Monday, April 9, 2018

Bank Stabilization

After a moderate flood - Click to enlarge
Like many other streams, Bull Creek is challenged in recent years by larger rain events and increased flooding.  Continued development in the upper reaches of the watershed includes more impervious surfaces such as roofs and paving.  Lawns replace native grasses, shrubs and trees with deep roots that previously captured some of the rain with each storm.  This leads to larger peak flow creating increased bank erosion and gravel deposition as well as silting in of Lake Taneycomo with serious implications for the economy of Rockaway Beach.  Below you can see the changes from 2008 to 2018.

Undercut bank
When the creek gives us more water it takes away more soil.  The Christmas flood of 2 years ago and the following April flood caused a loss of 50 feet of bank in a 300 foot stretch including 6 rows of recent riparian plantings.  More important it threatened the remaining mature trees along the east bank downstream.  This is located in the middle of an 8 mile stretch of Bull Creek which is designated as one of Missouri Outstanding Resource Waters.

Dave Woods, of the Missouri Department of Conservation fisheries division designed an initial plan for stream bank remediation with the construction of a bank stabilization structure which was just completed.  The project was funded by the Missouri Conservation Heritage Foundation through the Stream Stewardship Trust Fund which is described here.

The objectives of the project were to mitigate the unnatural rate of stream bank erosion, improve the channel stability by reinforcing three light equipment stream crossings, augment and protect more than 30 acres of bottom land forest to maintain a healthy riparian corridor.  It included establishing a perpetual easement to protect over 1.5 miles of the high quality Ozark stream, its tributaries and the associated corridor.  The easement permanently protects the high quality riparian areas along the creek from unnatural disturbance and development now and by any future land owner.

This remediation involved bringing in 1,400 tons of rock to stabilize 320 linear feet followed by replanting 2.7 acres of seedlings along the restored bank.  Detailed engineering plans were created by Chris Cash and the construction work was by Kelpe Contracting, a firm that specializes in riparian remediation.

Dave and Andy harvested 8' willow and sycamore poles (logs really) and these were held upright in trenches with the bottom end below water level in the hyporheic zone, the stream water that flows under a gravel bar.  Here they will sprout roots and grow to begin the riparian tree restoration even before the seedlings are planted next spring.

The project was completed in 5 days with a pause for a flood that tested the bank which passed with flying colors.  A video of the project is at this Youtube link.  Special thanks to Dave Woods who shepherded the project through a two year gestation to delivery and to Andy Humble for his logging skills and strong back.  Many thanks to the Missouri Conservation Heritage Foundation for all they do for conservation in our beautiful state.

Downstream portion of bank stabilization - Click to enlarge