A soil bioengineering success: Elm Creek stream bank stabilization.
Basic principles of fluvial geomorphology were applied to determine the elevation of the channel forming discharge in Elm Creek. Rock riprap was installed below this elevation to secure the bank toe. Soil bioengineering techniques were used above this elevation--specifically live fascines, brush mattresses, and live stakes--to stabilize the upper bank slope. The bridge downstream of this site causes turbulence; the natural floodplain is on the opposite side.
The drainage area for the site is 59,600 ha (230 square miles), and the 10-year peak discharge is 85 [m.sup.3]/sec (3,000 cfs).
The rock riprap was installed by excavating a 3.6-m (12-ft) wide construction platform into the eroded stream bank. The excavation was later backfilled and shaped to facilitate vegetative plantings secured with bioengineering techniques. The median size of the rock was 20 cm (8 in.). The thickness of the rock layer was 45 cm (18 in.) on the slope and 90 cm (36 in.) at the toe.
The project installation coincided with a NRCS training session on soil bioengineering in October 1998. This session provided 30 students with practical experience in harvesting plant materials and installing soil bioengineering measures. About 0.4 ha (1 acre) of sand bar willow was harvested within a 1.6-km (5-mile) radius of the site on the day before installation. This hardy plant material was selected with the expectation of "jump-starting" a natural succession of native hardwoods.
In May 2001, Elm Creek experienced 14.7 cm (5.79 in.) of rainfall accumulation in April (twice the normal amount). Floodwater overtopped the stream banks, as shown in the photo on page 9. In contrast, 2003 was a very dry year. Low flows exposed the channel bottom and the stream bank improvement, as shown in the photo, below. Despite the variable weather, a recent plant inventory shows a thriving population of willow, particularly in the area where brush mattresses were installed. Brush mattresses have a higher cutting density than fascines. The willow is expected to fill in uniformly along the project reach and become a nursery for native shrubs and hardwoods.
The 122-m (400-ft) reach of stream bank was protected for a total cost of $32,445 or $266 per m ($80 per lineal ft). Volunteers secured the vegetative plantings in about four hours. Project costs included the prices for commercial landscape labor and equipment, instead of the volunteers actually used.
RELATED ARTICLE: Soil bioengineering is ...
... a system of living plant material used as structural components. Adapted types of woody vegetation (shrubs and trees) are initially installed in specified configurations that offer immediate soil protection and reinforcement. In addition, soil bioengineering systems create resistance to sliding or shear displacement in a stream bank as they develop roots or fibrous inclusions. Environmental benefits derived from woody vegetation include diverse and productive riparian habitats, shade, organic additions to the stream, cover for fish, and improvements in aesthetic value and water quality. In some conditions, soil bioengineering installations work well in conjunction with structures to provide more permanent protection and enhance aesthetics.
Major attractions of soil bioengineering systems are their natural appearance and function and the economy with which they can sometimes be constructed. The main construction materials are live cuttings from suitable plant species. The design for a soil bioengineering project often involves an interdisciplinary team. Soil bioengineering measures require more monitoring and follow-up, especially in the first five years, while the vegetation is becoming established than do conventional structural measures. The success or failure of a soil bioengineering measure is not fully known until the measures have been in place at least five years.
ASAE member Sonia Maassel Jacobsen is an hydraulic engineer with USDA-NRCS, 375 Jackson Street, Suite 600, St. Paul, MN 55101 USA; 651-602-7879, fax 651-602-7914, email@example.com.
ASAE member Steve Becker is an area engineer with USDA-NRCS, 209 W Mulberry St., St. Peter, MN 56082 USA; 507-931-2530, fax 507-931-4619, firstname.lastname@example.org.
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|Title Annotation:||related article: Soil bioengineering is ...|
|Author:||Jacobsen, Sonia Maassel; Becker, Steve|
|Publication:||Resource: Engineering & Technology for a Sustainable World|
|Date:||Nov 1, 2004|
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