Environmental Flows in a Human‐Dominated System: Integrated Water Management Strategies for the Rio Grande/Bravo Basin

Water management in the transboundary Rio Grande/Bravo (RGB) Basin, shared by the US and Mexico, is complicated by extreme hydrologic variability, overallocation, and international treaty obligations. Heavy regulation of the RGB has degraded binationally protected ecosystems along the Big Bend Reach of the RGB. This study addresses the need for integrated water management in Big Bend by developing an alternative reservoir operation policy to provide environmental flows while reducing water management trade‐offs. A reach‐scale water planning model was used to represent historical hydrology (1955–2009), water allocation, and reservoir operations, and key human water management objectives (water supply, flood control, and binational treaty obligations) were quantified. Spatially distributed environmental flow objectives and an alternative reservoir rule curve were developed. We simulated current and alternative water management policies and used an iterative simulation–evaluation process to evaluate alternative policies based on water system performance criteria with respect to specified objectives. A single optimal policy was identified that maximized environmental flows while maintaining specified human objectives. By changing the timing but not the volume of releases, the proposed reservoir re‐operation policy has the potential to sustain key ecological and geomorphic functions in Big Bend without significantly impacting current water management objectives. The proposed policy also improved water supply provisions, reduced average annual flood risk, and maintained historical treaty provisions. Copyright © 2014 John Wiley & Sons, Ltd.     

后三峡工程时代长江口水源地盐水入侵规律及其应对措施

在简述长江口盐水入侵主要影响要素与特性的基础上,对三峡水库运行以来长江大通水文站年径流量、月径流量的变化规律进行了简析,发现长江下游仍呈现典型丰、平、枯水年特征,其季节变化规律也十分显著。同时对后三峡工程时代的长江口水源地盐水入侵特征进行了研究,结果表明,枯水期水源地咸潮入侵与其发生首日的大通水文站前6日日径流量相关性相对较好;影响期一般在农历九月至来年四月间,尤以二月最为严重;各月呈现出以初八和廿二为“双驼峰”型的氯化物质量浓度峰值分布特性。提出了进一步减轻长江口盐水入侵对上海水源地供水安全影响的建议,包括采取加强流域与区域信息资源共享、北支控制工程联建、长江口水源地（水库群）联动开发等措施。     

三峡水库运行以来入海径流与盐水入侵响应研究

为研究三峡水库运行以来盐水入侵对长江河口的影响,采用自行编译完成的Delft3D 4.01.01版本源代码,建立了大通到长江口外的二维水流盐度数学模型,综合分析入海径流量与盐水入侵的响应机制。研究表明Ddlft3D 4.01.01源代码能很好地模拟计算长江口水动力盐度分布,验证误差仅有10%~15%。从计算结果可以看出,盐水入侵情况与径流量关系明显,当大通站径流量为5 000 m~3/s时,长江口南支与北支均发生盐水入侵。随着径流量增大,淡水区域面积由南支右岸向下游进一步扩大。当径流量超过30 000 m~3/s时,南支基本不存在盐水入侵情况,可以保证水库正常取水安全。当存在风力作用时,盐水入侵明显,盐水浓度达到3.5 ppt以上,而无风情况下,盐水入侵趋势减弱,长江口南支河段区域的盐度一般满足灌溉水的标准(2.2‰)。     

Reservoir flood control operation model incorporating multiple uncontrolled water flows

This study presents a weighted pre‐emptive goal programming model formulation for coordinated reservoir operation, with easy inclusion of uncontrolled water flows. The model is combined with a multiple water inflows forecasting model, and can be used for real time reservoir operation. Water flow routing from various upstream sites is accounted by with a single compact equation. Integration of controlled and uncontrolled water flows in the optimization model simplifies the operation model, resulting in accurate computation of the downstream water flow. Multiple objectives with water storage and flow variables are used to derive optimal regulation for a reservoir system under flood conditions. For real time operations, the model can be used to determine optimal water release rates for a current period, on the basis of an optimal water release schedule for an operating horizon (T). The model is applied to the flood control operation of reservoirs in the Narmada River Basin (India), with three controlled and three uncontrolled water flows affecting the downstream flow at Hoshangabad. Reservoir water storage and downstream control point flows are zoned, with prioritized objectives used to derive the optimal water release rates. Model applications to the 1999 flood event in the Narmada River Basin with observed and forecasted inflows illustrates that, if water inflows were known through a forecasting technique well in advance, the coordinated operation of the reservoirs could substantially reduce the peak water flows at the control points. The study also indicates that uncontrolled channel flows at the damage site were sufficiently high to cause flooding at the damage site.     

Critical discharge at Datong for controlling operation of South-to-North Water Transfer Project in dry seasons

Previous research shows that there is a strong correlation between saltwater intrusion in the Yangtze Estuary and discharge at Datong. In the near future, the discharge of the Yangtze River during dry seasons will decrease due to the construction and operation of large water diversion projects, including the South-to-North Water Transfer Project, which will further exacerbate saltwater intrusion in the estuary. In this paper, a nested 1D river network model and a 2D saltwater numerical model are used to associate saltwater intrusion in the Yangtze Estuary with different values of discharge at Datong. It is concluded that 13 000 m3/s is the critical discharge at Datong for preventing saltwater intrusion and controlling the volume of water transferred by the South-to-North Water Transfer Project. Furthermore, based on the analysis of river discharge from Datong to Xuliujing and in consideration of the influence of all of the water diversion projects, operation schemes are proposed for the Eastern Route of the South-to-North Water Transfer Project for different hydrological years.     

Critical Environmental Flows to Support Integrated Ecological Objectives for the Yellow River Estuary,China

The volume of inflowing water needed to meet multiple demands in the Yellow River Estuary of China was examined and quantified. Pressure on available environmental flows comes from varied ecological objectives, including maintenance of freshwater habitat for hundreds of plant and animal species, salinity balance, sediment transport and general equilibrium of the hydrologic cycle. Temporal fluctuations of flow input and output were considered and the amount of water needed for both consumptive and non-consumptive uses was evaluated. The rule of summation was used to calculate consumptive water requirements and the rule of compatibility (i.e., maximum principle) was adapted to estimate the non-consumptive ones. It was determined that the minimum, medium and high levels of annual environmental flows are 134.22 × 10⁸, 162.73 × 10⁸ and 274.9 × 10⁸ m³, respectively, in the Yellow River Estuary, which represent 23.7, 28.7 and 48.5% of the natural river discharge. Water requirements differ across months. The months of May through June, August and October were identified as the most critical periods for maintaining the environmental flows. The basic purpose of water entering the system is to compensate for water losses due to evaporation and to maintain an acceptable level of salinity in the estuary. Sediment transport into and through the estuary area are likely to be directly impacted by variations in river discharge. Improved efficiency in the sediment transport regime of the Yellow River could potentially reduce environmental flow requirements of the estuary, thus freeing water resources for other beneficial uses.     

三峡水库2003年蓄水对长江中下游水情影响分析

三峡工程经过近10 a的建设于2003年6月上旬蓄水至135 m,工程进入围堰发电运行期,10月由于航运等方面的需要,水库第2次蓄水至139 m.水库蓄水减少了上游来水,使中下游的水情发生了相应的变化,其变化也引起了社会各界的关心.根据三峡水库的蓄水情况,对2003年三峡水库蓄水期间长江中下游主要站螺山、汉口、大通站水位、流量进行研究,分析三峡水库蓄水对长江中下游水情的影响.     

三峡水库试验性运行期生态调度效果评价

三峡工程是治理开发长江的骨干型水利枢纽工程,对国家经济、社会和生态环境影响深远。三峡水库建成以来,不仅在防御长江洪水威胁方面作用巨大,而且发电、航运等综合经济效益显著。为减轻工程运行造成的不利影响,对三峡水库2011—2014年运行期间开展了生态调度试验。为了更好地推进三峡水库生态调度工作,结合三峡工程设计阶段的生态环境影响评估结论和试验运行期生态调度目标的监测结果,对已开展的生态调度效果进行科学的评价,并对未来生态调度提出建议。     

Characterizing Sub‐Daily Flow Regimes: Implications of Hydrologic Resolution on Ecohydrology Studies

Natural variability in flow is a primary factor controlling geomorphic and ecological processes in riverine ecosystems. Within the hydropower industry, there is growing pressure from environmental groups and natural resource managers to change reservoir releases from daily peaking to run‐of‐river operations on the basis of the assumption that downstream biological communities will improve under a more natural flow regime. In this paper, we discuss the importance of assessing sub‐daily flows for understanding the physical and ecological dynamics within river systems. We present a variety of metrics for characterizing sub‐daily flow variation and use these metrics to evaluate general trends among streams affected by peaking hydroelectric projects, run‐of‐river projects and streams that are largely unaffected by flow altering activities. Univariate and multivariate techniques were used to assess similarity among different stream types on the basis of these sub‐daily metrics. For comparison, similar analyses were performed using analogous metrics calculated with mean daily flow values. Our results confirm that sub‐daily flow metrics reveal variation among and within streams that are not captured by daily flow statistics. Using sub‐daily flow statistics, we were able to quantify the degree of difference between unaltered and peaking streams and the amount of similarity between unaltered and run‐of‐river streams. The sub‐daily statistics were largely uncorrelated with daily statistics of similar scope. On short temporal scales, sub‐daily statistics reveal the relatively constant nature of unaltered stream reaches and the highly variable nature of hydropower‐affected streams, whereas daily statistics show just the opposite over longer temporal scales. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

供水水库多目标生态调度研究

根据我国北方地区径流特征及供水水库调度的实际需求,构建了供水水库多目标生态调度模型。模型将下游生态需水过程分为最小生态需水及适宜生态需水两个等级,要求枯水期水库放水过程能够满足河流最小生态需水要求,确保下游生态不退化;丰水期放水过程贴近适宜生态需水过程,为下游提供良好生境。基于该模型,采用自适应遗传算法,对承德双峰寺水库生态调度问题进行了优化求解,结果表明该模型能够对北方供水水库生态调度决策提供支持。     

基于EFDC的咸潮上溯对闽江下游水源地的影响

为保障咸潮上溯情况下闽江下游水源地供水安全,建立基于EFDC的二维水环境数学模型,利用2013年12月同步监测资料进行参数率定,模拟不同流量条件下咸潮上溯的距离以及对水源地的影响。结果表明:咸潮上溯距离与下泄流量成负相关关系;咸潮上溯距离的增加将延长下游水源地的不宜取水时间。为减缓咸潮上溯对闽江下游水源地的影响,建议优化水口水库调度方式,加大下泄流量。     

建立富春江库区高水位运行淹没补偿机制的探讨

富春江水库是一座河床式低水头径流水电站,设计规定不担负防洪滞洪任务和钱塘江下游沿岸供水的抗咸顶潮冲淡任务。电站仅在洪水时担负基荷运行,一年中大部分时间担负调峰、调频和事故备用任务。但电站为了满足有利于水库调度多发电和钱塘江下游沿岸供水抗咸顶潮冲淡任务的需要,在实际运行中均采用较高水位运行,不仅增加库区农田的淹没损失,为保护水资源还加大地方政府对环保生态的投入,库区所在地的负担在加重。因此,水库电站必须向地方支付一定的淹没补偿费用。     

Including environmental flow requirements as part of real‐time water resource management

South African water resources legislation requires that environmental flow requirements are included as part of water resource management. An operational management method is presented that relies upon simulating natural flow conditions based on inputs of near real‐time observations of rainfall and a set of operating rules. The operating rules define the reservoir releases and water use supply curtailments that ensure downstream environmental flow objectives will be met. The focus is on managing the variability of continuous low flows, while a suitable method for managing event‐based high flow releases remains elusive. The main limitation to the successful implementation of the low flow approach is the lack of legislated control over run‐of‐river water abstractions. While this limitation is expected to be overcome, as the provisions of new legislation are implemented, water managers may still lack the capacity to exercise the necessary controls over abstraction. There is no reason why the method could not be applied outside South Africa, given compatibility in the definition of environmental flow requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulating system‐wide effects of reducing irrigation withdrawals in a disputed river basin

Stakeholders in river systems often target larger upstream water consumers as an intuitive solution for increasing flows for downstream ecological needs. Within regulated river systems, simplistic panaceas may have unexpected and unintended results at a watershed level. The Apalachicola–Chattahoochee–Flint River Basin is a large watershed in the south‐eastern United States whose management has been the source of conflict for several decades. This paper tests the hypothesis of whether a reduction in consumptive losses to Flint River flows through the large‐scale implementation of water‐saving agricultural irrigation technologies and practices will have a positive effect on downstream ecosystem water requirements in the Apalachicola River. An existing integrated reservoir/reach model was used to explore multiple irrigation water use scenarios. Because of current federal reservoir operating rules in the Chattahoochee River, irrigation decreases in the Flint River do not always directly translate to elevated flows downstream in the Apalachicola River. In drought years, a large percentage of the Flint River water savings is captured as greater storage volume at upstream Chattahoochee reservoirs because of a requirement to supplement downstream flows to a prescribed minimum level. In nondrought years, the majority of irrigation decreases translate to increased flow in the Apalachicola River. Given these simulation results, public policy decisions need to be formulated with regard to what portion of the Flint River water savings from changing irrigation practices in drought years should be allocated to the upstream Chattahoochee storage reservoirs and what portion to supporting downstream environmental and social needs in the Apalachicola watershed.     

水库多目标生态调度

分析了现行水库调度方法的不足,指出应在实现社会经济多种目标的前提下,兼顾河流生态系统需求,实行水库的多目标生态调度。文中讨论了水库多目标生态调度的方法,包括建立相应法规体系;保证维持下游河道基本生态功能的需水量;模拟自然水文情势的水库泄流方式;进行水库泥沙调控及水库富营养化控制;减轻水体温度分层影响;进行防污调度以及增强水系连通性等方面的调度技术。     

一维二维耦合模型研究水库运行对下游河道水环境的影响

水库运行造成的河道水流条件的改变给下游的水生态系统带来重要影响。耦合水动力过程及生态过程的生态水力学模型可以有效地定量评价这种影响。本研究以广西漓江为实例，建立了全河流一维和局部河段二维水环境模型。其中的一维模型分析全河段水环境变化趋势，二维模型分析关键区间水环境的特点，并为后续的生物栖息地模型奠定基础。模型分析了典型水文年中自然径流和青狮潭水库运行两种模式下下游河道关键水环境因子的变化。模拟结果表明水库运行在平水年的影响大于丰水年和枯水年，局部浅水区的变化大于深水区，年内枯水期(10-12月)的影响大于年均值，而且这些变化沿程逐渐减弱。该研究成果为下一步的生态模型提供了外部因子。     

长江口深水航道(一、二期工程)回淤变化

利用长江口深水航道回淤资料,研究了北槽航道回淤的时空变化特征及其对流域来水来沙、河槽地形的关系.长江口深水航道治理一、二期工程实施后,北槽航道年淤积强度明显下降,工程治理效果得以显现.从空间上看,一、二期工程航道回淤的峰值位置和重心位置经历了下移和上提的过程.从时间上看,一、二期工程后北槽航道回淤年内呈现洪季多淤、枯季少淤;洪季淤积位置下移,枯季淤积位置上提的变化特点,季节性上、下移动约7～11km.深水航道淤积的泥沙来源有多种,仅流域悬沙输沙量减小并不能明显降低深水航道的回淤量.     

Classification of US Hydropower Dams by their Modes of Operation

A key challenge to understanding ecohydrologic responses to dam regulation is the absence of a universally transferable classification framework for how dams operate. In the present paper, we develop a classification system to organize the modes of operation (MOPs) for US hydropower dams and powerplants. To determine the full diversity of MOPs, we mined federal documents, open‐access data repositories, and internet sources. We then used CART classification trees to predict MOPs based on physical characteristics, regulation, and project generation. Finally, we evaluated how much variation MOPs explained in sub‐daily discharge patterns for stream gages downstream of hydropower dams. After reviewing information for 721 dams and 597 power plants, we developed a two‐tier hierarchical classification based on (i) the storage and control of flows to powerplants, and (ii) the presence of a diversion around the natural stream bed. This resulted in nine tier‐1 MOPs representing a continuum of operations from strictly peaking, to reregulating, to run‐of‐river, and two tier‐2 MOPs, representing diversion and integral dam‐powerhouse configurations. Although MOPs differed in physical characteristics and energy production, classification trees had low accuracies (≤62%), which suggested that accurate evaluations of MOPs may require individual attention. MOPs and dam storage explained 20% of the variation in downstream subdaily flow characteristics and showed consistent alterations in subdaily flow patterns from reference streams. This standardized classification scheme is important for future research including estimating reservoir operations for large‐scale hydrologic models and evaluating project economics, environmental impacts, and mitigation. Copyright © 2016 John Wiley & Sons, Ltd.     

Conceptual Modelling to Assess Hydrological Impacts and Evaluate Environmental Flow Scenarios in Montane River Systems Regulated for Hydropower

To improve understanding of natural and managed flow regimes in data‐sparse regulated river systems in montane areas, the commonly used Hydrologiska Byråns Vattenbalansavdelning (HBV) conceptual run‐off model was adapted to incorporate water regulation components. The extended model was then applied to the heavily regulated river Lyon (391 km²) in Scotland to reconstruct the natural flow regime and to assess the impacts of regulation at increasing spatial scales. Multi‐criteria model evaluation demonstrated that the model performed well in capturing the dominant catchment processes and regulation effects, especially at the timescales at which operation rules apply. The main change as a result of regulation in the river Lyon is a decrease in inter‐annual and intra‐annual variability of all elements of the flow regime, in terms of magnitude, frequency, and duration. Although these impacts are most pronounced directly downstream of the impoundments, the regulation effects propagate throughout the river system. The modelling approach is flexible and widely applicable and only limited amounts of data are required. Moreover, results are easily communicated to stakeholders. It has the potential to contribute to the development of flow regimes that may be more beneficial to the ecological status of rivers. In the case of the river Lyon, it is likely that this involves a more variable release regime. The approach developed here provides a tool for assessing impacts on flow regimes and informing environmental flows in other data‐sparse regions with heavily regulated montane river systems. Copyright © 2014 John Wiley & Sons, Ltd.