8/3/2019 Iowa; Green Meadows Park Rain Garden Project - City of Johnston

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Green Meadows Park Bioretention Project FAQ - 1

Green Meadows Park Bioretention ProjectFAQIntroduction

Across the state, communities are conducting studies and making plans to protect one of our most

precious natural resources water. During the past several years, the City of Johnston has been workingwith engineering professionals to evaluate the many ways rainwater and snowmelt affect the citys

drinking water supply. The purpose of the study was to identify problem areas and related solutions for

addressing standing water, erosion, runoff, chemical contamination, and other water quality issues.

What is the Green Meadows ParkBioretention Project?

The goal of the project is to collect rainwater, snowmelt

and other stormwater runoff and filter debris and

pollutants through infiltration before being released into

Beaver Creek.

Why was this project selected?This project was selected for many reasons: it is located

in a public park providing for high visibility and

opportunity for public education; addresses water

quality issues within the Beaver Creek watershed; will

significantly reduce the volume of runoff from the

Green Meadows area; and will provide measurable

removal of debris and pollutants found in the watershed

runoff.

How will the system work?A system of water infiltration areas and retention areas

(sediment forebays) will be installed where the concrete

flumes are currently located. A collection pipe will beburied under layers of soils that are engineered to filter

the water. In addition, retention areas will be placed

along the flume. These areas, designed to collect

sediment, will be constructed of concrete pavers, similar

to a residential patio.

Are bioretention areas best managementpractices that could be used anywhere?

They are appropriate here. They would not be used in

hot spots for example: a truck stop.

Will less water drain through the area?

No. The same amount of water will move through theGreen Meadows area. The change is that more water

will be infiltrated, and less water and pollutants will

reach Beaver Creek. More water will infiltrate because

it will be absorbed by the native plants, the engineered

soil, and collection pipe.

Do the engineered soils wear out over time?The system is designed so that the sediment forebays

catch as much sediment as possible and protect the

bioretention areas from large amounts of debris, which

could eventually impair the system. By using

engineered soils that include a high percentage of sand,

and lining the system with permeable fabric, the system

remains viable.

Should we be worried about higher watertable and flooded basements with moreretention?

No. This project is designed to address water qualityand water quantity and will not impact current water

levels already experienced.

Why are native plants proposed instead ofturf grass?

Native prairie plants are being used because they are

deep rooted and drought tolerant. Their deep roots also

work to maintain and aerate the soil. Turf grass is

shallow rooted and not tolerant of heat and drought, so

it does not filter runoff.

Proposed project change: in response to citizen

concerns about aesthetics and access across the park,some mowed turf grass will remain where possible

between bioretention areas.

How long will it take for the water to drain?The bioretention areas are designed to drain standing

water from a storm event within 24-48 hours.

Can this project fail?As with any improvement, a specific plan of installation

and maintenance must be followed. The City is

committed to the success of this project and will

provide ongoing monitoring.

Will trees be removed with this project?Yes. The willow tree near the playground has already

been removed. It was damaged by insects and wind and

was a hazard. A total of 13 other trees will be removed

and replaced, tree for tree. These trees show signs of

disease and damage.

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Green Meadows Park Bioretention Project FAQ - 2

How will the work be completed?Two contracts will be awarded for this project. A

construction contract will be awarded to a firm to

remove the flumes, complete the grading, and construct

the sediment traps.

A second, 2-year contract will be awarded to a qualified

landscaping firm. They will be responsible for planting

the areas. It is anticipated that the plantings will be

completed in two stages some in the fall and others

the following spring.

How will the city address concerns regardingmaintenance?

As two contracts are proposed, the installation of plants

will be done by a qualified contractor solely responsible

for the work, which will include a 2-year maintenance

contract. It is suggested that this work will include up to

4 trips/year for weeding, spot-spraying and replanting.

During this time, the contractor will provide on-the-job-

training for city staff so that they can learn how to care

for the area.

Will the area be all torn up, all at once?No. Construction of the project is proposed in five

phases, starting with the north end the project.

Does the city have a horticulturist on staff tohelp with this maintenance?

The city does not have a staff horticulturist, but does

have access to knowledgeable resources who can assist

with these issues.

Why cant Terra Pond be part of this projectso it will look better?

Terra Pond was originally constructed as the sewage

lagoon for the Green Meadows neighborhood. Now that

sanitary sewer pipes are connected to the neighborhood,

it is no longer needed for that purpose. Sewage lagoons

are not designed to receive stormwater so it would not

be functional, and the runoff from the park does not

drain to Terra Pond.

What are the pollutants the city is worriedabout?

During a precipitation event, water washes across

parking lots, rooftops, and other impervious surfaces

collecting pollutants along the way. In our current

system, these pollutants are then carried into rivers,

creeks and streams. Water sampling conducted this

spring in Green Meadows Park showed elevated levels

of heavy metals, as well as phosphorus and E. coli

bacteria. Sediment levels have also been high, which is

also considered a pollutant.

The Green Meadows neighborhood drains directly to

Beaver Creek, which then flows to the Des MoinesRiver where it serves as a drinking water source for Des

Moines Water Works, serving the metro area.

GlossaryBioretention: Utilizes soil and plants to remove

pollutants from stormwater runoff. This best

management practice (BMP) was originally developed

in the early 1990s and provides for a natural way of

filtering the stormwater runoff.

Infiltration: Downward movement of water through soil

Impervious: Hard surfaces that do not allow water to

filter through concrete, rooftops, parking lots.

Sediment forebay: Sediment collection areas located at

various points within the plantings. As runoff flows

through the system, sediment and other material will be

collected to be removed by staff, as needed.

Permeable surfaces that allow water to flow through

grass, gravel, pavers.

Resourceswww.jcswcd.org Johnson County Soil and Water

Conservation District rain gauge tool.

www.rainscapingiowa.org Rainscaping Iowa.

www.polk-swcd.org - Polk Soil & Water Conservation

District.

www.iowastormwater.org - Iowa Storm Water

Education Program

www.agriculture.state.ia.us Iowa Department of

Agriculture and Land Stewardship

Article authored by Wayne Petersen - A Watershed

Year, Anatomy of the Iowa Floods of 2008, page 244