Rain Garden Design Understanding Stormwater Runoff Sizing a Rain - - PowerPoint PPT Presentation

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Rain Garden Design Understanding Stormwater Runoff Sizing a Rain - - PowerPoint PPT Presentation

Feb 14, 2023 196 likes •556 views

Rain Garden Design Understanding Stormwater Runoff Sizing a Rain Garden Choosing a Location Garden Layout and Design Installation and Materials Care and Maintenance Stormwater Runoff Stormwater Runoff Rain Garden Design

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Rain Garden Design

  • Understanding Stormwater Runoff
  • Sizing a Rain Garden
  • Choosing a Location
  • Garden Layout and Design
  • Installation and Materials
  • Care and Maintenance
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Stormwater Runoff

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Stormwater Runoff

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Rain Garden Design

Stormwater Runoff is affected by…

  • Land Cover – paving vs. lawn vs. woodland
  • Soil Type and Properties
  • Steepness of the Land Surface
  • Intensity and Duration of the Storm Event
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Rain Garden Design

Rain Gardens are intended to capture runoff from storms producing 1” or less of rain.

  • the vast majority of our storms in PA are 1”
  • r less
  • “First flush” = pollutants and debris washed

from impervious surfaces (sediment, oils, etc.)

  • Provide slow release of water into soil
  • Remove nutrients and some pollutants
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Stormwater Runoff

Rain Gardens are intended to capture runoff from storms producing 1” or less of rain.

  • the vast majority of our storms in PA are 1”
  • r less
  • “First flush” = pollutants and debris washed

from impervious surfaces (sediment, oils, etc.)

  • Provide slow release of water into soil
  • Remove nutrients and some pollutants
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Choosing a Location

Which impervious areas to capture?

Rain Gardens – A How-to Guide for Homeowners

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Choosing a Location

  • Contact PA 1-Call at least 3 days before

digging Dial 8-1-1 or 1-800-242-1776

  • Check for private wiring, piping, or utilities
  • Keep more than 10’ from foundations
  • Avoid septic tank, leach field, on-site well,

seasonally wet areas, and tree roots.

  • Gently sloped areas are preferred
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Choosing a Location

Downspouts are often connected to storm sewers, moving runoff directly to watercourses.

The Vermont Rain Garden Manual

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Sizing the Rain Garden (4 steps)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (step 2)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (step 2)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (step 2)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (step 3)

The Vermont Rain Garden Manual

Is there room for 3:1 side slopes?...

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Sizing the Rain Garden (step 3)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (4 steps)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (4 steps)

The Vermont Rain Garden Manual

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Sizing the Rain Garden (step 3)

The Vermont Rain Garden Manual

3:1 side slopes, with a level bottom

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Sizing the Rain Garden (step 3)

The Vermont Rain Garden Manual

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Design Considerations

  • Shape?... kidney, tear drop, etc.
  • Overland flow vs. piping from downspouts

– Provide erosion control/energy dissipation

  • Overflow considerations
  • grade to direct surface overflow without impacts
  • Avoid discharge onto neighboring properties
  • Provide Erosion control measures downslope
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Garden Layout and Design

  • 1. Outline perimeter using string or paint.
  • 2. Remove grass/vegetation
  • Consider using black plastic as an option over pesticide
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Garden Layout and Design

  • 3a. Digging…on level ground
  • Level ground will be a depression below grade; dispose of soil.
  • Consider where water will overflow; provide a gentle dip to

direct away from neighboring properties

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Garden Layout and Design

  • 3b. Digging…on sloped ground
  • A downslope berm must be level and compacted
  • Consider where water will overflow; provide a gentle dip to

direct away from neighboring properties

The Vermont Rain Garden Manual; adapted from Rain Gardens: A How-to annual for Homeowners, UWEX

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Garden Layout and Design

  • 4. Leveling the Bed
  • Dig the bed 4-6” deeper to allow for adding soil mix & mulch
  • Avoid compaction; move from one side to the other or working

from the center out. Avoid wet conditions.

  • Loosen soil if it becomes compacted.
  • When dug to proper depth, use a 2x4 and carpenters level to

make sure the bed is level; this improves infiltration. *

  • Variation in the bed depth can be incorporated to provide wetter areas for

diversity of plant materials. Be sure to select plants that will tolerate standing water for a longer duration for any deeper areas of your garden.

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Installation and Materials

  • 5. Improve the Soil
  • Adding 2” of compost or soil mix helps the soil retain moisture,

and improve plant growth. (Rototilling makes this easier.)

  • Soil Mix: 50% topsoil, 30% sand. 20% compost
  • 6. Plant
  • Layout plants, loosen root balls, and plant.
  • Water immediately after planting. (2 times/week until

established)

  • 7. Mulch
  • Apply 2-3” of double-ground mulch to help retain soil moisture

and discourage weeds.

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Care and Maintenance

  • 1. While plants establish roots and fill in, pruning

and weeding may be needed.

  • 2. Remove leaf litter twice a year – after leaf fall

and before Spring growth.

  • 3. Cut back perennials and grasses in late fall.
  • 4. Replenish mulch for more manicured landscape

areas; naturalized areas may not need this.

  • 5. Check min. twice / year, and after major rainfall

events for sediment, erosion, vegetation needs.

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Rain Gardens are GARDENS with…

  • Managed runoff quantity for storms of 1” or less
  • Vegetation for evapotranspiration, soil health,

pollution absorption, nutrient uptake (N,K)

  • A mulch layer to hold water and assist with

uptake of heavy metals

  • Soil Biota and Pollution Reduction Properties

– Physical/chemical/biological matrix for living

  • rganisms

– Water cooling, infiltration and exfiltration

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Residential Rain Garden Guides

The Vermont Rain Garden Manual

http://www.docs.dcnr.pa.gov/cs/groups/public/documents/docum ent/dcnr_20028271.pdf

Rain Gardens, a how-to manual for homeowners

http://dnr.wi.gov/topic/shorelandzoning/documents/rgmanual.pdf

Rain Garden Alliance

http://raingardenalliance.org/right

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BioRetention Cells as Stormwater BMP

PA Stormwater Best Management Practices Manual

http://www.elibrary.dep.state.pa.us/dsweb/Get/Document- 67993/6.4.5%20BMP%20Rain%20Garden%20Bioretention.pdf

BioRetention Cells/Rain Gardens, a Stormwater BMP (Penn State)

https://extension.psu.edu/rain-gardens-bioretention-cells-a- stormwater-bmp

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Existing Environment

Invasive species: Canada thistle, crown vetch, mile- a-minute vine, Japanese stilt grass and knotweed

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Existing Environment

Site Slope 8% = 8” depth Silty Soil @ 8”= 0.16 size factor Drainage area= 5700 SF 5700 x 0.16 = 912 SF garden 70’ x 13’ wide = 912 SF

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Existing Environment

Dense plant spacing due to invasive species presence.

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Existing Environment