蝕溝沖蝕產砂量推估之研究

On Quantitative Estimation of Sediment Yield Due to Gully Erosion

李昶谷(Chang-Ku Lee)

指導教授 ： 李鴻源

國立臺灣大學/工學院/土木工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02967

摘要

「蝕溝」係土壤沖蝕作用初期在坡面上切割所形成之深溝，由於地形外觀特別顯著，且為坡面土壤強烈沖蝕作用之表徵，更是地形夷平過程之濫觴，因此蝕溝之形成乃為坡面加速沖蝕最具代表性之地形特徵。同時蝕溝形成後即會因下切、橫向沖蝕與溯源沖蝕之同時擴張，而使坡面之穩定條件急劇破壞，造成大量的土砂沖刷。
本研究使用全站式光波測距經緯儀進行集水區內現場蝕溝產砂狀態的測量，並且利用航空攝影圖以及數值高程模型(DEM)估算研究區域內的蝕溝數量及其規模。最後將上述成果佐以合理的假設，推估研究區域內(石門水庫白石溪流域)蝕溝沖蝕產砂總量。
現場蝕溝測量的結果，蝕溝產砂狀態依照其發育程度的不同，分為「產砂型蝕溝」以及「穩定型蝕溝」。產砂型蝕溝發育期較為年輕，其平均單位面積產砂量為0.2758m3/m2；穩定型蝕溝發展成熟，產砂量較少，平均單位面積產砂量為0.0108m3/m2。航空攝影圖上依照本研究設定的判釋標準，可以判釋出含有面積(polygon)資料的蝕溝41條、僅有長度(line)資料的蝕溝79條，共計120條。經集水區內小範圍(約占總面積13%)內現場勘查驗證，判釋準確度為77%。
研究期間內(2006年7月~12月)，集水區蝕溝產砂總量推估為2.7萬m3。假設產砂量與研究期間內累積降雨量為一線性正比例關係，並以石門水庫土砂密度2.32ton/m3計算，得白石集水區內年蝕溝沖蝕產砂量為14.69ton/ha/yr 。與土壤沖蝕量21.52ton/ha/yr 、崩塌地產砂量85.29ton/ha/yr 比較，蝕溝產砂量佔總產砂比例12.09%，為一不可忽略之產砂來源。

關鍵字

蝕溝 ； 土壤沖蝕 ； 集水區 ； 產砂量 ； 免稜鏡雷射全站儀 ； 航拍圖 ； 數值高程模型

並列摘要

Gullies are narrow channels cut by concentration flow on hillsides. With striking and noticeable outward appearance, gullies not only display the power of soil erosion but also indicate the beginning of land-flatting process. They are thus regarded as a major characteristic of hillside soil erosion. After gullies are formed, the stability of hillside soil deteriorates; consequently, a large quantity of sediment is produced by the interaction of incision, lateral erosion and headcut retreat.
This study aims to estimate the sediment yield due to gully erosion in Taiwan. The researcher figured out the number of gullies and surveyed their sizes in Baishi river Catchment, an area of the Shihmen Watershed, with the aid of Pulse Laser Total Stations (with a superior non-prism measurement capability), aerial photographs and Digital Elevation Models. The measurement results were then put into a formula to estimate the quantitative sediment yield in the study area.
According to the on-site survey carried out in this study, gullies can be divided into sand-yielding gullies and stable gullies. Sand-yielding gullies are newly-formed ones with an average sand yield of 0.2758m3/m2 whereas stable gullies are highly-developed ones with a relatively smaller average sand yield of 0.0108m3/m2.
There are totally 120 gullies read in the air photos taken to perform this study, including 41 with polygon data and 79 with only line data. A smaller-area (about 13% of the total area) on-site check shows the correctness of the data is 77%.
The survey and estimation performed in this study also show that total sediment yield due to gully erosion in Paishih Watershed from July to December, 2006 is 27,000 m3. On the assumption that sand sediment amount is in proportion to accumulated rainfall, the annual sediment yield due to gully erosion in this area is 14.69 with a average soil density of 2.32ton/m3. Compared to 21.52ton/ha/yr of sediment yield due to surface erosion and 85.29ton/ha/yr of sediment yield due to landslide erosion, the 14.69ton/ha/yr of sediment yield due to gully erosion makes 12.09%, which is undoubtedly an important source of sediment production in this area.

並列關鍵字

gully ； soil erosion ； watershed ； Laser Total Stations (non-prism) ； aerial photographs ； Digital Elevation Models

參考文獻

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