The Lake Wingra Watershed--A Field Trip

To fit within 2.5 hours, we will focus on...
  • A healthy natural waterway
  • Stormwater channels of various kinds, including one badly deteriorated, and a stormwater basin
  • A sick urban stream
  • Rain gardens
...stopping at five locations shown on the map...

AK = Toki Shool
WP = Westmorland Park (lunch stop)
Samp = water sampling location at Wingra Park
----- = route of water from Odana Pond to Lake Wingra

Concepts to define and discuss
Groundwater, groundwater flow
filtering water
Ice age--ended about 15,000 years ago.
Rain gardens--one form of "green infrastructure"
Seepage lakes
Stormwater and runoff
Impervious surfaces
Stormwater structures: outlets/inlets, flume, channel, swale, sediment pond="grey infrastructure."
The water cycle
The "land ethic" of Aldo Leopold

Stop 1: UW Arboretum Curtis Prairie, accessed from Seminole Highway.  Stop at the parking lot at the Administration Bldg.

We'll walk to a shallow wetland channel in the middle of the prairie.  This is the headwaters of a creek that enters Lake Wingra from the south shore.

On the way to the wetland, we'll stop to pour water onto three surfaces, to see how readily it sinks in...
  • Packed turf, where many people walk
  • Normal turf, like your lawn
  • Prairie vegetation with no traffic
  1. How many seconds does it take for water to sink in at each test area?
  2. Where is infiltration the fastest?  Why?
  3. Where is infiltration the slowest?  Why?
At the wetland, no water is visible now, but the area is wet enough that a boardwalk has been built to ensure dry feet.  Students will see short but dense vegetation, and no signs of erosion.  Imagine this spot during a heavy rainstorm.  Flowing water will encounter thousands of stems that will act like a filter.  If this area floods a foot deep, it will store a lot of water.  The current will be very slow.

1. Where is the water here coming from, just upstream?
2. Can this area store flood water?
3. Are there obstacles to flow, to slow the water?
4. Can you see any erosion or other damage?
5. Is there any evidence how high the water floods?
6. Any signs of animal life?

Stop 2: Stormwater flume leading from Westgate to Odana Pond.  Stop near corner of Dearholt Rd and Milward Dr.

You can see a lot of debris and litter coming from the nearby shopping center.  What other kinds of pollution are in the runoff, besides litter?

You can see that the concrete bottom of the flume is coming apart.  Fast-flowing water scours the earth from under the cracks, undermining the flume, causing more cracking and damage.  Soil is eroded, and moves to the pond, filling it in and carrying nutrients.

Do you see any signs of wildlife?  What kinds do you think live here?

Conclusions: This flume is a source of phosporus and sediment.  Stormwater pipes, flumes, and ponds are expensive.  They have to be rebuilt every 30 to 100 years.  This is called "grey infrastructure," as opposed to "green infrastructure."

1. Where does the water come from, just upstream?
2. What kind of damage or erosion do you see?  What caused it?
3. Is there evidence of flooding?  How high?
4. Do you see evidence of wildlife?
5. What other problems do you see?

Stop 3:  Overlook of Odana Pond, from Odana Rd.  We don't leave the bus.

This pond is part of the same wetland as Orchard Ride Valley Park, that was cut in two when the Beltline was built.

The pond is about 1,500 feet long by 700n feet wide.  Now the pond doesn't change much in level, because the level is controlled by a dam at the east end.

A hundred years ago, the pond was more of a wetland, probably with vegetation like cattails across most of the surface.  Without the dam, the water level must have changed a lot.  It may have become almost dry during droughts (except perhaps for a small pond in the center), becoming a large pond during wet years.

Much of the central portion of the golf course must have been marshy.  When the snow first melts, you can still see large areas of standing water on the golf green.

The water rose and fell because there was no outlet.  Those hills to the east are sand dunes left over from glacial times.

During recent construction, you could see a deep sand deposit at the corner of Segoe and Odana roads.

Sand drained out of the glacier in meltwater streams, then blew about.  Probably there was never a large lake here, because water could easily seep through the sandy hills--they made a very leaky dam.  This golf course was--in effect--a huge rain garden.

Odana Pond flows to a second pond.  There is a second dam controlling the level of the second pond.  If you follow a ditch draining the second pond, you come to... a pipe!

The golfers didn't like having the course flooded from time to time... so they asked City engineers to create an outlet.

To get the water to go under those hills to the east, they had to dig a very deep trench and lay a stormwater pipe in it.

The pipe connects to a long ditch that runs along the side of the southwest bikeway--which used to be a railroad track.

What kind of wildlife do you think live in or around these ponds?

Odana Pond can get very salty in March, when the snow first melts.

Conclusions: May changes have occurred here over the last hundred years.  There's been a major change in the way floodwaters and groundwaters flow here.  With the Odana Project, millions of dollars have been spent to do what the environment once did for free--replenish the groundwater.

Stop 4: Intersection of bikeway and Midvale Blvd.

Here on the west side of Midvale, the stormwater channel comes to an end.

You can see the sides are covered with "riprap," which is an armor of stone to prevent erosion.

During big rainstorms, this channel fills entirely, almost to the  top.  It could be designed to store even more floodwaters.

Notice the native prairie plantings.  What else could be done to this ditch to slow floodwaters?

What animals do you think live here or use this area?

Lessons: Large ditches are a cheaper alternative to stormwater pipes.  They provide more storage, and more habitat.  But they require more land, and aren't very good habitat.

Stop 5. Rain gardens at Thoreau School  Stop on Nakoma Rd.  The bus will met us on Manitou Way, a hundred yards S of Nakoma Rd.

There are two large rain gardens here, built in 2012 and 2013.  They absorb runoff from the sidewalk, the school's roof and the paved playground.  All this runoff was eroding a large gully, as the water ran rapidly downhill to the park.

The lower of the two gardens was difficult to build, because of snowplow damage, shade, a steep slope, and large volumes of water.  There is so much runoff here that the strategy is to build the gardens as large as possible.

1. What differences do you see between the two rain gardens?  What  could explain these differences?
2. Where does the water for these gardens come from?

We walk to the next two stations...

Nakoma Creek--a sick urban stream

There are severe floods here, as often as four times a year when there's heavy rain.  The opening at the bottom of Chippewa Drive becomes clogged with debris.  The channel overflows across the street, and runs down the street and through the garden at Thoreau School.

Walk into Nakoma Park where a large pipe emerges to form Nakoma Creek. This creek runs open to the sky for only about a block.  During floods, much water runs very fast over the ground.  You can see the scour marks (pits of eroded earth).

An absolute torrent of whitewater comes out this pipe during storms.

You can see that the pipe has shifted, and is being undermined, like the flume we saw at the pond.

Much erosion is being caused along the shore further down, especially along the north bank and hill.

The beautiful stone stairway is being undermined.  It is shifting and cracking.

Floodwaters go across Nakoma Rd., slowing or stopping traffic.  The waters flow very fast, and are very smelly.

Conclusions: At this lower level in the watershed, flooding becomes severe, because the Nakoma area is hilly, and rain runs off rapidly.

There's a lot of erosion occurring.
 Several dump trucks full of soil may be washed away in a single storm.  The soil particles could carry a lot of phosphorus to Lake Wingra, alongwith lots of debris.

Nakoma Creek is a good example of an "urban stream."  It's a torrent during a storm, and dry a few days after rain.  This isn't good for wildlife, because wildlife and wetland plants need constant wet conditions.

Actually, this creek may flow for a week after a storm, although it's not much more than a trickle.  That's because the three ponds at Odana store a lot of floodwater.  They slowly release some of that water to this creek.  But they don't store anywhere near as much as the ground and the sandy hills could, if there were no pipe through the ancient sand dunes.

During a flood, Manitou Way becomes knee-deep in swift water.  The homes are nearly flooded.

1. What signs of damage do you see in the park and streambed?  What are the causes?
2. What kinds of animals might live here?  Did you see any signs?
3. Why is this stream "sick?"  List several causes.
4. What do you see that could slow floodwaters?  Comparison to Curtis Prairie?
5. Why is flooding here a problem?

Secret Pond: A stormwater pond visible from Manitou Way

Water flowing through the pipe under Nakoma Rd and Manitou Way dumps out into "Secret Pond."

The pond was rebuilt a few years ago, after the earlier version filled in with sediment after about 75? years.  It was so full that Nakoma Creek was dumping sediment directly into the marshes around Lake Wingra.

The pond was built large enough so the fast-flowing stormwater has a chance to slow down.  When the water slows, the sediment has a chance to settle out to the bottom.  The cleaner water leaves the pond by that channel towards the arboretum and Lake Wingra.

The City is concerned that despite several (how many?) ponds like these around lake Wingra, still too much phosphorus is getting into the Lake.

So the City is planning a test, in the next pond to the east, to take the phosphorus out by chemical means, a method called "alum treatment."  That makes the phosphorus stick together like a scum, and sink to the bottom.  Alum treatment is expensive, and has to be repeated.

The City has to do something to reduce phosphorus flowing to the lake, because of standards set by the EPA.  Alum treatments is one of several different methods they could use.

What other things could the City do to prevent phosphorus and other pollutants from getting to Lake Wingra?

Conclusions: Stormwater ponds are very effective at catching sediment, debris, and litter.  But they are expensive and use a lot of land.  They don't catch all the phosphorus, and they aren't very good habitat.  They have to be dredged and maintained.

Overall: Bit by bit, people have made huge changes in our landscape over the last 160 years since Madison was founded.  The changes have had a huge effect on how water flows through the environment.  These changes in flow and land use are one of the main causes of problems in our lakes.

1. What are two purposes of this sediment pond?
2. Is this pond good habitat?  What wildlife might live here or use it?
3. Is this pond good for recreation?
4. What slows the floodwaters here?

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Link to stormwater map of Madison.

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