岩溶洼地内涝蓄水量与不同级次裂隙对溶质迁移影响的室内实验与模拟

Laboratory experiment and simulation of solute transport affected by different grades of fissures and water storage of waterlogging in karst depression

岩溶洼地在西南地区分布广泛,岩溶地下水为当地居民生产和生活的主要水源,研究岩溶洼地内涝条件下裂隙系统中的溶质迁移及响应规律可为峰丛洼地区岩溶地下水的污染防控提供科学依据。基于相似原理构建了岩溶洼地-裂隙系统物理模型,采用对流-弥散模型和脉冲响应模型对溶质迁移过程进行了模拟分析,探讨了不同级次裂隙和内涝蓄水量大小对溶质迁移的影响。结果表明:大裂隙作为优先水流通道,对溶质迁移起主要的控制作用;小裂隙对溶质迁移起暂时储存和缓慢释放的调蓄作用,其溶质迁移的叠加过程使总出口溶质迁移的"拖尾"效应更加明显;随着内涝蓄水量的增加,稀释作用增强,导致溶质峰值质量浓度降低、溶质质量浓度回归至本底值的时间延长、延缓释放溶质的质量增加。该物理模型是对复杂岩溶洼地系统内污染物迁移研究的一种新探索,其模拟结果进一步深化了对洼地内涝条件下面源污染物在岩溶水系统中迁移规律的认识。

The karst depressions are widely distributed in southwest China.In this area,the karst groundwater is the main water resource for the local residents to live and produce.Studying the solute transport and response law in the fissure system under karst waterlogging conditions can provide a scientific basis for karst groundwater pollution prevention and control peak-cluster depression.Based on similarity principle,a laboratory physical model of karst depression-fracture system has been establishea.The solute transport processes were simulated by advection-dispersion model and impulse response model,and the effects of different grades of fissures and water storage of waterlogging in depression on solute transport were discussed.The results indicate that the large fissure is performed as the priority flow channel,which plays a major role in controlling solute transport.The small fissures play an important role in adjusting the transient storage and slowing release in solute transport process,and the superposition processes of solute transport in small fissures makes the trailing more obvious in breakthrough curve at the total outlet.As water storage of waterlogging increases,the dilution effect enhances dramatically,which leads to the gradual decrease of solute peak concentration,the time extension of solute concentration returning to the background value,and the increase of the delay-release solute mass.This physical simulation model is a new exploration of pollutant transport in complex karst depression systems,which deepens the understanding of solute transport process in karst water system under waterlogging conditions in depression with surface pollution.