台灣地勢陡峭，降雨多集中於夏秋兩季，造成山區邊坡大面積崩塌頻繁。除去降雨與風蝕等氣候因子，水土流失亦與地形、地質等因子有關，地表逕流侵蝕出的蝕溝對於淘刷土砂，在特定情況下可達總土壤流失的70%，這對於集水區水土保持以及水庫淤積而言，無疑是一項重要課題。本研究區域位於曾文水庫集水區北邊，主要岩性為砂、頁岩互層，使得侵蝕現象更發達，研究目的在於結合光達資料與衛星影像，觀察蝕溝發育與植生覆蓋的相對情況與相互影響關聯。
由於3米解析度的CHM與林分面積的相關性較好，本研究使用1米解析度DEM計算水系推估，半自動化尋找蝕溝位置；在計算CHM時才以3米解析度DEM與DSM來進行。隨後將經幾何校正後的影像計算出NDVI當作一個圖層，同時搭配SWIR、NIR波段與CHM，以物件式分類法分類出崩塌地/裸露地、陰影、針葉林、灌木叢、混合林、竹林以及農作地等類別。
結果顯示分類精度最好時Kappa值可達0.75，本研究水系推估模型經現場驗證後，模擬蝕溝位置的成功率為83.3%，此外，人為整治之工程點位亦會呈現在水系推估結果中，意即推估方式可有效辨識地表逕流匯流路線，並可於現場確認該施工點是否有效運作，以降低崩塌復發。透過相減兩期DEM可量化蝕溝的發育情形，並以像元尺度觀察，發現整體向下侵蝕情況普遍為0.2至0.25米，堆積則多在1米以上且偶有5、6米的極值，推測後者主要為樹木傾倒。雖然台灣山區林相複雜，仍可看出趨勢：在本區以混合林分布的區塊侵蝕情形明顯較少；竹林與灌木則是侵蝕較堆積面積高出許多，表示兩者皆屬於無法保持水土的植生類型，尤其竹林分布區域在相同外在因素影響下其侵蝕情況較為嚴重。

Soil erosion by water is an important physical process that may lead to land degradation. Gully is one of the main ways for slopes to loss soil besides landslide, weathering or erosion. This study intend to use hydraulic connectivity and digital elevation models (DEMs) to detect the location of gullies, then calculate the development of gully by simple subtraction using LiDAR data gathered from different periods of time. On the other hand, distinguishing the types of land-use via methods of Object-Based Image Classification with two periods of satellite images. Finally discuss the relationship between several possible causing factors: different vegetation, slope degree and precipitation toward the development of gully.

The result shows that, the hydraulic connectivity model using in this study has an accuracy about 83.3% for searching the gully successfully and has been verified by field survey. Not only the nature gully, remediation project such as river training works will also be shown in the result. Which proves the model can identify the confluence of runoff effectively. Observe the development of gully in pixel level, general erosion height is about 0.2-0.25 meters and the general height of deposition is about 1 meter during a year. Though the forest in the study area is quite complicated, there is still some tendency could be found. Seldom erosion occurred in mixed forest region; the situation of erosion and deposition is the same in the coniferous region. While bamboo and bush covered region have a massive area of erosion and rare deposition, showing that both of them aren’t a good land cover plantation for soil and water conservation, especially the bamboo.

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