新竹及竹南地區的地下水區劃分與水資源探討

Abstract

摘要 區域水資源的供需平衡，維繫著作為高科技科學城的新竹都會區未來的發展，水資源的規劃建立在基礎水文量的掌握，本研究係以地理學的空間分析及水文學的水平衡觀點作為研究的途徑，從推估逕流量、進行地下水性質的空間分析、地下水可開發量的估算、劃分地下水區到區域水資源評估。具體的研究成果條列如下： 1）本研究顯示：研究區的氣候具有介於北部及中部的過渡性特徵；以等降水量線圖為基礎分析，得出研究區的降水量約以70mm/100m的趨勢由西向東遞增。2）以氣候水平衡法估算研究區各流域及全區總逕流量為19.7億噸／年，鳳山溪流域為3.26億噸／年、頭前溪流域為9.12億噸／年、客雅溪流域為0.57噸／年、鹽港溪流域為0.41億噸／年、中港溪為6.34億噸／年。3）透過地層剖面比對、地下水採樣及Piper水質結構圖的分析，確認地下水研究區各地均至少同時存在兩個含水層，是本研究的一個重要研究成果。4）利用地下水位調查及作圖分析，可將地下水研究區的自由水之地下水系劃分為：鳳山溪、頭前溪—客雅溪、鹽港溪、中港溪等4個地下水系，鳳山溪、頭前溪和客雅溪三地面水系，在新竹平原部份合為一個地下水系。受壓地下水系則可劃分為新竹平原、鹽港溪流域及中港溪流域3個地下水系。5）透過相關水質指標的檢測及分析，地下水研究區地下水質受沈積環境變化的影響，水中鹽基物的濃度，呈現的由東北部向西南部遞增空間規律性（尤其是受壓水）。6）本研究以地層係數為指標，將地下水研究區劃分為3個水文地質區；以及綜合地面水系、地下水系、水文地質、地面水及地下水的聯合使用，並考量人口及產業的分布情況，將地下水研究區劃分為4個地下水區。7）以地下水流動量為依據，地下水研究區自由地下水的可開發量，在新竹平原地下水系約為446×106m3/yr年、鹽港溪地下水系約為0.59×106m3/yr、竹南平原地下水系約為75.8×106m3/yr，總計為522.4×106m3/yr。新竹平原的地下水系受壓水可開發量約在1.54×106m3/yr以上、竹南平原地下水系約在1.20×106m3/yr以上，整個地下水研究區的受壓水可開發量應在3.00×106m3/yr以上，地下水總可開發量約在525.59×106m3/yr以上。8）新竹平原及竹南平原的自由水均屬豐富，但所調查的水井中約有65.9％的井水已經遭受農業及家庭污染，只宜作為灌溉用水。受壓水水量有限，僅可作為旱年及旱季的調節水源。 地下水研究區的地下水出水量及水質具有明顯的空間特性，各地的區域發展也有所差異。在進行地下水監測、評估及開發時，應因地制宜地考慮區內地下水質、量的空間差異。本研究的成果可提供政府部門及產業界，在新竹、竹南地區進行都市計劃、投資、開發時，水資源量預估的參考依據。

Abstract The purpose of this paper was to understand the characteristics of water resources in Hsinchu plain& Chunan plain catchments locate in northwest Taiwan. The outlines of the hydrological characteristics of study area summarized as follows： 1）The climate of study area possesses the transitional features from Northern Taiwan to Mid-Taiwan region﹒ According to the analysis of isohyet’s map﹐the precipitation of study area has the tendency of “increase of 70mm/100m from east to west”﹒ 2)The runoff of individual river catchment in study area was estimated as follows：Fengshan creek catchment as 326×106m3/a﹑Touchan creek catchment as 912×106m3/a﹑Kheya creek as 57×106m3/a﹑Yankang creek as 41×106m3/a﹑Jhongkang creek as 634×106m3/a﹐and sum of discharge as 19.7×108m3/yr﹒3)By investigating of groundwater in study area﹐demonstrated that there are two aquifers which consists of unconfined aquifer and confined aquifer﹒4）By the way of investigation of groundwater level and analysis of mapping﹐groundwater study area shows that the unconfined groundwater system can be divided into Hsinchu plain system﹑Yankang creek system and Jhongkang creek system﹔and confined groundwater system can be divided into Hsinchu plain system﹑Yankang creek system and Jhongkang creek system also﹒5）For analyzing the records of groundwater qualities（which obtained from fieldwork） showed that the discrepancy in groundwater qualities were under the influence of variation of sedimentary environments in groundwater study area﹒6）To rest on hydraulic constants﹐the whole groundwater study area can be divided into three hydrogeology regions﹔and to stand on rivers system﹑hydrogeology and use of the combination of surface runoff with groundwater﹐the whole groundwater study area can be divided into four groundwater regions﹒7）We can calculate the amount of exploitable groundwater according as the discharge of groundwater﹒The amount of exploitable groundwater of individual unconfined groundwater system is estimated as follows：Hsinchu plain groundwater system as 446×106m3/a﹑Yankang groundwater system as 0.59×106m3/a﹑Jhongkang creek as 75.8×106m3/a﹐and sum of amount as about 522.4×106m3/yr﹒ The amount of confined groundwater system is estimated as follows：Hsinchu plain groundwater system as about 1.54×106m3/a﹑Jhongkang creek as about 1.2×106m3/a﹐and sum of amount as above 300×106m3/a﹒ 8）Although the discharge of unconfined groundwater is abundant in Hsinchu and Chunan plains﹐the 65.9 percent of wells are polluted by agricultural and household pollutant﹒It can make use of irrigation only﹒The discharge of confined groundwater is insufficient It can make use of combating drought in dry season and year of drought merely﹒ The groundwater yields and water qualities have significant spatial characteristic﹐and the region development also have diversity in groundwater area﹒It must be to suit the measure to the spatial variation about the amount and quality of groundwater﹐when proceed to monitor﹑to assess and to exploit of the groundwater located in groundwater study area﹒The results we get could provide insight to schemes﹑investments and developments in Hsinchu and Chunan areas by the government institutions and industrial circles﹒