Estimaci´ on del potencial ecol´ ogico del embalse

For controlling soil erosion, installation of coconut coir fiber made into geonets such as coconets/mats, cocologs/fascines, cocotwines and coco peat as bioengineering materials is advisable. The following terms are used in this technology.

Coconut Geonets any coconut coir fiber-based placed on sloping ground and embankments to hold the vulnerable soil and permit vegetative growth to control surface erosion and preserve the productivity of the soil.

Coconet coconut coir fiber twine woven into blankets of different density.

Cocolog/Fascine a tubular structure of coconut coir fiber blankets of different diameter filled with coco coirand/or coco peat.

Coco Coir Twine a string made of coconut coir strands twisted together.

Coco Coir Peat a natural and residual materials from coconut coir which serves as soil conditioner.

5.4.3.1 Material (1) Coconut Coir

Coconut coir fiber materials for use in fabrication of coconut geonets shall be a multi-cellular fiber with 12 to 24 microns in diameter and the ratio of length to diameter shall be 35. The fiber shall also be hygroscopic, with moisture content of 10% to 12% at 65% humidity and 22% to 55% at 95% relative humidity.

(2) Coconet and Cocolog/Fascine

The hand-spun coco coir twine that is to be woven into coconut geonets shall have a diameter of 5mm plus or minus 10%. The coco coir twine shall have a tensile strength of not less than 150N. Coconet and cocolog/fascine shall conform to Tables 5.5 and 5.6, respectively.

Table 5.5 Physical properties (Coconet)

Type of Coconet

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Table 5.6 Physical properties (Cocolog) Type of Cocolog/Fascine Diameter (min)

(cm)

Weight (min) (Kg/m)

Cocolog 100 10 2.0

Cocolog 200 20 4.5

Cocolog 300 30 10

Cocolog 400 40 20

Cocolog 500 50 30

Figure 5.23 Coconet (CGN 700)

Figure 5.24 Cocolog/Fascine (CGR 200) (3) Bamboo Stakes

Bamboo stakes shall be mature and shall be 3 to 4 cm. wide and 25 to 30 cm. long.

(4) Live Plants Stakes

Live plant stakes shall be kept moist and installed the same day they were prepared. Live kakawate or equivalent local species maybe used.

Bamboo Stakes Live Plants Stakes Installation

Figure 5.25 Stakes

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(5) Coco Coir Peat (Soil Conditioner)

After the installation of coconut geonets, coco coir peat - soil mixture shall be distributed evenly on the net protected slope. Thumping and raking shall follow to make the mix settle underneath to ensure appropriate soil moisture and nutrients to the grasses and other planting materials.

Figure 5.26 Coco Coir Peat (6) Ropes

Nylon rope or equivalent is used to tie cocologs to the stakes.

Figure 5.27 Ropes

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5.4.3.2 Anchoring (1) Common Soil

The coconets shall be secured to the ground using bamboo pegs. An average of 3 pegs per square meter shall be used to ensure uniform contact and firm hold to the ground.

(2) Compacted Soil

A combination of bamboo pegs and U-shaped wire staples may be used for compacted, hard to penetrate soil. An average of 3 pegs/staples per square meter shall be used to ensure uniform contact of coco-net to the ground surface.

5.4.3.3 Vegetation

(1) Vetiver Grass Hedgerow

Live hedgerow of vetiver grass (or any local suitable species) slips shall be planted on the slopes at 10 to 50 cm. interval depending on the erodibility of the soil, the steepness of the slope and the design water flow. Row distance shall likewise depend on the steepness of the slope and shall range from 1 to 4 m.

(2) Grass cover

Fast growing leguminous creeping grass shall be used on slope surfaces requiring immediate vegetation cover. It shall be applied to the soil at a rate depending on the desired density and the calculated on-site mortality rate of the plants.

(3) Trees

If trees shall be used to stabilize a slope, species that have sturdy, long and deep-penetrating roots shall be selected.

5.4.3.4 Cross Section

Figure 5.28 Typical Cross Sections for Bio-Engineering Works

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5.4.3.5 Installation Procedure (1) Site Preparation

- The area shall be graded and sloped to the approved design.

- Any water runoff control such as diversions, berms or dikes shall be completed prior to installation.

- The face of the slope shall be smoothened and rocks, clods, vegetation (deemed detrimental to the erosion control system to be installed), and other obstructions shall be removed to ensure complete contact of the net with the soil.

- In most cases, existing vegetation shall be retained, but shall be trimmed down to facilitate the installation of the coconet.

(2) Laying of Nets

- Installation shall begin at the top of the slope with the net laid down and securely anchored 1 m. from the edge.

- The net shall be unrolled downslope in the direction of the water flow.

- The edges of adjacent rolls of coir fiber nets must be spliced together using coir fiber twine ropes.

- The coconet shall be laid loosely-not stretched- on the ground. Direct contact with the soil shall be maintained at all times.

Figure 5.29 Site Preparation Figure 5.30 Laying of Nets (3) Anchoring

The coir fiber net shall be secured to the ground using bamboo pegs 25 to 30 cm long. An average of 3 pegs per square meter shall be used to ensure uniform contact of net to the ground surface. For loose soils, longer pegs may be used to have sufficient ground penetration to resist pullout. U-shaped wire staples may be used for compacted, hard to penetrate soil.

(4) Sewing

There are many ways of connecting the nets together to cover the slopes but sewing

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them together is the best and most economical way of installing the nets.

Figure 5.31 Anchoring Figure 5.32 Sewing

5.4.3.6 Planting of Grass Cover

Fast growing leguminous creeping/twining grasses shall be used for slope faces requiring immediate vegetative cover. They are either hydroseeded or sowed by hand.

The dominant grass in the surrounding areas can be carefully uprooted and planted on the slopes after the nets have been installed.

Figure 5.33 Hydroseeding 5.4.3.7 Watering

Watering is very important especially during the early days of germination of seeds, when the roots are not established yet or when newly replanted. Upon seed germination, daily watering is necessary for a month and fifteen days for transplanted grass.