**4.7 Rainfall simulation**

In this study, a laboratory test was performed using the Artificial Rainfall Simulation Apparatus at the Hydraulic Laboratory of the Flood Control and Sabo Engineering Center (FCSEC) of DPWH to assess the effectiveness of Hydroseeding with Coconet in erosion control and water run-off. The rainfall simulator is capable of creating uniform drops and desired intensities. This is used to apply uniform rain over the entire area of the specimen. In this study the researchers will use the worst rainfall rate which is 120 mm/hr. The rainfall simulator used is shown in Fig. 6.

The FCSEC artificial rainfall simulator is a device with adjustable /changeable nozzle for rainfall intensity variation. The said simulator has a dimension of 10m x 5m x 10m that produces drops simulating rainfall intensity of up to 235mm/hr. Raindrop sizes are representative of typical heavy rains/storms in the country. The spatial distribution of rain is essentially uniform, and the control of application rates is within the accuracy requirement of most experimental protocols.

For the rainfall simulation on the study's test specimen, the rainfall applied was at 120mm/hour for every 10 minutes. The sediment and water runoff from the test box were collected.

Combined Hydroseeding and Coconet Reinforcement for Soil Erosion Control 221

Fig. 8. Sediment Concentration (g/L) for Hydroseeding with Coconet Reinforcemen

It is shown that in each three trial boxes that were first used for bare soil specimen and the vegetated specimen, the first ten (10) minutes deposit higher sediment concentration. But, comparing the values obtained between bare soils and soil with hydroseeding and coconet reinforcement, it shows that as expected there is lower sediment concentration in the latter

Table 2 and Figs. 9 and 10 present the sediment yield on bare soil and on soil covered with

Fig. 7. Sediment Concentration (g/L) for Bare Soil

while higher sediment concentration in the former.

combined hydroseeding and coconet.

Fig. 6. Artificial Rainfall Simulation Apparatus at the Hydraulic Laboratory of the Flood Control and Sabo Engineering Center (FCSEC) of the Department of Public Works and Highways (DPWH).
