Effect of ecological water replenishment on groundwater recharge in the Beijing-Hangzhou Grand Canal
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Abstract:
Ecological water replenishment is an important measure to improve the ecological environment of rivers and lakes and reduce the groundwater deficit. The dynamic change of groundwater level is the most intuitive index to evaluate the effect of the short-time ecological water replenishment. In order to scientifically evaluate the effect of the ecological water replenishment on the Beijing-Hangzhou Grand Canal since 2022, it is necessary to explore the dynamic changes of the groundwater levels in different reaches of the Grand Canal.Based on the groundwater level data from 419 phreatic water and 173 confined water monitoring wells along the Beijing-Hangzhou Grand Canal (the north section of the Yellow River, including Xiao Canal, Wei Canal, South Canal, North Canal, and Tonghui River) during the replenishment period in 2022-2023, the river channel infiltration was calculated by the water balance method, and the variations of the groundwater level was analyzed along the river channel and in the agricultural irrigation water source replacement regions.Results showed that: (1) The volume of ecological water replenishment for the Beijing-Hangzhou Grand Canal in 2023 was 926 million cubic meters, and the infiltration volume was 149 million cubic meters. Compared to the lining channels such as Xiao Canal, North Canal, and Tonghui River, Wei Canal and South Canal had a high permeability, which can recharge groundwater around the river channel more efficiency. (2) During the replenishment period, the phreatic water level in the range of 0~10 km around the river decreased 0.80 m, which confirmed that the current water replenishment amount is not enough to fully eliminate the impact of spring irrigation water withdrawals in March to May on the groundwater level. (3) The average decrease of groundwater level in regions beyond 10 km from the center line of the river channel (unaffected area) was 1.01 m. And the average decrease of groundwater level in regions within 10 km from the center line of the river channel was 0.80 m, which was significantly lower than that in the unaffected area, indicating that ecological water replenishment effectively mitigated the downward trend of groundwater level. (4) Groundwater level has risen by 0.48 m compared to the same period of last year and the decrease of groundwater level has reduced by 0.19 m during the spring irrigation period, indicating the positive impact of replenishment on the groundwater level recovery. (5) There had a delayed effect on the response of the groundwater level to the water replenishment, which was shown as the closer distance to the river, the smaller decrease of the groundwater level. (6) In the agricultural irrigation water source replacement regions, compared with the same period of last year, the confined water and phreatic water levels have risen by 3.17 m and 0.27 m respectively, which showed the water source replacement can effectively alleviate the decline in groundwater levels caused by irrigation water withdrawals.This study is of great significance to grasp the changing law of groundwater level by ecological water replenishment, which can provide the basis for further optimization of ecological water replenishment plan. Changes in groundwater levels in the Beijing-Hangzhou Grand Canal after the two consecutive years of ecological water replenishment indicated that the downward trend in groundwater levels due to irrigation withdrawals was difficult to reverse through the ecological recharge. While continuous implementation of ecological replenishment on rivers with strong infiltration and high irrigation water demand can promote the recovery of groundwater levels effectively.
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