Research On Evolution Of Groundwater Circulation Environment In Sanjiang Plain

Sanjiang Plain is a fertile flatland located in Northeast China, with Songhua River flowing through the plain. Heilongjiang and Ussuri River respectively constitute the northern and eastern border. After a 50-year agricultural development, Sanjiang Plain, which was once called "Great Northern Wilderness", turns into North Warehouse and has become an important commodity grain production base now. However, over cultivation has destroyed the ecological environment, such as Ground water level continue to decline, wetland significantly reduce, and a large number of species disappear. Therefore, the rational exploitation and effective use of groundwater resources, the harmonious development between ecological environment protection and agricultural production become an important issue in the future development plans on Sanjiang Plain.Materials of hydrology, meteorology, geology and hydrogeology in study area were largely collected, then groundwater occurrence form, groundwater recharge and discharge, groundwater dynamic types were analyzed. This paper focus on the study of water exchanged between river and aquifer and groundwater circulation. Finally, numerical model of groundwater flow was established to predict the groundwater level and analyze the trend of groundwater circulating evolution.Sanjiang Plain is a typical continental monsoon climate with concentrated precipitation in hot season. The material of main exploited aquifer is quaternary unconsolidated rock, such as sand and gravel. The study area could be divided into two aquifer system by the watershed of Wanda Mountain, the small Sanjiang Plain system and Muling-Xingkai Plain system. Groundwater flows from southwest to northeast, which is controlled by terrain elevation. The main recharge items include infiltration of precipitation, lateral runoff, surface water seepage and irrigation permeance. The main discharge items include exploitation, phreatic water evaporation, overland flow and lateral runoff. The dynamic types of groundwater can be divided into three types include infiltration-evaporation, runoff and exploitation.There is frequently hydraulic connection between surface water and groundwater in study area. The simulation result shows that groundwater discharge to the river in dry season and the opposite situation occurs in wet season. Overall, river recharges more to aquifer in a whole year due to the riverside exploitation of groundwater, which amount could be 277 million cubic meters.The condition of groundwater circulation has changed so much since the agricultural development in mid-20 century. The hydraulic gradient became larger and groundwater discharge diversified. Artificial exploitation has become the main way of discharge. Groundwater recharge and discharge increased 70%. Groundwater level continues to decline and the cone of depression has generated in some area. On the other hand, on the surface, wetland area lost more than 80%, while the cultivated area has increased by about 38.55×105hm2. The correlation analysis among the change of land use, precipitation, temperature and groundwater level shows that the main driving force of the evolution of groundwater circulation is the large increase in groundwater exploitation. Changes in land surface conditions caused by expansion of cultivated area, changes in surfacewater dranage, as well as changes in temperature and precipitation exacerbated this trend.The simulation results show that groundwater storage will increase under the gradually decrease of groundwater exploitation and the total recovery amount could be 3.03 billion cubic meters. Regional groundwater decline will be curb and groundwater level will increase in some area. The increase rate of irrigated land should be controlled water-saving irrigation measures should be promoted. The need of ecological water should be given full consideration.