Description
Lateral walls are also called "guiding walls" (Eisbacher and Clague 1984) or "training walls" (Government of Japan 1984); they are constructed parallel to the desired path of the debris flow to force the debris to travel in a straight path avoiding lateral movement that could be unsafe for a certain area in the debris fan.
Usually, this type of control work should be located downslope of the apex of the debris fan where the slope is higher, and the path of the flow is better known (VanDine, 1996) and far from the deposit area because they only have to mark the path. If deposition occurs, coarse material has to be removed.
Figure 1 Lateral berm plan and oblique view (VanDine,1996)
Design methods
Variables that should be considered for the design are the maximum discharge and the flow depth of the debris close to the control works. With regards to the freeboard above the estimated flow depth, indications in table 1 could be exploited:
|
|
Discharge < 200 m3/s |
200 m3/s < Discharge < 500 m3/s |
|
Freeboard height |
0.6 m |
0.8 m |
Table 1 Government of Japan 1984
Regarding the front of these works, the expert has to consider the design from both stability and flow hydraulics point of view. Concerning the erosion and scour from coarse debris close to the structure, rip-rap, concrete or dimension stone can be used as a form of erosion protection and armouring.
As mentioned before for deflection structures, usually also these structures can be built with concrete, earth or composite materials.
Functional suitability criteria
Type of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 4 | Will be updated soon |
| Topple | 4 | |
| Slide | 2 | |
| Spread | 2 | |
| Flow | 10 | |
Material type |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 8 | Will be updated soon |
| Debris | 9 | |
| Rock | 6 | |
Depth of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 9 | Will be updated soon |
| Shallow (0.5 to 3 m) | 8 | |
| Medium (3 to 8 m) | 3 | |
| Deep (8 to 15 m) | 1 | |
| Very deep (> 15 m) | 0 | |
Rate of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 9 | Will be updated soon |
| Slow | 2 | |
| Very slow | 0 | |
| Extremely slow | 0 | |
Ground water conditions |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 8 | Will be updated soon |
| High | 8 | |
| Low | 6 | |
| Absent | 6 | |
Surface water |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 9 | Will be updated soon |
| Snowmelt | 7 | |
| Localized | 7 | |
| Stream | 6 | |
| Torrent | 6 | |
| River | 4 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 5 | Will be updated soon |
| Feasibility and Manageability | 6 | Will be updated soon |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 5 | Will be updated soon |
| Environmental suitability | 6 | will be updated |
| Economic suitability (cost) | 5 | Will be updated soon |
References
- Debris Basin and Deflection Berm Design for Fire-Related Debris-Flow Mitigation – A. B. Prochaska, P. M. Santi, J. D. Higgins - Environmental & Engineering Geoscience, Vol. XIV, No. 4, November 2008, pp. 297–313
- Debris Flow Control Structures for Forest Engineering - D.F. VanDine 1- Res. Br., BC Min. For., Victoria, BC, Work. Pap, 8, 1996.
- A framework for landslide risk assessment and management - R. Fell, K.K.S. Ho, S. Lacasse, E. Leroi. 2005
- Earth and Earth-Rock Dams - Sherard, J. L., R. J. Woodward, S. F. Gizienski, and W. A. Clevenger. 1963
- Engineering Principles and Practices for Retrofitting Flood Prone Residential Buildings - FEMA 259, Federal Emergency Management Agency. 1995
- Soil Slumps and Debris Flows: Prediction and Protection – R. Hollingsworth, G. S. Kovacs - Environmental and Engineering Geoscience (1981) xviii (1): 17-28.
- Destructive mass movements in high mountains: hazard and management – G. H. Eisbacher, J.J. Clague. Geological Survey of Canada Paper 84-16, Ottawa. 1984
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