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WINTER STORM MUDSLIDE AWARENESS Mudslides or debris avalanches, combined with trees felled by high winds, and saturated ground have resulted in power outages, closed roads, damaged property, and loss of life. Most rainstorms are of such low intensity that they do not trigger debris avalanches. However, when the ground is already saturated from previous rain, even relatively short high-intensity rainstorms may cause debris avalanches in areas of steep terrain and lose soil. Normally, the source of excess water is intense rainfall, although broken water pipes or misdirected runoff concentrated on roads, roofs, or large paved areas can contribute to debris avalanches. Debris flows are known to start on slopes as low as 15 degrees, but more dangerous, faster moving flows are more likely to develop on steeper slopes and follow natural stream courses. Assume all drainage in hilly or mountainous areas is capable of carrying debris flows, especially if relatively loose, sandy soils are present in the watershed when soil is saturated. Areas that have been burned over by large fires are especially vulnerable. The following indications of potential damaging debris avalanches include:		New cracks or widening of cracks in foundations, concrete or tile floors, retaining walls, driveways, roads, or soil parallel to the contours of a hill above and below a structure.
	Excessive water seepage from the toe of a cut, such as behind a structure.
	Doors or windows stick or jam for the first time, and new cracks appear in plaster or brickwork.
	Stairs, fences, walls, utility pools, or trees that start to lean, or trees that have been previously leaning and are now straight.
	Any drainage that is blocked by small soil slumps. Ponding can occur behind the slumps, and when saturation occurs, the entire system can move and create a debris avalanche.
	Bare ground that shows signs of erosion, movement or bulging.

If these conditions are observed, homeowners are advised to contact a civil, soils, or geo-technical engineer to ascertain the debris (mud) avalanche potential, in order to take appropriate action. Homeowners whose property is protected by retaining walls and drainage systems are advised to:

Ensure that interceptor drains are clear and free of blockage.

Check retaining walls drainage outlets, and ensure that they are flowing freely.

Blocked drains should be annually flushed from the "clear-out" or rodded out.

Check retaining walls to ensure that they are not sagging or leaning away from the hillside.

For additional information, contact your local Planning and Building Inspection Department, or the Office of Emergency Services at 796-1900.

DEBRIS AVALANCHES POSE HAZARDS THAT ARE OFTEN OVERLOOKED.

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Mudslides - Debris Avalanches

WINTER STORM MUDSLIDE AWARENESS