Urs, stormwater bmp construction

Rain Garden and Bioretention Construction:
Excavation, Grading, & Structures
(presentation 2 of 2)

Photos: David Dods, URS

David Dods
URS, Overland Park, Kansas
914.344.1022, david.dods@urs.com

Installation and Maintenance of Stormwater Treatment BMPs Workshop, December 2011

This is a presentation given at the 2011 Stormwater BMP Installation and Maintenance
Workshop, sponsored by the Johnson County, Kansas Stormwater Management
Program, and held at Johnson County Community College in December.

Two files have been posted. The first presentation illustrates how urbanization
changes our landscape and the way water moves through it, the consequences of
those changes, and how green infrastructure can help restore ecological function to
the built environment.

The second presentation (this one) is an introduction to rain garden and bioretention
construction for commercial applications (rather than residential yards).

These materials were developed by the URS Green Solutions Team in Kansas City. Feel
free to contact us with any questions about these materials.

David Dods, Senior Environmental Engineer, david.dods@urs.com, 913.344.1022
Jessi Veach, Civil Engineer, jessi.veach@urs.com, 913.344.1029
Todd Bond, P.E., Senior Civil Engineer, todd.bond@urs.com, 913.344.1010
David Kocour, Environmental Scientist, david.kocour@urs.com, 913.344.1058


If you need information for residential yards, look for

“The Blue Thumb Guide to Raingardens, Design and Installation for
Homeowners in the Upper Midwest”

by Schmidt, Shaw, and Dods

Image: Waterdrop Innovations


Topics
Earthwork & Structures
• Pre-Excavation
• Excavation & Grading
• Rain Gardens vs. Bioretention
• Restoring & Placing Soils
• Underdrains, Outlets, Inlets

Landscaping
• Fine Grading
• Planting & Mulch
• Edging & Finishing Touches


Pre-Excavation
Basic BMP Project Goals:
1. Catch stormwater &
promote infiltration
2. Establish healthy, lush
vegetation

So, we want to:
• Preserve existing vegetation
• Prevent soil compaction
• Prevent garden clogging
Photo: David Dods, URS


Equipment Staging
Don’t drive or park on/near garden



Tree Protection
Minimize work/disturbed areas
Preserve the existing landscape
Stay off tree roots

Photos courtesy of Rusty Schmidt, Washington Conservation District, Stillwater, MN


Erosion Control
Mud and sediment ruin BMPs

Stabilize site upstream of
BMP before starting work

Block inlet to BMP

Keep erosion & sediment
controls in-place at all times Photo: David Dods, URS


Test Pits/Potholes
Helpful to see subsurface conditions, if
not done in design stage

• Soil Type, Compaction, Debris
Photo: David Dods
• Depth to Bedrock, Groundwater
• Utilities

Asphalt
layers

Photo: Kurt Leuthold, Barr Engineering


Definitions


Rain Garden

Illustration: Craig Drummond, URS

• Native soil
• Typically shallow
• Requires space
• Promoting Infiltration


Rain Garden



Bioretention

Bioretention
Soil Mix

Underdrain


• Engineered soil
• Underdrain
• Typically deeper, so can use less area
• Filters runoff + promotes infiltration


Bioretention

Photos: Rusty Schmidt


In-Line vs. Off-Line

In-Line

Off-Line


In-Line vs. Off-Line Design

Photos: David Dods and Rusty Schmidt, URS


Excavation & Grading – Rain Gardens

• Cut sod
• Excavate to rough depth
• Restore compacted soil
• Add compost and rototill
• Fine grading
Photo: Kevin Slates, URS


Sod Removal
• Use sod cutter
instead of heavy
equipment, if
possible
• Reduce soil
compaction
• Reuse sod
elsewhere


Excavation
Excavate from edge when Keep equipment out of garden
space allows to avoid soil compaction



Excavation
• It is easier to stay out of small gardens
• Low Ground Pressure equipment, if available, may
help reduce compaction in large gardens

Photo: DRG Engineers Photo: David Dods, URS


Soil Compaction Ruins Rain Gardens


Excavated with a Skid Loader. Small rototiller was unable to solve
compaction
Fix: Hand dig, install drain pipe, change plant selections to more
wet tolerant species


Inlets, Outlets, & Concrete Work
Typically installed after rough grading
or before excavation



Restoring Compacted Soil
Rip or overdig to break up compaction

Photo: Rusty
Schmidt



Add Compost and Till



Hand Tilling on Small Site



Fine Grading

• Rake by hand on
small sites
• Drag on large
sites
• Keep heavy
equipment off
after restoring
soil Photo: David Dods, URS


? Questions About
Rain Garden Grading ?


Bioretention


• Excavate similar to rain garden, but deeper
• Install underdrain
• Rip & till compacted soil
• Backfill with engineered soil


Bioretention:
Rough Grading & Underdrain



Bioretention:
Underdrain Installation



Bioretention:
Underdrain Connection to Storm Drain

Photo: Rusty Schmidt


Bioretention:
Soil Mix Placement

Cleanout Riser



Bioretention:
Planting bed final grade



Bioretention Discussion

Pipe & Gravel Types

Gravel: Clean, Double Washed

Filter Fabric
Flow Control on Outlet Pipe


Outlets
Safely overflow large storms
Grading and elevations are important for success



Restoring Compacted Soil & Backfilling

• Install underdrain
• Mark drain location with stakes
• Rip compacted soil
• Place 4 - 6” of engineered soil
• Rototill to blend native and
sandy soil
• Place remaining soil lifts
• Tele-Belt may be useful on
large sites
• Some specs require watering
between lifts to settle soil Photo: Rusty Schmidt, URS

• Rake to grade


Test Infiltration Before Planting
• If drainage problems show up, it is easier to fix before planting
• Touch up soil level if excessive settling

Photo: Carla Dods


Bad Soil Mix

Installer substituted
on-site soil for
compost in the mix to
save money

Fix: Remove and
replace everything



Engineered Soil
• Typical mix: sand, compost, topsoil
• Specs vary for different goals
• Slow vs. fast infiltration
• Plant choices

• Variations include:
• Mix percentages
• With or without topsoil
• Coarseness of sand
• Compost vs. peat moss


Engineered Soil – Typical Mix Ranges

Material % by % by Weight
Volume
Sand 50 – 80 % 80 – 90%
Compost 10 – 30 %
Topsoil/Planting Soil 0 - 30%
Fines (silt, clay) 5 - 15%,
with clay <5%
Organic Matter Content 3 – 5%


Engineered Soil

Topics to discuss with designer:
• Mix by volume vs. weight
• Sand: fine vs. coarse
• Compost: Well aged, mature product;
Allowable sources
• Topsoil: Allowable sources, weed seeds


Engineered Soil – Infiltration Test

70% Sand, 70% Sand,
30% Peat 15% Peat,
15% Topsoil

David’s Home Soda Bottle Infiltrometer

Photo: David Dods


Time: 0 Minutes

Photo: David Dods


Time: 5 Minutes

Photo: David Dods


Time: 30 Minutes

Sand & Peat
Mix Drained in
7 Minutes

Photo: David Dods

Time: 2 Hours

Sand, Peat &
Topsoil Mix:
17 hours to
drain

Photo: David Dods


Inlets:
Control water flow into garden to prevent erosion
Should extend to low point of garden



Inlets
Forebay to Collect Sediment & Debris



Sump Catch Basin
with Pipe into Rain Garden

Sump

Illustration: Courtesy of Kurt Leuthold, Barr Engineering


Inlets

If garden is designed for
sheet flow down banks,
you should see sod or
erosion control blanket
on sideslopes

Flowing water will cause
erosion, even on small
slopes



Fine Grading, Landscaping Introduction,
& Finishing Touches

Photo: Carla Dods Photos: David Dods, URS

David Dods
URS, Overland Park, Kansas
914.344.1022, david.dods@urs.com


Fine Grading
What’s wrong with the grading here?



Fine Grading
What’s wrong with the grading here?

Low Point is
not in channel

Channel
should be
this shape



Fine Grading
Water will flow to the
lowest point

Inches matter – Fine
grading is critical to
success. At inlet, outlet,
edges, bed.

If grading plan is
unclear, Photo: David Dods, URS

talk to designer


Planting Zones

Edges:
Dry

Sides:
Average
Bottom: Moist

Illustration: Dan Shaw, Waterdrop Innovations,
Source: The Blue Thumb Guide to Raingardens, by
Schmidt, Shaw, and Dods


Planting Zones
• Different locations in
gardens are wet or dry

• Plants are chosen for
specific locations

• Plants need to go where
specified

• Please don’t substitute
without talking to designer


Bioretention
• Well-drained
environment

• Likely dries out
faster than rain
garden

• So different
plants may be
Illustration: Kurt Leuthold, Barr Engineering
used than in rain
gardens


Plant Materials
• Pots – Fast to establish, “Instant gratification.” Most expensive.
• Plugs – Less costly than potted material, but fairly quick to
establish.
• Seeding – Slowest to establish. Typically only used on large sites
for cost savings. Concerns over wash-out, weeds, appearance
first couple years.
• Care, Handling, & Planting to be covered later in class



Planting Large Pots
Remove, not distribute, excess soil dug for planting, or allow
for it in grading
(don’t want to fill in garden bed)



Mulch


• Coarse, Shredded Hardwood: Heavy, Binds together,
Resists floating away
• Don’t use finely ground
• Pinebark nuggets and chipped mulch float
• Don’t overfill mulch depth


Edging


• Many Options: Steel, brick, stone, pavers, concrete
• Ask designer if water is supposed to flow in or out over
edging; Installation depth critical if water is to go over


Finishing Touches

Photo: Carla Dods Photo: Rusty Schmidt

• Borders, fence, walls, decorations often included
• Take care to avoid compacting soil during installations


Control Water Level Until Plants are Established
(and keep upstream erosion controls in place)

Photo: Barr Engineering Photo: Rusty Schmidt

Inlet temporarily blocked Outlet rim will be raised
once plants are established


Thanks & Credits
Thanks for sharing photos, illustrations, and advice:

Todd Bond, Jessi Veach, Kevin Slates, URS, Overland Park, Kansas
Rusty Schmidt and Dan Shaw, Waterdrop Innovations, River Falls, Wisconsin
Carla Dods, Shockey Consulting, Lenexa, Kansas
Kurt Leuthold and Fred Rozumalski, Barr Engineering, Minneapolis,
Minnesota
Matt Schoell-Schafer and Lisa Treese, Patti Banks Associates, Kansas City,
Missouri
Meg Babani, Taliaferro & Browne, Kansas City, Missouri
Steve Roth, DRG Engineers, Bonner Springs, Kansas
Lee Skabelund, Kansas State University, Manhattan, Kansas
Jim Scheussler, BNIM Architects, Kansas City,Missouri


Questions

?

david.dods@urs.com,
913.344.1022

Urs, stormwater bmp construction

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