Historical Studies On Water Environmental Changes And Water Resources Carrying Capacity In Haihe River Basin

Water is essential to the survival and reproduction of mankind and all other life-forms. Sustainable utilization of water resources and steady-going security of water environment are necessary to the sustainable development of economy and society. At present the problems on water resources shortages and environmental degradation have been paid attention to increasingly. With the Haihe River basin taken as the sample, which is most problematical on water in China, and within the relatively long period of the Xian Qin ( - 221 BC) to the twentieth century investigated, this dissertation has systematically researched the historical movement of water environment, including rivers, lakes, marshes and other low-lying water-bodies. Based on the analyses of both natural and artificial factors such as climate, vegetation, population increase and river basin development, where the water environment resulted from, this dissertation also provided corresponding recognition and strategy on water environment improvement of the river basin.The main contents and conclusions of the dissertation are following,1. The water system of Haihe River resulted from a very complex evolvement in the long history. From Dong Han Dynasty (25-200 A. D. ) to the end of the Sui Dynasty (581-618 A. D), being silted and extruded by the Yellow River and the Yongding River delta, additionally with canalling by mankind, river systems in the Hebei plain had gradually evolved to confluences to the sea over the original distributaries. The present situation of the water system was also due to the reconstructions by all dynasties later on. Records on water transport in past dynasties, verified by some other discrete historical and archaeological documents, showed that river courses of Haihe basin generally had a larger runoff and a smaller water level variation in the ancient time than those of present, though in the history the seasonal and annual runoff had evident variations also. After the Song (960-1279 A.D.) Dynasty and Yuan Dynasty (1271-1368 A.D.), sedimentation of the main rivers increased distinctly thus watercourses silted up and changed its route very often, and thus damages of them became sever. In latter-day, with water usages and discharged pollutions increasing, the immoderate water resources ' utilizations and development made the river dried and polluted seriously, the description of 'all rivers are dried and allwater-bodies are polluted' is an important token of the severe water environment degeneration in present time. 2. Researches showed that in the Haihe River basin lakes and marshes distributed everywhere while as water-bodies covered large area in the plain before time of the Qin Dynasty. During the Han Dynasty and Tang Dynasty, lakes and mashes were still stably in developing. In the Song Dynasty, to control the water level along the Daqing River, the 'Tang-Luo' water defense line which was long of 400 km was formed by projects; this made the low-lying shallow lake areas reached its historical maximum in the middle part of the basin. Estimated by the data from history, the maximum total area of the lakes and all low-lying water-bodies was over 10, 000 km2, and the maximum total cubage amounted to 24. 82 billion m'\ In the Ming Dynasty (1368-1644 A. D.), the Qing Dynasty (1644 - 1912 A. D.) and later on, lakes and all low-lying water-bodies were diminished and reduced in a accelerating trend. The modern water reservoir projects also have displaced most of water surfaces existing to the upriver mountain areas from its original in the plain. Amounts of springs and full wells in this area in the history, indicating the abundance and high level of groundwater of that time, now almost had all disappeared. This fact reflected the great changes in water environment of the river basin.3. Natural factors' variation brought certain effects to the water environment changes. Air temperature and precipitation showed obvious fluctuation in the history, floods and droughts also had certain periodicity. In the past 2000 years, it tended to be drier for the climate, including the variations of drought and flood in the millenarian, centurial and yearly periods. Rivers and lakes varied its amount and area of water visibly due to corresponding climate, including precipitation, flood and drought. But for a long period, such as for the period of more than 2000 years, the climate change especially in recent 50 years was not the leading factor in the great change of water environment in the Haihe basin. More over, the northern branch of Yellow River and the Yongding River were among the main powers of the landscape creation for the Haihe basin, they took comparative effect to the outcome of the Haihe River water system, including lakes and low-lying water-bodies.4. The mankind activities have been more and more the leading factor of the changes in water environment. Population increase, economy and society expansion led the increasing demands on water resources and farming lands, and thus directly changed the water environment. Cultivation in tilted mountain areas destroyed the water sources, increased water loss andsoil erosion. Land reclamations from rivers and lakes reduced the space of water environment. From the modern times started, huge amount of groundwater have been exploited, the discharges of industrial pollution and domestic sewage also have increased significantly; more and more severe impacts have been brought to the water environment. Further more, the constructions of water control projects also brought negative effects to the water environment while as huge benefits produced.5. The changes of water environment in Haihe basin reflected the limitations of water resources and water environment carrying capacity. From the Han Dynasty and Tang Dynasty to the Ming Dynasty and the Qing Dynasty, population of Haihe basin maintained a level of millions to 10 million. During the Yuan, the Ming and the Qing Dynasty, on the one hand, new drought-tolerant crops were introduced into the region to meet the basic food demands of increased population, on the other hand, agricultural technologies and multiple cropping index were also kept in improving. Reclaiming farm land and developing rice fields and irrigation works were also tried ceaselessly, but under the restriction of natural water conditions, the achievements of these activities were limited. In that times, the annual requirements of grains, which weretransported to the capital through watercourses and canals, were 3- 6 million dan (ldan - 60kg), and these requirements proved the limitations of the natural carrying capacity of the river basin. The amount of annual virtual water of the water transported grains were about 8. 1 X 108 m3 to 9. 72 X 108 m during the Ming Dynasty and the Qing Dynasty, it was 3. 7% to 4. 4% of the mean annual runoff amount of the Haihe basin in that time, and it was over 10% of the reasonable water resources quantity that could be exploited within the international standard. The water transported grain reduced the regional agricultural water'requirements and had once relaxed the conflicts between the population increase and water environment. But in the recent 50 years, the increase of population, the expansion of irrigation area, the improvement of grain production, the high-speed development of economy, are all at the cost of environment. Water demands from the social-economical development have far more exceeded the water resources carrying capacity of the river basin.6. The history of water environment evolvement of Haihe basin illuminated it profoundly that water resources and water environment are essential factors of sustainable development. It' s necessary to identify and to deal with the dialectical relationship between mankind and nature correctly. In thedevelopment of a river basin, attentions need to be paid to the potential and cumulate impacts on water environment. The multiple value of water environment also should be understood in-depth, and water environment carrying capacity should be sufficiently taken into the account of social-economical development. Water resources and water environment have been come into important constraints to social-economical development; environment protection should be focused on too while as the economy in developing. From the history study, it showed that there is a possibility to restore water environment moderately.