Severe erosion at Nakoma Park

As the City begins its study of the Lake Wingra Watershed,* citizens need to begin thinking about creative approaches to the watershed's management.  Input from citizens can encourage the study to be more creative and comprehensive.

Caving bank on north side of creek in Nakoma Park.

I've been spending days exploring the watershed.  Of all the problems found, Nakoma Park erosion jumps to the top of my list for action in the near future.

The creek that comes down the median of Cherokee Dr is one of the largest stormwater channels to Lake Wingra.  It runs uncovered and unconfined by concrete for just a short distance within Nakoma Park.  That's the park below Thoreau School at the junction of Cherokee Dr and Nakoma Rd.  The banks are severely eroded, especially a high caving bank on the north side.

Path erosion

A path from the school to a play area in the park has become eroded to form a shallow gully (below)

The area is heavily shaded by large trees--which no doubt made it difficult for grass to grow here.  The primary cause of the erosion is heavy runoff from a paved play area to the south of the school.  All the runoff flows around the east end of the school, and then down the eroding area.

Recently, a large rain garden has been constructed at the downstream end of the paved playground (below).

But this rain garden won't be able to capture more than a fraction of the runoff headed down the gully.
If we ask the City to deal with the runoff from the paved area, they would probably connect it with the nearest storm sewer, or else pave a flume through the park to the stream.

I would like to see something more creative--a series of rain gardens down through the park.  These could be used to deflect the runoff more to the east--away from the present pathway.  There's plenty of room for rain gardens.  This could be a chance to demonstrate an alternative solution.

When you build a chain of rain gardens that--in severe storms--may pass a great deal of runoff from one garden to the next, they have to be sturdy.  I believe that Deltalok bags could do the job.  Vegetation can take root in the bags.  The bags won't shift, because the upper bags are fixed to the lower ones by a plate with spikes.  The bags could be filled with earth dug from the center of the rain garden.  Perhaps two layers of bags (rising one foot) would be sufficient for the rim of each rain garden.

The streambank erosion is a bigger problem.

This stream experiences very high flows during severe storms.

The flow is too great for the pipes, with much overflow going through the park to the open stream.  I would like to see a living wall built withDeltalok bags, seeded with woodland plants and maple saplings.  Probably the City would say this couldn't withstand a flood.

The City's preferred solution would be to bury the stream completely.  I'd argue that the stream should be kept open for three reasons:

  • It's an educational opportunity--to demonstrate a sick urban stream.
  • It's an opportunity to experiment with greener solutions, like the living wall.
  • If, over the decades, we can improve infiltration enough within the watershed, perhaps the stream will recover some flow.  We should leave the open channel as a reminder of the task ahead.
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*  The Friends of Lake Wingra initiated a partnership with City Engineering, to undertake a study of the lake's watershed, so stormwater and other kinds of management could be carried out in a more comprehensive manner.  There have been as number of differences between the two over objectives--but these have been mostly ironed out, and a contract is about to be signed with Strand Associates, who will  conduct the study.

More photos.     Or, a slideshow.

1 comment:

  1. I like your ideas. Have you researched what other groups/municipalities have done to restore urban streams?


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