Estimation of Soil Loss in Watershed
|關鍵字:||土砂生產量;河川集水區管理;Soil Loss;river watershed management|
The existed reservoirs in Taiwan are mostly constructed at the middle and upper reaches of the rivers. Frequently due to the steep topography and frail geology or due to improper cultivation and deforestation, they have resulted in serious erosion to the top-soil. The river water carries abundant of sand to the reservoir; subsequently, the latter’s capacity is reducing day by day, which is very disadvantageous to the operation of reservoir. According to the measured results to the sand-depositing volume of reservoir in the past years, the average deposit volume of the reservoirs throughout entire Taiwan has reached up to 14.6 million cubic meters, which is nearly equivalent to the total storage capacity of Ming-Te Reservoir. It is obviously indicating that the deposit situation of existed reservoirs in Taiwan has been very serious and urgently needs to search resolutions. Recently, the domestic hydraulic organizations have aggressively implemented the works of river watershed management and adopted the existed erosion formula used by the soil conservation field to estimate the soil loss at watershed. However, the factors of sediment origin and loss volume, that will impact the river watershed, are very complicated and also very difficult to formulate a prospective strategy of sediment extraction at watershed. Therefore, the precise estimation of sediment origin and loss at watershed has become an important issue with great urgency, nowadays. Moreover, owing to the factors that the geologic structure of Taiwan is complicated and fragile and the unconsolidated materials are plentiful, adding that the gradient of main rivers is steep and the rainfall is concentrated in short periods of time, they have resulted in great sediment yields. Consequently, the measures for mitigating sediment yields have also become important factors to be considered in administrating rivers. At the planning stage of river management, it is hard to obtain parameters of boundary conditions for deriving a sound hydrographic model for understanding the sedimentation and sediment transportation process. Therefore, it is highly required to have an approach to obtain an estimation of sediment yields. This research, to the aforesaid issues, is using the Ta-Pu Reservoir at Hsinchu and Miaoli districts as the study area to proceed to an estimating research of soil loss volume in river watershed. The research measure is firstly evaluating and selecting the influence factors that will affect the soil loss volume at watershed. Subsequently, through the hydrological statistical analysis and remote sensing satellite image processing, we can obtain the linear relation between each influence factor and soil loss volume at watershed respectively and then reach the model of soil loss applicable to this watershed through principal component analysis and regression analysis. Models with different combinations of parameters are scrutinized in this study. It is revealed that there are three models established in this research showing good prediction of sediment yields. They are the models applying factors of accumulated rainfall variable at watershed, accumulated runoff variable at watershed, and an assembled variable model of accumulated rainfall and accumulated runoff at watershed. The multi-temporal remote sensing satellite image processing procedure adopted in this study shows a very good time-series estimation of the land use and land cover. Similar procedure can be applied in extracting thematic information such as physiographic, hydrologic and environmental features. The principal component analysis adopted by this research, besides reducing the amount of variables in regression statistical analysis, can relatively increase the correlation coefficient for the regression conditions. In addition, it can also effectively solve the problem of the correlation of variables of compound regression analysis. The model of soil loss for Ta-Pu Reservoir as established in this study can be applied as the referential bases of reservoir operation and sediment yield mitigation. Furthermore, the result of remote sensing satellite image processing through multi-temporal image change analysis can be further applied as an important basis for the administration of watershed.
|Appears in Collections:||Thesis|