Groundwater Dynamic Response And Regulation Under Variational Environment In Canal-Well Combined Irrigation District

Under the impact of climate change and humanactivities, northern irrigation district water resource became short, the contradiction between supply and demand of prominent, ratio of well and canal water imbalance in recent years, resulting to disorderly exploitation of groundwater, farmland ecological environment deterioration, serious impact on irrigation district of sustainable development. So studying the groundwater level dynamic change under the changing environment and discussing reasonable program are contribute to a deeper understanding of groundwater cycle, scientific and rational response to influence of the changing environment on water resources. It has an important value on safe and efficient utilization of water resources.In this paper, selected Jinghui canal irrigation district in shannxi province as the research object, based on the analysis of the groundwater system, the characteristics of circulation of groundwater, and the external environment factors of groundwater, build groundwater dynamic response model. Simulate groundwater dynamic in different situations, and study reasonal program of groundwater regulation. Obtained the following results and conclusions:(1) The paper generalized the irrigation groundwater system, and analyzed groundwater level evolutive characteristics based on analyzing irrigation area landform features and hydrogeological conditions. The results showed that the main input of Irrigation area groundwater system are precipitation infiltration recharged, river and canal seepage recharged, the field irrigation infiltration and well irrigation regression supplies, etc., the main output of the groundwater system are artificial exploitation, phreatic water evaporation and lateral discharge of river, etc.; groundwater level cumulative decline was 11.88 m in nearly 31 years, at a speed of 0.38 m every year.(2) This paper expounds the relationship between the groundwater system and the external environment, analyzed the main external environment changing factors of the groundwater system of the irrigation area. Using Sliding average method, Spearman test and Mann-Kendall method analyze evolution characteristics of the climate change and human activity factors. The results showed that the external environment factors of groundwater including precipitation, evaporation, Irrigation intake water from canal head, field irrigation water use, water ratio of channel and well and groundwater exploitation. In nearly 30 years, precipitation declines significantly, its linear slope is 2.09mm/a, with the characteristics of annual uneven distribution and large interannual changes, evaporation declines but not obvious, its linear slope is 0.04mm/a; Irrigation intake water from canal headand field irrigation water use declines significantly, and linear slope respectively are 5.8833 million m3/a and 2.22026 million m3/a; groundwater exploitation declines non-significant, and its linear slope is 0.1 thousand m3/a; and water ratio of channel and well declines significantly.(3) Response model of groundwater depth affected by external environment was established based on the BP artificial neural network model and the CAR model. Identify the sensitive factors of groundwater level dynamic response by path analysis. The results showed that according to the calculation accuracy, BP model accuracy is higher than the CAR model overall, only in the IB area CAR is higher than BP, so choose the CAR model in the IB area, and choose BP model in the rest of the district as the regulation model in the later; Influenced by hydrogeological conditions, sensitivity factors show tiny difference.The maximum and minimum sensitive are water ratio of channel and well, irrigation intake water from canal head in IA and IB. In IIA and IIB in turn are water ratio of channel and well, field irrigation water use, groundwater exploitation, irrigation intake water from canal head and precipitation. The maximum and minimum sensitive are irrigation intake water from canal head and precipitation in IIC and IIIB. The sensitive order in IV is irrigation intake water from canal head, field irrigation water use, precipitation, groundwater exploitation and water ratio of channel and well. Due to the decrease of precipitation, replenishment to groundwater weaken, and groundwater exploitation is the main way of drain, so groundwater exploitation is a sensitive factor, and rainfall is relatively insensitive.(4) Using BP neural network model to predict the precipitation of 2011 to 2020 based on the historical rainfall data.Based on the mean irrigation intake water from canal head and groundwater exploitation of 31 years, setting people actions under different precipitation conduct groundwater level dynamic simulation of different change situation,and take the minimum amplitude as the criterion, and confirm the reasonable regulation scheme.The results showed that in the setting controlled period, each partition of the groundwater depth range is not big in addition to IIA in 2014,basically can achieve balance of the groundwater dynamic;.In the whole irrigation area, the largest amplitude is 0.7m(2017), the minimum amplitude is-0.01m(2012), the corresponding water ratio is 1.24.If implement reasonable groundwater dynamic control scheme the next 10 years, the cumulative amplitude is 1.32 m, which means the groundwater level of whole irrigation area will recover 1.32 m on the basis of average of many years, and achieve the goal of inhibition groundwater level continuing to decline and gradually recovered.