Urs, stormwater bmp construction

Rain Garden and Bioretention Construction:Excavation, Grading, & Structures

(presentation 2 of 2)

David Dods

URS, Overland Park, Kansas

914.344.1022, [email protected]

Installation and Maintenance of Stormwater Treatment BMPs Workshop, December 2011

Photos: David Dods, URS

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 bioretentionconstruction 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, [email protected], 913.344.1022

Jessi Veach, Civil Engineer, [email protected], 913.344.1029

Todd Bond, P.E., Senior Civil Engineer, [email protected], 913.344.1010

David Kocour, Environmental Scientist, [email protected], 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



Test Pits/Potholes

Helpful to see subsurface conditions, if

not done in design stage

• Soil Type, Compaction, Debris

• Depth to Bedrock, Groundwater

• Utilities

Photo: Kurt Leuthold, Barr Engineering

Asphalt

layers


Photo: David Dods

Definitions


Rain Garden


• Native soil

• Typically shallow

• Requires space

• Promoting Infiltration

Illustration: Craig Drummond, URS

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 gradingPhoto: 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

space allows

Keep equipment out of garden

to avoid soil compaction


Excavation

Photo: DRG Engineers Photo: David Dods, URS

• It is easier to stay out of small gardens

• Low Ground Pressure equipment, if available, may

help reduce compaction in large gardens

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

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


OutletsSafely 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

• Rake to grade

Photo: Rusty Schmidt, URS

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

Volume

% by Weight

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,

30% Peat

70% Sand,

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



InletsForebay 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


David Dods

URS, Overland Park, Kansas

914.344.1022, [email protected]

Photos: David Dods, URSPhoto: Carla Dods

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,

talk to designer



Planting Zones


Illustration: Dan Shaw, Waterdrop Innovations,

Source: The Blue Thumb Guide to Raingardens, by

Schmidt, Shaw, and Dods

Edges:

Dry

Sides:

Average

Bottom: Moist

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

used than in rain

gardens


Illustration: Kurt Leuthold, Barr Engineering

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


• Borders, fence, walls, decorations often included

• Take care to avoid compacting soil during installations

Photo: Rusty SchmidtPhoto: Carla Dods

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


Photo: Rusty SchmidtPhoto: Barr Engineering

Inlet temporarily blocked Outlet rim will be raised

once plants are established

Thanks & CreditsThanks 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


[email protected],

913.344.1022

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