沙質海岸海灘劣化與復育策略：以宜蘭海岸為例

宜蘭海岸的永續經營應以減量、復育為基本原則，為有效利用管理及達成天然資源保育之工作，必須對海岸地帶進行劣化評估。本研究以海灘功能的衰退作為劣化的定義，參考評估遊憩型海灘環境之常用指標，歸納四項評估指標：1.海灘侵淤、2.海灘垃圾、3.海灘設施及4.海灘使用者觀點。前三者為海灘劣化之客觀評估指標，後者為主觀評估指標。本研究使用多時序濱線判釋變遷，並利用數值地形模型等地理資訊系統模擬海灘地形，以多時序方式比較量化之灘體來檢視宜蘭沙質海灘的侵蝕劣化程度；以垃圾最多的海灘垃圾線為抽樣區，進行每月的調查，記錄垃圾的數量、面積及垃圾來源等項，分析海灘劣化的情況；以遊客、住戶、漁夫等海灘使用者為對象，進行問卷及深入訪談，以獲取海灘劣化的定性評估。綜合海灘侵淤變化、分析及海灘使用者觀點評估的結果，可用來了解海灘劣化的現象與成因，進而提出可能的復育辦法，以達到海岸地帶永續經營之目標。就海灘劣化的客觀評估而言，無論在長、中或短期下皆呈現侵蝕的狀態。其原因除了連續的突發事件造成灘沙沒有足夠的時間回淤及季節性的波浪影響外，就以人為活動造成之蘭陽溪輸沙量減少及北方設置的突堤最有影響；此現象使海灘因生活功能、生態功能及生產功能的衰退而劣化。消波塊放置後，海灘坡度變陡，海灘可能變得不穩定，容易受到侵蝕。長期而言，消波塊的放置不僅無法達到防止海灘侵蝕的目的，反而將助長海灘的侵蝕，進而影響到海灘之原有功能。透過逐月之海灘廢棄物調查可發現冬季有增加的趨勢，尤以廢棄物面積的增加情況最為明顯，造成海灘生活功能、生態功能及生產功能的衰退而劣化。就海灘劣化的主觀評估而言，海灘使用者皆認為提供休閒遊憩空間與國土保安之生活功能、生物棲地之生產功能的在衰退而劣化中。並認為近50至70年間有逐漸變窄的趨勢，該結果與客觀評估結果相符；且廢棄物也有變多的趨勢，多來自海灘活動，這是日後進行海灘廢棄物減量宣導時需注意的部分。為改善海灘的劣化現象，應透過減緩海灘侵蝕及海灘廢棄物減量，以恢復原有之功能。海灘劣化雖部份歸因於自然營力，但仍可以透過改善人為影響減緩海灘侵蝕的速率。

關鍵字

海灘劣化；侵淤變化；海灘垃圾；海灘使用者觀點；永續經營

並列摘要

This study is to conduct a comprehensive investigation of beach degradation in the Yilan coastal area, in order to facilitate the effective management and preservation of natural resources in the region. The degradation of beach functions is assessed with both objective and subjective measures, including 1) beach sedimentation, 2) beach littering, 3) beach facilities, and 4) perspectives of beach users. Multiple time series of coastal line alterations are composed and digital elevation models are applied to simulate the study area. Seasonal and long term volumetric variations were computed to examine the degree of sand beach erosion in the Yilan coast. To study the impact of beach litter, monthly surveillance is carried out at the most heavily littered beach segment to record the amount of litter, the area covered with litter, and the types and sources of litter. Questionnaires are also collected from and interviews are conducted with beach users, including local residents, tourists, and fishermen, to gather their inputs in this subject.The study of beach sediment reveals significant erosion in either the recent, median, or long-term period. The observed erosion is partly attributed to series of unexpected events with insufficient time in between for the sediment to recover, and partly attributed to the expected effects of seasonal waves. Nevertheless, the reduction of sand flow in Lanyan River resulted from human activities and the construction of north rock cliffs also add to the impact. Instead of preventing beach erosion as intended, the placement of breakwater complexes, in the long term, has likely resulted in the steepening of beach slope and therefore makes the beach unstable and subject to more erosion. The study of beach litter reveals a gradual increase of littering, most remarkably in the measurement of beach area covered by litter, especially during winter. These findings agree with problems reported by many beach users, that is, the beach is slowly shrinking and littering, mostly from activities on the beach, is worsening. These changes have started to compromise all aspects of beach functions as in recreational usage, ecological health of habitats, and industrial production.The results of this study suggest that, although beach degradation in the Yilan coastal area is partly driven by natural processes, it can also be effectively intervened with actions centered on the reduction of beach litter and beach erosion. The promotion of beach preservation through the prevention of littering should be the primary policy in future public education targeting the beach users.