Annex A - Site assessment pro forma

Complete one pro forma per site. Use additional forms if there are more than three segments on the site

Site location and chainage:
Date of assessment:	Assessor's name:
Sketch of site			[Label segments]
Scale:		Orientation:
Segment number	(1)	(2)	(3)
(a) Erosion and failure processes
(b) Other factors
(c) Slope angle(s)
(d) Slope length
(e) Material drainage
(f) Segment moisture
(g) Altitude

Assessment criteria. See Roadside Bio-engineering Site Handbook, Annex A, pages 127-129 for details

(a)	Erosion and failure processes.	List the erosion or failure processes. State their size and severity.
(b)	Other factors.	List any physical factors that might affect the site. State their size and severity.
(c)	Slope angle(s).	Measure and place in one of 3 classes: <30°, 30 - 45°, or >45°.
(d)	Slope length.	Measure and place in one of 2 classes: <15 metres or >15 metres.
(e)	Material drainage.	Assess and place in one of 2 classes: good or poor.
(f)	Segment moisture.	Assess and place in one of 4 classes: wet, moist, dry or very dry.
(g)	Altitude.	Determine: ± 100 metres. Use an altimeter, map or site drawing.

Figure A1: The main erosion and failure processes

MECHANISM	DESCRIPTION
Erosion on the surface	Rills and small gullies form in weak, unprotected surfaces. Erosion should also be expected on bare or freshly prepared slopes.
Gully erosion	Gullies that are established in the slope continue to develop and grow bigger. Large gullies often have small landslides along the sides.
Planar sliding (translational landslide or debris slide)	Mass slope failure on a shallow slip plane parallel to the surface. This is the most common type of landslide, slip or debris fall. The plane of failure is usually visible but may not be straight, depending on site conditions. It may occur on any scale.
Shear failure (rotational landslide)	Mass slope failure on a deep, curved slip plane. Many small, deep landslides are the result of this process. Large areas of subsidence may also be due to these.
Slumping or flow of material when very wet	Slumping or flow where material is poorly drained or has low cohesion between particles and liquefaction is reached. These sometimes appear afterwards like planar slides, but are due to flow rather than sliding. The resulting debris normally has a rounded profile.
Debris fall or collapse	Collapse due to failure of the supporting material. This normally takes the form of a rock fall where a weaker band of material has eroded to undermine a harder band above. These are very common in mixed Churia strata.
Debris flow	In gullies and small, steep river channels (bed gradient usually more than 15°), debris flows can occur following intensive rain storms. This takes the form of a rapid but viscous flow of liquefied mud and debris.

(a) Erosion and failure processes

A number of erosion and failure processes are to be found. The types of erosion and slope failure found in Nepal are given in Figure A1. All sites have a combination of these mechanisms at work on them. During site assessment, you should check for these.

Figure A2: The main physical factors affecting slopes

POTENTIAL FACTOR	DESCRIPTION
Fault lines	Small fault lines may cause differential erosion in parts of the site.
Springs	There may be seasonal springs within the site, which cause localised problems of drainage or slumping.
Slip planes	The main plane of failure may not be the only one. Many sites have secondary, smaller slip planes additional to the main failure mechanism
Large gullies	Large gullies nearby may erode backwards and damage the site. Alternatively, they may discharge on to the site, causing deposition there.
Landslides	Nearby landslides may extend headwards or sideways, or may supply debris on to the site.
River flooding	A large river below the site may flood badly, damaging the site by either erosion or deposition, or a combination of both.
River cutting	Rivers below the site may move in floods, undercutting the toe of the site.
Catchments	If there is an extended catchment area above the site, it could lead to a large discharge, which causes bad damage by erosion or deposition.
Drain discharge	The discharge of drainage water must be safeguarded to avoid causing erosion or mass failures. Poorly sited or inadequately protected discharge points can cause severe problems.
Khet and kulos	Khet (rice paddy) land or a kulo (irrigation leat) above a site usually means a large volume of water infiltrating into the slope, with a greater potential for failure or large-scale erosion.
Construction activities	Construction activities on or near the site may lead to undermining through excavations, or surcharging through spoil disposal in the wrong places.

(b) Other factors

In addition to erosion and failure mechanisms, other factors may affect the site. Some are internal (e.g. springs) while others are external (e.g. river undercutting). During site assessment, you must check for signs of any of the potential damaging factors listed in Figure A2.

(c) Slope angle(s)

Measure the average slope angle of the slope segment and place it in one of three classes:

< 30º,
30 - 45°, or
> 45°.

If there is more than one dominant slope, record all main slope angles.

Figure

(d) Slope length

Measure the average length of the slope segment and place it in one of two classes:

< 15 metres or
> 15 metres.

Figure A3: Common features indicating soil drainage characteristics

MATERIAL DRAINAGE CHARACTERISTICS	TENDENCY TOWARDS GOOD DRAINAGE	TENDENCY TOWARDS POOR DRAINAGE
Overall drainage	Freely draining material; dries quickly after rain storms	Slowly draining material; tends to remain wet for long periods after rain; behaves like firm dahi
Soil particle size	Coarse textures; loams and sandy soils	Fine textures; clays and silts
Porosity	Large inter-connecting pores	Small pores
Material types	Stony colluvial debris; fragmented rock; sandy and gravelly river deposits	Residual soils of fine texture; debris from mud flows, slumps, etc. rato mato
Slope types	Fill slopes; cut slopes in stony debris (colluvium)	Cut slopes in original consolidated ground

(e) Material drainage

Assess and place in one of two classes: good or poor (see Figure A3).

Figure A4: Environmental factors determining site moisture

SITE MOISTURE FACTOR	TENDENCY TOWARDS DAMP SITES	TENDENCY TOWARDS DRY SITES
Aspect	Facing N, NW, NE and E	Facing S, SW, SE and W
Altitude	Above 1500 metres; particularly above 1800 metres	Below 1500 metres; deep river valleys surrounded by ridges
Topographical location	Gullies; lower slopes; moisture accumulation and seepage areas	Upper slopes; spurs and ridges; steep rocky slopes
Regional rain effects	Eastern Nepal in general; the southern flanks of the Annapurna Himal	Most of Mid Western and Far Western Nepal
Rain shadow effect	Sides of major ridges exposed to the monsoon rain-bearing wind	Deep inner valleys; slopes sheltered from the monsoon by higher ridges to the south
Stoniness and soil moisture holding capacity	Few stones; deep loamy* and silty soils	Materials with a high percentage volume of stones; sandy soils and gravels
Winds	Sites not exposed to winds	Large river valleys and the Terai
Dominant vegetation	e.g. utis, katus, chilaune, amliso, nigalo, bans, lali gurans	e.g. khayer, babiyo, khar, dhanyero, salla, imili, kettuke

* Loam is the name given to a soil with moderate amounts of sand, silt and clay, and which is therefore intermediate in texture and best for plant growth.

(f) Segment moisture

Assess and place in one of four classes:

Wet:	permanently damp sites (e.g. north-facing gully sites).
Moist:	sites that are reasonably well shaded or moist for some other reason.
Dry:	generally dry sites.
Very dry:	sites that are very dry; these are usually quite hot as well (e.g. south-facing cut slopes at low altitudes).

See Figure A4.

(g) Altitude

Determine: ±100 metres. Use an altimeter, map or site drawing.