河道型水库水动力特征与气候条件的响应关系

Responses of hydrodynamical characteristics to climate conditions in a channel-type reservoir

气候条件(降雨、气温)的变化对流域内水资源、河道、湖库的径流影响较大.河道型水库由于具有河道和湖泊的双重特点,受气候条件的影响则更为显著.本文以广东省梅州的河道型水库——长潭水库为例,耦合流域分布式水文模型SWAT与环境流体动力学模型EFDC,研究了河道型水库水动力特征(以水龄表征)与气候条件的响应关系.根据梅县气象站1953-2010年共58年的年均降雨量资料的频率分析,选取降雨量保证率分别为20%(丰水年)、50%(平水年)和90%(枯水年)年份的气候条件作为3种气候方案,对应的典型年分别为1992、1988和2004年,并将各典型年的日均降雨量和气温作为SWAT水文模型的输入条件,模拟了进入长潭水库各主要支流的日均变化过程.并将该流量过程作为长潭水库库区水动力模型的入流边界,模拟了各种降雨典型年情景下长潭水库的水动力变化过程.结果表明,长潭水库库区水龄沿程逐渐增大,呈指数增长的趋势,且受气候条件的影响很大.与丰水年相比,平水年、枯水年年降雨量分别减少了14%和49%,入库径流分别减少了23%和62%,水库出库坝址附近水龄分别增大了66%和247%,支流区域水龄增幅可达81%和290%左右,可见水库水动力特征受气候条件影响很大,而支流区域受气候条件影响更显著.不同气候条件下,河道型水库分别呈现出河道和深水湖泊的双重特性.丰水年时,坝址附近垂向上水体交换频繁,水龄均匀,呈现出河道的特性;平水年与枯水年时,坝址附近水体垂向交换较弱,逐渐呈现出深水湖泊的垂向分层特性.另外,流域分布式水文模型SWAT与环境流体动力学模型EFDC的联用,为弥补历史长系列高频监测资料的缺失,提高湖库水动力模型模拟的精度提供了有效的方法.

Changes of rainfall and temperature caused by climate changes have a great impact on water resource and runoff in watershed. Channel-type reservoir, due to its characteristics of river and lake, is affected intricately by climate. As a case study of Changtan Reservoir in Meizhou City, Guangdong Province, coupled watershed hydrological model SWAT and Environmental Fluid Dynamic Code （EFDC） have been used to study the responses of hydrodynamics （characterization by water age） to climate condition in the channel-type reservoir. According to frequency analysis of 58 years rainfall data from 1952 to 2010 in Meizhou City, selected rainfall guarantee rates are 20% （ wet year）, 50% （ average year） and 90% （ dry year） as three climate schemes. Tributaries of Changtan Reservoir were simulated with the rainfall and temperature in the typical years as input conditions for SWAT model, and hydrodynamics process was simulated with the inflow of the tributaries as boundary conditions. The results showed that, water age increased exponentially along Changtan Reservoir, and was greatly affected by climate conditions. Compared to wet year, in average year and dry year, annual rainfall reduced 14% and 49% , and inflow reduced 23% and 62% , and water age increased 66% and 247% near the outlet dam, and up to 81% and 290% in tributaries, respectively. So, climate conditions had a great effect on the reservoir＇s hydrodynamics, especially in the vicinity of tributaries. Changtan Reservoir exhibited the characteristics of river and lake under different climatic conditions. Near the dam, it exhibited the characteristics of river in wet year, and the characteristics of lake in average and dry year gradually. Additionally, coupling of watershed hydrological model SWAT and EFDC, it is an effective method for making up the needed long series of high frequency measured data and improving the accuracy of hydrodynamic model simulation in lake and reservoir.