Mike Novotney, P.E. (MD) Center for Watershed Protection - PowerPoint PPT Presentation

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Mike Novotney, P.E. (MD) Center for Watershed Protection

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  1. Putting It All TogetherIntegrated Natural Resource Protection, Stormwater Management and Site Design Mike Novotney, P.E. (MD) Center for Watershed Protection

  2. Stormwater & Site Design Criteria Runoff Reduction WQV Channel Water Quality Flood Control Aquatic Resource Protection Flood Control

  3. Meeting the Stormwater & Site Design Criteria • Satisfying these criteria requires the successful integration of natural resource protection and stormwater management with the site planning and design process • This integrationcan be accomplished by using an approach to the site planning and design process that: (1) identifies and protects valuable natural resources (2) limits land disturbance and the creation of new impervious and disturbed pervious cover (3) reduces and manages post-construction stormwater runoff rates, volumes and pollutant loads

  4. Natural Resource Protection & Stormwater Management Practices & Techniques • This approach involves the use of two distinct, but complementary groups of natural resource protection and stormwater management techniques: • Green Infrastructure Practices: • Natural resource protection and stormwater management practices and techniques (e.g., better site planning and design techniques, low impact development practices) that can be used to help prevent increases in post-construction stormwater runoff rates, volumes and pollutant loads • Used to protect natural resources from the direct impacts of the land development process, limit land disturbance and the creation of new impervious and disturbed pervious cover, and reduce post-construction stormwater runoff rates, volumes and pollutant loads • Stormwater Management Practices • Stormwater management practices (e.g., wet ponds, swales) that can be used to manage post-construction stormwater runoff rates, volumes and pollutant loads.

  5. How do I best use these practices during the site planning and design process? • Need guidance for the developer, site designer and plan reviewer • Stick with the existing process • But make sure that we consider natural resource protection and stormwater management from the very beginning of process

  6. Six-step stormwater management planning and design process

  7. Have a project idea or find a site that leads to an idea Develop knowledge of all applicable constraints and requirements Make a basic “go or no go” decision Goal is to understand the site constraints and possibilities without investing too much time and money Prior to Site Assessment

  8. Complete site assessment & natural resources inventory Develop site fingerprint Identify primary and secondary conservation areas and buildable area Goal is to ID important resources and reduce impacts of land development “by design” Prior to Site Layout

  9. Step 4: Prepare Stormwater Management Concept Plan

  10. Can complete iterative process using Coastal Georgia Site Planning & Design Worksheet…

  11. Let’s walk through an example Peachtree Strip Mall

  12. Basic Site Analysis PEACHTREE STRIP MALL – CONVENTIONAL DESIGN Farm Field Natural Vegetation Our site is pretty basic: Small Pond

  13. Peachtree Strip Mall Conventional Design

  14. Sketch Plan Parking Restaurant Shops VL = (a . C) . P6 Shops Parking Anchor PEACHTREE STRIP MALL – CONVENTIONAL DESIGN

  15. 0 100 200 Concept Plan Concentrated Parking Area Disturbed Pervious Area Restaurant Shops Drugstore Shops Supermarket Detention Pond Disturbed Pervious Area PEACHTREE STRIP MALL – CONVENTIONAL DESIGN

  16. HSG B Soils Area = 18 acres Impervious Cover = 15.2 acres I = 84% impervious RRv = (0.05+ 0.009*84)*1.2÷12*18 = 1.46 ac-ft Assume Tc = 15 min. P = 3.6 in ARPv = 2.65 ac-ft Peachtree Strip Mall Conventional Design

  17. 0 100 200 Concept Plan Concentrated Parking Area Disturbed Pervious Area Restaurant We can probably do a better job protecting natural resources and reducing stormwater runoff rates, volumes and pollutant loads… Shops Drugstore Shops Supermarket Detention Pond Disturbed Pervious Area PEACHTREE STRIP MALL – CONVENTIONAL DESIGN

  18. Peachtree “Glen” Innovative Design Using Green Infrastructure Practices

  19. Basic Site Analysis Farm Field Our site is pretty basic: Natural Vegetation Better Site Planning Technique:Preserve Secondary Conservation Areas Small Pond

  20. Better Site Design Technique: Reduce Clearing and Grading Limits Better Site Design Technique: Reduce Parking Lot Footprint Better Site Design Technique: Create Landscaping Islands in Parking Lot

  21. Sketch Plan Shops Drugstore Shops Shops Supermarket Restaurant PEACHTREE GLEN – INNOVATIVE DESIGN

  22. Reduced Parking Lot Footprint Reduced Clearing & Grading Parking Lot Landscaping Islands 0 100 200 Concept Plan Shops Drugstore Shops Shops Supermarket Restaurant Conservation Areas PEACHTREE GLEN – INNOVATIVE DESIGN

  23. Site Information • Assume Tc = 15 min. • P = 3.6 in • ARPv = 2.35 ac-ft • 12% savings • HSG B Soils • Area = 18 acres • Impervious Cover = 13.6 acres • I = 76% impervious • RRv = = (0.009*76+0.05)*1.2÷12*18 = 1.31 ac-ft • Was 1.45 ac-ft • 10% savings even before stormwater management “credits” Next, apply “credits”…

  24. 3.9 A 0 100 200 Same number of parking spaces but with slightly narrower widths Conservation Area Shops Drugstore Shops Shops Supermarket Restaurant Conservation Area PEACHTREE GLEN – BETTER SITE DESIGN

  25. After Better Site Planning/Design “Credits” • RRv = = (0.009*76+0.05)*1.2÷12*(18-3.9) = 1.03 ac-ft • Was 1.45 ac-ft, then 1.31 ac-ft • 29% savings over conventional design with “credits”

  26. Low Impact Development Practice Selection • In general, the following information should be considered when deciding what green infrastructure practices should be used on a development site: • Ability to Help Satisfy the Stormwater Management Criteria (Table 7.1) • Overall Feasibility (Table 7.2) • Site Applicability (Table 7.3) • In addition, site planning and design teams should consider how the following site characteristics and constraints, which are commonly encountered in coastal Georgia, will influence the use of green infrastructure practices on a development site: • Poorly drained soils, such as hydrologic soil group C and D soils • Well drained soils, such as hydrologic soil group A and B soils • Flat terrain • Shallow water table • Tidally-influenced drainage

  27. Table 7.1: Ability to Help Satisfy the Stormwater Management Criteria

  28. Table 7.2: Overall Feasibility

  29. Table 7.3: Site Applicability

  30. Practice Selection: • We might have picked grass channels or dry swales for conveyance • But we protected the natural drainage features as a secondary conservation area • We might consider green roofs or permeable pavement • We might also think about rainwater harvesting or stormwater planters • Let’s start with bioretention areas and sheetflow to conservation areas • Can use distributed landscaping areas to “receive” stormwater runoff

  31. Bioretention Area Area 1 4.7 ac Conservation Area Bioretention Areas Area 2 1.5 ac Area 3 3.8 ac 3.9 ac Conservation Area 0 100 200 Sheetflow to Cons. Area 0.4 ac Shops Drugstore Shops Shops Supermarket Restaurant Sheetflow to Cons. Area 1.8 ac PEACHTREE GLEN – INNOVATIVE DESIGN

  32. Bioretention Area 1 Areas 2 & 3

  33. Apply Runoff Reduction “Credits” • Target RRv = 1.03 ac-ft • Apply runoff reduction “credits” for each of our low impact development practices • Site Planning & Design Worksheet helps automate this process, so let’s go there…

  34. Check Stormwater Management Criteria • If we haven’t completely satisfied the criteria, we may want to go back to the concept plan to apply additional low impact development practices to further reduce post-construction stormwater runoff rates, volumes, and pollutant loads…

  35. Apply Stormwater Management Practices • If we determine that the criteria cannot be satisfied exclusively through the use of green infrastructure practices, the next step is to apply stormwater management practices to the site • Let’s try a stormwater pond to satisfy the remainder of the criteria…

  36. Bioretention Area Area 1 4.7 ac Conservation Area Bioretention Areas Area 2 1.5 ac Area 3 3.8 ac 3.9 ac Stormwater Pond Conservation Area 0 100 200 Shops Drugstore Shops Shops Supermarket Restaurant Overland Flow Area 1.8 ac PEACHTREE GLEN – INNOVATIVE DESIGN

  37. Stormwater Pond

  38. Discuss concept plan with local development review authority Further develop stormwater management plan Include details about green infrastructure and stormwater management practice design Moving on to Final Design