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WHAT DO THEY HAVE IN COMMON ? THE GREAT WALL OF CHINA - SEATTLE HOME OWNERS THE FARMERS OF THE SLOPES OF THE HIMALAYANS AND EAST INDIA
SEATTLE LANDSCAPE COMPANY
THEY HAVE IN COMMON the need to protect their slopes and keep their soil from moving downhill., either to protect from attack, to create level ground, to protect from erosion, or to protect from loss of their homes from mudslides and debris avalanches. For 12 years A & J Retaining Walls
division of Seattle Landscape Company has been protecting King county real
estate with the completion of 1000 construction projects involving: 99,000,000 POUNDS OF STONE. That's experience The result has also been tons of satisfied customers And you can become one of those satisfied customers by contacting us by email or call (206) 621-0608 For more solutions continue reading. It is no surprise that you can see the similarity in quality and scale of of work of A & J Retaining Walls. The owners of the company, a family business, are American citizens of East Indian origin with three generations of wall building experience. Just as farmers rely on stone walls to preserve precious top soil, so Seattle relies upon A & J Retaining Walls to preserve their precious Real Estate and anticipate and prevent Mudslide erosion that could lead to condemnation. Sudden "mudslides" gushing down rain-sodden slopes and gullies are widely recognized by geologists as a hazard to human life and property. Most "mudslides" are localized in small gullies, threatening only those buildings in their direct path. They can burst out of the soil on almost any rain-saturated hill when rainfall is heavy enough. Often they occur, without warning, in localities in which they have never been seen before. The slopes in residential communities in King County are especially susceptible to "mudslides" during and immediately after major rainstorms. Those who live down-slope of such an area should be aware of this potential for slope failure that is present until new vegetation rebinds the soil. What Are Debris Avalanches and Debris Flows? Debris avalanches and debris flows (both popularly called "mudslides") are shallow landslides, saturated with water, that travel rapidly down-slope as muddy slurries. The flowing mud carries rocks, bushes, and other debris as it pours down the slopes. A debris avalanche (Figure 1) is a fast-moving debris flow that travels faster than about 10 mph or approximately 25 yards in about 5 seconds. Speeds in excess of 20 mph are not uncommon, and speeds in excess of 100 mph, although rare, do occur.
Figure 1. Sketch of a typical debris avalanche scar and track. Although this figure shows the "zone of deposition" as quite near the source, debris avalanches can travel thousands of feet or, in exceptional cases, miles from the point of origin. Original drawing by Janet K. Smith. What Dangers Are Posed by Debris Avalanches? Debris avalanches pose hazards that are often overlooked. Houses in the path of debris avalanches can be severely damaged or demolished. Persons in these structures can be severely injured or killed. Most rainstorms are of such low intensity that they do not trigger debris avalanches. Some intense storms may trigger only a few debris avalanches. However, when the ground is already saturated from previous rain, even relatively short high-intensity rainstorms may trigger debris avalanches. For example, in January 1982, an intense rainstorm triggered literally tens of thousands of debris avalanches in the San Francisco Bay Area. These 1982 debris avalanches caught people unaware and caused 14 deaths and many injuries and destroyed or damaged several hundred homes and other structures. What Causes Debris Avalanches and Debris Flows? The most common cause of debris avalanches and debris flows is the combination of heavy rainfall, steep slopes, and loose soil. Most fairly steep slopes have enough soil and loose rock for potential landslides. Although "stable" when dry, such slopes can produce local debris flows, often without warning. Normally the source of the excess water is intense rainfall, although broken water pipes or misdirected runoff concentrated by roads, roofs, or large paved areas may trigger, or help to trigger, debris avalanches and debris flows. In King Country, most debris flows occur during wet winters. Where Do Debris Flows and Debris Avalanches Occur? Debris avalanches occur all over the world. They are particularly common in mountainous areas underlain by rocks that produce sandy soils. Debris avalanches have been noted in southern California during at least nine rainy seasons since 1915. They have occurred in northern California during at least 14 rainy seasons since 1905. In Seattle they were significant in 2000. Debris flows are known to start on slopes as low as 15 degrees, but the more dangerous, faster moving flows (debris avalanches) are more likely to develop on steeper slopes. About two-thirds of all debris avalanches start in hollows or troughs at the heads of small drainage courses. Typically, a debris avalanche bursts out of a hillside and flows quickly down-slope, inundating anything in its path. Because the path of a debris flow is controlled by the local topography just like flowing water, debris avalanches and debris flows generally follow stream courses. Slopes burned by range and forest fires are especially susceptible to debris avalanches and debris flows because of the absence of vegetation and roots to bind the soil. The areas directly down slope are especially subject to damage from debris flows. What Can Be Done to Avoid or Reduce the Hazard Posed by Debris Avalanches? To be safe, assume that all drainages in steep, hilly, or mountainous areas are capable of carrying debris flows, especially if relatively loose, sandy soils are present in the watershed. Areas that have been burned by regional fires are especially vulnerable. Avoid building sites at the bottoms and mouths of steep ravines and drainage courses. These areas are the most likely to be inundated by debris flows. The outer "banks" of bends along such ravines also should be avoided because swiftly flowing debris avalanches can "ride up" out of the bottom of the stream channel where it bends. Avoid building on or below steep slopes. In general, the steeper the slope the greater the risk. If these areas must be used, consult with a soils engineer and an engineering geologist. These specialists will be able to evaluate the potential for mudslide problems and give advice on the best way to minimize the risk to life and property. The hazard from debris flows that occurs in modified slope cuts can be decreased by 1) limiting the height and slope of cuts and fills, 2) properly compacting fills and keying them into bedrock, and 3) properly controlling the flow of water onto slopes. If steep cuts or fills occur below the discharge points of runoff water from streets, downspouts, or similar drainage facilities onto a slope, it may be wise to obtain advice from an engineering geologist or erosion control specialist. In some cases, walls can be built to deflect potential mudflows away from or around structures (Figure 2). To be effective, diversion walls must be properly designed and regularly maintained.
Figure 2. Methods to reduce the hazard from debris avalanches include construction of a) deflection walls and b) debris fences. Because of the extreme force of impact associated with debris flows, these and similar structures should be carefully engineered and constructed. The specifics of these designs will vary from site to site.
"Mud Floods" and "Debris Floods" Pose Hazards, Too Residents living directly down slope of mountainous wildfire areas should be aware that, in addition to life-threatening potential debris flows and other forms of mass movement, there is another, perhaps deadlier hazard-- debris flooding or mud flooding at and near the mouths of channels that drain burned-over, ashy slopes. Studies have shown that, in the first year following a wildfire, sediment yields and peak discharges or such streams can increase up to 35-fold. Thus occupants of dwellings near such drainage channels could be endangered by floods that incorporate enormous amounts of debris and mud washed off the burned hillsides. Tips and Clues That May Save Your Life...
Where Can More Information Be Obtained? For general information about debris avalanches and other kinds of landslides, contact your city or county geologist, or any office of the Division of Mines and Geology. For an assessment of the landslide risk to an individual property or home-site, obtain the services of a state-licensed engineering geologist (see the Yellow Pages of the telephone directory). The Division of Mines and Geology does not perform individual site assessments or recommend particular consultants. For more information about the design and construction of debris basins, debris fences, deflection walls, or other protective works, consult your city or county engineer, local flood control agency, or the U.S. Department of Agriculture, Natural Resources Conservation Service. In King County talk to Jess Singh, the owner of A & J Retaining Wall Company at (206) 621-0608 or E-mail him to discuss your needs and schedule an inspection. The Singh Family, has three generations of experience constructing Retaining Walls, Landscape, Walkways, Patios, Mudslide Retaining Walls, Reinforced Walls, Curbs, Side-walks, and Steps using Rocks, slate, paving stone, and materials of all description to customer specifications.
A & J Retaining Wall Company Seattle Landscape Company 2214 Brier Road Brier, Washington 98036
Washington State Contractors License #AJRETW*984R7 Tel (425) 778-7737 |
