Research On Flood Estimation Methods For Ungauged Small Basins

Detailed information is always unavailable in midsize and small basins, due to the low density of gauge station. Meantime, flash flood in small ungauged basins is still a big threat to local people and flood estimation in these places is nowadays a hot issue and also a difficult problem for hydrologists around the world. Searching for proper methods that could be used in small ungauged basins can provide essential supports for project-design and decision-making, as well as enrich and improve hydrological theory. This thesis mainly concerns with design flood calculation in ungauged basins, and the main work could be summarized as follows:1) Methods and researches about flood estimation for ungauged basins were reviewed, including design flood estimation, flood routing, and analysis of region composition. Rational method and several kinds of UH (Unit Hydrograph) are widely employed in design flood calculation. The UK and the USA use regional frequency analysis, while in China regional synthesis is more frequently applied to ungauged basins; and all of these methods are based on regionalization.2) Flood estimation contained three parts in this thesis: design flood calculation, reservoir routing and river routing. Due to the scarcity of flow discharge data, Regional Synthesis method and L-moment method were applied to calculate the design rainfall. Both Rational Method and Zhejiang Empirical Method were used to acquire the design flood and the comparison about their advantages and disadvantages helped to choose the better one, so that the result could be more acurate.3) Different hole-sizes of dam were tried for reservoir routing to protect downstream villages. The result showed that the reservior could have a great contribution to reduce the peak flow and postpone the peak time. Moreover, Muskingum-Cunge method proved to be a feasible way of solving river routing for ungauged basins, where there is no explicit geomorphological data.4) Flood region composition was performed in this thesis and two scenarios were compared to find out the most disadvantageous situation of flood that might happen in the downstream cross sections. The final result indicated that to build a reservoir in the upstream of WenJia village was applicable and beneficial for the downstream villages.