| Author | Asni Molagool |
| Call Number | AIT Thesis no. 32 |
| Subject(s) | Water balance (Hydrology)|xThailand, Northeastern
|
| Note | A thesis submitted in partial fulfillment if the requirements for the degree of Master of Engineering in the SEATO Graduate School of Engineering, Bangkok, Thailand. |
| Publisher | Asian Institute of Technology |
| Abstract | The water balance in North-eastern Thailand is studied herein
from the standpoint of the agriculturist and irrigation engineer who
are interested not only in the magnitude, duration and geographic
variation of the soil moisture deficit but also in the availability
of supply and the losses caused by evaporation, transpiration and
infiltration that precede the application of water to the land.
The balance was calculated for representative localities using
Thornethwaite 1s method for assessing potential evapo-transpiration
which, although hitherto not extensively applied in tropical regions,
yields very reliable results, the assessed runoff agreeing with the
observed runoff. Infiltration during the wet season amounts to
about 20mm/month. Overall 80 percent of the rainfall is returned to
the atmosphere by evapo-transpiration, 7.1/2 percent is lost in infiltration and the remaining 12.1/2 percent runs off into the Mekong
River. There is a soil moisture deficit over the whole area amounting
to 400-700 mm which is worst around Chaiyaphum, least severe in the
extreme northeast where the rainfall is highest. Comparing supply
and demand it is evident that no more than 10-15 percent of the
North-east can be irrigated for year-round crop production without
bringing in additional water from the Mekong,
As an aid in planning and designing irrigation works correlations
were established between the comparatively wide-spread Piche atmometer
and the little-used U.S. Weather Bureau Class A evaporimeter, using a
special statistical technique due to Gumbel - the circular normal
distribution - for smoothing the observations, which for the most
part covered no more than a year or two.
Lake evaporation was assessed from climatic elements by means
of the basic equation and a nomograph derived in the recent tests at
L. Hefner in the United States. The comparison between assessed and
observed evaporation at thirty-four irrigation tanks scattered throughout the region was excellent; all big discrepancies could be accounted
for. In the river valleys in which irrigation tanks are usually'constructed infiltration seldom exceeds 5 mm/month.
Monthly and annual lake/Class A pan ratios were calculated on the
assumption that the climalogically-assessed lake evaporation was the
true evaporation. The annual pan coefficient was found to vary with
locality between 0.61 and 0.96; the average is 0.72. Seasonally
there is very little difference in lake/pan ratios |
| Year | 1962 |
| Type | Thesis |
| School | Student Research Before 1979 |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Thesis (Year <=1979) |
| Degree | A thesis submitted in partial fulfillment if the requirements for the degree of Master of Engineering in the SEATO Graduate School of Engineering, Bangkok, Thailand. |