Drainage and early retaining-wall warning signs

Separate routine observation from an active hazard

A leaning or cracked wall is not enough to diagnose a landslide, and a neighborhood ECA layer cannot diagnose one either. Wall distress can involve settlement, inadequate drainage, deterioration, local earth pressure, construction defects, impact, or movement of the larger slope. Some landslides show warning signs and others occur suddenly. Treat observations as reasons to obtain qualified evaluation, not as a do-it-yourself failure classification.

If movement appears sudden, material is falling, the ground is opening, utilities are breaking, or a wall supports an occupied structure or public way, stop approaching the area. USGS guidance for a landslide in progress is to leave the area when it is safe and report it to local authorities. Do not stand below the wall to photograph it or attempt to release water by digging into a moving slope.

Sources: [5], [1]

What to observe after prolonged or intense rain

Seattle SDCI Tip 324 recommends inspecting property during or after prolonged rain or an intense storm for surface erosion and deposits of silt, sand, or mud. It also calls for checking downspouts, roof drains, drainage ditches, and street drainage for obstruction; identifying concentrated surface flow entering from adjacent areas; and looking at the top and bottom of steep slopes for saturated soil or ponded water.

From a safe, repeatable viewpoint, record whether water is flowing over the wall, emerging through new locations, ponding above or below it, carrying soil, or bypassing a drain outlet. Photograph the wider grade as well as the face. A close picture of a crack without a reference scale, date, or surrounding drainage path is difficult to compare later.

• Use the same camera position and include a fixed reference when it is safe.
• Record the date, recent rainfall, and whether the condition changes after the storm.
• Note new leaning, bulging, displaced blocks or stones, widening joints, soil loss, and movement in paving or fences above.
• Do not enter a taped-off, undermined, or actively moving area to improve the photograph.

Sources: [1], [5]

Water is a design load and a discharge question

WSDOT's retaining-wall guidance states that drainage should be provided for walls and that, when drainage cannot be provided, hydrostatic pressure must be included in design. The principle is important: a drain detail is part of the wall system, not an optional landscaping accessory. The correct detail and discharge depend on the wall, soil, groundwater, site, and applicable Seattle requirements.

Seattle's prescriptive rockery detail illustrates the components that may be involved in one specific system: drainage aggregate, a perforated pipe, surface grading away from the rockery, and an approved discharge. It is not a universal detail to copy behind every wall. SDCI also says a side sewer permit is required when drainage behind a wall connects to a side sewer.

Do not redirect a downspout or drain onto a steep slope, adjoining property, or an improvised outlet. USGS warns that concentrated stormwater can saturate slope materials and advises checking local restrictions before piping water to a storm sewer, road ditch, or other drainage network. Ask the designer to show both how water is collected and where it may legally and safely discharge.

Sources: [4], [2], [3], [6]

Possible slope-movement indicators need escalation, not interpretation

USGS lists new cracks or bulges in the ground, new flowing or ponded water, deformed fences, tilting trees or poles, sticking doors or windows, new cracks in structures, broken utilities, and soil pulling away from foundations among possible landslide indicators. No single item proves a landslide, but a new cluster of changes—especially after prolonged rain—warrants prompt professional attention.

For non-emergency evaluation, look for a geotechnical engineer, engineering geologist, or other qualified professional with relevant slope and retaining-wall experience. Share the dated observation record, available plans and permits, drainage changes, and any history of repairs. Avoid excavation at the toe, adding loads above the wall, cutting drainage paths, or dismantling part of the structure before the condition is assessed.

Sources: [5], [6]

What a repair proposal should make explicit

A useful proposal distinguishes investigation from construction. It identifies who evaluates the cause, who designs the repair, what temporary safety measures are assumed, whether permits are included, how water will be managed during construction, the permanent drainage components, the approved discharge point, excavation and soil disposal, access restoration, inspections, and exclusions.

‘Drainage included’ is not enough to compare bids. Ask for the drainage aggregate or drainage product, filter and separation details where specified by the designer, pipe and outlet arrangement, cleanouts or maintenance access if applicable, surface grading, and responsibility for connection approvals. The final design must come from the project documents and authorities—not from this general checklist.

Sources: [2], [1], [4]