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The hilly
highland watershed; Liang tai and Wangpo are subwatrshed of Mae Sakon
Watershed which situate on the right side of the Nan watershed. The
watershed area of Natong, Liang tai and Wangpo is 8.91, 2.07 and 1.88
km2 respectively. These watersheds are located on east side of the East
Phee Pan Nam respectively. These watersheds are located on the east side
of the East Phee Pan Nam Mountain Range. Topography of the area are very
steep in slope due to folding of geological structure. Fractured
sandstone interbedded with shale expose everywhere in the study area.
Moderately deep soil in the area is covered with Mixed Deciduous Forest,
Dry Dipterocarp Forest and Plantation. The alignment of major creeks in
the study area are in the same directions of the major faults of
Thailand. The threshold amount of rainfall that can initiate flow in the
beginning and the ending of wet season of these watershed are 17 mm and
10 mm respectively. Very steep rising limb, sharp peak and slowing
recession are the major characteristics of the hydrographs and unity
hydrograph of the three watersheds. The recession coefficient of Natong,
Liang tai and Wangpo watershed are 0.92, 0.91 and 0.89 respectively.
Mean annual discharge of the watersheds are 2.78, 0.175 and 0.263
million m3 respectively. Specific yields of these watersheds are runoff
and rainfall ratio of 21.9%, 9.8% and 11.7% respectively. The direct
runoff and base flow ratio for each rain storm are 0.74, 1.81 and 2.17
respectively. From the above results implies that the Hilly Lower
Highland Watershed show abrupt rising limb of direct runoff and very
slow recession flow characteristics. The very annual discharge and the
ratio of runoff and rainfall of these watersheds may be caused by the
subdrain leakage due to the fractured rock in the study area.
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