Bio-Engineering tips

1. Following are the Bio engineering notes that I have prepared during execution of works in
different projects of Nepal.

2. Brush Layer:
Woody cuttings (or hardwood cuttings) are laid in lines across the slope, usually following the
contour (to be laid in double layer). The main engineering functions are to catch debris, and to
armour and reinforce the slope. In certain locations, brush layers can be angled to provide a
drainage function.
Sites:
This technique can be used on a wide range of sites up to 45 degree. It is particularly effective on
debris sites, fill slopes and high embankments.
Avoid using the technique on materials that are poorly drained and are subject to high
rates of small-scale slumping.Fascines are appropriate for poorly drained sites.
Materials:
1. Cutting made from woody material that is 6 to 18 months old. They should be 20 to 40mm
in diameter and 450 to 600mm long.When taking the cuttings, cut the top at right angles
to the stem and the bottom at 45 degress to make it clear as to which way it should be
inserted. If possible, take the cuttings the same day that they are planted.
2. Wrap it with jute and water it to keep cuttings moist until planting.
3. For brush layering on gravel fill the embankments, a supply of forest topsoil at the rate of
1 cu.m per 20 meters of layering.
Spacings:
Spacing between brush layers depends on the steepness of the slope. The following spaces
should be used.
Slope Less than 30 degrees 2m interval
Slope 30 to 45 degress 1 m interval

3. Within the brush layers, cuttings should be at 50mm centers. A wider gap than this is acceptable
in gentle slopes, but on steep slopes this spacing is required to give adequate protection.
Construction steps:
1. Using string, mark the lines to be planted, starting 500mm from the base of the slope.
2. Always install brush layers from bottom of the slop, and work upwards.
3. Form a small terrace, with a 20% fall back into the slope. The terrace should be 400mm
wide. If you are brush layering a gravel-filled road embankment you should lay a 50mm
thick layer of soil along this terrace to improve rooting conditions.
4. Lay the 1st
layer of cuttings along the terrace, with a 50mm interval between cuttings.
Leave at least one bud and up to one-third of the cuttings sticking beyond the terrace edge
and the rest inside. The branch growing tips would point towards the outside of the terrace.
5. Lay a 20 mm-thick layer of soil in between the cuttings to provide a loose cushion.
6. Lay a second layer of cuttings on top of this, staggered with the first layer. On a gravel-
filled embankments slope lay an 80mm layer of soil over the cuttings before you do any
backfilling.
7. Partly backfill the terrace with the excavated materials. This should not be more than
50mm thick.
8. Mark a line 1 meter above the first brush layer and set the string for the next layer.
9. Follow steps 3 to 7. As the next terrace is cut always fill the lower branch with the material
excavated from above and compact it reasonable well by gentle foot pressure.

5. Use of Brush Layering into different projects of Nepal.

6. Fig : Use of Brush Layering in Solu-3 Hydropower Project

7. Fig:Use of Brush layering in Narayanghat Mugling Road

8. Fig: Use of Brush layering in Narayanghat Mugling Road

9. Palisades:
A palisade is a fence or wall made from wooden stakes or tree trunks. Palisades were used
historically as a defensive structure. In slope protection, palisades are barriers made from live
wood cuttings or bamboo installed across a slope following the contour in order to trap debris
moving down the slope, to armour and reinforce the slope, and to increase the infiltration rate.
Palisades are used to prevent the extension of deep, narrow gullies and the erosion of V-shaped
rills (Figure 20) by forming a strong barrier which stabilizes the gully floor and traps material
moving downwards (Lammeranner et al. 2005). They are also effective on steep landslide or
debris slopes. Palisades can be used on a wide range of sites with slopes of up to about 60°.
Function:
Woody (or hardwood) cuttings are planted in lines across the slope, usually following the contour.
These form a strong barrier and trap material moving down the slope. In the long term, a small
terrace will develop. The main engineering functions are to catch debris, and to armour and
reinforce the slope. In certain locations, palisades can be angled to give a drainage function.
Sites:
This technique can be used on a wide range of sites up to about 60°. It is particularly effective on
steep landslide debris slopes. Materials that are poorly drained and are subject to high rates of
small-scale slumping should be avoided (Fascines, which may be more appropriate for poorly
drained sites of up to 45°).
Materials:
Cuttings made from woody material that is 6 to 18 months old. They should be 20 to 40 mm in
diameter and 300 to 500mm long. Cut the tops at right angles to the stems and cut the bottom at
45 degree: it is then clear as to which way each cutting should be inserted. If possible, take the
cuttings the same day that they are to be planted. Hessian and water to keep the cuttings moist
until planting.
Spacing:
Spacing between palisades depends on the steepness of the slope. The following spaces should
be used.
Slope less than 30 degree 2 m interval
Slope 30 to 60 degrees 1m interval
Within the palisade lines, cuttings should be at centers of between 30 to 50mm. a wider gap than
this is acceptable on gentle slopes.

11. Construction steps:
1. Trim and clean the site well in advance of the planting operation. Remove irregularities
and loose debris.
2. With string, mark out the lines to be planted.
3. Always start at the top of the slope and work downwards.
4. Using pointed bar, make a hole in the slope that is bigger than the cutting and deep
enough to take at least two thirds of its length.
5. Carefully place the cutting in the hole, so that at least two thirds is buried. Firm the soil
around it, taking care not to damage the bark. Ideally, only one node of the cutting or
about the top 100 mm should protrude from the soil. On steep, unstable sites, however,
a greater protrusion helps to raise the delicate new shoots above the zone of moving
debris, and to catch more debris.
Note: Palisades are not as strong as brush layering.
Figures of using palisades into different projects in Nepal.

12. Fig : Palisades for Solu-3 Hydropower Project

13. Fig: Palisades for Narayanghat Mugling Road

14. Fig: Palisades from Narayanghat-Mugling Road

15. Vertical Grass
plantation
Diagonal Grass
plantation
Random Grass plantation to be used
in combination with jute netting
Grass Planting (Contour/Horizontal)*
*(It can be vertical, diagonal and random also)
Grass Slips (rooted cuttings), rooted stem cuttings or clumps grown from seed are planted in
lines across the slope. They protect the slope with their roots and by providing a surface cover,
reduce the speed of runoff and catch debris, thereby armouring the slope. The main engineering
fucntions are to catch, armour and reinforce.
Horizontal or Contour Grass plantation
Sites:
Almost any slopes less than 65 degrees. This technique is mostly used on dry sites, where
moisture needs to be conserved. It is most widely used on well drained materials wehre increased
infiltration is unlikely to cause problems. On cultivated slopes less than 35 degrees, horizontal
lines planted at intervals across the field can be used to avoid loss of soil and to help conserve
moisture, as a standard soil conservation measure. Planted grass lines at intervals are essential
if cultivation has to be carried out on slopes greater than 35 degrees.

16. Spacing:
Line spacing depends largely on the steepness of the slope.
Within rows: plants at 100mm centres
(except padang and tite nigalo bans,
which should be spaced at 500mm centres.
Row Spacings: Slope<30 degrees; 1000mm
Slope 30-45 degrees: 500mm
Slope >45 degrees: 300mm
Construction Steps:
1. Prepare the site will in advance of planting. Remove all the debris and either remove or fill
in surface irregularities so that there is nowhere for erosion to start. If the site is on backfill
material, it should be thoroughly compacted, preferable when wet.
2. Always start grass planting at the top of the slope and work downwards.
3. Mark out the lines with string, using tape measure and spirit level. Make sure the lines run
exactly as required by the specification along the contour.
4. Spilt grass plants out to give the maximum planting materil. Trim off long roots and cut the
shoots off at about 100mm above ground level. Wrap the plants in damn hessian to keep
them moist until they are planted. Remember that you will need two slips cutting per
drill(planting hole if the grass is a fibrous rooting type (e.g babiyo, kans, khar, phurke etc.)
but only one if it is rhizomatous (e.g. amliso, padang, bans etc), and only one rooted stem
cutting or seedling.
5. With a planting bar, make a hole just big enough for the roots. Place the grass into the
hole, taking care not to tangle the roots or have them curved back to the surface. Fill the
soil in around them, firming it gently with your fingers. Take care to avoid leaving an air
pocket by the roots.
6. If compost or manure are available, scatter a few handfuls around grasses. This is
especially important on very stony sites, where compost or manure can help to improve
early growth. You may have to incorporate it into the surface material to prevent it being
wasted off.
7. If it looks rather dry and there is no prospect of rain for a day or two, consider watering the
plants by hand.
Main Limitations of Horizontal/Contour Plantation:
Contour Grass lines can increase the infiltration rate to the point of liquefaction on poorly drained
materials, particularly on steeply sloping, fine textured debris.

17. Planted Grass Lines: Downslope/Vertical:
Functions:
They protect slope with their roots, provide surface cover and helps
To drain surface water. They do not catch debris. Using this
Technique, a slope is allowed to develop a semi-natural drainage
System, gullying in a controlled way.
Sites:
Almost any slope less than 65 degrees. Mostly on damp sites, where moisture needs to be shed.
It is also most widely used on poorly drained materials where an increase in infiltration can lead
to liquefaction of the soil.
Spacing:
If the site is a newly cut slope, then a simple geometrical pattern can be used. The normal spacing
is as follows:
Within rows: plants at 100mm centres(except) padang and tite nigalo bans, which should be
spaced at 500mm centres)
Row spacings: 500mm
However, if a gully system has already partly developed, then the spacing is defined naturally.
Lines of grass should not be more than 500 mm apart if possible, and, if ridge are bigger, a series
of small lines in a chevron pattern (<<<) is required to protect gaps. Careful supervision is required
on site to ensure that all planted lines follow the direction of natural fall.
Always start grass planting at the top of the slope and work downwards.
Main Limitations:
On impermeable materials, runoff can become damaging. In drier sites, grass plants can suffer
from drought due to the increased drainage. On some weak materials, rills can develop down the
side of the plant line, damaging the grass slips and reducing their growth.

18. Planted Grass lines: Diagonal:
Diagonal grass lines armour and reinforce slopes
effectively, and can also drain and catch material moving
down the slope. This system appears to combine the
best features of both horizontal and vertical planting in the majority of the sites.
Spacing:
If the site is a newly cut slope, then a simple geometrical pattern can be used. The normal spacing
is as follows:
Within rows plants at 100mm centres (expect padang and tite nigalo bans, which should be
spaced at 500mm centers. Row spacing: 500mm.
However, if a gully system has already partly developed, then the spacing is defined naturally.
Lines of grass should not be more than 500mm apart if possible and if ridges are bigger a series
of small lines in a chevron (<<<) or herringbone () formation is required to protect gaps.
Always start grass planting at the top of the slope and work downwards.
Figures showing usage of grass planting in different project of Nepal.
Fig : Grass plantation for Solu-3 Hydropower Project

19. Fig: Grass plantation for Narayanghat Mugling Road

20. Fig: Grass plantation for Narayanghat Mugling Road

21. Grass Seeding
In grass seeding, spread the seeds or grass seed heads liberally over the slope. Ideally, the
whole surface should be very lightly covered in seed material.
Grass seeding armours surfaces effectively, it can be used to create an even cover over all
surfaces. It reinforces slopes after a few years of growth.
This technique gives none of the structural advantages of grass slip planting. Plants take longer
to develop from seed than from slips. Very heavy rain in the days immediately after sowing can
lead to seeds being washed off the slope, or to damage to the very small seedlings.
Function :
Grass is sown directly on to the site. This technique is often used in conjuction with mulching
and jute netting to aid establishment.
Sites:
Almost any bare site with slopes up to 45 degrees. Grass seeding is mostly used on well
drained materials, where increased infiltration doesnot give rise to problems.
Construction steps:
1. Before sowing seeds, removing all irregularities of the site, and clear debris away.
2. Immediately before sowing, scarify the surface of the slope. Provide loose surface into
which the germinating grass seeds can send their roots.
3. Start sowing from the top of the slope and work downwards. Ideally, the whole surface
should be very lightly covered in seed material. An application rate of 25 grammes per
square meter is normal.
4. Cover the seed completely with a layer of mulch, made from cut herbs such as banmara,
or with hessian sheeting. A vegetation mulch is preferable. Wide mesh jute netting

22. (150mm X 500mm mesh size) should be used to hold mulch on to the surface if the
slope is greater than 30 degrees.

23. Shrub and Tree Planting
Shrubs and tree are planted to reinforce and anchor the slope by establishing a community of
lager plants. Its main limitation is that it take about five years to contribute significantly to slope
strengthening.
Sites:
This method can be used without adverse effects on almost any slope up to 30 degrees. Also if
done properly and carefully could be used on slopes between 30 and 45 degrees.it can be sued
on any material and in any site.
Spacings:
Spacing of 1 X 1 meters is necessary, requiring 10,000 plants per hectare. Plants should be
planted in off-set rows unless a different pattern is needed for specific bio-engineering
requirements.
Constructions steps:
1. Remove all debris and any irregularities on the site. Incase of backfill material,
thoroughly compact, preferably when wet.
2. Dig pits of 300mm deep and 300mm dai. When the ground is wet enough to support
reasonable growth, plant the seedlings.
3. Polypot(in which seedlings are provided from nursery) shall be carefully removed, by
slicing it down the side with a razor blade or tear it carefully along the fold. Be careful not
to cut roots.
4. Plant the seedling in the pit, filling the soil carefully around the cylinder of roots and soil
from the polypot. Ensure there are no cavities. Firm the soil all around the seedlings with
gentle foot pressure.
5. If available, mix a few handfuls of well rotted compost with the soil around the roots
when you are backfilling the hole.
6. Remove any weeds around the plant. Add mulch around the seedling, but with a slight
gap so that it doesn’t touch the stem.
Plants and species for shrubs and tree plantation is provided below.

25. CHECK DAM:
Functions:
Check dams are simple physical construction to prevent the downcutting of runoff water in
gullies. They ease the gradient of the gully bed by providing periodic steps of fully strengthened
material. check dams are designed to accept an active pressure if it applied in the future, while
permitting a safe discharge of water (and perhaps debris) via spill way.
Sites:
Any Loose or active gully. In any rill that threatens to enlarge. In general, anywhere on slope
where there is a danger of scour from running water.
By trapping sediment on their upstream side, check dams create a stepped channel bed profile,
thus reducing velocities and channel down cutting, and thereby ultimately halting the progress of
erosion. The principle of check dam spacing is that each check dam is placed at the taper of the
sediment wedge formed behind the check dam down-stream. However, mountain streams are
generally too steep to allow channels to be protected in this way, as this would result in an
excessive number of check dams. Furthermore, the final location of each check dam is
determined more bythe need to find a stable cross-section with strong-points for founding and
keying-in the structure, rather than by hydraulic considerations alone.
Because check dams need to be flexible and free draining they are almost always constructed in
gabion and to heights of up to 4-5m. It is important that their margins are adequately keyed into
channel banks, although it may not be possible to achieve this in channels whose banks are
composed of soil, river deposits or weak rock. Unfortunately, it is usually under these conditions
where check dams are most needed. Where appropriate, bank revetments or side-walls should
be constructed upstream and downstream of each check dam to provide additional support and
to reduce the potential for scour around the sides of the check dam. The strength of a check dam
can be increased by constructing it with an arc shape in plan, its convex side facing upstream.
However, this may tend to concentrate stream flow against vulnerable stream banks before the
sediment wedge has been deposited, or afterwards, if it is later scoured out. Scour and seepage
erosion on the down-stream side can be reduced by constructing a masonry or rip-rap toe apron.
Where scour potential downstream of the structure is severe, larger scale protection works in the
form of gabion or rip rap revetments, masonry sills and cascades can be considered.
If the primary function of a check dam is to reinforce a natural knick point that is being undermined
by erosion, and where foundation conditions are good, check dams can be built of bound
masonry. These are especially useful in places where space is limited, or where the geometry of
the ground is too awkward for a gabion structure. For very small watercourses with low erosion
potential, unbound masonry check dams, or check dams built of logs, may suffice.
Where erosion is already well-advanced, or where foundation conditions are poor, check dam
construction may only be possible with large structures, placed on deep foundations or anchored
into the bedrock at depth. Plans for such structures must be carefully considered in the light of
cost, practicality of construction, probable life of the structure and overall effect.
Practical features:

26. 1. Excavate a foundation in the gully bed until you find a sound layer to build on. The base
of the dam should be at least 660mm thick if it is one meter height; for every additional
metre of ht, add a further 330mm to the width.
2. The ends of the dam should be keyed right into gully sides and should be raised at least
250mm to form a central spillway or notch: this ensures that water coming over the dam
will then run down the middle and not scour the ends.
3. Apron must be provided below the dam to ensure that energy is dissipated and that flow
continues in the centre of the gully below the check dam.
4. If there is a risk of people or animals damaging the top of the dam, or if it is in a gully likely
to take a large flow of water, point the top layer with cement mortar.
5. Once the construction of the check dam is completed, backfill behind the wings and sides
and compact the fill thoroughly.

27. Fig: Showing small check dam being effective even in small gullies.
Typical Drawing from Overseas road note 16:

29. Check dam design for Rasuwa district: