Dynamic characteristics of groundwater level and exploitable amount of groundwater source in Jiuxian county, Tai'an
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摘要: 泰安市城区水资源供需矛盾突出,地下水资源开采引发了岩溶塌陷等地质环境问题,亟需查明岩溶塌陷生态水位约束下水源地的允许开采量,确定水源地最优取水方案。以旧县水源地1980—2021年的地下水位、年降水量、地下水开采量、岩溶塌陷等数据为基础,探讨人类活动对水源地地下水位的演变的影响因素,分析发生岩溶塌陷的地下水临界水位。基于Modflow-GWM软件构建泰安城区−旧县岩溶水系统流动与管理耦合模拟模型,探讨防止岩溶塌陷发生的地下水允许开采的资源量。结果表明:(1)孔隙水水位年内动态受降水影响明显,呈现“降水−补给”型特点;岩溶水水位变化呈“枯低丰高”的特征,水位动态变化属降水入渗−开采型;(2)旧县水源地地下水位自1980—1990年呈现大幅下降,1990—2003年岩溶地下水位基本呈现波动下降,2004年后水源地地下水位上升较为明显;(3)研究水位动态与岩溶塌陷关系得出,防止发生岩溶塌陷的水源地临界水位为108 m,处于岩溶含水层顶板以上2 m;(4)通过地下水管理模型,确定在临界水位时模拟区岩溶水可开采量为8.2~8.5 万m3·d−1,其中旧县水源地可开采资源量为3.2~3.5万m3·d−1。Abstract:
In this study, the effect of human activities on the evolution characteristics of groundwater levels in the water source area of Jiuxian county and its influencing factors have been discussed, based on the data of groundwater levels, annual precipitation, groundwater mining output and karst collapse in the study area from 1980 to 2021. The critical groundwater level to prevent karst collapse has also been determined. In addition, based on Modflow-GWM software, a coupled simulation model for the flow and management of karst water system in Tai'an City and Jiuxian county has been constructed, thereby exploring the allowable extraction of water resources in terms of the karst collapse prevention. The research results indicate that, (1) The annual dynamics of interstitial water are significantly affected by precipitation, with the lowest annual water level in late June and the annual highest from late August to late September during the rainy season, presenting the characteristics of "precipitation-replenishment" type. The dynamics of karst groundwater within the year are affected by the obstruction of pore water discharge in the Quaternary system. The highest water level within the year generally lags slightly behind the concentration from September to October, while the lowest water level occurs from May to June. The groundwater level changes by about 5 meters within the year. The water level changes exhibit a characteristic of "a low water level in the dry season and a high water level in the wet season", and the dynamic changes of water levels are characterized with the type of "precipitation infiltration-mining". (2) The groundwater level in the water source area of Jiuxian county showed a significant downward trend from 1980 to 1990, and the karst groundwater level showed a basic fluctuation and decline from 1990 to 2003. The groundwater level in the water source area has increased significantly since 2004. (3) Since 1988, the water source area in Jiuxian county has entered a period of high incidence of karst collapse. From then on to 1994, the water level had rebounded, fluctuating between 96 m and 108 m and was located near the bedrock surface. This period had also experienced a high incidence of karst collapse in this area, with the collapse area expanding northward from Jiuxian county to the Yuanzhuang-Yanglou area. After 1995, the intensity of karst collapse in the area decreased, but there still occurred collapse from time to time. By 2001 the development period of karst collapse in the area, the water level showed an overall downward trend and fluctuated above and below the bedrock surface, with an elevation of 95–110 m. In the first half of 2003, high-intensity mining continued, with water levels ranging from 86 m to 98 m. In 2013, the high-intensity mining in the rainy season and continuous low water levels caused geological disasters of high-intensity karst collapse at a large-scale. Since 2005, water levels have shown an overall upward trend, fluctuating between 106 m and 116 m above the bedrock surface. During this period, one time of collapse occurred in 2006, and no new collapse was observed. Based on the relationship between water level dynamics and karst collapse, the critical water level of the water source area to prevent karst collapse is 108 m, located 2 m above the roof of the karst aquifer. (4) According to the groundwater management model, the mining output of karst water in the simulation area at the critical water level is determined to be 82,000–85,000 m3·d−1, of which the exploitable volume of centralized exploitation in the water source area of Jiuxian county is 32,000−35,000 m3·d−1. This study is of great significance for the sustainable development and utilization of karst groundwater resources and the tackling of environmental geological problems. -
表 1 识别验证后模拟区降水入渗系数取值一览表
Table 1. Values for precipitation infiltration coefficient in the simulated area after identification and verification
参数分区 参数分区 参数分区描述 1 0.12 山前基岩裸露区 2 0.20 丘陵山前地带,岩性为砂质黏土夹砾石粉砂,厚度薄 3 0.30 牟汶河河道两侧,岩性为砂含砾石 4 0.14 基岩裸露区 5 0.25 位于牟汶河西侧,土地类型主要为农耕地、林地,植被覆盖率较高 6 0.22 位于泰安城区及以西,岩性主要为粉质黏土夹中粗砂 7 0.22 分布于城区水源地周边 8 0.21 丘陵山前地带 表 2 识别验证后模拟区孔隙水渗透系数和给水度赋值
Table 2. Pore groundwater permeability coefficient and yield value in the simulated area after identification and verification
分区 水平K/m·d−1 垂向/m·d−1 给水度 分区 水平K/m·d−1 垂向K/m·d−1 给水度 1 0.15 0.000 10 0.040 8 3.00 0.000 30 0.23 2 0.15 0.000 10 0.040 9 0.85 0.000 15 0.30 3 2.80 0.000 18 0.070 10 0.75 0.000 15 0.30 4 3.00 0.000 30 0.230 11 3.00 0.000 50 0.35 5 15.50 1.500 00 0.200 12 0.50 0.000 10 0.25 6 0.15 0.000 15 0.045 13 5.00 0.000 50 0.35 7 3.00 0.000 30 0.230 表 3 识别验证后模拟区岩溶水渗透系数和贮水系数赋值
Table 3. Values of permeability coefficient and storage coefficient of karst water in the simulated area after identification and verification
分区 水平K/m·d−1 垂向K/m·d−1 弹性储水率/m−1 0 15.0 104.00 6.0×10−4 1 5.0 0.50 5.0×10−4 2 4.5 0.45 3.0×10−4 3 2.5 0.25 2.5×10−4 4 2.8 0.28 3.0×10−5 5 2.0 0.20 5.5×10−4 6 2.3 0.21 3.5×10−5 7 4.0 0.40 5.0×10−5 8 4.5 0.80 9.5×10−5 9 4.0 0.20 5.0×10−5 表 4 模拟开采10年地下水量均衡分析表
Table 4. Equilibrium analysis of groundwater amount in simulated mining for 10 years
均衡项 流入流出量/万m3·d−1 流入流出量/万m3·年−1 百分比/% 补给项 孔隙水 降水入渗量 6.80 2 482.00 83.64 河流入渗量 0.28 102.20 3.44 灌溉入渗量 0.85 310.25 10.46 侧向流入量 0.20 73.00 2.46 小计 8.13 2 967.45 100 岩溶水 降雨入渗量 0.58 211.70 6.61 河道渗漏量 2.55 930.75 29.04 侧向径流量 0.65 237.25 7.40 越流补给量 5.00 1 825.00 56.95 小计 8.78 3 204.70 100 排泄项 孔隙水 农业开采量 1.50 547.50 23.08 越流排泄量 5.00 1 825.00 76.92 小计 6.50 2 372.50 100 岩溶水 水源地集中开采量 3.50 1 277.50 41.18 分散开采量 5.00 1 825.00 58.82 小 计 8.50 3 102.50 100 孔隙水补排差 1.63 594.95 / 岩溶水补排差 0.28 102.20 / -
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