Water age and thermal structure of LakeMead were modeled using the 3-dimensional hydrodynamic Environmental FluidDynamics Code (EFDC). The model was calibrated using observed data from 2005 and then applied to simulate 2 scenarios: high-stagewith an initialwater level of 370.0mand low-stagewith a projected initialwater level of 320.0 m. The high-stage simulation described predrought lake hydrodynamics, while the low-stage simulation projected how lake circulation could respond under significant lake drawdown, should drought conditions persist. The results indicate that water level drawdown plays an important role in thermal stratification and water movement of Lake Mead during receding water levels. The impact of the dropping water level on lake thermal stratification is more significant in shallow regions such as Las Vegas Bay. Depth-averaged (the mean value of 30 vertical layers) water temperature in the low-stage was estimated to increase by 4–7 C and 2–4 C for shallow (<20 m) and deep (>70 m) regions, respectively. Further, depth-averaged water age decreased about 70–90 d for shallow regions and 90–120 d for deep regions under the simulated drought scenario. Such changes in temperature and water age due to continuous drought will have a strong influence on the hydrodynamic processes of Lake Mead. This study provides a numerical tool to support adaptive management of regional water resources by lake managers.

Flowing water bodies often have plants that differ greatly in size and type, which interfere with fluid flow structure. Although there are studies describing vegetation–flow interactions in ideal laboratory conditions, their practical application is sometimes still difficult. This paper presents results of research involving laboratory simulations channel flow and the effects upon its structure as it passes through a combined layer of submerged and emerged vegetation in an open-channel flume. Instantaneous time-average velocity and turbulence at various locations were measured with a 3D acoustic Doppler velocimeter. The experimental results showed that the mean velocity profiles can be divided into three layers: bottom, middle and upper. The velocity profiles show the flow structure was complex variable over time creating mixing velocity layers associated with inflection points and velocity spikes.Turbulence intensity urms, vrms, wrms was nearly invariant for the flow depth at the bottom layer in most locations within the vegetation area. Maximum turbulence intensity occurred within the middle layer and migrated vertically as frontal width of the plant increased. Maximum turbulence intensity fluctuated at the velocity mixing layer where there is significant momentum exchange.The Manning’s vegetation roughness coefficient n(v) due to vegetation resistance increased with vegetation density as expected. In all, the results show flow structure varies substantially at the stem section and at the canopy top of submerged vegetation. These analytical findings will be useful in understanding river channel hydraulic transport and mixing processes and useful in river engineering applications and modelling.

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. 河道型水库由于其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）、90%（枯水年）年份的气候条件作为三种气候方案，对应的典型年分别为1992年，1988年和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较少了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65.7%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.