A Study on Hydrological Characteristics, Sediment Transportation and Nutrient Loss in Lang Suan Small Watershed Representative, Chumporn Province   Prapat Jindapol   ABSTRACT         The hydrological characteristics, sediment transportation and nutrient loss on 2 representative watersheds in Chumporn province during 1988 to 1992 were found that Huai To and Huai Khean are in the tropical rainforest, watershed form are rectangular, watershed area were 1.90 and 3.32 km2., slope were 11.70 and 10.84 %, landuse of Huai To were forest 20%; horticulture 60% and crop 20%, Huai Khean has 20% of forest and 80% of horticulture, average rainfall was 1,778.87 mm./year, average runoff were 268.94 and 557.88 mm./year, evapotranspiration were 1,509.93 and 1,220.99 mm./year, discharge coefficient were 0.15 and 0.31 per year, suspended sediment and bed load was 32.96 and 86.77 kg./rai/year and sediment delivery ratio was 3.80 and 7.78 percent/year. The average plant nutrients loss estimation per unit area from Huai To were nitrogen, phosphorus and potassium in form of ammonium sulphate or urea, triple super phosphate and potassium chloride were 0.478 or 0.218, 0.025 and 0.690 kg./rai/year, economic cost were 1.19 or 0.83, 0.19 and 2.83 baht/rai/year respectively. The total loss was 4.21 baht/rai/year. And Huai Khean were 1.209 or 0.552, 0.133 and 1.980 kg./rai/year, or 3.02 or 2.10, 1.03 and 8.12 baht/rai/year respectively. The total loss was 12.17 baht/rai/year.         Keywords : Hydrology , Sediment, Nutrient loss