Rain Garden Design Workshop and Tour

Transcription

1 Rain Garden Design Workshop and Tour James Pillsbury PE, ASCE Kathryn Hamilton, RLA, ASLA Westmoreland Conservation District Mount Pleasant PA October 20, 2011

2 Urban, Industrial, Residential, Agricultural Flooding, Erosion, Pollution, Degradation

3 The Natural Watercycle

4 Pre-Development: illustrates the NATURAL hydrologic cycle

5 Post Development: illustrates the IMPAIRED hydrologic cycle

6 Stormwater Retrofitting A Stormwater Retrofit provides stormwater treatment in locations where practices previously did not exist or were ineffective Provides runoff capture and treatment Requires data collection Fingerprinted around existing elements Public and private involvement

7 Why use Stormwater Retrofits? Flooding Stream degradation Water quality issues Combined Sewer Overflows (CSOs( CSOs) Regulations

8 Water Pollution Costs $17 billion annually in the USA Causes 14,000 deaths worldwide each day Comes from the land s surface to create Non-Point Source and Point Source Pollution

9 Non-Point Source Pollution When rain falls on the land, the runoff may carry with it sediment, debris, chemicals, or other pollutants. Earth disturbance and land development are big sources of Non-Point Source pollution.

10 Point Source Pollution Water pollution might come from a single point source - as a pipe from a factory dumping pollutants into a river OR Combined Sewer Overflow

11 Over 380 CSO Locations around Pittsburgh!

12 Sewage treatment agencies which have CSO permits across PA

13 Changing Regulations! Why are we required to construct BMP s?? Regulations have been created to reverse the effects of dead zones developing in the Chesapeake Bay and Gulf of Mexico where much of the USA s s polluted stormwater runoff ends up The new SWM regulations have the force of many environmental agencies behind them, each with a different focus.

14 Regulating Agencies! EPA DEP County Conservation Districts PA Fish & Boat Commission Army Corps of Engineers Municipalities PennDOT Utility consent order agreements

15 Regulations Provide Guidance PA DEP regulates: Activities that might reduce water quality including Land development NPDES permits and Erosion + Sediment Control Permits both need Post- Construction Stormwater Management (PCSM) plans and BMP s. PA Stormwater BMP Manual (DEP 2006)

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17 Objectives Fix past mistakes & maintenance problems Solve chronic flooding problems Stormwater demonstration & education

18 Objectives (cont.) Pollutant removal Reduce runoff volumes Stream corridor/watershed restoration

19 Rainfall and Retrofits 98% of Rainfall Events are less than 1 inch

20 What is a Rain Garden Utilizes a plant bed to infiltrate water into the ground Captures first 1 inch of rainfall Can be used in series with rain barrels to treat overflow Can become a focal point in a landscape

21 Rain Garden Anatomy Ponding Zone Retention/filtration Zone Retention/recharge Zone 6 to to 36 6 to 12

22 Rain Garden Location Gently sloping site downhill from a downspout, or defined water runoff area Blend in with other garden or site features At least 10 feet away from building foundation to prevent seepage Do not place a rain garden over a septic system Full or partial sun is best, not under a large tree Don t t put it where water already ponds (It is meant to encourage infiltration; a wet patch shows where infiltration is slow)

23 Rain Garden Plants Mix of trees, shrubs and perennials Growth requirements matching: Garden size Tolerant of sun exposure Tolerant of moist to wet soils Tolerant of drought conditions Seasonal interest

24 Rain Garden Function

25 Residential Rain Garden LOCATION Rain gardens are often located downhill from a downspout to collect rainwater before it gets to the street SIZE A rain garden is typically sized to capture the first 1 inch of rainfall from the area draining to it, and built to allow the excess to pass through safely INFILTRATION In a rain garden, water collects on the surface until it can soak into the ground to be used by the plants SOILS Rain gardens usually contain a mix of 50% on-site topsoil with 30% coarse sand and 20% compost, covered with 3 inches of shredded bark mulch PLANTS Plant choices for a rain garden can be an attractive variety of low maintenance shrubs and perennials

26 Mount Pleasant Residential Rain Gardens stormwater retrofit Mount Pleasant PA Spring 2010 Project Partners: Westmoreland Conservation District Mount Pleasant Borough Residents of Mount Pleasant PA Department of Environmental Protection Contractor: Silvis Group Inc. Mount Pleasant PA

27 Multiple Grants Green infrastructure Education Administration Quarterly reporting Reimbursements Adjustments Grant Process

28 Grant Application Stormwater Retrofit Project Phase II Environmental need Department wide priorities Regional priorities Commonwealth investment criteria Justification of funding Scope of work BMP designs BMP construction Maintenance and upkeep Partnerships

29 Grant Budget Growing Greener Plus 2008 Salaries/benefits $ 3,000 Travel $ 0 Equipment/supplies $ 0 Administrative $ 5,000 Contractual $ 16,500 Construction $450,750 Match $ 80,425 Total $555,675 67, ,250

30 Match Municipal, Partners, Landowners, Grants Time Services administrative, engineer/landscape architect, solicitor, Equipment Property value Cash

31 Public Interest Partnerships Municipalities Non-profits/volunteers Other Public outreach Advertisements, news releases, news coverage Public meeting Correspondence

32 Typical rain garden scenarios were presented to the homeowners, to encourage them to participate DOWNSPOUT Possible Rain Garden Locations for Roof Water Treatment DOWNSPOUT FLOW OF RUNOFF

33 Correspondence Announcement / Interest Form Reminder / FAQs Thank you for responding Appointment / Site Survey Suitability Next Steps

34 Mt Pleasant s Ramsay Terrace neighborhood was targeted for SW retrofits because of flooding and sewer overflows

35 Suitablility Site assessment Site survey, design one-call, interview Ranking (A,B,C) Front yard, access, roof runoff collection system, utilities, existing landscaping

36 Design Existing conditions Conceptual plan Plant selection Calculations Section Details

37 Landowner Agreement DEP Standard Landowner Agreement Language not specific to urban project Lacked detail for uninformed landowners Lacked enforceablility and permanence Operations and maintenance must be site specific

38 Each homeowner had to sign a RAIN GARDEN RIGHT-OF OF-WAY AND EASEMENT AGREEMENT Whereas the Grantor owns a certain tract of land Whereas the Grantee received a grant for design, construction and installation of a rain garden Whereas the Grantor desires to be a steward of the land and participate Whereas the Grantee requires certain easements and rights-of of-way to enable construction Whereas Grantor desires to grant and convey to Grantee the easement and right-of of-way

39 RAIN GARDEN RIGHT-OF OF-WAY AND EASEMENT AGREEMENT Grantee shall construct in good and safe condition said rain garden and appurtanances Grantor, its agents, successors and assigns agrees to the sole responsibility of the maintenance of the rain garden after construction for a period of 20 years Exhibits included plan, details

40 Bidding and Construction Public bid process Bid documents Knowledgeable contractors Clean construction site One year maintenance

41 Each rain garden was marked and approved prior to digging

42 Excavation was done carefully to avoid utilities, protect existing features and minimize disturbance

43 Each rain garden excavation was checked for proper depth to meet design requirements

44 The Contractor was able to minimize disturbance on each property and minimize inconvenience to neighbors

45 An underdrain layer included a perforated pipe surrounded by clean stone and a geotextile wrap

46 A soil mix of 50% topsoil, 30% sand, 20% compost was placed 18 to 24 deep

47 Finished grade of the soil mix was checked to ensure sufficient surface ponding depth

48 Completed rain garden: rock dissipater at downspout, landscaping with mulch, basket grate overflow riser

49 Each underdrain outlets safely to the street gutter or to the municipal storm system

50 The location of each rain garden was approved by the homeowner and designed to capture roof water

51 The rain garden was designed to fit in with the homeowner s s existing landscape

52 The rain garden plants should eventually provide full cover in the rain garden and seasonal interest

53 Rain Garden Maintenance While vegetation is being established, pruning and weeding may be required. Debris may need to be removed approximately twice per year, and perennial plantings should be trimmed before the start of the next growing season. Inspect and repair rain garden for washouts. Replace mulch every 2 to 3 years

54 Homeowner Feedback GOOD Pleased with garden Drained quickly Level of involvement Construction efficient NOT SO GOOD Plants not full enough Lawn needed reseeded Difficult to mow berm

55 Mount Pleasant Parking Lot Rain Gardens stormwater retrofit Mount Pleasant PA Spring 2010 Project Partners: Westmoreland Conservation District Mount Pleasant Borough Mount Pleasant Parking Authority PA Department of Environmental Protection Contractor: W.G. Land Inc. Champion PA

56 St Clair Street Smithfield Street

57 Construction plans included a new street storm system (where none existed) to tie the proposed rain garden overflow system into

58 Mount Pleasant Borough parking lots generated stormwater which ran uncontrolled into the streets, flooding downhill neighbors

59 Existing pavements had to be saw cut and removed to install rain gardens and storm system piping

60 Five rain garden locations were excavated at the low point in each parking lot

61 Each rain garden has an underdrain layer which includes a perforated pipe and clean stone wrapped in fabric

62 A full-depth concrete curb was poured to protect each rain garden, and two curb cuts allow surface water to enter the rain gardens

63 Each rain garden has topsoil-sand-compost soil mix and an overflow riser connected to the underdrain

64 The rain gardens are landscaped with native plants, mulch with stone at the curb cuts to slow and infiltrate runoff

65 Rain water rushes into the rain garden through curb cuts and onto rock energy dissipaters

66 An unsightly paved island with crumbling curbs increased runoff and provided little aesthetic value

67 The paved and curbed island was replaced with porous concrete and trees in over-excavated tree planting pits

68 A trench drain picks up a portion of the parking lot runoff and directs it to the rain garden below the porous concrete

69 Without an accurate survey of off-site areas, the rain garden became overloaded by un-anticipated off-site runoff

70 Excavation of the failed rain garden found no perforations in the underdrain to help drain the garden in large storms

71 A flow splitter was designed to capture a portion of the runoff and to allow large storms to bypass the rain garden

72 The flow splitter allows half the volume from the trench drain to enter the rain garden

73 Economics Mt Pleasant Parking Lot Rain Gardens 1,500 sf in (5) rain gardens 1,300 sf porous concrete 4,500 cf runoff capture Bid price: $75,000 Average cost commercial rain gardens*: $20-$30 $30 / sf Average cost porous concrete*: $12 / sf *NOTE: costs include demolition and site preparation

74 Economics Mount Pleasant Residential Rain Garden project 100 sf to 200 sf rain gardens in 14 locations 1,800 cf runoff capture Bid price: $55,000 Average rain garden cost*: $25-$35 $35 / sf *NOTE: costs include site preparation

75 Reality Check Time meetings with staff, partners, public / homeowners, contractor, document preparation, construction oversight Money grants, match, budget People Municipal officials, staff, engineer and solicitor, partners with variety of disciplines Ideas identifying problems, prioritizing sites / neighborhoods, prior experience, communication Feedback complaints, hand-holding holding Problems large storm before stabilization, inadequate survey, overloading, bad press, prioritizing

76 References: Pennsylvania Stormwater Best Management Practices Manual 2006 Provides guidance on the design and installation of stormwater best management practices and post construction stormwater management plans for NPDES permits Center for Watershed Protection s s Urban Subwatershed Restoration Series - Manual 3: Urban Stormwater Retrofit Practices

77 Questions? Contact: 218 Donohoe Road Greensburg PA