摘 要

本研究分析宜蘭地區水文、氣候資料，水文環境調查、地下水位
觀測、地層調查、抽水試驗、水質化驗分析及訪問並配合相關資料研
判分析，得到下列之結論：

一、宜蘭地區年平均面積雨量為3050.9公釐，平原地區約2500～3000公釐
，山區在3500公釐以上。年平均可能蒸發散量為1011公釐，實際蒸發散
量為707.8公釐，山區與平原大致可以1000公釐作為分界。全縣年平均
逕流水深為2343.1公釐，年逕流量為49~52億立方公尺，各流域之逕流
係數在0.76~0.79之間。

二、宜蘭平原西側有頭城、礁溪、大小礁溪、大湖溪、蘭陽溪等沖積扇，
南側有羅東溪、新城溪沖積扇，均為地下水補注區；平原三角洲以砂
或砂土地層為主，透水性差；迫使部分地下水流出地面，形成得子口
溪小支流和冬山河小支流的源頭。宜蘭平原的地下水，北部匯集於得
子口溪及宜蘭河,南部多匯集於冬山河,形成三個地下水系;地面水系及
地下水系均受阻於行海岸砂丘，其淘選度佳、透水性好，成為淡水障
壁，減少海水入侵和減弱東北季風及其所帶來的鹽份。
三、宜蘭地區主要斷層及褶皺構造，分布於平原西側及南側沖積扇之邊界
上，山地、平原之地下水系並不連貫。主要含水層為粗砂及礫石層，
多分布於沖積扇扇頂至扇央地帶。地下水位年變動量大致與地面標高
成正比。沖積扇的導水係數有自南向北遞減的趨勢，此與礫石層厚度
相對應。

四、宜蘭平原的土壤化育過程中，深受土壤滯水及地下水的影響，多發育
為水成土，地下水與成土作用互為因果關係的循環。土地利用的改變
，皆會破壞水文環境或使生態環境惡化；各沖積扇地下水補注區宜維持
水田土地利用，較有利水資源之保育。

五、宜蘭平原地下水流動量約為1.3億立方公尺/年，可開發量約為2.20億
立方公尺/年。適當的開發地區，在宜蘭河和蘭陽溪間的縱貫線以西，
可開發量約為0.95億立方公尺/年，平原南部蘭陽溪南岸的溪底城至丸
山一線以西，可開發量約為0.8億立方公尺/年。
六、地下水質與地下水流路徑十分符合，沖積扇頂扇央地區水質良好，沿
海地區已有鹽化現象。全區地下水質有鐵、錳、硬度及氨氮含量稍高
。冬山、五結鄉部份地區地下水中含砷量偏高及新馬地區之地下水已
受污染。地下水的鹽化應是抽取海水養殖入滲或古潟湖海水殘留所致
，海水是否入侵有待進一步研究。

七、以逐步回歸、變異數分析、多項分期延滯迴歸，得知影響年水位變化
最主要因子為降水量；長期來宜蘭地區地下水位並無明顯下降，降水
後自由水位延滯時間短，受壓水較自由水約延後一天，降水與地下水
位變化情形，並非單純線性關係，有待日後進一步的探討。
八、有效合理的利用水資源，應充分運用豐水期的地面水及影響層面較小
的攔河堰或伏流水的開發，對水利局規畫中之幾處攔河堰及伏流水開
發區，就水質、水量及對地下水補注加以評估。

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.
ABSTRACT