印尼熱帶氣候環境下的流域健康指數評估

Watershed Health Index Assessment under Tropical Climate Environment of Indonesia

江達(Chandra Setyawan)

指導教授 ： 李錦育

國立屏東科技大學/國際學院/熱帶農業暨國際合作系/博士(2020年)

https://doi.org/10.6346/NPUST202000021

摘要

作為地球系統的一部分，集水區經營提供許多功能，對生態系統服務至關重要。集水區資源的過度開採已導致環境惡化問題。為了確保其功能的可持續性，顯然需要集水區監測和評估，作為集水區管理戰略的基礎。這項研究旨在評估熱帶集水區目前的健康狀況。透過使用集水區系統的概念進行了研究，以提出和評估用於集水區健康評估的框架。通過使用代表集水區系統的輸入，過程和輸出的指標進行評估，這些指標包括水土流失、地表逕流係數、泥沙輸送比、水質、年降雨量、植被覆蓋率、排水密度和土壤深度。指標的數量皆為考慮當地情況所訂定，缺乏相關實驗數據仍然是集水區評估研究的主要挑戰，使用加權因子對指標進行定量分析，以集水區健康指數 (Watershed Health Index, WHI) 表示集水區的狀況。每個指標值都歸為一類，即好（分數= 1），中等（分數= 0.5）或差（分數= 0）。指標的標準值由各種來源確定。
通過各種方法計算指標值，侵蝕是通過在地理資訊系統 (Geographic Information System, GIS) 中使用RUSLE模型計算的，利用Mock水文 模型 計算了地表逕流係數，利用迴歸方程計算出泥沙輸送比，通過現場觀察和評估對水質，年降雨量和土壤深度進行評估；同時利用GIS中的空間分析 (Arc GIS 10.1) 估算植被覆蓋度和排水密度。結果表明，該集水區健康指數總值為0.42，表明該集水區健康狀況較差。超過半數指標屬於較差的類別，如水土流失、泥沙輸送比、地表逕流、植被覆蓋和排水密度。為了改善集水區的健康狀況，需要針對上述超過半數不良指標進行恢復計劃.
本研究還揭示了指標的許多典型特徵，特別是與土壤侵蝕控制和植被土地利用管理有關。由於這兩個因素具有很強的相關性，並且對沉積和地表逕流事件具有重要影響，因此侵蝕和植被覆蓋已成為本研究的主要關注點。我們還研究了地形(坡地)和植被對侵蝕的影響。地形形式分為五類，例如低坡度(0~10％)、中坡度(10~15％)、強坡度(15~25％)、陡坡(25~35％)和非常陡坡的區域( > 35％)。結果表明，大部分水土流失來自陡峭/非常陡峭的坡地，僅佔集水區總面積的30％。在低坡度地區發現坡度對侵蝕的影響最大。根據上述研究結果，提出了5個土壤侵蝕與土地坡度的相關方程式。
同時，對植被侵蝕相關性的調查表明，植被覆蓋率從現有的3.7％上升到10％，減少約55％的土壤侵蝕。植被覆蓋率從10％增加到30％，表示每增加5％的植被覆蓋率，約減少14,8％的侵蝕。此項研究還強調了在保護實踐節制水壩的性能。節制水壩對於控制河底泥沙和增加河水氾濫是有效的，透過使用植被或自然保護結構(小型水壩)進行的自然保護類型對於集水區健康恢復都是合理的。使用WHI可以進行評估，該指數考慮集水區系統的整體重要層面，並提供有關集水區管理須關注的基本知識。

關鍵字

水土保持 ； 熱帶集水區 ； 集水區評估 ； 集水區健康指數

並列摘要

As a part of the earth system, a watershed has vital roles for ecosystem services by providing many needs for the living. Excessive exploration of watershed resources has been resulting in environmental degradation problems. To assure the sustainability of its function, watershed monitoring and evaluation is obviously required as the basis for watershed management strategies. This study is aimed to assess the present watershed health condition in a tropical watershed. The study is also performed to propose and evaluate a framework for watershed health assessment by using the concept of a watershed system. The assessment was conducted by using indicators representing input, process and output of the watershed system such as soil erosion, coefficient of surface runoff, sediment delivery ratio, water quality, annual rainfall, vegetation cover, drainage density and soil depth. The number of indicators was determined by considering local circumstances, where lack of data availability was still being the main challenge for watershed assessment studies. The indicators were then quantitatively analyzed by using the weighting factor and the status level of the watershed was expressed in a watershed health index (WHI). Each indicator value was classified in a category i.e. good (score= 1) moderate (score= 0.5) or poor (score= 0). The standard value of indicators was determined from various sources.
The value of indicators was calculated by using various methods. Erosion was calculated by using the RUSLE model in a Geographic Information System (GIS). The coefficient of surface runoff was calculated by using hydrologic model of Mock. The sediment delivery ratio was calculated by using the regression equation. Water quality, annual rainfall and soil depth were assessed by using field observation and assessment. Meanwhile, vegetation cover and drainage density were estimated by using spatial analysis in GIS (Arc GIS 10.1). The result shows the total value of the watershed health index is 0.42 means that the watershed is in the poor level of health condition. More than half of indicators are found in poor category i.e. soil erosion, sediment delivery ratio, surface runoff, vegetation cover and drainage density. To improve the health status of the watershed, recovery programs are required for those poor indicators.
The present study also reveals many typical features of indicators particularly related to soil erosion control and land use management for vegetation. Erosion and vegetation cover have become the main concern in this study since these two factors have a strong correlation and have a significant effect on sedimentation and surface runoff events. We also investigated the effect of terrain form (land slope) and vegetation on erosion. Terrain form was divided to five different classes i.e. low sloping (0~10%), moderate sloping (10~15%), strongly sloping (15~25%), steep sloping (25~35%) and very steep sloping area (>35%). The result shows that most of the soil erosion is sourced from steep/very steep sloping areas which just occupy about 30% of the total watershed area. The strongest land slope~soil erosion correlation is found in the low sloping area. Five equations of soil erosion~land slope correlation are proposed based on the result of this study.
Meanwhile, investigation of vegetation~erosion correlation reveals that the rise of vegetation cover from the existing condition 3.7% to 10% reduce about 55% of soil erosion. The increase of vegetation cover from 10% to 30% signifies that there is about 14,8% of erosion reduction for each increase of 5% vegetation cover. This study also highlighted the performance of the check dam for conservation practices. The result indicates that the check dam is effective for sediment control and increase water inundation in the river. The study findings reveal that both conservation types by using vegetation or conservation structure (small~scale dam) are reasonable for watershed health recovery. The use of watershed health index (WHI) enables an assessment that considered whole important aspects of a watershed system and provides essential knowledge for watershed management concern.

並列關鍵字

soil and water conservation ； tropical watershed ； watershed assessment ； watershed health index

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