基于MIKE21模型模拟的异龙湖水动力特性与生态补水效果研究

Research on ecological water replenishment scheme of Yilong Lake based on MIKE21 model

异龙湖是云南九大高原湖泊中面积最小、水量最少、最易受人类活动干扰的湖泊,近年来湖泊水质波动性变化特征明显,湖区水质尚未企稳向好。针对异龙湖流域水文资料匮乏、水质资料较少且湖区水质受气候及人类活动干扰响应明显等特点,依托数值模拟技术来模拟并反演湖区水动力与水质演变过程十分必要。采用GPS示踪浮标法、声学多普勒流速剖面仪监测法和加密加频监测入湖河流与湖泊水质的方式,开展异龙湖生态补水前后的湖泊水动力与湖区水质监测,具象化分析及展示补水水质改善效果,并同时构建了基于MIKE21的平面二维水动力与水质耦合模型。模拟预测结果表明,在常年主导风场西南偏西风下,南北湖岸流向为西北—东南,湖心呈顺时针环流,湖东存在逆时针小环流,在湖西有明显的弱流区,不利于水量、物质交换;年内水质浓度COD总体呈现湖西低-湖中湖东高、雨季明显高于旱季的时空分布格局;在年补水量约3 500万m^(3)和多点、最大补水能力1.95 m^(3)/s的“旱季(11月至次年5月)补水”方案下,湖西、湖中、湖东3个点位COD年均浓度分别可改善约27.6%、24.0%、18.1%,补水带来的水质改善效果十分明显,可为异龙湖生态调度与湖泊水生态修复改善提供良好的决策支撑。

Yilong Lake is the lake that is the most easily disturbed by human activities with the smallest area and the least water amount among the nine plateau lakes in Yunnan Province.Due to obvious fluctuations of its water quality in recent years,it is in urgent need of improvement.In view of the lack of hydrological and water quality data in Yilong Lake basin and the obvious disturbance of water quality by climate and human activities,it is necessary to simulate and invert the evolution process of water dynamics and quality in Yilong Lake basin by using numerical simulation technology.In this study,the GPS-based tracking buoy,acoustic Doppler current profiler and intensive monitoring of the water quality of incoming rivers and the lake are used to monitor the hydrodynamics and water quality in Yilong Lake before and after ecological water replenishment,so as to concretely analyze and demonstrate the improvement effect of water replenishment quality and build a two-dimensional coupling model of hydrodynamic and water quality based on MIKE21.The simulation results show that WSW winds are prevalent in Yilong Lake all the year round,with a northwest-to-southeast flow direction at the north and south lakeshores,a clockwise circular current in the center of the lake and a small counterclockwise circular current in the east.In the west of the lake there is an obvious weak flow area,which is not conducive to water and material exchange.The water quality concentration COD during the year generally shows a spatial and temporal distribution pattern of low in the west-high in the middle-high in the east,which is significantly higher in the rainy season than in the dry season.Under the conditions of annual replenishment volume of about 35000000 m^(3) and multiple points and maximum water supplement capacity of 1.95 m^(3)/s,the average annual COD concentration of three points in the west,middle and east of the lake can be improved by about 27.6%,24.0%and 18.1%respectively during the dry season(from November to May next year),with significant water quality improvement effect brought by replenishment,which can provide references for decision-making for ecological scheduling and lake water ecology restoration in Yilong Lake.