Slope Drains (Tightlines)

Slope drains in this website are solid wall pipes which carry collected water down a steep slope gradient without exposing the slope face to soil saturation and channel erosion. These drains are usually combined with some energy dissipating structure at the discharge point such as a rip rap pad (apron) or manhole.

Example of a tightline.


It is critical that the slope drains be anchored properly along the slope face. If pipes are not buried, it is important that along steep bluff faces or along unstable landslide zones you should not have pipe connections which could fail and create serious stability problems. Use a continuous length of pipe in these locations. For situations where the pipe cannot be supported underneath, use smooth interior wall pipe (instead of corrugated wall inside and out) which increases the flow capacity of the pipe and reduces the flow friction on the pipe. Remember using smooth pipe will increase the flow velocity and forces acting on the pipe coupling and bends at the slope toe. Therefore, it is critical to support bends in pipes, anchor pipe lengths, and minimize the number of couplings.

Limitations:

Hard to support pipe along vertical bluff faces. May require special anchoring and flow energy dissipation along length. Erosion gullies can start along pipe trenches if not properly compacted and stabilized.

Advantages:

Conveyance system does not place water on the slope. Good steep slope technique.

Disadvantages:

Piping is commonly undersized. If failures occur the effects on slope stability and erosion control can be rapid and serious. Without proper energy dissipation such as manholes and rip rap aprons at the slope toe, the discharges cause erosion at the slope toe and beach.

Applicability

Compatibility