ABSTRACT
In this research, we analyzed the hydrology and meterology in I-
Lan, surveyed its hydrological
environment, observed groundwater table, did
pumping tests and water quality analysis, interviewed and
researched related data and
concluded with the following
1. The annual mean areal precipitation in I-Lan is 3050.9㎜,
2500-3000㎜ in the plain and
3500㎜ and above in the mountain area. The potential
evapotranspiration is 1011㎜ while actual evapotranspiration is
707.8㎜. The mountain area and the
plain are delineated by the 1000mm contour line.
The annual runoff is 490~520 million cubic meter with runoff
coefficient between 0.76~0.79.
2. There are five alluvial fans to the west of I-Lan Plain and
two to its south, both being the
recharge area for groundwater. The plain delta
mainly consists of fine sand or silt with poor permeability,
forcing groundwater to become
the origins of Derzeko Hsi and Donahan Ho. The
groundwater in I-Lan can be divided into three systems. The
surface water and groundwater are
blocked by the coastal sanddunes ,which is of high
sorting quility and forms fresh water barrier ,reducing sea
water intrusion.
3. The main faults and structures in I-Lan are located to the
sides of the alluvial fans to the
west and to the south. The groundwater systems in
the plain do not connect to those in the mountains. The aquifer
consists mainly of coarse sand and
gravel.Changs in the water tables gerenally are
in proportion to the elevation. The K values of the alluvial
fans as one goes from south to north
,corresponding to the thickness of the gravel.
4. The pedogenesis in I-Lan was affected by its groundwater.
Often hydromorphic soil was formed. The
groundwater and the soil-forming process form a cause-effect
chain. Changes in land use may destroy the hydrological
environment. Keeping land use in the
groundwater recharge area to rice field use may prove beneficial
to water resource conservation.
5. The groundwater runoff in I-Lan plain is about 130 million
cubic meter/year, with a perennial yield
of 220 million cubic meter/year. The area most suitable
for development is the alluvial fan to the west of the railroad.
6. The groundwater routes correspond to groundwater quality.
Water quality is high in the alluvial
fan area, while that in the coastal area shows signs
of salinization. The amounts of Fe and Mn, hardness and NH3-N
are high. So are the amount of As in
Dongshan and Wujie areas The groundwater at Shinma
has been polluted. Whether salinity intrusion actually took
place or not needs to br studied ,and ,if
it did ,it's not sure if was caused by seepaged of
sea water or remains of sea water in previously -existing
lagoons.
7. Stepwise regression, analysis of variance and polynomial
distributed lag regression have
shown that the most important factor in the annual water
table fluctuation is the amount of rainfall. There has not been
observable change in watertables for
quite sometimes. There is short lag in the change
of the water table of unconfihed water after rainfall .There is
a one-day lag for that of confined
water.The relationship between rainfall and changes
in water tables is nonlinear .This calls for future study.