Study On Runoff Evolvement And Its Driving Mechanism Of Naoli River Basin In Recent50Years

Runoff is an important object of water recycle research. Due to runoff variation is involved in many factors and relations among their interactions are very complex, which is still difficult content during of performing hydrology and water resources research tasks. Due to the interaction effects between runoff process and ecological are very obvious, runoff is an important focus for hydro-ecology or eco-hydrology, and also is highly focused by scientists. Runoff flowing into wetlands is decreasing, the spatial-temporal variation difference between runoff process and ecological water demand process of natural wetland is existing, which lead structures and function of wetland to degrade, this is a typical phenomena that runoff influences ecological process. Selecting a watershed as an unit, identifying variation factors influencing runoff formation and explaining their driving mechanism, comprehensively regulating anthropogenic factors, reasonably utilizing natural factors, restoring ecological processes of wetland based on hydrological processes are of great importance scientifically and practically.Runoff variation is a key of hydrological processes of watershed. Areal runoff formation processes of watershed will control water level, velocity and flow variation processes of river, and even influence inputs and outputs of materials and energies in various ecological systems, therefore, runoff will make a great influence on ecological security pattern of watershed. Watershed runoff evolution can make an objective response to natural factors variation and anthropogenic activities, but this responses shows both accumulative and dramatic variation features.Naoli river basin(NRB), with an area of24,863km2, is the largest basin and also the largest marsh distribution area in Sanjiang Plain, Heilongjiang, China. The hydrological evolution process of wetland in NRB has made a marked ecological responses to anthropogenic activities, also reflected the drying trend of the Sanjiang Plain, Northeast China. Performing a study on evolution features and its key driving factors and driving mechanism of NRB is greatly typical and representative, which will be of great importance for scientifically allocating water resources for NRB and even Sanjiang Plain in future.During of performing this study, the underlying variation processes controlled by four different hydrological stations in NRB are analyzed, in combination with variation factors such as precipitation, evapotranspiration, temperature, and groundwater, and etc, respectively. Besides, the leading factors influencing runoff variation and theirs developing trend in future are also analyzed. Response features of runoff variation to influencing factors in catchment controlled by fours hydrological stations are analyzed. Based on the spatial-temporal rules of runoff evolution in NRB, in accordance with two-dimension nature-artificial evolution theories of runoff, explaining how to effectively performing sustainable water resources regulation mechanism in these watersheds holding wetland conservation object of cold regions in north.Runoff evolution features in NRB in this study mainly include:(1) The monthly average water level of Naoli river at Caizuizi hydrological station in different ages showed a marked decline tendency, the annual mean water level dropped from96.63m during1960-1969to95.59m during2000-2005, the water level drawdown is1.04m;(2) The annual runoff flowing into wetlands in NRB decreased. Duration of Naoli river and its tributaries being thoroughly frozen from riverbed to river-water-surface showed an prolonged trend, and the water level drawdown in frozen seasons increased. The water storage capacities of wetlands in NRB declined.(3) The interactions between ground water and surface water in wetland areas are close. The ground water level variation span is bigger than that of surface water level in wetland areas of NRB. The drawdown of ground water level promotes the surface water level to decline, correspondingly. In recent20years, the cultivated area extension of rice field in upstream NRB has made an adverse influence on the hydrological processes of wetlands.Runoff evolution driving mechanism in NRB in this study are summarized as below:(1) Land use pattern changes greatly contribute to the evolution of hydrological processes. Wetland area decrease and farmland area increase significantly contribute to the runoff depth decrease of wetlands in NRB;(2) Reservoirs, ditches and dykes in NRB have greatly changed the runoff generation processes.(3)Thickness of the seasonal frozen soil layer becoming thinner and the evaporation potential becoming bigger also contribute to the runoff depth reduction and the water level drawdown of rivers.In a word, the runoff depth variability in NRB has been mostly posed by anthropic activities. The drying trend of NRB to some extent also represents the Sanjiang Plain. Northeast China, which have made an adverse impact on wetland hydrological regime and biodiversity conservation. However, the commodity grain base construction in NRB and Sanjiang Plain will be a priority option, due to the grain security is a severe challenge for China. Therefore, water saving methods for agriculture irrigation is urgent to be adopted and popularize. Moreover, the ecological hydraulic projects suitable for wetland water supply and storage is also supposed to be developed and designed. Global climate warming also makes a contribution to the evolution of hydrological processes of wetland in NRB.The present study results will provide a scientific basic for developing an integrated watershed management program for NRB, especially, restoring the wetland hydrological processes, maintaining or improving the wetland structure and enhancing the wetland service functions.