Technical Studies

Steep slope, severe bed change and young geologic texture are the characteristics of Taiwan’s rivers. These characteristics often case huge sediment transport rate which the general common sediment transport formulas have the limit to apply in Taiwan’s river.This study will divide into three years to develop a new sediment transport formula which is suitable for the characteristics of Taiwan’s rivers.The flow and sediment data are surveyedand collected during the floods. These measured data are used to develop a new sediment transport formula, which wll be installed in the numerical model.

The existing formulas reviewed in the study will be applied to calculate the sediment transport rate under the flow and sediment conditions. In the first year, Dajia River is selected as the study site. Their calculated sediment transport rates will be compared with the measured ones. Then the three top performing formulas will be selected as potential candidates for the development of new formula.

Two approaches will be used to develop the new formula. The first approach will use the top three formulas selected by the review of general common formulas, and recalibrate their coefficients using the collected data. The best performing one will be the final formula to be used.The second approach uses the basic theories of sediment transport, including Bagnold’s stream power, Yang’s minimum stream power, diffusion theory, gravitational theory, dimensional analysis, etc.

According to Wu et al (2000), the bed-load transport rate is highly related to grain shear stress, and the suspended-load transport rate is highly related to the stream power available in the flow system. In addition, the hiding and exposure mechanism in the nonuniform bed material significantly affect sediment transport and should be taken into account. After comparison, Wu et al. (2000) formula has the best performance in Dajia River.

The new formula will be also tested and validated using the large sediment database used by Wu et al. (2000) and in the late development and test of sediment transport formulas by Wu (2007). This database is comprised of thousands of data sets collected through a large number of laboratory experiments and field studies in the last decades since 1940s conducted by scientists all over the world.