ENIVRONMENT ASIA

Volume 11, No. 03, Month SEPTEMBER, Year 2018, Pages 45 - 64

Influence of rainfall distortion on hydrograph lag time of naturally full-covered hill-evergreen forest watershed in mountainous land

Kasem Chunkao, Nipon Tangtham, Samakkee Boonyawat, Pricha Dhammanonda, Somnimitr Pukngam, Piyapong Tongdeenok, Yutthaphong Kheereemangkla, Chatri Nimpee, Kittichai Duangmal, Pavin Wichittrakarn, Noppawan Semvimol and Sakonwan Mokatip

Abstract Download PDF

The research is aimed to study influence of rainfall distortion on hydrograph lag time in three periods of normal climate (1966-1987), transition (1988-2008) and climate change (2009-2015) over the first-order stream watershed covering natural hill-evergreen forest in mountainous land. The results found the total average annual rainfall 2,046.5 mm from the periods of 2,084.1 mm (plus another fog drift 2.3% of annual rainfall) for 1966-1987, 2,021.8 mm for 1988-2008 and 1,993.3 mm for 2009-2,015; falling 155 rainy days; humidity ranging 58.5-89.7%, pan evaporation 3.1 mm/day; average temperature 16.7-23.3 oC with extreme maximum 35 oC and minimum 4.5 oC, and wind speed 5.4-22.6 km/hr. Measuring streamflow was approximately 1,2233 MCM/ km2 which divided to wet flow 57% and dry flow 43%. Accordance with 3-period rainfall of normal climate (1966-1987), transition (1988-2008), and climate change (2009-2015) played vital role in decreasing lag time 18, 13, and 9 hours due to the distortion of rainfall quantity but the first-order stream watershed covering with dense-nature hill-evergreen forest was still functioned on its flow regime without interruption. The abundances of organic matter, clay minerals, high soil porosity, deep soil profile and plant cover over 80% are regulated to rainwater absorption for continuously feeding streamflow all the year, even the driest and wettest years.

Keywords

Watershed hydrology; First-order stream watershed; Hydrograph lag time; Soil water

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