End of live pole drain. There is not a lot to see here since most of the structure has been covered with backfill. To view it prior to placement of backfill, see the photo below right.
The purpose of live pole drains is to provide stability where excess moisture has created instability. In its simplest form a drain is composed of a bundle of cuttings placed horizontally, similar to live fascines. However the drain is oriented quite differently, as it runs directly downslope rather than along (or slightly off) the contour. As the name implies the function of the structure is to facilitate the movement of water off the slope. By locating it along a low drainage, the water flows where gravity naturally takes it. But the vegetation slows the speed at which the water can move, reducing erosion, and preventing gully formation.
It is important on wet sites to not reduce the flow of surface water too much. Doing so could increase infiltration catastrophically, causing slope failure, as noted in the hydrological influences section. The pole drain provides a slow and strong path for water to follow, that gets it off the slope, but at a measure pace.
Live Pole drains can be combined with live fascines and brushlayers to form an overall drainage system on a slope. In this situation the fascines and brushlayers are pitched slightly, rather than running level along the contours of the slope. Instead they direct surface flow into the drain, thereby regulating the movement of water off of the entire area of slope that is under their influence.
Continued: Spilling walls