WILLOW POSTS AND POLES

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

Spatial Application:

	Instream
	Toe
	Midbank
	Top of Bank

Hydrologic / Geomorphic Setting

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

Conditions Where Practice Applies:

Willow posts and poles can be used in most areas in need of revegetation. Those most conducive to this practice are midbank areas on banks with a 1V:2H slope or shallower. Although posts and poles can be planted in the toe and upper bank areas, vigorous growth is rare, due to drowning and desiccation of the poles, respectively.

Complexity:

Low.

Design Guidelines / Typical Drawings:

Willow cuttings should be planted while dormant, and care should be taken to prevent desiccation or dormancy break of cuttings between harvest and planting. Basic considerations for harvest, handling, and contracting for installation of plant materials are available from several sources, including Federal Interagency Stream Restoration Working Group (1998) and the Special Topic: Harvesting and Handling of Woody Cuttings.

Poles and posts should be deeply (1 to 2 m (3 to 7 ft)) planted in holes created using an auger or metal "stinger" mounted on a hydraulic hoe, or an excavator bucket. Poles should be planted to such a depth that desiccation does not occur during summer (for sites with water tables lower than the stream) and poles are not undermined by local scour during high flows. Augered holes offer the advantage that soils adjacent to the planted stem are not compacted. Good contact between the plant stem and soils is essential, so holes that do not collapse must be refilled with compacted soil to prevent desiccation of the plants due to air pockets. High flows that occur shortly after planting can ensure collapse of the holes and filling of air pockets. Water jetting, in which stems are rapidly inserted into soils that are locally liquefied using a high-pressure stream of water, offers many advantages over other planting techniques when applied to sandy soils (Drake and Langel, 1998).

Only a small portion of the pole should remain above the surface of the ground – about 80% of the cutting should be buried, to prevent desiccation and ensure good stem to soil contact.

Willow success is governed by soil texture and moisture regime (Pezeshki et al. 1998). Workers in drier climates have stressed the importance of planting Willow posts deeply enough to maintain contact with groundwater throughout the growing season (Swenson and Mullins, 1985). Evaluation of a large-scale Willow planting project in northwest Mississippi highlighted the success of Willow posts planted in middle-bank elevations (Watson et al., 1997), while those at the bank toe died due to excessive moisture and those at top bank experienced low survival due to droughty conditions (Shields et al., 1998). Although the cuttings need moisture for survival, evidently they lack the arenchymous tissue found in wetland plants grown from seed, and any level of soil moisture leading to oxidation-reduction potential (Eh) less than about 200 mV is extremely detrimental. Ideal conditions for survival and growth involve abundant soil moisture, but well-drained conditions that produce levels of soil Eh > 350 mV.

Willow planting schemes must specify a standard spacing. Generally, cuttings are planted in denser arrays than those typical of mature plants, in order to reduce near-bank velocities to non-erosive levels. Accordingly, only 40 to 50% survival may provide acceptable performance if the spatial distribution of survivors is fairly uniform. Laboratory flume experiments indicate that near-bed velocities and shear stresses within an array of erect, emergent posts will be reduced about 50% by a density in which the average distance between adjacent posts is equivalent to the square root of 20 times the stem diameter (Lopez and Garcia 1997, Wilkerson and Watson 2000). Staggered patterns apparently do not offer any greater reduction than uniformly-arranged rows (Wilkerson and Watson 2000).

Willow Posts and Poles Typical Drawing
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