Thompson Bend Riparian Corridor Project – Power Point Slides, click on the thumbnail images to view a full size image.
Dry Bayou Scour Hole Location – before damage was induced.
Note row of trees along river bank and lack of trees inland.
The arrow is pointing to the same location as the arrow in slide 1
and is the location where the Mississippi is attempting to break through.
Same location as the arrows in the first two slides, but in 1983
after the river had initiated its’ attempt to cut across the neck of
Thompson Bend. The
approximate distance from the river to the photo foreground is 0.5 miles.
Typical overbank scour and erosion in 1985.
Estimates of 40,000 tons of top soil per acre were being eroded
with each flood event. Also
note the large trees which had to be removed after each flood event prior
to preparing the land for agricultural purposes.
Typical post 1993 Flood damage. While the vegetation died, it provided valuable erosion
protection. But, subsequent
flood events in 1994 and 1995 prevented natural re-growth and removed the
dead trees, once again leaving the bend vulnerable to a catastrophe.
See next slide.
This slide illustrates
one of the positive aspects of the riparian corridors.
This portion of the screens planted in 1986 survived, and it is
clearly evident that the trees catch massive amounts of drift, and the
scour holes are actually stabilizing and in some instances showing signs
of healing. Actual
velocity measurements taken during times of floods have shown entrance
velocities into the tree screens are consistently reduced by at least 50%
as they pass through the screens.
Maximum entrance velocities have been measured at 10 to 11 feet per
second with Acoustic equipment. The
existing soil has a scouring threshold of 5 to 6 feet per second.
Thus, the 50+% reduction of the velocities through the screens
reduces erosion and scour to almost negligible amounts. After the last flood event in 1999, some landowners were
complaining of deposition, a situation which has never happened in fifty
17. Year 2000 re-planting rows after Permanent Easement Acquisition was initiated by the Corps.
Future actions include
continued acquisition of easements and planting and managing of Riparian
corridors along this 30 mile reach of river.
The project life is perpetual, with the amount of yearly work
directed at it being dependant on previous years river stages. Some years substantial re-plantings may be required, but
during periods of drought very little activity will occur outside of the
selective harvesting of trees.
The perpetual easements and Memorandum of Agreement signed by the
Corps and Landowners ensure that all will do whatever is necessary to
ensure the successfulness of the project.
21. The Corps
also committed to establishing Riparian Corridors (tree screens) along a
300 foot strip of high bank along the river bank of the bend and at
certain key locations across the throat of the bend. The Corps would
purchase approximately 1000 acres in permanent restrictive easements along
a 12 mile stretch of river. On these easements, the Corps would
establish Riparian Corridors where necessary, and manage existing Riparian
areas to maximize their effectiveness to retard erosion. In
exchange, the land owners would get monetary compensation for their
valuable farm land, and have first refusal right of any timber which could
be harvested from the easements. Numerous meetings and briefings
were held to develop these plans. Here Lester Goodin, left,
president of the Thompson Bend Soil Management Association, meets with St.
Louis District Engineer Col. Morrow(middle).
map shows the areas where easements have been or will be purchased.
The majority of the areas are locations where the individual land owners
had initially tried to establish vegetation prior to the devastating
floods of the 1990's.
23. These two photos visually show the effect tree screen can have on velocities. The photo on the left is velocity data recorded with an Acoustic Doppler Current Profiler (ADCP) on the upstream side of a Riparian Corridor, and the photo on the left is ADCO data on the downstream or backside of the corridor. Data collected during various flood events has continuously shown a 50% reduction in velocities, which in every case has reduced the velocities below the scour threshold of the soil.