Building a rain garden at Thoreau School

During October of 2012, the Friends of Lake Wingra group was asked to help Jack Nolan select an Eagle Scout project.  Jack wanted to do something to help Lake Wingra.  I volunteered to help Jack.

Our first step was to take Jack--and his dad Rich--on a tour of the watershed, so they could see how Jack’s project fit into the big picture.  We visited key areas in the watershed, and places where a project could help solve watershed problems.  Jack decided to build a second rain garden at Thoreau School.

The garden would help control runoff from a paved playground, and the school’s roof.  During storms, torrents of water flowing down a hill towards Nakoma Park had eroded a deep gully.  A garden here would also teach children about green storm water control, replenish groundwater, and increase biodiversity--for improved community health.

Plans take shape--slowly

Jack didn’t have experience gardening.  While I had built a few small rain gardens with donated plants, I had never built a large one, or coordinated volunteers.  We’d bitten of a mouthful.  Perhaps this would be the largest Eagle Scout project in history.

A large rain garden is a complex project.  For location, you have to consider…
  • Education and public awareness
  • Flow of water
  • Soils
  • Pedestrian traffic
  • Watering during summer
  • Protection from snowplows
  • Trees and sunlight
  • Underground utilities
It takes time to gather information about these issues.  You have to consult with school personnel, various experts, and depend on your own judgment.  It takes months for the pieces to fall into place--gradually, your plans begin to take shape from the mist of possibilities.  You have to proceed with uncertainty about some parts of the plan.

There was only one place big enough for our garden--and far enough from snow plows.  But it was very shady, and had a substantial slope.  We began to realize it would be challenging to build a garden here.  We started to consider locations at other schools, but it was too late to begin the approval process all over again.

We decided we could handle the slope of our site by “terracing” the garden, like the rice paddies in Indonesia.  There were “silt socks” at the Edgewood Campus, left over from a construction project.  Edgewood gave permission to recycle the socks, to create the dams for our terraces.

Our next hurdle was to secure funding.  By now, spring was approaching, and it was too late to apply for most grants.  Fortunately, the Friends of Lake Wingra approved a grant of $1,500.  For FOLW,  this would be a pilot project--the first of a grant program to improve storm water management on school grounds.

The third major deadline was to select plants, select a supplier, and order plants.  A rule of thumb is one plant per square foot.  With snow on the ground, it was impossible to lay out our garden’s outline in detail.  But sketches estimated about 750 square feet, so we planned to order that many plants.  Agrecol has by far the lowest prices--but they are a wholesaler, and we had to persuade them that FOLW qualified for purchase.  But Agrecol didn’t have all the species we wanted, so we also ordered from Prairie Nursery.

We selected shade tolerant plants, except for some butterfly weed planned for a corner that would receive some direct sun.

With the arrival of spring, we refined our plans, with an eye to organizing construction of the garden in an efficient way.  We decided we couldn’t afford hiring a Bobcat to move the earth.

So… how do you move earth with shovels, efficiently?  We built a 1/4 scale model at Vilas Beach.  This showed us that the downstream berm would be large--we needed to plan sufficient space for it.

We also inspected existing rain garden #1 at Thoreau, to see what we could learn.  Recent rains had eroded a breach in its berm.  We also saw that the berm has to be level--always the same altitude--so that it will overflow everywhere at the same time.

Final preps

We went to Edgewood, to inspect the silt socks, and decide how to move them.  Each one was 20’ long, weighing 400 soggy pounds.  We lined up four strong backs and one van for moving the socks.  We moved about 4,800 lbs of socks.  Now Rich’s van smelled like a mushroom farm.

Next, we went to Thoreau School and used yellow rope to lay out the boundaries of the new rain garden, #2.  Due to slope and limited space, we planned to build two basins.  And each basin will be terraced, with a silt sock across the middle, so less excavation will be required.  The gardens will be located in the turf area in the photo below (right rear).

While we were laying out the garden, a large snapping turtle arrived to inspect our work.  Traffic was backed up while she crossed Nakoma Rd.

The layout was inspected by John Finnemore, head of MMSD physical plant later today.  Diggers Hotline cleared our garden.

We scheduled pickup times for our plants--each nursery located over an hour‘s drive away.

With construction only days away, problems remained.  The turnout of scouts for digging would be low, due to a scheduling conflict.  Additional adults were cajoled to help.

Some of the plants we picked up died.  Some plants ordered didn’t germinate, so we had to substitute another species.

Construction Day

On Saturday, June 1, from 9:00 to 1:00, about 17 people helped dig two basins for the second rain garden at Thoreau School. This included 10 people from Jack's scout troop.  A few of us started at 8:15 and worked through 2:30 pm.

One parent of a scout helped to shape and level the berm.

The basins were completed, then protected against rain with silt socks and tarps.  Excess dirt was piled, for later pickup by the School District personnel.

We ran into an extensive root system while digging the upper basin.  We decided not to cut any roots larger than 1" in diameter.

This slowed us down, and reduced the volume of the basin.

Planning for Planting Day

On Sunday, Liz McBride met with Jack to decide precisely where the plants would go.  Although Jack had already presented a rough plan to FOLW, their goal was to refine that plan, based on Liz's expertise, on a revised plant list, and on how the basin actually looked.

On Monday, Liz began to put markers into the basins, indicating zones and plant locations.

At this point, we realized the basins weren't as large as originally planned.  Where to put the excess plants?   David figured out  a design for a third rain garden located upstream,  in dense shade under the basswood tree (see photo above, rear).  This area will be planted with our most shade-tolerant plants.  Instead of digging a basin where roots are thick, we'll hold the water here with silt socks.  While the plants are becoming established, silt socks will divert runoff from this area.

Liz produced a handout of instructions for planting day.

On Tuesday, David and Jack laid an erosion control blanket over the berm, to protect against forecast rain.  David and Jack were "on call," to shore up erosion controls, in case of heavy rain.  We picked up 3 more gargantuan silt socks from Edgewood, for use in constructing the third area.

On Wednesday, I picked up 480 plants from Agrecol..  If there had been one more tray, I would have been driving with 32 plants in my lap.

The garden survived the light rain of Wednesday and Thursday just fine.

On Friday, I finished placing stakes, indicating plant locations.

Planting took place on Saturday, June 8, from 9:00 to 1:00.  Scouts from Jack’s troupe helped, but classes from Thoreau didn’t participate, since the end of classes was near.

The biggest concern of planting was to avoid stepping on plants, in the very tight space of the garden.  So planters were divided into teams of two, with one inside the garden doing the planting, and the “partner” outside the garden, passing in plants, compost, and other needed items.

Liz gave planting instructions, then handed out plants and area assignments.  Since the basins were dug into the subsoil, compost was added to each hole dug for a plant.  Planters cut holes in the erosion control mat with scissors, before putting in their plants.  This slowed them down a bit, but saves weeding and erosion repair later.

Of the $1,500 granted, $1,057 had been spent so far, mostly on plants.

Remaining expenses anticipated are a hose, replacement plants (next spring), educational materials, and materials to reinforce the gardens against damage during major storms.

Followup--garden protection

Mulch is a problem in rain gardens, because most kinds just float away when the garden fills.  We’d postponed a decision till now.  David tested the wood chips from silt socks.  Since the socks had been sitting in the woods for a year, only about half of the wood chips floated.  We mulched half the garden.  But since the mulch moved around a lot during subsequent storms--burying some plants--we decided to stop.

A rain garden is at risk of washout, until the plants become well-established.  So we decided to observe how the garden responded to rain, before designing detailed protections against erosion.  We didn’t know where the water might overflow, from one terrace to the next.  And the lowest garden had a big basin.  If the berm there overflowed, a large gully could form, destroying the garden.

Knowing a severe storm was coming, I beefed things up while Jack was in Chicago.  I dragged silt socks around to keep as much water out of the gardens as possible.

On June 12 and 13, there were many heavy rainstorms.  The fledgling garden was under siege!

During the first rain, torrents of water came down the drainage way, headed for the garden!

But I saw it was possible to deflect half the water, so it would bypass the garden on one side.  We hadn’t planned to deflect water--so it was essential for me to be there during the storm, observing and taking corrective action.

I managed to deflect about half the water coming down the swale.

Suspense building, the pool filled to within 6" of the top.  But it didn't overflow, so almost no damage was done to any part of the garden--except for the plants looking a bit muddy.

The week of June 23 brought more severe storms.  We built a spillway from basin #2 to basin #3.  We planted more plants.  After each storm, we dug out plants buried in debris.

Two silt socks began to shift--we stabilized them with metal stakes.

At dawn on June 26, there was a cloudburst with severe flooding in Nakoma Park.  Torrents of water washed over our silt socks and into the garden.  The berm on pool #3 overflowed--but since one of our volunteers made the berm so perfectly level, there was no one discharge channel, and so the berm survived.  We brought more silt socks from Edgewood, building a second tier on the bypass side.

As of June 26, the garden has survived many severe storms.  Jack and myself have learned volumes about rain gardens and organizing volunteers.  And the project has set a powerful example for what citizens can do to improve watershed management.

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