University of Twente Student Theses


Design flood estimation for the Quang Tri Province in Vietnam

Vilsteren, M. van (2010) Design flood estimation for the Quang Tri Province in Vietnam.

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Abstract:Estimating design floods for catchment areas is an important activity in hydrology. The sizing of bridges, culverts and other facilities; the design capacities of levees, spillways and other control structures; and reservoir operation or management depend upon the estimated magnitude of various design flood values. Design floods are also important for political decisions in hydrologic discussions. The research goal of this study was to find the design floods for all the sub-catchment areas of the Ben Hai River, the Thach Han River and the O Lau River in the Quang Tri Province using Flood Frequency Analysis and the rainfall-runoff model MIKE-NAM. Quang Tri is located in the middle of Vietnam. Flood- and rainfall frequency analysis has been done with FFA Spreadsheet 2.0. This was the first part of the research. Because discharge data were available for only one sub-catchment area, a rainfall runoff model called MIKE-NAM had been used to produce flood hydrographs for the other subareas. This model has been calibrated with flood data from 1998 and 1999. It was easier to find a set of parameters of catchment area characteristics for the 1999-flood than for the 1998. The final set of parameters has a value for R2 = 0.761 for the 1998-flood and R2 = 0.925 for the 1999-flood. This R2 describes how the modeled graph fits to the observed graph and has a minimum of 0 (no fit) and a maximum of 1.0 (perfect fit). Because the output of this method wasn’t as accurate as planned two additional methods had been added. The ‘rational method’ uses characteristic times to estimate design floods. The three-day rainfall method uses an increase factor and a historical rainfall to get an approach of the design floods. However, this last method is especially important for the total discharge volume. The most important conclusion of the research is that the limited available data is a limitation for the accuracy of the research. Hourly rainfall data during storms will improve the accuracy of the results. Discharge data for more than one gauging station in the subarea also will improve the accuracy of the research. Another important conclusion is that MIKE-NAM isn’t suitable for design flood estimations. An more advanced model including techniques to translate design rainfall in design floods is recommended for further research.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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