Impact Of Urbanization On Runoff In Panlong River Basin

As the development of urbanization, the mount of urban population is increasing and the road construction is building rapidly, so that the impermeable area of underlying surface in urban has extended. Reducing soil infiltration and surface evaporation, and increasing surface runoff, cause the urban rain runoff process curve steepening and raise the risk of urban flood disaster. In addition, the maldistribution of rainfall leads to the unbalanced ratio of population to water demand, and the phenomenon of lacking water resources appears. The research of urbanization hydrological effects has become a hot spot in recent years.Panlong River is the mother river of Kunming city, and it has the largest watershed and the longest river channel above all rivers that run into Dianchi Lake. With the constant development in Kunming city, the urbanization process has become increasingly apparent and the underlying surface conditions in Panlong River watershed have changed a lot as well, which lead to a significant influence on the hydrological response of Panlong River. This paper set up the SWAT model by using the DEM data, the land use data, the soil data, the meteorological data, et al on the basis of the characteristics of urbanization process that the terrain and human activities have strong disturbance to Panlong River watershed. The SWAT model has certain suitability in Panlong River watershed is confirmed through simulation and test of the case in the domain under control of Songhua Dam station and Furun Bridge station. This paper used the model to research the hydrological response process under the change of land use in upper stream of Furun Bridge station, and then analyzed the influence on river runoff caused by land use type’s variations, and studied the influence on river runoff under different urbanization process simultaneously. The results provide scientific guidance for effective basin management, reasonable water and land resources planning in Panlong River basin under the urbanization process. In general, the research mainly achieved the following results:1、 Established an appropriate SWAT model, including the determination of model parameters, on basis of Panlong River watershed data, such as the DEM data, the land use data, the soil data, the meteorological data, the measured hydrology data and so on.2、 Simulated the hydrological process, respectively, in Songhua dam station and Furun bridge station with the SWAT model, and the results showed the Songhua Dam station basin which lies in nature domain has a better simulation result than the Furun Bridge station basin which locates in urban domain.3、Set up the land use transfer matrix of the years 1994-2000 and 2000-2008, which is based on the land use data in the 1994,2000,2008. The results showed that the land use types in watershed changed majorly in forms of forest land, agricultural land and urban land during these 15 years.4、Appling the land use data of the year 1994,2000,2008 as variables, the monthly surface runoff in 108 months, from 1999 to 2007, was simulated with the calibrated SWAT model, and the affections from variations of land use on watershed runoff were analyzed. The simulation results showed that the annual runoff variations are respectively-19.18%,19.18% and 7.31%, which means the self-restraint ability of the underlying surface is gradually reducing.5、Taking the land use data in 1994 as original states and the land use types data in 2008 as human-act-affecting states, the surface runoff from 2006 to 2007 was simulated and compared with the measured values. The results showed that the assumption of simulated surface runoff which is under no human activities is generally lower than the measured values, but the simulation values of runoff under the influence of human activities turned out higher or lower than the measured ones in many times, which means the measured values under human activities’ influence turned out to be lower than the simulated ones when the rainfall condition is equal, and the variation is relatively big.6、Within the calibrated SWAT model, buffer the area of land type on the basis of area of urban land in 2008 and set up scene simulation of different urbanization process. The results showed that annual runoff increases in 0.23m3/s-0.34m3/s when the area of urban land increases 1km2.