Browsing by Author "Loof, R."

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    AGNPS Model Assessment for a Mixed Forested Watershed in Thailand
    (ScienceAsia, 2006) Najim, M.M.M.; Babel, M.S.; Loof, R.
    Watershed modeling, as a tool to identify environmental problems, is becoming more popular. The modeling approach will allow evaluating present scenarios and possible remedial measures and strategies. The present study attempts to verify the suitability of the Agricultural Non-Point Source (AGNPS) pollution model developed for an agricultural watershed, for a mixed forested watershed. The study watershed, Huai Nong Prong in Southeastern Thailand, is a mixed forested watershed with 26% forest, 25% mangrove forests, and 36% agro-forests. Extensive fieldwork was completed to collect data and information needed for the model preparation and application. The study revealed that the AGNPS model produces satisfactory results regarding runoff volume and soluble nitrogen yields for the watershed. The sediment yield prediction is marginal for the selected watershed, partially attributed to the mangroves and the pools in the streams, which act as sediment traps. This suggests that mangroves in the downstream end of the watershed could act as natural wetlands capable of neutralizing or reducing environmental problems created by a watershed. The model, however, could not accurately simulate the peak flows, suggesting the peak flow simulating approach in AGNPS does not suitably predict peak flows from mixed forested watersheds.
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    Assessment of Agricultural NonPoint Source Model for a Watershed in Tropical Environment
    (Journal of Environmental Engineering, 2004) Najim, M.M.M.; Babel, M.S.; Loof, R.
    Very little work on the application of watershed modeling has been done in the tropical climatic conditions of Thailand to explore the nature of environmental problems arising from nonpoint source pollution due to agricultural activities, and to evaluate possible remedial measures and strategies. The present study attempts to verify the suitability of a nonpoint source pollution model, the Agricultural NonPoint Source model, for the Huai Nong Prong watershed in Southeastern Thailand. Extensive fieldwork was carried out to collect data and information needed for the model preparation and application. The study has revealed that simulated runoff volume, sediment, and nutrient yield from the watershed with mixed land use and relatively high slopes match favorably with observed data. For the ten rainfall events simulated, the coefficient of performance, a measure of model efficiency (equal to zero for a perfect match), was 0.09, 0.47, 0.09, and 0.03 for runoff volume, sediment yield, total nitrogen, and total phosphorus, respectively. The model, however, could not accurately simulate peak flow rates, suggesting the need for changes in the modeling approach or governing equations and relationships to calculate peak discharges in a tropical environment.