Response Of Groundwater Level To Utilization Ratio Of Canal To Well And Canal System Water Saving In Canal-well Combined Irrigation District

Jinghui canal irrigation district is located in the middle of the guanzhong plain in Shaanxi province. It is a typical well and canal irrigation district in northern plains. Although the total amount of runoff is more than water demands, but distribution in a year is uneven, and the storage capacity of reservoirs is very low. In recent years, due to the implement of some water-saving measures such as canal system and field water-saving improvement project, leads to a sharp decrease of the canal seepage and irrigation infiltration recharge. The imbalance between groundwater discharge and recharge leads to many phenomenons such as excessive ground water lowering and soil and water environment deterioration in some areas. Thus, the suitable canal water-saving measures and water utilization ratio of canal to well have a great significance on water resource management and water-saving reconstruction project.Taking Jinghui canal irrigation district as the study area, according to the irrigation area of underground water dynamic observation data in different years, using GIS technology and trend analysis method, the paper analyzed the variation characteristic and controlling factors of underground water, made a calculation of water balance, established a support vector machine regression model to simulate the irrigation water ratio of canal to well in different hydrological years; created a three-dimensional groundwater numerical simulation model with a numerical simulation FEFLOW software to simulate the response of groundwater to different situation of water-saving irrigation measures, provided the basis for water resource management and water-saving reconstruction project. The main contents are as follows:(1) The variation characteristic of groundwater level in irrigation district and it’s causes were analyzed. The groundwater is greatly influenced by precipitation, irrigation, and shows a trend of recovery after the first drop in a year. At the beginning of year, the water level is high, except in 2011, the water level in the end of 2012 and 2013 can’t return to initial value. The decline of groundwater level is due to the precipitation infiltration recharge and irrigation infiltration recharge reduced year by year, and in the decreasing trend of precipitation, the reduce of summer precipitation account is the main effect and the decline of groundwater exploitation has a less trend than irrigation water volume. The decrease of precipitation and irrigation recharge lead to the imbalance of groundwater.(2) Put six administrative zonings of canal irrigation district as the groundwater balance calculation units, the calculation of each unit obtains recharge, discharge and balance, the recharge includs precipitation infiltration recharge, canal water leakage quantity, irrigation infiltration recharge, mining return amount, the lateral recharge of groundwater. The discharge includs evaporation and lateral discharge. The irrigation district water balance calculation results show that: in 2011 and 2012, the total water balance volume is-13.42 million m3 and-25.85 million m3, the results are consistent with the basic dynamic variation character of groundwater.(3)Use precipitation, irrigation system, groundwater irrigation production, potential evapotranspiration(ET0) and average groundwater level in last year as input, average groundwater level in this year as output, set up a groundwater level regression model based on support vector machine(SVM). The model regular rate and validation period of RMSE are 0.003 m and 0.010 m respectively, the correlation coefficient(R) are 0.995 and 0.987, the fitting effect is acceptable; using support vector machine to simulate the water utilization ratio of canal to well in different hydrological years, to find a appropriate ratio of canal to well, and eventually get the ratio is 1.45~2.38 in wet year, 1.67~1.91 in median year and 1.50~2.00 in dry year.(4) Creating the irrigation district hydrogeology conceptual model and mathematical model, using FEFLOW software to simulate the response of groundwater to different canal scenarios of water-saving irrigation measures. The model test result shows that 80% of the water level error of observation well is within 1m; considering canal system effective utilization coefficient, field irrigation water-use coefficient and net irrigation quota. In the paper there are 11 kinds of canal system water-saving scenes which to analyze the underground water level dynamic response to different scene systems. The results show that: the response of groundwater to under branch canal water use coefficient is greater than the irrigation quota, than the main canal water use coefficient. Situation 11 is the most optimal scene, the best main and branch canal water use coefficient is 0.71, the under branch canal water use coefficient is 0.90. In the actual production, we can increase the field water use coefficient firstly, which has a positive effect on groundwater conservation.