City of Fort Worth. December 1, 2004

Transcription

1 City of Fort Worth December 1, 2004

2 Storm Water Issues in our Region Disappearing water features and habitat Erosion and degradation of natural streams Flooding in new and old developed areas Pollutants of concern: TSS, metals, etc.

3 Who shoulders the burden? Local Governments Development Industry Pressure from: Citizens TX Water Code USACE FEMA USEPA TCEQ

4 What is the solution? Cannot effectively address each issue individually unto itself or solely within a political boundary Storm Water Management System is just that A SYSTEM Imperative to succeed with Best Management Practice Approach vs. End-of-Pipe Advanced Treatment Solution must be comprehensive, systematic, and integrated into everyday drainage design

5 NCTCOG to the rescue integrated quality and quantity management integrated throughout all phases of development integrated with regulatory requirements integrated into everyday drainage design integrated Storm Water Management System

6 NCTCOG s iswm project Cooperative cost-shared initiative of 65 local governments begun in 2002 Overseen by local government Steering Committee & Associated Advisors from development industry and various agencies Consultant team of Freese & Nichols, AMEC, Alan Plummer Assoc., & Caffey Engineering Producing a Design Manual to allow all the SW issues to be addressed in an integrated & comprehensive manner Manuals will have been prepared, reviewed and tested by more local experts that any other manuals ever created in this region

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8 iswm Multi-Year Plan April 2001???? FY2003 FY2004 FY Municipal Buy In On-going Develop Draft iswm Policy Guidebook & Design Manual for Dev/Redev. Update Design Manual for Construction Test Design Methodology & Finalize Manuals for Regional Review NCTCOG Endorsement of Manuals Implementation Tools & Training Adoption of iswm by Cities Watershed Approaches & GIS Components Education and Training

9 Three Stages to Success Stage One Is it possible to craft a technically-sound policy approach and design manual that integrates water quality protection, streambank protection & flood control? Answer Yes, the FY03&04 work produced iswm draft guidance documents detailing an iswm Site Plan that will accomplish that integration. Stage Two What are the benefits and costs of implementing iswm? Why should I adopt it? Answer Cost impacts and benefits were identified in FY2004 from individual project and watershed lab studies. From these results, manuals will be finalized and cities will have the information to justify local adoption of iswm. Stage Three Do we have all the tools necessary to effectively implement iswm? Answer Not yet. Tasks identified to begin in the FY2005 Work Program develop those tools.

10 iswm: What s Been Done Evaluated current storm water practices from North Central Texas Cities Developed Manuals iswm Policy Guidebook Regional Review Draft iswm Design Manual for Development/Redevelopment - RRD iswm Design Manual for Construction - Completed Completed Individual Site Case Studies Completed a Watershed Study in Big Fossil Creek Provided Ongoing Education and Training

11 iswm Fundamental Goals Create an integrated Storm Water Management Site Plan that will address: Water Quality Protection reduce Total Suspended Solids (TSS) in runoff from development and redevelopment sites Streambank Protection minimize downstream streambank and channel erosion Flood Control safely pass or reduce the runoff from extreme storm events and reduce localized site flooding of streets, sidewalks and properties

12 Central Focus of iswm iswm Site Plan Enhanced version of current project drainage plans Integrates quantity and quality considerations Emphasizes nonstructural site design solutions Includes Storm Water Pollution Prevention Plan during construction Provides operations and maintenance guidance following construction

13 iswm Site Plan 1) Consider Five Principles of Storm Water Management Site Planning I. Integrated Approach Quality, Streambank, Flood Control II. III. IV. Natural Systems Integrated Site Design Multi-purpose Asthetics and Maintenance V. One-size doesn t fit all 2) Review Local Requirements 3) Perform Site Analysis and Inventory 4) Prepare Conceptual iswm Site Plan 5) Prepare Preliminary iswm Site Plan 6) Complete Final iswm Site Plan

14 Step 1: Five Principles of Storm Water Management Site Planning 1) The site should utilize an integrated approach to deal with storm water quality protection, streambank protection and flood control requirements 2) Storm water management practices should strive to utilize the natural drainage system and require as little maintenance as possible 3) Storm water controls should be implemented only after all integrated site design options have been exhausted 4) Storm water solutions should attempt to be multi-purpose and be aesthetically integrated into the site s design 5) One size does not fit all in terms of storm water management solutions

15 Step 2: Review Local Requirements 1) The site developer should be familiar with the local storm water management and developer requirements and design criteria that apply for the local jurisdiction, including: Current land use plans Comprehensive plans Zoning Ordinances Infrastructure plans Special overlay districts or public facility plans 2) Determine the possibility of partnering with a local community for the development of greenways, preservation of riparian corridors, or retaining open space

16 Step 3: Perform Site Analysis and Inventory Collect and review information on the existing site conditions and map the significant site features including: Topography, drainage patterns and basins Intermittent and perennial streams Soils, ground cover and vegetation Existing development, storm water facilities and infrastructure Wetlands, critical habitat areas and boundaries of wooded areas Floodplain boundaries Steep slope areas Required buffers or open space Proposed stream crossing locations Other required or identified protection areas

17 Step 4: Conceptual iswm Site Plan 1) Use integrated site design approaches 2) Determine reduction credits for integrated site design practices 3) Calculate preliminary estimates of the integrated design criteria based on concept plan site layout 4) Perform screening and preliminary selection of appropriate structural storm water controls and their potential locations

18 Step 5: Preliminary iswm Site Plan Should include the following sections: Existing Conditions Hydrologic Analysis Project Description and Design Considerations Post-Development Hydrologic Analysis Storm Water Management System Downstream Analysis

19 Downstream Assessments Promotion of more effective stormwater management through implementation of a requirement to assess potential downstream impacts of urban development 10% Rule 10 acres 80 acres 40 acres 190 acres 120 acres

20 Step 6: Final iswm Site Plan Should include revised elements of the preliminary plan, as well as the following: Construction Storm Water Pollution Prevention Plan Landscaping Plan Operations and Maintenance Plan Evidence of Acquisition of Applicable Local and Nonlocal Permits Waiver Requests

21 Local Community iswm Site Plan Review 1) Concept Plan Review Stage Review conducted as part of the pre-development meeting or at time of submittal of concept review plans Elements to review will be iswm Site Plan Steps 1-4 2) Preliminary Plan Stage Review conducted as part of Preliminary Plat Phase Elements to review will be iswm Site Plan Step 5 3) Final Plan Stage Review conducted as part of Final Plat Phase Elements to review will be iswm Site Plan Step 6

22 Other Local Community Responsibilities Construction Inspections Pre-construction meeting Periodic site inspections Final inspection Ongoing Maintenance Inspections Identification and notification of responsible parties Preparation of a maintenance plan Annual inspections of storm water management facilities

23 iswm Site Plan Design Tools integrated Site Design Practices nonstructural approaches used during site planning Reduction Credits for integrated Site Designs reducing the size of structural control and conveyance facilities by using integrated Site Design Practices integrated Design Criteria requirement for water quality protection, streambank protection, and flood control Storm Water Controls facilities to provide conveyance, discharge control, and/or pollutant removal Updated Hydrologic and Hydraulic Technical design data runoff estimation methods and conveyance facility design criteria

24 integrated Site Design Practices Manage storm water (quantity and quality) as close to the point of origin as possible Minimize collection and conveyance Prevent storm water impacts rather than mitigating them Use simple, nonstructural methods for storm water management Create a multifunctional landscape Use minimization of impact to the natural environment as a framework for site design Identify Identify Natural Natural Features Features and and Resources Resources Delineate Delineate Site Site Conservation Conservation Areas Areas Design Design Site Site Layout Layout to to Preserve Preserve Conservation Conservation Areas Areas and and Minimize Minimize Storm Storm Water Water Impacts Impacts Use Use Various Various Techniques Techniques to to Reduce Reduce Impervious Impervious Cover Cover in in the the Site Site Design Design Utilize Utilize Natural Natural Features Features and and Conservation Conservation Areas Areas to to Manage Manage Storm Storm Water Water Quantity Quantity and and Quality Quality

25 Conservation of Natural Features and Resources Preserve Undisturbed Natural Areas Preserve Riparian Buffers Avoid Floodplains Avoid Steep Slopes Minimize Siting on Permeable or Erodible Soils

26 Lower Impact Site Design Techniques Fit Design to the Terrain Locate Development in Less Sensitive Areas Reduce Limits of Clearing and Grading Utilize Open Space Development Consider Creative Development Design

27 Reduction of Impervious Cover Reduce Roadway Lengths and Widths Reduce Building Footprints Reduce the Parking Footprint Reduce Setbacks and Frontages Use Fewer or Alternative Cul-de-Sacs Create Parking Lot Storm Water Islands

28 Utilization of Natural Features for Storm Water Management Use Buffers and Undisturbed Areas Use Natural Drainageways Instead of Storm Sewer Systems Use Vegetated Swales Instead of Curb and Gutter Drain Runoff to Pervious Areas

29 integrated Site Design Examples of integrated Site Design from the iswm Design Manual for Development/Redevelopment Section1.2

30 Traditional Design Approach Site is Mass Graded Natural Drainage Patterns Destroyed Existing Tree Cover Removed Character of Site is Destroyed Extensive Storm Drain System Required Amenity Center is Only Open Space 96 Lots

31 integrated Design Approach Undisturbed Vegetation Natural Drainage Patterns Guide Layout Only Building Envelopes are Graded Character of Site is Preserved No Storm Drain System Required Impervious Cover Reduced Provides Open Space for Community Narrower Streets Natural Drainage Preserved Undisturbed Vegetation Grass Swales Instead of Curb and Gutter Cul-de-sac with Landscaped Island 102 Lots (6 more) 20% Avg. Lot Size Reduction

32 Example of an existing development in North Texas that has utilized many of the proposed integrated site design practices by complying with existing development standards

33 Implementation of integrated Site Design Existing community policies must be reviewed for compatibility with the integrated site design principles. Some of these include: Zoning Ordinances and Grading Ordinance Procedures Street Standards or Road Design Subdivision Codes Manual Storm Water Management or Parking Requirements Drainage Criteria Building and Fire Regulations and Tree Protection or Landscaping Standards Ordinance Septic/Sanitary Sewer Buffer and Floodplain Regulations Regulations Local Comprehensive Plan Erosion and Sediment Control Ordinance

34 Reduction Credits for integrated Site Designs Promotion of integrated site design and low impact development practices through the use of reduction credits which offset a site s stormwater control requirements Natural area conservation and restoration Stream buffers Use of vegetated channels Overland flow filtration/infiltration zones Low imperviousness development Reduction Credits reduce the amount and size of storm water controls required on the site based on the amount of integrated site design practices used on the site

35 integrated Design Criteria Guidance on an integrated approach for designing and sizing storm water systems to meet water quality pollutant removal, streambank protection for channels, and flood control objectives at development/ redevelopment sites. Flood Control Streambank Protection Water Quality Protection

36 integrated Design Criteria Water Quality Protection Reduce Total Suspended Solids (TSS) from development/redevelopment sites for the runoff resulting from rainfalls of up to 1.5 inches Achieved by a combination of integrated site design practices, on-site controls, and approved community storm water pollution prevention programs/activities in designated areas.

37 Water Quality Volume Calculation 85% Rule WQ V = (1.5 in) (R V ) (A)/12 where: WQ V = water quality volume (ac-ft) 1.5 = 85 th % storm in inches R V I A = (I) = percent imperviousness = site area (ac)

38 integrated Design Criteria Streambank Protection Provide streambank protection from erosion due to increased storm water volumes and velocities caused by development/redevelopment. Achieved by providing on-site controlled release of the 1-year, 24-hour storm event over a period of 24 hours.

39 1-Year Storm Post development Discharge Bankfull flow Minutes Detained flow

40 integrated Design Criteria Flood Control Onsite: Minimize localized site flooding of streets, sidewalks, and properties by a combination of on-site storm water controls and conveyance systems. Downstream: Manage downstream flood impacts caused by the increase of storm water discharges from development/redevelopment by a combination of on-site control, downstream protection, floodplain management, and/or other mitigation measures. Not a detention policy Only required to mitigate flood impacts caused by specific site development (not required to fix all flooding problems downstream).

41 Storm Water Controls BMPs Storm Water Ponds Storm Water Wetlands Bioretention Areas Sand Filters Infiltration Trenches Enhanced Swales Grass Channels Filter Strip Organic Filter Gravity (Oil-Grit) Separator Porous Concrete Modular Porous Pavers Systems Alum Treatment System Proprietary Systems Street and Roadway Gutters/Inlets/Storm Drain Pipe Systems Open Channels Energy Dissipation

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43 Wet Pond Example Extreme Flood elevation Channel Protection elevation Water Quality elevation Permanent Pool elevation

44 Storm Water Controls BMPs Examples of Storm Water Controls from iswm Design Manual for Development/Redevelopment Section 3.1 Section Section Section Section Section Section

45 Updated Hydrologic and Hydraulic Technical design data H&H modeling methods and parameters New regional runoff data and IDF curves Design process for Structural and Nonstructural BMP s Hydraulic design tables and examples Soils data and Landscaping guidelines Maintenance guidelines Section 2 Estimating Runoff

46 Individual Site Case Studies

47 Individual Site Case Studies Selected 6 sites 2 residential, 2 redevelopment, 2 commercial Small and large sizes Developed 2 Conceptual iswm Site Plans Retrofit (No changes in Planning criteria) iswm (integrated Design and Planning criteria) Cost Comparison Identified other benefits

48 Small Residential Predeveloped & As- Developed Conditions Predeveloped 48 AC of cropland Natural stream along southern boundary with FEMA-defined floodplain As Developed 282 lots 1/8 AC average lot size 29 wide asphalt streets Channel Modifications Realigned Concrete-lined and rip-rap Underground storm drainage system Concrete curb-and-gutter

49 Small Residential iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control - + SB Protection WQ Protection Infrastructure Cost Lot Difference Lot Revenue Net Revenue Regulatory $11,500 per acre -4% $7,700 per acre $3,600 per acre Review Time + + Annual Onsite Maintenance Cost $200/ac + $11,000 per acre $8,200 per acre $2,800 per acre $200/ac + POSITIVE NEUTRAL - NEGATIVE Retrofit & iswm Design Features Leave stream natural modify property line Micropool Extended-Detention Wet Ponds Filter Strips, Underground Storm Drainage Systems

50 Large Residential Predeveloped & As Developed Conditions Predeveloped 100 AC of cropland and trees Large electrical easement Northern half to Fish Creek; Southern half to Lynn Creek As Developed 366 lots 1/6 AC average lot size 29 wide concrete streets Underground storm drainage system; concrete curb-and-gutter Portions re-directed north to Fish Creek No detention

51 Large Residential iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control - + SB Protection - WQ Protection - Infrastructure Cost Lot Difference Lot Revenue Net Revenue Regulatory Review Time Annual Onsite Maintenance Cost + + $1,800 per acre -10 % $6,700 per acre $8,500 per acre - $260/ac $1,200 per acre +2 % $3,300 per acre $4,500 per acre - $260/ac + POSITIVE NEUTRAL - NEGATIVE Retrofit & iswm Design Features Natural Area Conservation (treed) Micropool Extended-Detention Wet Ponds Enhanced Swale, Underground Storm Drainage Systems

52 Small Redevelopment Predeveloped & As Developed Conditions Predeveloped 3.4 AC (150,000 SF) Mixed use Strip commercial, older Residential/Retail Drains to bar ditches, then underground storm drainage system As Developed Along DART line Planned Mixed Use Residential and Commercial Parking Garage & Extensive Landscaping Extension of existing underground drainage system ties into system in DART ROW No detention

53 Small Redevelopment iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control SB Protection - + WQ Protection Infrastructure Cost Parking Difference Annual Onsite Maintenance Cost $2 per SF $1,900 per acre $0.20 per SF $90 per acre + POSITIVE NEUTRAL - NEGATIVE Park Pond Design Features Retrofit: Green Roof with storage area, Proprietary Systems, Planter Boxes iswm: Enlarge existing pond in adjacent Park for Water Quality and Flood Control Site

54 Large Redevelopment Predeveloped & As Developed Conditions Predeveloped 10 AC (480,000 SF) Large Commercial business and Strip Retail North half drains to residential alley South half to underground storm drainage system As Developed Large Commercial Business Mitigation of Existing Flooding 10-yr detention provided with oversized storm drain (South) City limited drainage area to residential area (North) Ponding allowed in parking lot

55 Large Redevelopment iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control * + + SB Protection - + WQ Protection - + Infrastructure Cost Parking Difference Annual Onsite Maintenance Cost *Detention provided in some areas Design Features $4 per SF $6,500/ac + + $0.23 per SF -15 % $300/ac Retrofit: Underground Detention, Proprietary Systems, Green Roof iswm: Dry Extended Detention, Proprietary Systems Both limited release rate to downstream capacity + POSITIVE NEUTRAL - NEGATIVE

56 Small Commercial Predeveloped & As Developed Conditions Predeveloped 20 AC (870,000 SF) Open field with scattered trees Existing underground storm drainage system along interstate (east) Drains south to Farmer s Branch with FEMA-defined floodplain As Developed Car Dealership Utility Easement Underground storm drainage system along southern boundary Underground systems outfall south to Farmer s Branch No detention

57 Small Commercial iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control SB Protection - + WQ Protection - + Infrastructure Cost - $0.86 per SF Parking Difference -6 % Annual Onsite Maintenance Cost $850/ac $0.57 per SF -1 % $600/ac + POSITIVE NEUTRAL - NEGATIVE Design Features Both: Same storm drainage system as As Developed, Dry Extended Detention Basins, Proprietary Systems Retrofit: Bioretention Areas iswm: Surface Sand Filters

58 Large Commercial Predeveloped & As Developed Conditions Predeveloped 73 AC (3,200,000 SF) Open field and scattered trees Some C soil Existing swale in center of property drains south to creek with FEMAdefined floodplain As Developed Two large Commercial Properties Strip Retail; Large Parking Areas Existing swale piped underground Underground storm drainage systems outfall into existing channel with no detention

59 Large Commercial iswm site plans Element As Dev d Retrofit iswm Downstream Flood Control SB Protection - + WQ Protection - + Infrastructure Cost Parking Difference Annual Onsite Maintenance Cost - $0.24 per SF $560/ac $0.13 per SF -1.6 % $740/ac + POSITIVE NEUTRAL - NEGATIVE iswm Design Features Both: Same storm drainage system as As Developed with an enhanced existing Grass Channel Both: Dry Extended Detention Basins, Surface Sand Filters, Proprietary Systems Retrofit: Underground Detention iswm: Filter Strips (Grass Paving)

60 Value Added Benefits On-site flood control reduces liability, improvement costs and maintenance cost downstream of the site. Downstream channels will be preserved and maintenance reduced by applying the streambank protection criterion. Preserving a natural stream allows for its aesthetic benefits to be retained and provides the opportunity for a linear park and/or walking trail along the stream corridor as it is developed. These elements provide additional amenities for the residents, as well as greater market value for the property Storm water controls provide value in addition to meeting individual storm water control criteria. Landscaping, planter boxes, grass paving, grass channels, and aquatic benches in storm water ponds provides aesthetic benefits that are not present in the existing development condition. Grass channels and infiltration devices as opposed to underground conveyance systems results in reduced runoff velocities, more impervious area and open space Green roofs can decrease rooftop temperatures and noise levels, and increase insulation for buildings.

61 Watershed Study Big Fossil Creek Watershed

62 Big Fossil Creek Watershed

63 Flood Control Results Type of Analysis 100-Yr Peak Discharge (cfs) Upstream of St.Hwy Yr Peak Discharge (cfs) Upstream of St.Hwy. 121 Type of Analysis 100-Yr Peak Discharge (cfs) Upstream of St.Hwy Yr Peak Discharge (cfs) Upstream of St.Hwy. 121 Existing Watershed Conditions Future without iswm Watershed Conditions Percent Increase from Existing to Future 34,204 38, % 5,742 8, % Existing Watershed Conditions Future with iswm Watershed Conditions Percent Increase from Existing to Future with iswm 34,204 34, % 5,742 5, %

64 Flood Control Results Location Existing Watershed Conditions WSEL (ft) Future without iswm WSEL (ft) Increase in Future WSEL from Existing Conditions (ft) Upstream of Hwy Upstream of T&P RR Upstream of Western Ctr Blvd Location Existing Watershed Conditions WSEL (ft) Future with iswm WSEL (ft) Increase in Future with iswm WSEL from Existing Conditions (ft) Upstream of Hwy Upstream of T&P RR Upstream of Western Ctr Blvd

65 Water Quality Results Type of Analysis TSS Loading (lb) For the entire watershed Season Future without iswm Watershed Conditions Future with iswm Watershed Conditions Percent Reduction with iswm Sept.- Oct. 1,593,323 1,312, % Nov. Feb. 3,171,456 2,634, % March June 5,807,871 4,725, % July Aug. 1,398,523 1,161, %

66 Streambank Protection Description Location 1 Parameters 1-Yr Event Future 1-Yr Event Future iswm Percent Reduction with iswm Active channel Width (ft) % Drainage Area, (mi 2 ) Active Channel Depth (ft) % Location 2 Drainage Area, (mi 2 ) Active channel Width (ft) % Active Channel Depth (ft) % Difference between Future and Future iswm is 797,916 yd 3 of silt (83,991 yd 3 per mile of stream).

67 Channel Geomorphology Elevation Station Existing Conditions Future w/o iswm Future w/ iswm TOB - Left TOB - Right

68 2001 LandSat

69 iswm Site Plans throughout the region will Ease the development process through heightened predictability of SWM requirements Improve drainage designs and site plans Spur creation of associated training Reduce flooding risks and minimize future litigation Reduce stream degradation Enhance our green infrastructure & help conserve open space Provide storm water permit compliance for Post- Construction Allow multi-jurisdictional watershed planning incorporating GIS mapping and modeling

70 Upcoming Project Activities Complete Report of iswm Lab Studies to post by end of December Open Regional Review Period for assessment of draft documents Nov 2004 thru Mar 2005 Meet with Stakeholders in Jan/Feb workshops throughout region to get input and buy-in Continue meetings of Project Review Team to address comments & refine draft documents Hold Public Works Roundup on March 31, 2005 to assess progress and recommend next steps

71 integrated Storm Water Management (iswm) Regional Storm Water Program Center of Development Excellence For more information contact Kenneth Calhoun at NCTCOG or