormwater Management in Expansion Area 2.” This report can be obtained from the Division of Engineering. The report contains the location and size of stormwater management structures to control flooding and to protect water quality. Stormwater Master Plans Prepared by Developers The following developments currently have a regional stormwater master plan to control flooding: • Beaumont Centre • Coldstream • Hamburg • Reynolds Road STORMWATER MANUAL 1-6 January 1, 2009 LEXINGTON-FAYETTE CO., KY.
• Masterson Station Watershed hydrologic models have been constructed for these areas. The Division of Engineering will continue to work with the Developer’s Engineer to ensure that off-site flooding impacts are evaluated. The objective will be to maintain the capacity of the drainage system, minimize the impact to existing flooding problems, and protect the stream water quality from construction activities. 1.4.4 Construction in the Waters of Fayette County In general, construction activities shall not be allowed in the waters or post-development floodplains of Fayette County. Filling the floodplain to allow more land to be developed shall be prohibited. Excavation in the floodplain to lower flood levels shall not be permitted. Only the following activities shall be undertaken in the waters or post-development floodplains • temporary sediment ponds that will be converted to a permanent stormwater management pond • roadways and utilities that cross at angles within 10 degrees of being perpendicular to the stream or floodplain • sanitary sewers, constructed outside the horizontal limits of the 10-year postdevelopment floodplain, with manhole covers set at an elevation one foot higher than the 100-year post-development floodplain, using the procedures described in Chapter 3 of this manual; surface fill may not be placed in the floodplain to cover a sanitary sewer; any excess material from excavation of the sewer must be removed from the post-development floodplain • storm sewer pipe outlets where the outlet terminates at the edge of the postdevelopment floodplain • regional flood control or water quality control ponds constructed by the LFUCG • other flood control practices that do not disturb below the normal top of bank of the stream • water quality practices that do not disturb below the normal top of bank of the stream • pedestrian crossings and trails If situations arise where there are no feasible alternatives to construction in a water or floodplain, the construction will only be allowed if the water or floodplain can be enhanced in the area of construction or if enhancement work is done on another water as mitigation. 1.4.5 Mitigation It is the intent of the LFUCG to ensure that impacts to streams and wetlands are mitigated. Some impacts are regulated by the U.S. Army Corps of Engineers (COE) and the Kentucky Division of Water (KDOW) and require mitigation plans to be approved by those agencies. In those cases, the mitigation plans approved by the COE and the KDOW will satisfy the requirements of this section if the mitigation takes place in Fayette County. For stream impacts in the Jacobson Reservoir Watershed and the Royal Springs Aquifer, every effort shall be made to keep the mitigation within those watersheds. STORMWATER MANUAL 1-7 January 1, 2009 LEXINGTON-FAYETTE CO., KY.
Page 1 and 2: Stormwater Manual Lexington-Fayette
Page 3 and 4: 1.1 Introduction Chapter 1 gives th
Page 5 and 6: 1.3 Definitions 1.3.1 Public Draina
Page 7: • the Division of Engineering det
Page 11 and 12: • only one corporation or busines
Page 13 and 14: 1.5 Water Quantity Criteria for New
Page 15 and 16: TABLE 1- 1 OPTIONS FOR STORMWATER M
Page 17 and 18: TABLE 1- 2 FLOW CRITERIA FOR STORMW
Page 19 and 20: contained in Chapter 10. The water
Page 21 and 22: 1.7.4 Water Quality Criteria for Re
Page 23 and 24: • new development commercial site
Page 27 and 28: CHAPTER 2 PERMITS
Page 29 and 30: 2.1 Land Disturbance Permit 2.1.1 P
Page 31 and 32: If the analysis described in the de
Page 33 and 34: 2.3 Kentucky Division of Water KPDE
Page 35 and 36: 2.5 401 and 404 Permits - Kentucky
Page 37 and 38: 3.1 Introduction Watershed studies
Page 39 and 40: • detailed description of any nat
Page 41 and 42: 3.3 Runoff Models 3.3.1 General The
Page 43 and 44: 3.4 Post-Development Floodplain Ana
Page 45 and 46: APPENDIX 3-A - SOURCES OF DATA
Page 47 and 48: National Oceanography and Atmospher
Page 49 and 50: Pond/Culvert Inventory Data Sheet P
Page 51 and 52: 4.1 Overview 4.1.1 Introduction An
Page 53 and 54: 4.3 Improvement Plans 4.3.1 50 Perc
Page 55 and 56: • culvert outlet appurtenances an
Page 57 and 58: 4.4 Record Drawings A record drawin
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5.1 Introduction 5.1.1 Purpose The
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5.3 Design Rainfall Event 5.3.1 Sin
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TABLE 5- 2 GREEN-AMPT INFILTRATION
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5.5 Stormwater Management Model (SW
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TABLE 5- 4 MANNINGS N FOR OVERLAND
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APPENDIX 5 A DESIGN STORM DISTRIBUT
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6-HOUR RAINFALL DISTRIBUTIONS Cumul
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100-YEAR - 24-HOUR RAINFALL DISTRIB
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CHAPTER 6 INLETS / STORM SEWERS / M
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6.1.4 Storm Sewers Storm sewers sha
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For d ≥ 1.0’, use the orifice f
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6.4 Construction Specifications All
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7.1 Introduction As used in this ma
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7.2.6 Culvert Skew A culvert shall
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Barrel Area and Shape Barrel area i
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7.5 Bridge Design Procedures Use HE
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CHAPTER 8 CONSTRUCTED CHANNELS
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8.2 Permanent Constructed Channels
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The earth fill materials used to co
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8.3 Paved Channels A paved channel
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9.1 Introduction The streams of Fay
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9.2.3 Material Specifications Veget
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TABLE 9- 1 SUGGESTED RIPARIAN SPECI
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9.3 Riparian Buffer Zones 9.3.1 Gen
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9.4 Bioengineering Techniques Bioen
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9.4.3 Root Wad Revetment Root wad r
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Dead stout stakes shall be installe
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Willow tree species are the best fo
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9.5.3 Maintenance All structures sh
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10.1 Introduction Non-point source
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TABLE 10- 1 WATER QUALITY DEPTH VER
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Grade the top of the planting soil
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10.4 Infiltration Systems Infiltrat
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Design Criteria To be considered a
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If desired, large infiltration basi
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When the contributing area draining
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Provide sufficient access to the de
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Select underdrain gravel to meet AA
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Compute the total surface area of b
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10.6 Prefabricated Treatment Device
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landscaping plan for the pond and t
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When necessary, compact subgrade su
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After the embankment has been built
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Embankment heights shall not exceed
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10.9 Wet Ponds In this manual, wet
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Q = A (2gH) 0.5 /(1 + K e +K b + K
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Provide a drain with a valve at the
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CHAPTER 11 EROSION AND SEDIMENT CON
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11.1 Purpose This chapter describes
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1. The limitations on coverage set
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11.2.2 Non-Structural Practices Thi
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Figure 11-1. “Seed mats” may be
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peak discharges during construction
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Locations of proposed controls, uti
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11.4 Structural Soil Stabilization
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When using a mulch net, it shall be
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Material Specifications Seed shall
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Material Specifications Soil materi
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11.4.5 Road/Parking Stabilization R
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To reduce maintenance and loss of a
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Effective netting and matting requi
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Maintenance Outlets shall be inspec
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Temporary or permanent seeding and
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A standard flared end section or a
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11.5 Structural Sediment Control BM
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The amount of sediment entering a t
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Detention storage shall be provided
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The emergency spillway shall have a
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PHYSICAL PROPERTY Filtering Efficie
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Fasten fabric securely to the stake
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SEEDING MIXTURE AND SITE SUITABILIT
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Upon removal of the structure, the
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11.5.10 Concrete Washout Pits Concr
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Inspection of Sediment Controls The
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12.1 Introduction As Fayette County
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12.2 Dry Detention Pond 12.2.1 Desc
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12.3 Dry Extended Detention Pond 12
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12.4 Wet Detention Pond 12.4.1 Desc
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12.5 Constructed Wetlands 12.5.1 De
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12.6 Biofiltration Practices 12.6.1
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12.7 Infiltration Practices 12.7.1
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12.8 Modular Pavement 12.8.1 Descri
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12.10 Prefabricated Treatment Devic
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1Lexington-Fayette Urban County Gov
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2Infiltration Basin Maintenance Ins
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3Infiltration Swale Maintenance Ins
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Action to be taken: If any of the a
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6Filtration Facility Maintenance In
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Summary of Changes to the LFUCG Sto
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11.5.5 Storm Drain Inlet Protection
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Stormwater Manual - Pima County Flood Control District

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