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| :::Hydrogeological Investigation Study, Groundwater Observation Net |
| A. |
Analyze Geological Information, Recommend The Structure of Groundwater Observation Wells for The Various Stations
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| (1) Investigating Groundwater Recharge Areas on Pingtung Plain |
Major groundwater recharge areas for the Pingtung Plain groundwater system are situated at the apexes
of the alluvial fans of Laonunghsi, Ailiaohsi, Linpianhsi, and Lilihsi. Rivers A groundwater recharge
area is the ground surface area at the margin of a groundwater region where surface runoffs in the
forms of rainwater, river water, and irrigation water percolate down the ground and travel downward
through the unsaturated zone to reach the groundwater table, and recharge the groundwater. Through
researches on hydrogeological framework, groundwater flow net, distribution of sand layers on the
ground surface, thickness of subsurface clay layers, depth of the groundwater table, distribution to
dissolved solid particle values, and characteristics of nitrogen nitrite it was pointed out that the
apexes ofo alluvial fans of the Laonunghsi, Ailiaohsi, and the Linpianhsi Rivers, as well as the
Linkou Hills are the major areas of recharge for the groundwater system of the Pingtung Plain.
Under the goal of sustained management of groundwater resources, land use in areas of groundwater
recharge should be placed under appropriate administration and planning, thus effectively assure
that the groundwater will not be polluted.
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| (2) Evaluation on Parameters for Twin-Well Pumping Test on Pingtung Plain |
The Pingtung Plain groundwater is recharged by rainwater, irrigation water, and river water
percolation and lateral recharge by subsurface water situated at the margin of the groundwater system.
Major recharge areas are situated at apexes of alluvial fans of Laonunghsi, Ailiaohsi, Lilihsi, and
Linpianhsi Rivers. Observation data indicated that the groundwater showed signs of reaction, and
gradually rise or fall within several days after a sufficient rainfall, the strongest reaction sign
occurred at apexes of these alluvial fans. This indirectly manifested that recharging of the
groundwater is strongest at the apexes of the alluvial fans. Estimating the quantity of groundwater
recharge is a challenge. Analysis through the groundwater time/history curve is more direct, simple
and accurate than analysis through water budgeting method. Using the groundwater table time/history
curve to calculate and analyze the groundwater recharge of an area should first obtain the water yield
ratio Sy of a non-pressurized groundwater layer and the coefficient water storage S of a pressurized
aquifer.
In Pingtung Plain, the value of water yield ratio Sy of a non-pressurized water layer ranges from
0.71 to 0.239, with the mean around 0.17. The coefficient of water storage S for a pressurized
aquifer ranges from 3.79X10-5 to 1.64X10-3 with the mean 5.14X10-4. These parameters will be used
to conduct analysis on groundwater recharge using groundwater table time/history curves.
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