Terrain assessment, drainage and erosion - Geotechnical Investigation and Design Tables - page 187

Terrain assessment, drainage and erosion

15.1 Terrain evaluation
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Terrain evaluation is particularly useful in linear developments and large projects.

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This involves an extensive desktop study of aerial photos, geology maps, topog-
raphy, etc, before any need for extensive ground truthing. Phasing of the study
is important here. Refer Chapter 1 as various corridor/site options are still under
consideration at this stage of the study.

Table 15.1 Terrain evaluation considerations.

Consideration Terrain evaluation Comments

Accuracy of Geology maps The maps are likely to be at different accuracy scales.

data scale Aerial photos using this data in a GIS analysis for example, is likely

Orthophotos to produce inconsistencies in accuracy. A trade off

Development plan between the largest useable scale and some loss of

data accuracy is here made.

Development Grades Construction/Access as well as long term.

Size

Geology Lithology Rock/soil type.

Structure Dip/orientation with respect to proposed slope.

Drainage Surface Hydrology considerations. Also affected by vegetation

Ground and land cover.

Erosion
Catchment area

Slope Transverse batters Affects horizontal resumptions/stability measure

Longitudinal grades required.

Height Above flood levels Affects vertical alignments, which could mean

Cuttings a horizontal alignment shift if significant

cut/fill/stability issues.

Aspect of slope Orientation With respect to development as well as true north.

southern aspect wetter in southern hemisphere
(Greater landslide potential).

Land use Existing Roads, rails, services, and developments.

proposed Environmental considerations. Adjacent affects

considered here.

Vegetation Type, intensity Forested, agricultural, barren.