防洪优化调度多约束启发式逐步优化方法

决策者的经验和知识判断对实际洪水调度有着非常重要的影响,为此,将决策者预泄控制的实践经验和泄流状态持续性要求纳入模型约束条件中,提出了防洪优化调度多约束启发式逐步优化方法。该方法以最大削峰为控制目标,将水库泄流的一般操作原则概化为启发式信息,以洪水涨落和水位升降作为泄流增减的判别依据,与优化搜索相结合,采用启发式逐步优化算法求解。以水口水库为例,采用5个方案对所提方法进行了对比分析。结果表明,提出的方法可以充分考虑决策者的经验和知识判断,降低了预泄腾库水位过低造成的回蓄风险,避免了泄流过程的波动,得到符合实际洪水调度要求的计算结果。     

基于动库容曲线的水库调洪高水位查算方法研究

河道型水库因动库容特性显著,传统的静库容调洪方法难以适用,研究动库容调洪方法是亟待解决的问题。当坝前水位爬升到最高点时,库区内的洪水演进到达一种临界状态,库区内的水文、水力条件相对稳定,在出库流量和入库流量一定的情况下,可望获得最高坝前水位与同时刻库容之间良好的对应关系。依托三峡库区水文水动力耦合预报模型,建立了一组以出库流量、入库流量为参数的动库容曲线,以供调洪时快速查算最高坝前水位。采用2009年以来三峡水库16场场次洪水资料,检验所建动库容曲线的合理性。结果表明,各场洪水的最高库水位查算值与实况平均偏差仅0.20m,证明建立的基于动库容曲线的三峡水库最高库水位查算方法具有较好的实践价值。     

Floodwater utilization for cascade reservoirs based on dynamic control of seasonal flood control limit levels

Reservoirs play an important role in flood control and conservation, in which the flood control limit level (FCLL) is the most significant parameter of the tradeoff between flood control and comprehensive utilization of water resources. This study was aimed at constraining the seasonal FCLL for cascade reservoirs to obtain more economic benefits without reducing the original flood prevention standards. Based on flood initiation and ending times during the flood season, fuzzy set theory was used to build the experiential and theoretical membership function of each day, which clarified the relationship between the seasonal FCLL and the designed FCLL, and then the total flood season was divided into sub-seasons. The seasonal FCLL was revised by analyzing numerous flood control operation schemes of cascade reservoirs to satisfy a given flood prevention standard. Using the case study of ShiQuqn and XiHe cascade reservoirs in the Hanjiang River, the proposed method was demonstrated to provide an effective design for the seasonal FCLL, which increased the FCLL in the pre-flood and post-flood seasons. Forty-five operation schemes with different combinations of ShiQuqn and XiHe reservoir’s FCLLs under five flooding frequency scenarios were evaluated to revise the seasonal FCLL. An optimization model with real-coded genetic algorithm was proposed to maximize hydropower generation by dynamic control of the FCLL. The results show that compared with the traditional operation, joint operation based on dynamic control of FCLL can generate 0.23 × 108 kWh (3.18%) more hydropower for the cascade reservoir system during the flood season without increasing the flood risk.     

凤滩水库降雨预报精度分析及应用研究

由于天气预报有限准确性,给水库电站调度造成不便,使水库效益难以充分发挥。分析凤滩水库流域天气降雨预报精度,研究流域对径流调节能力,探讨预报精度对水库调度决策的影响,探索运用实时降雨预报产品进行水库调度的方法。水库调度决策,暴雨以上注重降雨过程,依据提前5天的降雨预报;大雨注重降雨量值,依据提前4天的降雨预报;中、小雨注重降雨起讫时间,以实际降雨为依据,优化水库水位控制,提高洪水资源利用率,为水库创造可观的效益。     

三峡水库动态汛限水位洪水调度风险指标及综合评价模型研究

汛限水位是综合利用水库运行和调度的重要参数之一,也是协调防洪和兴利矛盾的焦点所在。现行的汛限水位过多地考虑了小概率洪水事件,不能充分挖掘水库汛期的兴利效益,因此,采用动态汛限水位进行调度,对综合利用水库的运行具有重要的理论意义和实用价值。根据三峡水库围堰发电期的调度规程,建立预报预泄调度模型,采用宜昌站1882-2001年汛期实测日流量资料,实现了考虑预报信息的动态汛限水位洪水调度模拟;提出了多目标风险指标体系;计算了9种动态汛限水位方案下的风险指标值,通过综合评价模型对各方案进行比较和优选,得到了相对合理的动态汛限水位方案。     

Evaluation of real-time flash flood forecasts for Haiti during the passage of Hurricane Tomas, November 4–6, 2010

The January 2010 earthquake that devastated Haiti left its population ever more vulnerable to rainfall-induced flash floods. A flash flood guidance system has been implemented to provide real-time information on the potential of small (~70 km²) basins for flash flooding throughout Haiti. This system has components for satellite rainfall ingest and adjustment on the basis of rain gauge information, dynamic soil water deficit estimation, ingest of operational mesoscale model quantitative precipitation forecasts, and estimation of the times of channel flow at bankfull. The result of the system integration is the estimation of the flash flood guidance (FFG) for a given basin and for a given duration. FFG is the amount of rain of a given duration over a small basin that causes minor flooding in the outlet of the basin. Amounts predicted or nowcasted that are higher than the FFG indicate basins with potential for flash flooding. In preparation for Hurricane Tomas’ landfall in early November 2010, the FFG system was used to generate 36-h forecasts of flash flood occurrence based on rainfall forecasts of the nested high-resolution North American Model of the National Centers for Environmental Prediction. Assessment of the forecast flood maps and forecast precipitation indicates the utility and value of the forecasts in understanding the spatial distribution of the expected flooding for mitigation and disaster management. It also highlights the need for explicit uncertainty characterization of forecast risk products due to large uncertainties in quantitative precipitation forecasts on hydrologic basin scales.     

Adaptive reservoir flood limited water level for a changing environment

As streamflow is non-stationary due to climate change and human activities, adapting reservoir operation in the changing environment is of significant importance. Specifically, the flood limited water level (FLWL) needs to be re-established to ensure flood safety when the reservoir inflow is altered. The aims of this study are: (1) to clarify the relationship between the FLWL and streamflow when statistical parameters of the flood peak and volume vary through time and (2) to re-establish the FLWL when the reservoir inflow changes under the non-stationary condition. The adaptive FLWL is derived based on flood routing of non-stationary design floods, and the flood risk probability is then estimated. With China’s Three Gorges Reservoir (TGR) as a case study, the changing pattern of FLWL is quantified when statistical parameters (i.e., mean, \( C_{\text{V}} \) and \( C_{\text{S}} \)) of design floods have a linear temporal trend. The results indicate that the FLWL is sensitive with design floods, i.e., (1) means of design flood peak, 3-day volume, 7-day volume, 15-day volume and 30-day volume yearly decrease by 33 m³/s, 0.008, 0.021, 0.482 and 0.905 billion m³, respectively, (2) when the non-stationary design flood is used, the cumulative flood risk probability of the reservoir water level exceeding 175.0 m during 2011–2030 decreases from 1.98 to 1.82% with the conventional FLWL scheme and (3) the FLWL of the TGR could be re-set without increasing the flood risk probability, and the FLWL would increase about 4.7 m by 2030 in this non-stationary streamflow scenario. These findings are helpful to derive the FLWL in a changing environment.     

Impact of River-Tide Dynamics on the Temporal-Spatial Distribution of Residual Water Level in the Pearl River Channel Networks

The behavior of the residual water level in estuarine environment is complex due to the highly nonlinear interaction between river flow and tide and the contributions made by these two external forcing to the dynamics of the residual water level are not yet fully understood. In this study, we investigate the effect of river-tide dynamics on the temporal-spatial changes of flow in terms of residual water level in the Pearl River channel networks, which is one of the complex channel networks in the world. Making use of a nonstationary tidal harmonic analysis, the continuous time series observations of water level covering a spring-neap cycle in 1999 (representing flood season) and 2001 (representing dry season) collected from around 60 stations in the Pearl River channel networks have been used to extract the temporal-spatial changes in stage and tidal properties (including amplitudes and phases) as a function of variable freshwater discharge and ocean tide. It was shown that the averaged residual water level during the flood season (ranging 0–5 m) is one order magnitude than that during the dry season (ranging 0–0.35 m). The distribution of the residual water level clearly indicates that the Pearl River channel networks feature two sub-systems, i.e., the central part of the channel networks being river-dominated with high value of residual water level and the eastern and western sides being tide-dominated with low value of residual water level. To understand the relative importance of river flow and tide on the temporal-spatial distribution of the residual water level, an idealized model is subsequently applied to the Modaomen estuary, which debouches the largest portion of river discharge into the South China Sea. Analytical results showed that the residual water level is mainly determined by the variation of the freshwater discharge for the flood season, while it is primarily controlled by the tidal forcing for the dry season and features a typical spring-neap cycle.     

基于水库防洪预报调度图的洪水资源化方法

为有效调节利用洪水资源,探讨以水库防洪预报调度为途径的洪水资源化方法,在分析水库调洪过程和洪水过程特性的基础上,拟定了基于3 h预报信息的水库防洪预报调度图,并以安康水库为例,采用模拟结合遗传算法进行优化计算,绘制了安康水库以洪水资源化为目标的防洪预报调度图,通过对其应用并与常规洪水调度过程进行对比分析表明,预报调度的调洪结果在消减洪峰和抬高调洪末水位两个目标上明显优于常规调度。     

Evaluation of the weather research and forecasting (WRF) model over Guyana

In the present study, diagnostic studies were undertaken using station-based rainfall data sets of selected stations of Guyana to understand the variability of rainfall. The multidecadal variation in rainfall of coastal station Georgetown and inland station Timehri has shown that the rainfall variability was less during the May–July (20–30%) of primary wet season compared to the December--January (60–70%) of second wet season. The rainfall analysis of Georgetown based on data series from 1916 to 2007 shows that El Niño/La Niña has direct relation with monthly mean rainfall of Guyana. The impact is more predominant during the second wet season December--January. A high-resolution Weather Research and Forecasting model was made operational to generate real-time forecasts up to 84 h based on 00 UTC global forecast system (GFS), NCEP initial condition. The model real-time rainfall forecast during July 2010 evaluation has shown a reasonable skill of the forecast model in predicting the heavy rainfall events and major circulation features for day-to-day operational forecast guidance. In addition to the operational experimental forecast, as part of model validation, a few sensitivity experiments are also conducted with the combination of two cloud cumulus (Kain--Fritsch (KF) and Betts–Miller–Janjic (BMJ)) and three microphysical schemes (Ferrier et al. WSM-3 simple ice scheme and Lin et al.) for heavy rainfall event occurred during 28–30 May 2010 over coastal Guyana and tropical Hurricane ‘EARL’ formed during 25 August–04 September 2010 over east Caribbean Sea. It was observed that there are major differences in the simulations of heavy rainfall event among the cumulus schemes, in spite of using the same initial and boundary conditions and model configuration. Overall, it was observed that the combination of BMJ and WSM-3 has shown qualitatively close to the observed heavy rainfall event even though the predicted amounts are less. In the case of tropical Hurricane ‘EARL’, the forecast track in all the six experiments based on 00 UTC of 28 August 2010 initial conditions for the forecast up to 84 h has shown that the combination of KF cumulus and Ferrier microphysics scheme has shown less track errors compared to other combinations. The overall average position errors for all the six experiments taken together work out to 103 km in 24, 199 km in 48, 197 km in 72 and 174 km in 84 h.     

Dynamic routing modeling for flash flood forecast in river system

A real-time flood-forecasting method coupled with the one-dimensional unsteady flow model was developed for the Danshuei River system in northern Taiwan. Based on the flow at current time, the flow at new time is calculated to provide the water stage forecasting during typhoons. Data, from two typhoons in 2000: Bilis and Nari, were used to validate and evaluate the model capability. First, the developed model was applied to validate and evaluate with and without discharge corrections at the Hsin-Hai Bridge in Tahan Stream, Chung-Cheng Bridge in Hsintien Stream, and Sir-Ho Bridge in the Keelung River. The results indicate that the calculated water stage profiles approach the observed data. Moreover, the water stage forecasting hydrograph with discharge correction is close to the observed water stage hydrograph and yields a better prediction than that without discharge correction. The model was then used to quantify the difference in prediction between different methods of real-time water stage correction. The model results reveal that water stages using the 1–6 h forecast with real-time stage correction exhibits the best lead times. The accuracy for 1–3 h lead time is higher than that for 4–6 h lead time, suggesting that the flash flood forecast in the river system is reasonably accurate for 1–3 h lead time only. The method developed is effective for flash flood forecasting and can be adopted for flood forecasting in complicated river systems.     

水库汛期限制水位控制理论与观念的更新探讨

传统的水库汛限水位的控制,只利用了洪水的统计信息,使水库在汛期要时刻预防设计与校核洪水事件的发生,致使一些水库在汛期不敢蓄水而汛后又无水可蓄,造成洪水资源的浪费。提出水库汛限水位动态控制的新理念及其综合推理模式,适应当前预报技术的发展水平,考虑降雨径流洪水预报与一定时间内的短期降雨预报,排除不可能发生的洪水事件,预报可能发生的洪水,实施水库汛限水位的动态控制。但预报不可避免地存在误差,当小概率预报误差事件发生时,仍可采取弥补措施以确保大坝的防洪安全。     

On the accuracy of atmospheric forcing for extra-tropical storm surge prediction

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.     

陆气耦合模型在实时暴雨洪水预报中的应用

采用加拿大区域性中尺度大气模式MC2(Canadian Mesoscale Compressible Community)和新安江模型单向耦合模型系统,对2005年7月4～15日发生在淮河流域的一场暴雨洪水,进行了实时预报.采用王家坝以上流域的实测降水和王家坝断面的实测洪水资料,对MC2预报降水的时空分布和陆气耦合模型预报的洪水过程进行了分析.结果表明,MC2对该场强降水过程具有很好的预报能力,陆气耦合模型有效地增长了洪水预报的预见期,具有很好的应用前景.     

Integrated assessment of nonpoint source pollution of a drinking water reservoir in a typical acid rain region

Nonpoint source pollution generated by agricultural production and city construction has been studied for decades, but very few researches have been conducted on the regional assessment of nonpoint source pollution in the acid rain regions, particularly relating to the control of pollutant in the drinking water source areas. In this study, an integrated framework was applied to estimate nitrogen and phosphorous load in a typical acid rain influenced reservoir, China. The method comprised three separate steps: (1) a watershed model—soil and water assessment tools—was used to estimate nitrogen and phosphorous load from the upper stream watershed; (2) collection of acid rain samples, together with a GIS-based calculation to estimate the atmospheric deposition flux; (3) introduction of a simple export coefficient method. The case study indicated atmospheric deposition accounted for 56.75 % of total nitrogen load during the year, with the highest level of deposition load taking place during the wet season. Maximum phosphorous (93.37 %) was linked to the upstream runoff, originating from the upper watershed. Further analysis by watershed model and export coefficient method indicated forest exported most total nitrogen (27.72 %) and total phosphorous (58.78 %) in the upstream watershed. Results indicated that in the region influenced by acid rain, the nitrogen management should encompass the management of land use practices and the control of acid rain in catchments feeding into drinking water storage areas. It could be inferred that NOX emissions might cause both globe warming and eutrophication in the drinking water sources. This paper could provide a basis for water quality management in such regions.     

考虑综合利用要求的三峡水库提前蓄水方案

采用三峡水库汛期分期方案,将蓄水时间提前至汛末期,综合考虑上下游防洪、发电、通航和蓄满率等要求,建立了多目标蓄水调度模型,构建了"优化-模拟-检验"的算法流程,采用遗传算法进行求解。结果表明,最优方案在满足上下游防洪安全要求的前提下,蓄水期可增发电量17%,减少弃水44%,蓄满率和通航保证率显著提高。通过对汛末期防洪库容进行科学划分和对蓄水调度图进行优化,既确保防洪安全又最大限度挖掘兴利效益,为研究水库汛末蓄水调度问题提供了一种新的思路和方法。     

Assessment of flood inundation mapping of Surat city by coupled 1D/2D hydrodynamic modeling: a case application of the new HEC-RAS 5

Surat city of India, situated 100 km downstream of Ukai Dam and 19.4 km upstream from the mouth of River Tapi, has experienced the largest flood in 2006. The peak discharge of about 25,770 m³ s^?1 released from the Ukai Dam was responsible for a disaster. To assess the flood and find inundation in low-lying areas, simulation work is carried out under the 1D/2D couple hydrodynamic modeling. Two hundred ninety-nine cross sections, two hydraulic structures and five major bridges across the river are considered for 1D modeling, whereas a topographic map at 0.5 m contour interval was used to produce a 5 m grid, and SRTM (30 and 90 m) grid has been considered for Surat and the Lower Tapi Basin. The tidal level at the river mouth and the release from the Ukai Dam during 2006 flood are considered as the downstream and upstream boundaries, respectively. The model is simulated under the unsteady flow condition and validated for the year 2006. The simulated result shows that 9th August was the worst day in terms of flooding for Surat city and a maximum 75–77% area was under inundation. Out of seven zones, the west zone had the deepest flood and inundated under 4–5 m. Furthermore, inundation is simulated under the bank protection work (i.e., levees, retaining wall) constructed after the 2006 flood. The simulated results show that the major zones are safe against the inundation under 14,430 m³ s^?1 water releases from Ukai Dam except for the west zone. The study shows the 2D capability of new HEC-RAS 5 for flood inundation mapping and management studies.     

洪水预报模型输入与输出的误差分布及相关性分析

降雨预报信息作为洪水预报模型的输入,该信息的准确性直接影响洪水预报模型输出的准确性.为探究模型输入(降雨预报)误差与输出(洪水预报)误差之间的关系,以英那河流域为例,分析了不同雨量等级下,预报模型的输入误差与输出误差的分布规律,并定性分析了两种误差的相关关系.结果表明,降雨量等级若为无雨及小雨时,两种误差不相关;若为中...     

Risk decision-making model for reservoir floodwater resources utilization

Floodwater resources utilization (FRU) can alleviate the shortage of water resources, but there are risks. To safely and efficiently utilize the floodwater resources, it is necessary to study the risk of reservoir FRU. In this paper, the risk rate of exceeding the design flood water level and the risk rate of exceeding safety discharge are estimated. Based on the principle of the minimum risk and the maximum benefit of FRU, a multi-objective risk decision-making model for FRU is constructed. Probability theory and mathematical statistics method is selected to calculate the risk rate; C–D production function method and emergy analysis method is selected to calculate the risk benefit; the risk loss is related to flood inundation area and unit area loss; the multi-objective decision-making problem of the model is solved by the constraint method. Taking the Shilianghe reservoir in Jiangsu province as an example, the optimal equilibrium solution of FRU of the Shilianghe reservoir is found using the risk decision-making model, and the validity and applicability of the model are verified.     

Impact assessment of Three Gorges Dam’s impoundment on river dynamics in the north branch of Yangtze River estuary,China

As one of the world’s largest hydropower projects, the Three Gorges Dam (TGD)’s 156–175 m height storing test in flood recession seasons during 2006–2011 has aroused international attention. The novel approaches of cross-wavelet transform and wavelet coherence were firstly introduced to reveal the significant coherence and time lag property in time–frequency space between river dynamics in hydrological stations along Yangtze River. Then, using the optimum lag time nodes, corresponding regression models between river dynamics in these stations were established and utilized to assess the river dynamics in stations downstream under the impact of TGD’s impoundment. Results showed that the average decrease ratio of 24.3 % in the Three-Gorge reservoir outflow was caused in TGD’s impounding periods during 2006–2011. The corresponding average decrease ratios of 25.1, 16.5 and 1.9 % in Yichang flow, Datong flow (with 6 days lag), and estuarine Santiao river stage (with 32 days lag), respectively, were caused by TGD’s impoundment during 2006–2011. In addition, the impact weights of multiple driving factors on estuarine river dynamics were discussed, and the main factor of the combined impacts of estuarine tidal fluctuation and sea level change while the secondary factor of the upper stream inflow were demonstrated. A further suggestion about the optimization design of TGD’s safety impounding scheme was proposed to prevent estuarine saline water intrusion by guaranteeing the average daily increase of Three Gorges reservoir water level lower than 1.11 m/day during TGD’s impounding period.