Technical Studies

Located in the University of Mississippi, the National Center for Computational Hydroscience and Engineering (NCCHE) is founded by several US federal agencies and the US Congressional Appropriation. The NCCHE developed the 1D (CCHE1D) and 2D (CCHE2D) sediment transport models which have been applied to river and coastal problems in the USA and abroad with significant by successful achievements after through rigorous tests and verifications of the models.

This project will be carried out in a three-year term in cooperation with the NCCHE for the introduction of the 1D and 2D numericalsediment transport models. With Chou-shui River chosen as the target of study, the work is shared among NCCHE, Water Resources Planning Institute, Water Resources Agency, and the NCTU Hazard Mitigation Research Center. One of the main purposes of this project is the building of a model base of NCCHE’s hydraulics and sediment transport models.

The first-year plan of this project aims at the application of CCHE1D model to investigate Chou-shui River’s bed change. This study started by reviewing the theories, numerical methods, and the capabilities and limitation of the model. The assessment results showed that the CCHE1D model is an advanced numerical model with plentiful functions. Apart from its reasonable prediction shown in the hydraulic and sedimentation simulations, the CCHE1D model is capable of integrating geo-morphological tools (TOPAZ) and hydrology tools (AGNPS) with consideration of the effect of watershed land use on the rivermigration. At the meantime, the basic information about the Chou-shui River was collected, categorized and analyzed for model verification.

The cross-section geometry measured in 1999 was used as the initial condition for the valification (2001 bed) and validation (2004 bed) of this model, by considering the significant typhoon events during 1999-2004. The simulation showed that the CCHE1D model is able to simulate the flow and sediment transport in the Chou-shui River. This simulation for the upstream steep slope reach showed that the model is numerically stable. The sensitivity analysis showed that the model is not sensitive to the suspended-load adaptation coefficient α, but it is affected by the thickness of the mixed layer. The results showed a deeper erosion when a thickness of 0.3 m is used instead of 0.2 m. In the model comparison studty, the CCHE1D and EFA1D both gave reasonable results in this case.

To predict the bed change in future by using the CCHE1D model, the cross-section geometry measured in 2004 was adopted as the initial condition significant typhoon events during 2005-2007 were considered. Due to the unavailability of the inflow sediment size composition data, 5%, 10% and 20% of the total inflow sediment were assumed as bed-material load. The simulation predicted deposition upstream of the Chi-chi Weir, erosion in the downstream of the Weir, and deposition in the reach downstream of Xizhou Bridge. It should be noted that the reliability of the predicted bed profiles in 2007 in this study depends on the inflow sediment composition condition and the composition of vertical distribution of bed-material size.

In the process of building up the model base, the portal and its related digital documents have been developed which enables the user to learn CCHE1D model from the website. Moreover, the education and training of the CCHE1D model was successfully conducted with invitation of researchers from NCCHE for this technical communion in Taiwan.