Slope Toe Drainage Control

Many developed properties on Puget Sound have some form of shore protection (bulkheads, alternative soft protection, etc.) on the beach or at the toe of the slope. These structures have earth pressures which try to slide the construction forward and/or overturn them. Consequently, it is critical that adequate drainage control is placed behind these structures to reduce water pressure buildup and water piping failures.

Water collected from upslope areas should not be introduced into soils behind structures. Impermeable walls have more potential problems than permeable systems such as revetments and biotechnical protection systems. Should marine waters also flood backfill behind these structures, the drainage control system must be able to quickly drain the material to prevent potential failures. Providing excess drainage capacity and weep holes in walls is very important to the long-term performance of coastal structures.

Tightlines that extend down a slope and end near marine waters, should have an erosion prevention device that slows and spreads the collected water along the area above the beach without eroding beach sediments. Manholes, rip rap aprons, rock spillways, and rock channels are commonly used for different slope situations to dissipate flow energy. The discharge force of water leaving a pipe is high for smaller pipes so it is important to anchor or encase the pipe with concrete and/or large rock.


Shoreline areas tend to be dynamic and change configuration constantly from soil creeping down the slope, from landslides, and from coastal erosion. Consequently, drainage control must be flexible enough to adapt to these continuing changes. Must be careful working at the toe of unstable slopes.


Helps reduce piping of fine-grained soil away from slope. Reduces static water pressure in slope debris material and in wall backfills.


Can be expensive construction. Work may require slope stability analyses.