Changes Of River System And Hydrological Process Under The Impacts Of Urbanization

Rapid development of urbanization improves living standards, socio-economic development. However at the same time, it also brings a range of issues including ecological environmental degradation, depletion of river systems, and intensified flood. In economically developed river plain regions, the extreme environmental events caused by urbanization have become a threat to people’s normal life and work, limiting the sustainable development of the region and causing wide attention of society. Thus, conducting research about the river system in terms of structure and function, connectivity, hydrological response and flood risk is urgent and practical.Yinfeng plain lies in Zhejiang Province. Under the intensive interference of urbanization on behalf of human activities, changes of river system speed up, regional water environmental and ecological problems increases, and impacts of floods are also increasing. Therefore, it has theoretical and practical significance to study the river system structure and function, connectivity, hydrological processes and flood risk of Yinfeng plain and Yongcaopu area.This paper took Yinfeng plain as typical research area, comprehensively using geographic information system and remote sensing technologies, geostatistical methods, time series analysis, and physical geography comprehensive analysis to analyze changes of land use, river system’s structure and function, connectivity, hydrological characteristics and flood risk, exploring the impacts of human activities, especially urbanization, on river system, hydrological process and flood risk based on the theory of physical geography, geographical hydrology, stochastic hydrology, river geomorphology and other disciplines. It would be a reference and data support for the management, protection and planning of river system and flood control under changing environment, as well as a sustainable urban development strategy. The main contents and results are as follows:(1) Yinfeng plain land use and cover change research. Interpreting, classifying and extract urban construction land, agricultural land and water body from land-use maps and remote sensing images. Dividing Yinfeng plain into West Yin River plain and East Yin River Plain according to water conservancy planning, also rapidly developing area and slowly developing area according to the degree of urbanization. The area of three land use types in 1990a,2003a and 2010a are then calculated to establish land use change evaluation index to evaluate the magnitude of the change, the average annual rate of change, land use dynamics, urban land expansion strength index and the information entropy of land use structure. The results showed that in the process of urbanization, the urban construction land replaced agricultural land intensively. For Yinfeng plain overall, construction land increased by 226.53%, agricultural land decreased by 71.67%, and water area decreased by 19.47%, in 20a. Urban construction land expanded greatly and chaos of land use structure increased.(2) Changes of river system structure and function in Yinfeng plain under the impacts of urbanization. Evaluating indicators of river structure and function in 1990a, 2003a and 2010a using digital data of river system. Results showed that length and area of river system reduced, structure simplified, connectivity of the channels decreased, and regulation and storage capacity weakened in 20a. The higher the degree of urbanization in the region, the more obvious changes are. Pearson correlation test showed that the type of land area, water general characteristics indicators and river system connectivity indicators are highly correlated with the urbanization rate of Yinfeng plain.(3) The impacts of human activities, with the representative of urbanization and water conservancy construction on hydrological regime of Yinfeng plain. Based on daily rainfall and water level data from 1960s to 2000s, analyzing annual rainfall, flood season and dry season rainfall variation trends, anomaly percentage. Then predicting precipitation variation trends and difference in different degree of development areas using R/S analysis method. As for the water level, comparing rainfall variation, rainfall coefficient and coefficient of elasticity in different degree of development areas, as well as the impacts of urbanization on regional rainfall patterns, using the t test, KS test, regression analysis and the range of variability approach to analyze water level trends, process and degree of variation, as well as water connectivity changes;The results showed that water level and rainfall had responded to intensive human disturbance in nearly 45a. Annual rainfall showed an upward trend, annual rainfall, flood season and dry season rainfall anomaly percentage reaches its maximum in the 1980s or 1990s; Hurst exponent indicated that future changes in rainfall and differences within two different degree of development areas will maintain growing trends; With the development of urbanization, enhancement coefficient of rainfall continued to increase, and the elasticity coefficient in flood season rainfall had the maximum value, which all indicated that rainfall changes is positively related to the degree of urbanization, and the flood season rainfall is under the greatest impacts; average annual heavy rain and rainstorm number increased, urban rain island effect intensified. Daily water level data highly dispersed which does not fit the normal distribution; average annual water level showed general upward trend; the RVA analysis shows that under the regulation of the water conservancy project, extreme changes in water level stabilized; hydrological connectivity declined in the 1990s at first, then gradual recovered; In the rapid developing period, hydrological connectivity increased in February to April. Finally, comprehensively quantify the relation within rainfall, human activities and water level showed that rainfall changes and human activities attributed 79% and 21% to the water level changes.(4) Assessment of flood risk and changes of flood risk under the influence of urbanization in Yongcaopu region. Based on GIS and Analytic Hierarchy Process, the impacts of urbanization on flood risk from the aspects of time and space were analyzed. The result showed that:from the aspect of time, the most rapidly developed areas, such as Jingbo city, Xiaoshan district Hangzhou, had the biggest flood risk; from the aspect of space, the flood risk during the year 2001a-2006a increased more quickly than that during the year 1991a-2001a, which indicated the positive relation of flood risk and urbanization.