Live Pole Drain

1. CATEGORY

4.0 – Slope Stabilization

2. DESIGN STATUS

Level II

3. ALSO KNOWN AS

None known.

4. DESCRIPTION

Live pole drains are drainage systems composed of bundles of live willow (Salix spp) branches (live fascines or willow wattles) placed in areas where excess soil moisture results in soil instability. They are intended to drain excess water away from an unstable bank.

5. PURPOSE

Live Pole Drains collect subsurface drainage and concentrated surface flow and channel it to the base of the bank. Once established, their draining function is increased, as the plants absorb much of the water that is conducted along their stems. Because they are long and fibrous, the bundles act like a conduit. The water will take the path of least resistance, in this case, running down the bundle. Soon the willow will begin to root and sprout. The developed root system acts like filter fabric, stabilizing fine particles and reducing piping and sapping.

6. PLANNING

Useful for Erosion Processes:

	Toe erosion with upper bank failure
	Scour of middle and upper banks by currents
	Local scour
	Erosion of local lenses or layers of noncohesive sediment
	Erosion by overbank runoff
	General bed degradation
	Headcutting
	Piping
	Erosion by navigation waves
	Erosion by wind waves
	Erosion by ice and debris gouging
	General bank instability or susceptibility to mass slope failure

Hydrologic / Geomorphic Setting
(Not Applicable. This is a top of bank treatment)

	Resistive
	Redirective
	Continuous
	Discontinuous
	Outer Bend
	Inner Bend
	Incision
	Lateral Migration
	Aggradation

Conditions Where Practice Applies:

Live pole drains are most applicable on streambanks and slopes where excessive soil moisture is causing piping, erosion or slumping. Live pole drains tend to be used most frequently on outer bends.

Complexity:

Low.

Design Specifications / Typical Drawings:

When designing a project, one must decide whether to use willow wattles or live fascines. Both are constructed of the same size poles, and in the same manner, with the exception of the orientation of the cuttings. Fascines have all the cuttings oriented one way (all butt ends together), while wattles are composed of poles oriented in both directions.

The use of live fascines will facilitate rooting, as cuttings grow best when the tips are pointed uphill. The use of willow wattles, on the other hand, will provide more efficient drainage, as half of the tapering tips are pointed downward, but rooting success will likely be lower. Therefore, one must decide whether the goal of the project is drainage or plant establishment.

Live pole drains have been used successfully in British Columbia for years, especially for treating slumping road cuts on glacial till slopes. The excess water running through the bundle was outleted at the toe of the slope safely, without contributing to additional slope failure. David Polster, of Polster Environmental Services (personal communication, 2001), illustrated the longevity of live pole drains. Polster showed photographs of sites treated with these structures. During the first year, water can be observed draining through the bottom of the bundle, and some new sprouts are also seen. During the second year, the gully is completely revegetated and water is still observed draining through the bundle. By year four, the entire cut slope is covered with a large willow bush, while still draining excess water (D. Polster, personal communication, 2001).

Live Pole Drain Typical Drawing
.dwg	.dgn

7. ENVIRONMENTAL CONSIDERATIONS / BENEFITS

Live Pole Drains can safely drain excessive water off of the slope, while the fibrous root system adds mechanical strength, anchoring the soil in place. An additional environmental benefit is supporting and establishing some riparian vegetation on the streambank.

8. HYDRAULIC LOADING

Not applicable.

9. COMBINATION OPPORTUNITIES

Live Stakes are frequently used to anchor Pole Drains. Live fascines placed on a slight gradient and tied into a central pole drain can be used as "tributary" or collector drains to improve the collection/drainage efficiency of the pole drain (see typical drawing).

10. ADVANTAGES

Live pole drains provide drainage and stabilization immediately after installation, and once established, produce roots, which further stabilize bank and levee slopes. Pole drains and tributary fascines provide vegetative cover, shade the stream, and are a source of carbon and large woody debris (McCullah, 2002). In addition, sediment deposition increases the rooting success and efficacy of the pole drain; as opposed to slotted drain pipe, which gets clogged, and must be cleared when excessive sediment is deposited. Sotir and Fischenich (2001) also claim that willow fascines can "assimilate contaminants within the water column and reduce non-point pollution by intercepting sediment and attached pollutants coming into the stream from flow and overbank areas."

11. LIMITATIONS

Live pole drains work best if installed when willows are dormant; if they are installed during the summer, irrigation may be required. This technique is labor-intensive and requires large quantities of plant material (Schiechtl and Stern, 1996).

Live pole drains should not be used in well-established drainage channels, as they will not increase drainage, but will plug the channel and cause erosion as the channel adjusts to the increased capacity.

Fascines with axial subdrains should be considered as an alternative to live pole drains in swales or slope depressions that are saturated and that intercept and convey large amounts of subsurface groundwater or seepage. These axial drains extend to greater depths and have a much higher drainage capacity than pole drains.

12. MATERIALS AND EQUIPMENT

Live Pole Drains are essentially willow wattles or fascines constructed with longer than usual poles, with many of the branches left on (for construction specifications of these, see Technique: Live Fascines), live willow stakes or construction stakes, or a combination of the two.

13. CONSTRUCTION / INSTALLATION

Place the wattles or fascines in an excavated trench or existing drainage gully in an area of seepage, such that they intercept and control excess moisture on the bank (McCullah, 2002). Key the bundles into each other by jamming the ends together firmly and stake into place with live or inert stakes at 1-2 m (3-6 ft) intervals (Sloan, 2001). Stakes should be placed near rope ties and in transitional areas for additional support.

14. COST

Live fascine cost in year 2000 dollars: $33 to $100 per m for 15-20 cm diameter bundles ($10 - $30 per ft for 6 in - 8 in diameter bundles), installed (Sotir and Fischenich, 2001). Other sources vary from 0.5-1.0 work hour per linear m (3 linear ft) (McCullah, 2002) to 1.0-3.0 work hours per linear m (3 linear ft) (Schiechtl and Stern, 1996).

15. MAINTENANCE / MONITORING

Regular inspection and maintenance of wattle installations should be conducted, particularly during the first year, and repairs should be made promptly. Any stakes that loosen because of saturation of the slope or frost action should be re-installed. Rills and gullies around or under wattles should be repaired using brushlayers and Live Gully Fill Repair as necessary (See Techniques: Live Brushlayering, and Live Gully Fill Repair). All temporary and permanent erosion and sediment control practices should be maintained and repaired to assure continued performance of their intended function.

16. COMMON REASONS / CIRCUMSTANCES FOR FAILURE

Using a subsurface drainage technique, e.g., Live Pole Drains, when a surface runoff control measure is necessary.

17. CASE STUDIES AND EXAMPLES

Live Pole Drains were used to drain subsurface flow from this Decomposed Granite slope in Shasta County, CA. The last picture shows the growth attained during 5 months of summer heat.

18. RESEARCH OPPORTUNITIES

None Identified.

19. REFERENCES

McCullah, J. A. (2002). Bio Draw 2.0. Salix Applied Earthcare, Redding, CA

McCullah, J. A. (2000) Stafford Slide Biotechnical Erosion Control Project http://www.salixaec.com/stafford.htm.

Schiechtl, H. M.& Stern, R. (1996). Ground Bioengineering Techniques for Slope Protection and Erosion Control. Blackwell Science. London, England.

Sloan, R. (2001). Modified Brush Layers and Live Pole Drains for Landslide Reclamation, Erosion Control, July/August pp. 44-47.

Sotir, R. B.& Fischenich, J. C. (2001). Live and Inert Fascine Streambank Erosion Control EMRRP Technical Notes Collection (ERDC TN-EMRRP-SR-31), U.S. Army Engineer Research and Development Center, Vicksburg, MS (pdf)

	Instream
	Toe
	Midbank
	Top of Bank