Terrain 3

[Mapping and Assessing Terrain Stability Guidebook Table of Contents]

Appendix 3. Example classification: Soil erosion potential

Class

Rating

Example criteria

Management implications

VL

Very low

Blocky colluvial deposits

Terrain dominated by competent bedrock

No or only very minor surface erosion.

L

Low

Morainal veneers; most rubbly colluvial deposits with high coarse fragment content

Expect minor erosion of fines in ditch lines and disturbed soils.

M

Moderate

Morainal blankets (depends on texture and coarse fragment content; varies across the province)

Glaciofluvial gravels

Soft, friable bedrock

Expect moderate erosion when water is channeled down road surfaces or ditches.

H

High

Some morainal blankets steeper than 60%, or steeper than 30% if gullied or poorly drained (depends on texture and coarse fragment content; varies across the province)

Fine textured lacustrine (silts & clays), glaciolacustrine, glaciomarine, glaciofluvial or aeolian silts, slopes less than 15%

Glaciofluvial or fluvial sands with low bulk density, slopes less than 30%

Colluvial deposits derived from the above materials with the same slope or moisture criteria

Colluvium derived from soft, friable rock (e.g., soft phyllites, some pyroclastics), steeper than 60% or steeper than 30% if gullied

Significant erosion problems can be created when water is channeled onto or over exposed soil on these sites.

VH

Very high

Fine textured lacustrine (silts & clays), glaciolacustrine, glaciomarine, glaciofluvial or aeolian silts, slopes steeper than 15%, or gullied or poorly drained.

Glaciofluvial or fluvial sands with low bulk density, steeper than 30% or gullied or poorly drained

Peat, organic soils or tufa on sloping ground

Colluvial deposits derived from the above materials with the same slope or moisture criteria

Severe surface and gully erosion problems can be created when water is channeled onto or over these sites.

^aThis is an example classification only. Modifications will be necessary to suit local conditions.

Class	Rating	Example criteria	Management implications
VL	Very low	Blocky colluvial deposits Terrain dominated by competent bedrock	No or only very minor surface erosion.
L	Low	Morainal veneers; most rubbly colluvial deposits with high coarse fragment content	Expect minor erosion of fines in ditch lines and disturbed soils.
M	Moderate	Morainal blankets (depends on texture and coarse fragment content; varies across the province) Glaciofluvial gravels Soft, friable bedrock	Expect moderate erosion when water is channeled down road surfaces or ditches.
H	High	Some morainal blankets steeper than 60%, or steeper than 30% if gullied or poorly drained (depends on texture and coarse fragment content; varies across the province) Fine textured lacustrine (silts & clays), glaciolacustrine, glaciomarine, glaciofluvial or aeolian silts, slopes less than 15% Glaciofluvial or fluvial sands with low bulk density, slopes less than 30% Colluvial deposits derived from the above materials with the same slope or moisture criteria Colluvium derived from soft, friable rock (e.g., soft phyllites, some pyroclastics), steeper than 60% or steeper than 30% if gullied	Significant erosion problems can be created when water is channeled onto or over exposed soil on these sites.
VH	Very high	Fine textured lacustrine (silts & clays), glaciolacustrine, glaciomarine, glaciofluvial or aeolian silts, slopes steeper than 15%, or gullied or poorly drained. Glaciofluvial or fluvial sands with low bulk density, steeper than 30% or gullied or poorly drained Peat, organic soils or tufa on sloping ground Colluvial deposits derived from the above materials with the same slope or moisture criteria	Severe surface and gully erosion problems can be created when water is channeled onto or over these sites.