Quantcast Dormant Post Method.

 
  
 
Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Figures 32 and 33 show photographs of the Upper Truckee River site both before and
after construction. The latter figure was taken in July 1995 after an extended high flow
period from May 21 through July 21. There, Mr. Matt Kiese4 (pers. communication)
described building the lifts with the use of long angle iron forms. The angle irons were 8 ft
long and were fashioned to form a frame into which plywood boards were inserted. Then,
the forms were wrapped with two fabrics similar to those described above and soil dumped
into the forms and compacted. The fabrics were wrapped back over the soil and the forms
removed. Willow whips were laid on top of each lift and then the next lift was prepared. The
installation at the Upper Truckee was no more than five feet tall and 123 ft long. Care must
be taken to provide rock or some other hard material at each upstream and downstream end
to prevent flanking of the treatment. For instance, one may either tie into existing vegetation,
such as trees, or create hard ends by placing rock. Also, it is important to prevent scour at
the bottom lift and to provide a good footing by creating a ditch and filling it with cobble or
rock. The first lift is placed on top of the cobble ditch. The ditch at the Upper Truckee River
site was about 2-ft wide by 2-ft deep.
This treatment was very successful on the Upper Truckee River despite the 5-yr flood
event in May 1995 that produced overbank flows. The treatment remained in place since
since October 1993. Further discussion about this treatment can be found in Volume II.
Dormant Post Method. This treatment consists of placing in the splash zone and perhaps
the lower part of the bank zone dormant, but living stems of woody species that sprout stems
and roots from the stem, such as willow or cottonwood. Willows are normally used and are
cut into 10-14 ft posts when the leaves have fallen and the tree is dormant. The dormant
posts store root hormones and food reserves (carbohydrates) that promote sprouting of stems
and roots during the growing season. According to Roseboom (1993), dense stands of 4-6
year old willows make the best harvesting areas. He also uses posts that are 4-6 inches in
diameter at the base. His examples are based on fast-growing eastern species, however, and
smaller willow may have to be used in the western states.
Roseboom (1993) prescribes shaping a bank to a 1:1 slope with the spoil placed in a 6-
inch deep layer along the top of the bank. In major erosion sites, post holes are formed in the
bed and bank so that the end of the post is 2 ft below maximum streambed scour (that portion
of the streambed that is subject to movement). Hoag (1993) suggested that for bank
stabilization, the cutting (post) should extend 2-3 ft above ground so as it leafs out, it can
provide immediate bank erosion protection. He also recommended the cutting should be
planted as much as 3-5 feet into the ground. If they are not this deep, moving water can
erode around the cutting and rip it out of the ground. Roseboom places the posts four feet
apart up the streambank. The posts in one row are offset from the posts in adjacent rows.
4
Matt Kiese, Interfluve Inc., October 1993, personal communication
B-51

 


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