Study On Basin-oriented Hydrological Effects Of Urbanization

With the accelerative development of global urbanization, urban river system and natural hydrological cycle have been disturbed and destroyed. These disturbances and destruction result in a series of water eco- environment problems, such as fresh water shortage, flooding disaster frequency, water pollution, river discontinuous flow, wetlands decrease, desertification expansion, groundwater overexploitation, seawater intrusion, water loss and soil erosion, river ecosystem destroyed, etc. The hydrological effects of urbanization have been one of the leading edge and hot issue in the global climate and environment change fields.Now, researches on the theory and cases studies on hydrological effects of urbanization are mainly conducted from viewpoint of the urban itself. The problem-solving strategies on hydrological effects of urbanization focus on engineering methods which involves the water supply, water purification, flood and waterlog controlling engineering. However, these engineering measures could not really resolve the water problems produced by urbanization, only transformed the urban water problems to the other regions of the basin or other basins. Have recognized of the defects of present research perspective, author of this dissertation proposes a new research idea on hydrological effects of urbanization at basin scale, whose focus is put on the disturbed natural hydrological cycle during urbanization in a basin. In the study on basin-oriented hydrological effects of urbanization many different kinds of relationships should comprehensively be consider, including research scales from nodes to lines to areas, the distributed proportion of precipitation among the"runoff-evaporation-storage-infiltration", between the upper and the lower reaches, between the society water requirement and ecological water requirement, etc. Study results could be used for establishment of scientific urbanization model and urban system planning at a basin scale, and for the rehabilitation and eco- compensation to natural hydrological cycle during urbanization.Based on an analysis of the interaction processes between natural and social hydrological cycle, the dissertation deepens the concept of healthy hydrological cycle. The healthy hydrological cycle reflects human recognition degree to the structure and function of the river system. Both the social and natural functions of a river system should be ensured at the same time. Sustaining fluidity of a river system, well water quality and water ecosystem are the main signs of a healthy hydrological cycle. The evaluation indexes of healthy hydrological cycle include hydrological characteristic parameters, river system structure, hydrological location index and water quality etc. Based on the characters of urbanization and the function of river system, this dissertation puts forward the pressured-state–response coupling mechanism model between urbanization and natural hydrological cycle. The urbanization process relevant to the natural hydrological cycle could been understood from 4 aspects, namely the amount of urban population and economy increasing, urban water supply-drainage system expanding, urban space expanding and city number increasing, the interaction of the cities. Then, a concept model for the coupling mechanism and its evaluation index between natural hydrological cycle and every aspect of urbanization is discussed. The evaluation index system includes 10 common indicators as following: drought index, urbanization level, stage of economic deployment, land-use intensity, proportion of construction land, hydrology orderliness, proportion of water resources development and utilization, hydrological location index, water quality, damage degree of vegetation cover. Using the grade assessment method assign to each index, a mathematical expression for synthetically evaluation of the healthy state of hydrological cycle during urbanization can be obtained. Research results illustrate that the hydrological cycle is extreme diseased, if the exponential valuation is below 0.2; while diseased, if the exponential valuation ranges from 0.2 to 0.4, sub-healthy, if the exponential valuation ranges from 0.4 to 0.6, healthy, if the exponential valuation ranges from 0.6 to 0.8, very healthy, if the exponential valuation ranges from 0.8 to1.Taking YiShuSi basin as the study region, this dissertation deals with the hydrological effects of urbanization in this region at different scale: urban node, sub-basin, whole basin, analyzes the damaged natural hydrological cycle, and evaluates the healthy hydrological cycle index in different urbanization stages. The results show that the main hydrological effects of urbanization express as the water scarcity, water quality and flooding disaster at urban node scale, however, at basin scale, hydrological effects of urbanization more manifest as disturbance and damage to the basis hydrological cycle and ecological function of natural hydrological cycle. From the primary urbanization stage to start-up of accelerative urbanization stage, then to the middle of accelerative urbanization stage, the healthy hydrological cycle index during urbanization trends to decline. In connection with the characteristics and disturbance degree at different scale and different urbanization level, different management strategies of urbanization hydrological effect are put forward in this dissertation based on the eco-compensation and rehabilitation of hydrological cycle.