李一平，学者凯发k8国际首页主页-凯发网

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.

lake taihu, china’s third largest freshwater lake, exemplifies the severity of eutrophication problems in rapidly developing regions.we used long term land use, water quality, and hydrologic data from 26 in-lake and 32 tributary locations to describe the spatiotemporal patterns in nutrient loads, nutrient concentration, algal biomass, measured as chlorophyll a (chl-a), in lake taihu. point and nonpoint sources, as determined by chemical oxygen demand,contributed pproximately 75 and 25% of the total nutrient loads to the lake, respectively. spatial patterns in total phosphorus (tp) and total nitrogen (tn) concentrations in lake taihu strongly corresponded with observed loads from adjoining rivers with high concentrations proximate to densely populated areas. chl-a concentrations exhibited spatial patterns similar to tp and tn concentrations. generally, nutrient and chl-a concentrations were highest in the northwestern region of the lake and lowest in the southeastern region of the lake. seasonally, the largest nutrient loads occurred during summer. the annual net retention rate of tp and tn in lake taihu was approximately 30% of the total load. this study identifies regions of the lake and the watershed that are producing more nutrients to develop targeted management strategies. reducing external p and n input from both point and nonpoint sources is obviously critical to address water quality issues in the lake. in addition, atmospheric deposition and resuspension of existing lake sediments also likely play a role in eutrophication processes and harmful algal blooms occurrence.

to improve water quality and alleviate eutrophication in lake taihu, the third largest freshwater lake in china, a yangtze river water transfer project was initiated in 2002 to bring water from the yangtze river to lake taihu to dilute and divert pollutants out of the lake. we used a three-dimensional numerical model,environmental fluid dynamics code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. in particular, the influences of inflow ributaries and wind forcing on water age were investigated. model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. during the simulation year (2005), the water ages in lake taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in meiliang bay, the most polluted bay. in terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100m3/s. the spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. this study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.

to mitigate eutrophication by enhancing water exchange in lake taihu, the third largest freshwater lake in china, a water transfer project was initiated in 2002. the project was designed to flush pollutants out of the lake by transferring water from the yangtze river. however, the original yangtze river diversion did not significantly enhance water exchange in the meiliang bay, the most polluted area of lake taihu. to overcome this deficiency, the improved yangtze river diversions have been designed recently by adding two new pump stations named meiliang and xingou around meiliang bay. effectiveness of water transfer projects was investigated in this study by using a three-dimensional hydrodynamic model, environmental fluid dynamics code (efdc), based on the concept of water age. model results showed that adding new pump stations significantly improved the effectiveness of yangtze river diversion in meiliang bay. success of water transfer is also strongly associated with the inflow or outflow rate of water transfer projects and wind conditions. southeastern winds which dominate in summer increase performance of water transfer and improve water exchanges in meiliang bay. considering water age and cost, an economically effective influent flow rate from wangyu river (the original yangtze river diversion) was predicted to be 120 m3/s, and the corresponding appropriate outflow rate from the meiliang pump station was about 15–20 m3/s on the basis of multi-objective optimization method, which decreased the average water age in meiliang bay by 24.32% of the original yangtze river diversion. adding xingou pump station had the similar contribution to reducing the water age in meiliang bay as the meiliang pump station. in general, the improved yangtze river diversions played a supplementary role for the original yangtze river diversion in solving algal bloom problems in meiliang bay.

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.

摘要: 选取国内外常用的水动力学模型( efdc) 和典型的浅水湖泊( 太湖) ，采用拉丁超立方取样( lhs) ，研究湖泊水动力模块中常用的5 个重要参数( 风拖曳系数、床面粗糙高度、涡粘性系数、紊流扩散系数以及风遮挡系数) 对湖体水位和流速的影响。结果表明: 针对大型浅水湖泊，湖泊岸线形状和湖底地形、湖泊周围地形、湖泊水面风场对模拟结果产生决定性影响。尤其是在湖湾区和周边地形比较复杂的地区，风场参数对水动力模拟结果不确定性的贡献率最大。在垂向上，表层流速受到参数不确定性的影响最大，底层次之，中层最小。床面粗糙高度对水动力模拟结果不确定性贡献率较风场参数要小，水体涡粘滞系数和扩散系数影响则更小。故在选择大型浅水湖泊水动力模型参数时，要充分考虑湖泊岸线和周围地，着重率定风场参数以及床面粗糙高度。