On Quantitative Estimation of Sediment Yield Due to Gully Erosion
Date Issued
2007
Date
2007
Author(s)
Lee, Chang-Ku
DOI
zh-TW
Abstract
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.
Subjects
蝕溝
土壤沖蝕
集水區
產砂量
免稜鏡雷射全站儀
航拍圖
gully
soil erosion
watershed
Laser Total Stations (non-prism)
aerial photographs
Digital Elevation Models
Type
thesis
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