**1. Introduction**

212 Soil Erosion Studies

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erosion by water: A guide to conservation planning with the revised universal soil loss equation (rusle). United Department of Agriculture (USDA), Agriculture Soil erosion is a worldwide problem that washes away fertile farmlands, slopes of roadway cuts and embankments, produces undesirable deposits in rivers and reservoirs, and at a larger scale result to landslides (Kothyari, 1996 and Thakur, 1996) . Soil is eroded by water and wind (Toy, et.al, 2002). In tropical countries like the Philippines, precipitation is high and erosion by water is the dominant driving force based reported cases. Protection of soil surfaces especially of slopes is needed…

To protect the soil surface from erosion, it should be protected from direct contact with erosive forces. Plant cover helps protect the soil surface and provide supplemental soil stability (Morgan, 2005). Hydroseeding is an innovative method of growing vegetation and is designed for slope protection. In the Philippines, its effective application is showcased in the Subic-Clark-Tarlac Expressway (SCTEX) Project.

Another green technology being used is the application of coconut coirs or coconets. Coconets helped stabilize the slope and improved the growth of vegetation in pilot projects of the Department of Public Works and Highways (DPWH).

Newly planted vegetation on slopes could be easily washed away by heavy downpour of rain. Erosion of the slope and replanting of vegetation would be a costly consequence. Coconets, on the other hand, will show its full potential if coupled with a good growth of vegetation. Artificial vegetation is needed to facilitate the even growth of plants. Attempts of combining coconets with vegetation were done using grass (vetiver grass) and trees (Madre de Cacao and neem tree) (DPWH, 2005).

Limited and very little information about hydroseeding is available since it is newly introduced in the Philippines. Tests to assess this method were only made by private construction companies which makes the data's exclusive only for the company's use.

The use of combined hydroseeding and coconets in slope protection was investigated in this study. The study was aimed to assess the effectiveness of the combined technologies to control soil erosion in a representative slope at different series of tests.

The research involved an outdoor component of the experiment to facilitate growth of vegetation. Transportation of each representative slopes to the laboratory was by means of a forklift to minimize disturbance. To further minimize the disturbance factor, the test boxes were transported carefully. Only one type of soil, degree of slope and the intensity of rainfall were considered. However, results were captured at different times in the entire duration of the rainfall simulation.

Combined Hydroseeding and Coconet Reinforcement for Soil Erosion Control 215

flowing water. Once the growth of vegetation has occurred the function of the coir is over and the vegetation takes over the protection of the soil further. Coconut fiber also promotes the growth of new vegetations by absorbing water and preventing the topsoil from drying out. In the study conducted by Bureau of Research and Standards (BRS) of DPWH, results showed that the method of using Geonets (specifically, coconets) to protect developing vegetation against water and wind erosion have proven to be essential since it provides the soil surface with partial shading, moderation of soil temperatures and moisture retention. These materials are prescribed to initially stabilize the soil but without live plants and trees,

Bioengineering techniques such as the use of hydroseeding and coconets in accelerating vegetation helps control soil erosion and stabilize the soil. With the use coco coir products as slope protection, slope above the road will be prevented from caving in. Thus, damages triggered by soil erosion on infrastructure such as roads and bridges will be prevented if

To represent the slope covered with combined Hydroseeding and coconets, test boxes were constructed sloping at 65 degrees and having a surface area with dimension of 106 cm long by 63 cm wide as shown in Fig. 1. Three (3) trial boxes were constructed. The test boxes were covered with soil. These test boxes covered with soil only were all initially subjected to artificial rainfall simulator for the bare soil tests. After the bare soil tests, the test boxes were covered again with soil and covered with combined hydroseeding and coconets for another three (3) sets of samples. Vegetation was allowed to flourish for 21 days before subjected to

**Test Box** 

the effective erosion control would not be achieved. The benefits of applying

slope protection is present.

**4. Methodology** 

the rainfall simulator.

Fig. 1. Dimensions of the test box.
