河水下悬挂饱水带及非饱水带水分布与运移特征试验研究

Study on water distribution and migration characteristics of inverted saturated zone and unsaturated zone beneath river

地球陆地表层非饱和带是自然界水循环的枢纽,研究其水分布与运移特征具有重要意义。本研究通过室内砂箱试验,开展不同河水深和地下水埋深的河水渗漏补给地下水模拟试验。结果表明:河水渗漏过程中,随地下水埋深的增加,河水下渗水流由饱水状态逐渐转化为非饱水状态,河水与地下水发生脱节。脱节后,河水下保留悬挂饱水带,悬挂饱水带与地下水饱水带之间为非饱水状态,具有负压,且负压值随着与饱水带距离的增大而增大。靠近饱水带的支持毛细水,可以在水头差驱动下形成连续水流流出。悬挂饱水带大小与河水深成正比,非饱水带流动水的空间分布不均,可传导水压,在重力及压力共同作用下运动,并发生弥散作用和横向运动。示踪试验显示,河水补给地下水时垂向水流速度大于横向。综上,脱节型河水下存在悬挂饱水带,大气降水或地表水可经由非饱水带形成持续的下渗水流补给地下水。该研究可以加深对降水、地表水与地下水相互作用的理解。

The unsaturated zone,situated on the Earth’s land surface,serves as the central hub for natural water circulation.Understanding the distribution and transport characteristics of water within this zone is of great importance.This study employed an indoor sandbox test device to simulate and investigate the leakage of river water and the recharge of groundwater.Various scenarios were considered,including different river water depths and groundwater burial depths.The results showed that during the continuous leakage of river water,as the depth of groundwater increases,the seepage of river water beneath the river undergone a transition from a saturated state to an unsaturated state,resulting in a disjointed pattern.Even after the disjoint,an inverted saturated zone persisted beneath the river.The relationship between the inverted saturated zone and the groundwater saturated zone was characterized by unsaturation and negative pressure,with the negative pressure value increasing as the distance from the saturated zone increased.The supporting capillary water near the saturated zone formed a continuous water flow driven by the hydraulic head difference.The size of the inverted saturated zone was directly proportional to the depth of the river.The spatial distribution of water movement in the unsaturated zone was uneven,but water pressure facilitated its movement,enabling both gravity-driven and pressure-driven flow.Additionally,lateral movement through diffusion occurred.The tracer test indicated that the vertical flow velocity of the river water exceeded the horizontal flow velocity during groundwater recharge by the river water.Disjointed rivers harbor inverted saturated zones.Consequently,atmospheric precipitation or surface water can form a continuous infiltration flow and recharge groundwater through the unsaturated zone.The tracer test showed that the vertical flow velocity of the river water was greater than that of the horizontal when the river water recharged groundwater.In summary,the presence of an inverted saturated zone exist beneath a disjointed river implied that atmospheric precipitation or surface water had the capacity to establish a continuous infiltration flow through the unsaturated zone for the purpose of recharging groundwater.The research could deepen the understanding of the interactions between precipitation,surface water and groundwater.