| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2005: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2004: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
For evaluating the impact of grassland on the water resource and offering the suggestion of appropriate watershed management, the hydro-meteorological and landuse investigations were conducted on the small water-impounding watershed in the Philippines. The study area, which is in the barangay of Villa Boado, Talugtog, Nueva Ecija of Central Luzon, belongs to Type 1 Climate (Coronas Classification) characterized by pronounced dry and wet seasons, and has a small dam for the agricultural products during the dry season. However the agricultural water use according to plan has not been succeeded since 1999 when the dam was constructed. One of the reasons is considered that the watershed is covered with cogon grasses (Imperata cylindrica). Therefore, for clarifying the impact of cogonal land cover on the water resource, the property of hydrological processes in this watershed was studied through the comparison with that of woody plant (Leucaena leucocephala).
From the result of rainfall obse
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rvations on the open field and under the grass, it was clarified that the interception of rainfall by cogon reaches 22 %. The net rainfall, which is defined as the rainfall reaching the ground over the watershed, was calculated by using the rate of interception and the distribution of land cover. The value indicates 81 % compared with the rainfall in the open field, and twice as much as the volume of pondage. However the storing rate on the net rainfall is also suggested to be overestimated, since there is the possibility that the rainfall gauge used in this study tends to observe the rainfall with a 20 % of underestimation in comparison with the standard rainfall gauge in the Philippines.
The investigation of soil moisture pointed out that the root system of cogon had a strong influence on the flow of soil water. The formation of dry condition in the soil moisture under the cogonal land cover depends on the depth of root development. Additionally, the soil investigation showed that a swelling soil was expanded over the watershed, and that the soil was also the element of regulation on the flow of soil water. Less
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