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=Description of Opportunity= | =Description of Opportunity= | ||
CCAT is in a pressing need to secure a portion of the hill from landslides North-East of the house. There is already a small concrete retaining wall close to the building but it is clearly not sufficient considering the slope and composition of the soil. With the kind of rainfall we are having, soil erosion or small landslides are a | CCAT is in a pressing need to secure a portion of the hill from landslides North-East of the house. There is already a small concrete retaining wall close to the building but it is clearly not sufficient considering the slope and composition of the soil. With the kind of rainfall we are having, soil erosion or small landslides are a threat to some Redwood trees over that hill. In collaboration with Eghan working on rammed earth blocks, I am going to stabilize that slope by reshaping, planting vegetation and/or building a retaining wall with old car tires or another appropriate materials. This work should be done in a timely fashion since it is important to have a secure environment where we feel safe. | ||
=Criteria= | =Criteria= | ||
Revision as of 00:59, 1 May 2008
Background
Moving the CCAT building to a new location has caused new problems related the topography of this new spot. A concrete retaining wall was supposed to be built but it never happened. So CCAT members decided to take the matter into their own hands by trying to resolve the problem using appropriate technologies.
Description of Opportunity
CCAT is in a pressing need to secure a portion of the hill from landslides North-East of the house. There is already a small concrete retaining wall close to the building but it is clearly not sufficient considering the slope and composition of the soil. With the kind of rainfall we are having, soil erosion or small landslides are a threat to some Redwood trees over that hill. In collaboration with Eghan working on rammed earth blocks, I am going to stabilize that slope by reshaping, planting vegetation and/or building a retaining wall with old car tires or another appropriate materials. This work should be done in a timely fashion since it is important to have a secure environment where we feel safe.
Criteria
The criteria used in a future decision matrix are the following (in no particular order):
- cost
- efficiency of construction
- ease of maintenance
- durability
- use of natural materials
- aesthetics
- multi-usage
- security
- ease of deconstruction.
Literature Review
Slope Erosion
Slope erosion is caused mainly by the effect of wind, ice and rain. In the Pacific Northwest, rainfall is the most important factor. [1]
Erosion can be controlled by reducing the runoff water going over the slope and by modifying site conditions. Those properties can include the soil type, the steepness and the size of the slope and the vegetal cover. [1]
The soil type of the hill cannot be modified, except superficially, so we are planning to concentrate our efforts on the profile of the slope, adding some plant cover and using some of the following techniques. The benefits of having a densely planted slop are numerous, the plant with its leaves, reduce the amount of rain touching the ground by absorption and evaporation. The roots help consolidate the hillside and keep soil particles together. [1]
Slope protection will have to be designed in function of the time variable. Some protection is going to be needed from the beginning and up to, hopefully, a long time to come. Using much in the beginning is interesting because its effect is instantaneous and it provide a cover for grass, which is the second element to offer protection. After a longer period shrubs and trees will have to develop new roots and consolidate the earth. [2]
Possible Techniques
Seeding
Seeding is the easiest method and should be used in conjunction with other methods. After the seeds have been put in place, mulch should be put over the ground to protect the future seedlings from wind and water erosion. This technique is good for mild erosion and grass is relatively fast to grow so a shallow root layer is created to combat soil erosion. A diverse mix of native plants ranging from grass to shrubs and trees should be used.[1]
Container Planting
this method is relatively fast, it is at leat faster than waiting for plants of an interesting size to grow from seed. It is considered good practice to group different plants together so the root system can be diverse. Also, if some species are less adapted to the conditions of the hill, the dominant ones will take over. This method is the most expensive.[1]
Live Staking
If hardy woody plants are available, cuttings from those plants can be used as live stakings. 2 to 3 feet long stakes are inserted in the soil and eventually roots will grow and help support the hill. Species should be carefully selected because the stakes need to be taken from a shrub that roots easily.[1]
Contour Wattling
This technique use live staking to support long wattle made of tree branches that are partially inserted in pre-excavated horizontal trenches following contour lines of the slope. This technique is efficient against high runoff water but is material and time consuming.[1]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Myers, Ryan D., Myers Biodynamics, Washington (State). Dept. Of Ecology, and Washington (State). Shorelands & Coastal Zone Management Program. Slope stabilization and erosion control using vegetation : a manual of practice for coastal property owners . Olympia, Wash: The Program, 1993.
- ↑ Morgan, R.P.C., and R.J. Rickson. Slope stabilization and erosion control, a bioengineering approach. London, New York: E & FN Spon, 1995.