Research On Methods Of Design Flood Estimation In Ungauged Basin

In many countries and regions, many watersheds still lacking observation data, in addition to the intensifying of human activities which has caused great changes of underlying surface, ecological environment and climate conditions and made the observed data in gauged basins much less reliable, bring more difficulties to hydrologic analysis. At present, hydrological research in ungauged basin is one of the difficult and hot issues of water resources and environment field both at home and abroad. In 2003 International Association of Hydrological Sciences(IAHS) launched an international hydrological program called PUB, focusing on hydrological researches in areas short of data. In our country, a PUB working committee has been set up as well. This paper has discussed the methods of design flood estimation in ungauged basin which lacks hydrological data on the basis of summarizing the research progress of hydrological issues in ungauged basin. The main contents and results of this paper are as follows:(1)Taking the northern mountainous area of Fuzhou city for example, this paper has discussed the application of Xin’anjiang Model in basin short of hydrological data. The runoff-yield-under-saturated-storage mechanism of Xin’anjiang Model(three components) has been used to conduct runoff calculation. Through introducing hydrological model parameters from reference hydrologic station, the estimation problem of the runoff-module parameters under the shortage of measured runoff data has been solved. Genetic algorithm has been adopted in parameter optimization. According to the different confluent way, confluence process is divided to surface confluence, soil confluence and underground confluence. Soil and underground runoff are simulated by adopting different linear storage reservoir, while the surface runoff is simulated in the method of isochrones.(2) In order to make up for the defect of lacking runoff data, this paper uses DEM to extract river system, sub basins and the relative terrain information such as slope, area and isochrones. Deriving isochrones through the DEM avoids the tedious work of drawing them on the map. With the establishment of the Digital Elevation Model all over the country, it has important practical significance to apply it to the hydrologic calculation.(3) Uncertainty of model parameters inevitably exists. This paper analyzes the “Equifinality” phenomenon of the parameter groups and the uncertainty of each parameter by GLUE method, and the results show that uncertainty of each parameter is different. Then the sensitivity of each parameter is analyzed through perturbation analysis method. GLUE is a global analysis method while perturbation analysis is local. The two methods help us to have a better understanding of the uncertainty and sensitivity of each parameter and parameter groups.(4) Hydrology analogy is often used in ungauged basin. This paper estimates the peak flow through hydrology analogy to verify the rationality of the results obtained by the method of combing the DEM with Xin’anjiang Model which has been discussed previously.(5) The paper takes the northern urban region of Fuzhou city as an example to discuss the method of estimating urban runoff in ungaued basin. Specific way is: use reasoning formula method to calculate the peak flow of urban area based on the information extracted from DEM, and then obtain the flood process through generalized triangle method.