APPENDIX A – SUPPLEMENTARY INFORMATION FOR THE GIS ASSESSMENT
APPENDIX A – SUPPLEMENTARY INFORMATION FOR THE GIS ASSESSMENT
by M Harrison, A Gibson, A Forster, D Entwisle and G Wildman
Table A.1 – Criteria used to interpret BGS ROCK codes to indicate source material availability.
Score |
Criteria |
---|---|
10 |
|
9 |
|
8 |
|
7 |
|
6 |
|
5 |
|
4 |
This score has been assigned to bedrock lithologies that appear less likely to generate a granular regolith because:
|
3 |
|
2 |
|
1 |
These materials are those which are considered unlikely to be mobilised as a debris flow because
|
Table A.2 – Criteria used to determine the rating of available debris material score from the deceleration data.
Deceleration Range |
Material Score |
---|---|
0.0 to 0.025 |
8 |
0.025 to 1 |
6 |
Table A.3 – Criteria used to interpret BGS ROCK_D codes to indicate hydrogeological influence upon debris flow formation.
Score |
Criteria |
---|---|
10 |
|
9 |
|
8 |
|
7 |
|
6 |
|
5 |
|
4 |
|
3 |
|
2 |
|
1 |
|
0.1 |
|
Table A.4 – Criteria used to interpret CEH Landcover rating for debris flow hazard potential.
Score |
Landcover 2000 Level 1 |
Landcover 2000 Level 2 |
Landcover 2000 Level 3 |
CEH |
Comments |
---|---|---|---|---|---|
1 |
Sea/estuary |
Sea/estuary |
Sea, estuary |
22.1 |
Not applicable - effect neutral |
1 |
Water (inland) |
Water (inland) |
Water (inland) |
13.1 |
Not applicable - effect neutral |
1 |
Littoral rock and sediment |
Littoral rock |
Rock and rock with algae |
20.1 |
Bare coastal slope may promote debris flows otherwise not applicable |
1 |
Littoral sediment |
Mud, sand and sand with algae |
21.1 |
Not applicable - effect neutral |
|
1 |
Saltmarsh |
Saltmarsh (Grazed/ungrazed) |
21.2 |
Not applicable - effect neutral |
|
1 |
Supra-littoral rock and sediment |
Supra-littoral rock |
Rock |
18.1 |
Bare coastal slope may promote debris flows otherwise not applicable |
1 |
Supra littoral sediment |
Shingle, vegetated shingle, dune, dune scrub |
19.1 |
Bare coastal slope may promote debris flows otherwise not applicable |
|
1 |
Bog |
Bog |
Bog: shrub, grass/shrub, grass/herb Peat >0.5 m. |
12.1 |
Not applicable separate assessment |
0.85 |
Dwarf shrub heath |
Dwarf shrub heath |
Dwarf shrub heath (ericaceous/gorse) Peat <0.5 m thick |
10.1 |
Some reinforcement by shrubs, better than grass. |
0.9 |
Open shrub heath |
Open shrub heath (ericaceous/gorse) |
10.2 |
Some reinforcement by shrubs, better than grass. |
|
0.9 |
Montane habitats |
Montane habitats |
Montane vegetation |
15.1 |
Mixed, reinforcement depends on vegetation type - better than bare ground. |
0.7 |
Broad-leaved/mixed woodland |
Broad-leaved/mixed woodland |
Scrub, open birch and deciduous mixed, broadleaved evergreen, yew |
1.1 |
Good stabilising effect through root reinforcement and soil moisture demands |
0.7 |
Coniferous woodland |
Coniferous woodland |
Conifers, new plantation and felled |
2.1 |
Good stabilising effect through root reinforcement and soil moisture demands. |
1.2 |
Arable and horticulture |
Cereals |
Barley, maize, oats % wheat |
4.1 |
Bare ground - no root strengthening, loose condition |
1.2 |
Arable horticulture |
Bare, root crops, cropped legumes, linseed, rape, mustard, unknown. |
4.2 |
Bare ground - no root strengthening, loose condition |
|
0.9 |
Non rotational horticulture |
Orchard, ley, set aside |
4.3 |
Mixed, orchards 0.75 but ley and set aside 0.9. Will be mostly ley and setaside |
|
0.95 |
Improved grassland |
Improved grassland |
Intensive grazing, hay/silage cut, grazing marsh |
5.1 |
Slight reinforcement - better than bare ground. |
0.9 |
Setaside grass |
Grass set aside |
5.2 |
Some reinforcement - better than bare ground. |
|
0.9 |
Neutral grassland |
Rough grass |
Rough grass |
6.1 |
Some reinforcement - better than bare ground. |
0.9 |
Managed neutral grass |
Grass (neutral/improved) |
6.2 |
Some reinforcement - better than bare ground. |
|
0.9 |
Calcareous grassland |
Calcareous grass |
Calcareous (managed, rough) |
7.1 |
Some reinforcement - better than bare ground. |
0.9 |
Acid grassland |
Acid grass |
Acid |
8.1 |
Some reinforcement - better than bare ground. |
0.9 |
Acid with Juncus |
8.1 |
Some reinforcement - better than bare ground. |
||
0.9 |
Acid Nardus/Festuca/Molinia |
8.1 |
Some reinforcement - better than bare ground. |
||
0.85 |
Bracken |
Bracken |
Bracken |
9.1 |
Stoloniferous roots reinforce ground. |
1 |
Fen, marsh, swamp |
Fen, marsh, swamp |
Swamp, fen/marsh, fen willow |
11.1 |
Not applicable separate assessment |
1.1 |
Built up areas, gardens |
Suburban/rural developed |
Suburban/rural developed |
17.1 |
General infiltration impeded but potential for focused drainage |
1.1 |
Continuous Urban |
Urban residential/commercial |
17.2 |
General infiltration impeded but potential for focused drainage |
|
1.1 |
Inland bare ground |
Inland bare ground |
Despoiled/semi-natural |
16.1 |
Bare ground - no root strengthening |
Table A.5 – Algorithm for generation of flat areas above roads
Table A.6 – Criteria used to assess slope angle as part of debris flow hazard assessment.
Score |
Slope Angle (degrees) |
|
---|---|---|
0.5 |
0-7 |
Generally stable and only influencing the run-out characteristics of a debris flow. |
1 |
8 - 15 |
Slopes within this range that occurred between a road and an area of debris flow hazard were likely to maintain the movement of the debris flow and facilitate its impact on the road although it was unlikely to be sufficiently steep to allow the initiation of a debris flow within it. |
6 |
16 - 30 |
It appears that debris flows may be initiated on slopes within this range but it would be equally likely that additional material would be incorporated within this zone. |
9 |
31 – 45 |
This slope range is considered the most likely to initiate debris flows based on the experience of the working group. This would appear to be sensible in that the peak angle of shearing resistance of dry granular material might be expected to be in this range (BS8002:1994). |
10 |
Slope > 45 |
It is logical that slopes in the >450 class should have a factor or weighting greater than the 31- 45 class in recognition of the increased driving force associated with the increase in the down slope component of shear stress. |
Table A.7 – Weightings for the assessed factors. Min, Max, Range and Mean values given before weighting.
Factor |
Weighting |
Maximum Value |
Minimum Value |
Range |
Mean |
---|---|---|---|---|---|
Lithology |
x 1 |
10 |
1 |
9 |
6.68 |
Water conditions |
x 1 |
10 |
0.1 |
9.9 |
4.33 |
Vegetation |
x 0.75 |
1.2 |
0 |
1.2 |
0.92 |
Stream channel |
x 0.75 |
10 |
0 |
10 |
0.88 |
Slope angle |
x 1.25 |
10 |
0.1 |
9.9 |
2.08 |
Table A.8 – Class values for final data.
Class |
Value |
---|---|
A |
0-12.0 |
B |
12.1-15.0 |
C |
15.1-16.5 |
D |
16.6-18.0 |
E |
>18.1 |
Table A.9 – Shortened Field names for statistics calculated from the landslide data against the trunk road network.
Group of statistics calculated |
Number of points along section (only valid for trunk road network) |
POINT_NO |
X-coordinate of start point of road section |
START_X |
|
Y-coordinate of start point of road section |
START_Y |
|
X-coordinate of end point of road section |
END_X |
|
Y-coordinate of end point of road section |
END_Y |
|
Length of section |
S_LENGTH |
|
Highest point along section |
S_HIGH |
|
Lowest point along section |
S_LOW |
|
Average height along section |
S_MEAN |
|
Group of statistics calculated |
Number of catchments intersected |
C_COUNT |
Total catchment area (m2) intersected |
C_AREA |
|
Highest point in catchment |
C_HIGH |
|
Lowest point in catchment |
C_LOW |
|
Average height in catchment |
C_MEAN |
|
Maximum slope |
C_MAX_SLOPE |
|
Minimum slope |
C_MIN_SLOPE |
|
Average slope |
C_AVE_SLOPE |
|
Group of statistics calculated |
Maximum debris flow hazard score |
H_MAX |
Maximum debris flow hazard class |
H_MAX_CLASS |
|
Minimum debris flow hazard score |
H_MIN |
|
Minimum debris flow hazard class |
H_MIN_CLASS |
|
Average debris flow hazard score |
H_MEAN |
|
Average debris flow hazard class |
H_MEAN_CLASS |
|
Group of statistics calculated |
Maximum lithology score |
H_LITH_MAX |
Minimum lithology score |
H_LITH_MIN |
|
Average lithology score |
H_LITH_MEAN |
|
Maximum water conditions score |
H_WATER_MAX |
|
Minimum water conditions score |
H_WATER_MIN |
|
Average water conditions score |
H_WATER_MEAN |
|
Maximum vegetation score |
H_VEG_MAX |
|
Minimum vegetation score |
H_VEG_MIN |
|
Average vegetation score |
H_VEG_MEAN |
|
Maximum stream channel score |
H_STREAM_MAX |
|
Minimum stream channel score |
H_STREAM_MIN |
|
Average stream channel score |
H_STREAM_MEAN |
|
Maximum slope angle score |
H_SLOPE_MAX |
|
Minimum slope angle score |
H_SLOPE_MIN |
|
Average slope angle score |
H_SLOPE_MEAN |
Figure A.1 - Methodology Flowchart.