This is an Earthcache - there is no physical container here. To log this geocache as found, you need to read the description below, make some observations at the posted coordinates, and use that information to answer the questions below. Then you need to send the answers in a message to the cache owners (click on Message this owner above).
In order to log this Earthcache as a find, answer these questions:
1. As you look at the wide Mill Pond upstream from GZ, do you see any efforts to control erosion along the banks there? If so, what are they? If not, why do you suppose that is?
2. Looking at the rapids at GZ does the higher placement of limestone weirs near the shore direct the strongest water current away from the stream banks, slow the current along the bank, or both?
3. Besides the weirs (rock arches in the stream) do you see any other efforts used to control streambank erosion here?
4. Take a photo of your geocaching team or a personal item with your log (or send it to the cache owner) with the Welcome to Vernon Springs Park sign in the background.
5. Now go to Waypoint 2, which is across the river, on the downstream side of the bridge. Do you see any evidence of erosion or deposits of sediment as you look downstream? Any evidence of erosion control measures?
Geology of the Turkey River Watershed
The coordinates take you to the Turkey River and the Vernon Springs Mill Pond. The Turkey River travels over two geological landform regions as it travels 135 miles and enters the Mississippi River, just south of Guttenburg, Iowa.
The Turkey River begins in Howard County, an area known as the Iowa Erosion Surface (IES) region. The IES is a distinct landform region shaped by glaciers over 16,000 years ago. This region is identified by its gently rolling hills, loamy sediments, and large scattered erratic boulders. The bedrock is mostly Devonian dolomite and limestone, which is covered by layers of glacial deposits and wind-blown silt called loess. The landscape is shaped by erosion and the rivers are fairly shallow.
As the Turkey River flows southeast, it passes through a second geological region known as the Paleozoic Plateau. This area is characterized by narrow, deep valleys that are carved into sedimentary rock. The shallow limestone and dissolving action of groundwater gives way to numerous waterfalls, caves, springs, and sinkholes.
The Flood of 2008
The Vernon Springs Mill Pond was originally created in 1853 with a man-made concrete dam. But the historic floods of 2008 wiped out an 80 foot section of the dam, lowering the mill pond by 18 inches. The flood severly eroded the riverbanks downstream and the streambed below the dam.
Efforts to Control Erosion
In an effort to lessen erosion during future flooding events and improve the health and safety of the stream, the Howard County Conservation Board and Iowa Department of Natural Resources designed Iowa's first arch rock rapids - created with a series of weirs (rock arches). The weirs were created starting with a limestone rock base that was put in at a 3% slope. Then, using a GPS, large limestone blocks of rock from local quarries were strategically placed so that they would deflect water energy away from the river bank, and towards the center of the stream. In addition to lessening bank erosion, the weirs promote beneficial erosion in the center of the channel, and provide a more natural flow of the water and sediment transportation.
Permission to use the above graphic was granted by the Minnesota Department of Natural Resources
Other Ways to Control Erosion
There are other ways of slowing erosion along streambanks. Do you notice any of the following erosion-reducing measures here?
- Riprap - large rocks along the bank create a barrier against strong currents
- Gabions - large metal baskets filled with rocks, creating permanent retaining walls along the bank
- Native Vegetation - Willows, cottonwoods, and grasses with strong root systems that hold the soil in place
- Re-sloping the banks - grading them at a gentler slope to make them more stable
- Vegetated Concrete Mats
- Tree Revetment - place trees or logs horizontally along the riverbank, anchoring them in place