The state of the art for optimal water reservoir operations is rapidly evolving, driven by emerging societal challenges. Changing values for balancing environmental resources, multisectoral human ...system pressures, and more frequent climate extremes are increasing the complexity of operational decision making. Today, reservoir operations benefit from technological advances, including improved monitoring and forecasting systems as well as increasing computational power. Past research in this area has largely focused on improving solution algorithms within the limits of the available computational power, using simplified problem formulations that can misrepresent important systemic complexities and intersectoral interactions. In this study, we review the recent literature focusing on how the operation design problem is formulated, rather than solved, to address existing challenges and take advantage of new opportunities. This paper contributes a comprehensive classification of over 300 studies published over the last years into distinctive categories depending on the adopted problem formulation, which clarifies consolidated methodological approaches and emerging trends. Our analysis also suggests that control policy design methods may benefit from broadening the types of information that is used to condition operational decisions, and from using emulation modeling to identify low‐order, computationally efficient surrogate models capturing realistic representations of river basin systems' complexity in order to isolate key decision‐relevant processes. These advances in reservoir operations hold significant promise for better addressing the challenges of conflicting human pressures and a changing world, which is particularly important, given the renewed interest in dam construction globally.
Key Points
We review the evolution of water reservoir operation studies driven by emerging societal challenges
Simulation‐based control methods facilitate realistic problem formulations that are able to handle system uncertainties
Research opportunities remain to combine policy design with more information sources and emulation modeling
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
AbstractSynthetic hydrologic forecasts are often needed to evaluate water resources planning and management strategies when appropriate historical forecasts are not available. Synthetic forecasts can ...be generated to evaluate system performance with existing forecast products over historical periods when they were not available, or with different forecast products that do not yet exist. Synthetic forecast generation procedures should produce forecasts that are realistic and have the desired statistical properties. Two synthetic forecast generation techniques are proposed that create a time series of forecasts with (1) the desired mean, (2) the correct variance, and (3) the desired forecast precision. One uses a classical stochastic hydrology approach, and the other the generalized maintenance of variance extension (GMOVE) concept using historical hydrologic series as input. A critique is provided of several published synthetic forecast generation algorithms that produced unrealistic results. The GMOVE methodology is used in a stochastic optimization model of a single reservoir hydropower system. Using forecasts of varying precision, the example illustrates the ability of more precise forecasts to improve system operations.
The Grubbs‐Beck test is recommended by the federal guidelines for detection of low outliers in flood flow frequency computation in the United States. This paper presents a generalization of the ...Grubbs‐Beck test for normal data (similar to the Rosner (1983) test; see also Spencer and McCuen (1996)) that can provide a consistent standard for identifying multiple potentially influential low flows. In cases where low outliers have been identified, they can be represented as “less‐than” values, and a frequency distribution can be developed using censored‐data statistical techniques, such as the Expected Moments Algorithm. This approach can improve the fit of the right‐hand tail of a frequency distribution and provide protection from lack‐of‐fit due to unimportant but potentially influential low flows (PILFs) in a flood series, thus making the flood frequency analysis procedure more robust.
Key Points
Generalization of Grubbs‐Beck test to any order statistic of a normal sample
Derivation of semi‐analytical p‐values for generalized Grubbs‐Beck test
Application of test to frequency analysis for records with multiple outliers
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Flood frequency analysis generally involves the use of simple parametric probability distributions to smooth and extrapolate the information provided by short flood records to estimate extreme flood ...flow quantiles. Parametric probability distributions can have difficulty simultaneously fitting both the largest and smallest floods. A danger is that the smallest observations in a record can distort the exceedance probabilities assigned to the large floods of interest. The identification and treatment of such Potentially Influential Low Floods (PILFs) frees a fitting algorithm to describe the distribution of the larger observations. This can allow parametric flood frequency analysis to be both efficient, and also robust to deviations from the proposed probability model's lower tail. Historically, PILF identification involved subjective judgement. We propose a new multiple Grubbs‐Beck outlier test (MGBT) for objective PILF identification. MGBT PILF identification rates (akin to Type I errors) are reported for the lognormal (LN) distribution and the log‐Pearson Type III (LP3) distribution with a variety of skew coefficients. MGBT PILF identification generally matched subjective identification from a recent California flood frequency study. Monte Carlo results show that censoring of PILFs identified by the MGBT algorithm improves the extreme quantile estimator efficiency of the expected moments algorithm (EMA) for negatively skewed LP3 distributions and has little effect for zero or positive skews; simultaneously it protects against deviations from the LP3 in the lower tail, as illustrated by distorted LN examples. Thus, MGBT generally makes flood frequency analysis based on the LP3 distribution with EMA both more accurate and more robust.
Key Points:
Treatment of Potentially Influential Low Floods can make flood frequency methods more robust
The MGBT outlier test can be an effective tool for identifying PILFs
Using the MGBT to identify PILFs improves robustness of the EMA method, while not losing efficiency
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
AbstractIdentification of outliers in flood records can be an important step in a robust flood frequency analysis procedure. Bulletin 17B includes the Grubbs-Beck test (with α=10%) as an objective ...criterion of whether the smallest observations in a flood record are outliers. The Spencer-McCuen test extends the Grubbs-Beck test to consider explicitly whether the three smallest observations are outliers in log-Pearson Type 3 (or equivalently Pearson Type 3) distributed samples with log-space skew coefficients between −1,1, and three significance levels 1, 5, and 10%. Presented here are Monte Carlo experiments evaluating the performance of the Spencer-McCuen test. When that test relies on the sample skew coefficient as an estimate of the population skew, the test generally fails to achieve the nominal significance levels. The same is true when used with a generalized (weighted) skew coefficient. Thus, the test will often be inappropriate if used as originally proposed. More fundamentally, when a proposed test relies on the skew coefficient of a sample to test for outliers in that sample, it is no longer clear what it means for an observation to be an outlier.
Major multi-reservoir cascades represent a primary mechanism for dealing with hydrologic variability and extremes within institutionally complex river basins worldwide. These coordinated management ...processes fundamentally reshape water balance dynamics. Yet, multi-reservoir coordination processes have been largely ignored in the increasingly sophisticated representations of reservoir operations within large-scale hydrological models. The aim of this paper is twofold, namely (i) to provide evidence that the common modeling practice of parameterizing each reservoir in a cascade independently from the others is a significant approximation and (ii) to demonstrate potential unintended consequences of this independence approximation when simulating the dynamics of hydrological extremes in complex reservoir cascades. We explore these questions using the Water Balance Model, which features detailed representations of the human infrastructure coupled to the natural processes that shape water balance dynamics. It is applied to the Upper Snake River basin in the western US and its heavily regulated multi-reservoir cascade. We employ a time-varying sensitivity analysis that utilizes the method of Morris factor screening to explicitly track how the dominant release rule parameters evolve both along the cascade and in time according to seasonal high- and low-flow events. This enables us to address aim (i) by demonstrating how the progressive and cumulative dominance of upstream releases significantly dampens the ability of downstream reservoir rules' parameters to influence flow conditions. We address aim (ii) by comparing simulation results with observed reservoir operations during critical low-flow and high-flow events in the basin. Our time-varying parameter sensitivity analysis with the method of Morris clarifies how independent single-reservoir parameterizations and their tacit assumption of independence leads to reservoir release behaviors that generate artificial water shortages and flooding, whereas the observed coordinated cascade operations avoided these outcomes for the same events. To further explore the role of (non-)coordination in the large deviations from the observed operations, we use an offline multi-reservoir water balance model in which adding basic coordination mechanisms drawn from the observed emergency operations is sufficient to correct the deficiencies of the independently parameterized reservoir rules from the hydrological model. These results demonstrate the importance of understanding the state–space context in which reservoir releases occur and where operational coordination plays a crucial role in avoiding or mitigating water-related extremes. Understanding how major infrastructure is coordinated and controlled in major river basins is essential for properly assessing future flood and drought hazards in a changing world.
Summary
Background
The epididymis is the hallmark of all vertebrate species practicing internal fertilization. While the functions of the epididymis are well documented in laboratory rodents and some ...domestic animals, the structure and functions of the epididymis in humans remain poorly documented.
Objectives
Using human tissues obtained with the collaboration of our local organ transplantation program, the histology, cell types, and three‐dimensional organization of the excurrent duct were investigated. Microarrays were performed to determine the gene expression pattern along the human epididymis.
Materials and methods
The histology of longitudinal sections of the proximal epididymis was described, and immunohistochemistry using specific antibodies was used to characterize cell types of the efferent duct and caput epididymis epithelia. The epididymis was divided into eight segments permitting gene profiling by microarray and gene ontology analysis.
Results
The proximal region of the human epididymis is formed exclusively by efferent ducts. These ducts form a complex histological structure particularly at the junction of the efferent ducts and caput epididymis. The efferent ducts exhibit a specific cellular signature when compared with the adjacent epididymis tubule. Efferent duct gene expression is not segmented and is dedicated to cilium differentiation and movement. The gene expression pattern of the caput segment is homogeneous and specialized in defense and immune responses and fertilization.
Discussion
In murine species, the epididymis is segmented into the initial segment, caput, corpus, and cauda regions, whereas in humans, the proximal region is formed by efferent ducts. The caput tubules have their own histological organization with a well‐defined gene expression pattern. The distal corpus and cauda epididymis are distinct by a limited number of differentially expressed genes.
Conclusions
Knowledge of epididymis functions and structure obtained using laboratory species should be extrapolated to humans with caution.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The interleukin-6 receptor blockers tocilizumab and sarilumab were tested against standard care in a randomized trial involving patients newly admitted to the intensive care unit and requiring ...respiratory or blood-pressure support. The median number of organ support–free days was 10 with tocilizumab, 11 with sarilumab, and 0 with standard care.
Rivers are often assumed to be the main source of nutrients triggering eutrophication in the Great Barrier Reef (GBR). However, existing nutrient budgets suggest a major missing source of nitrogen ...and phosphorus sustaining primary production. Here, we used radium isotopes to resolve submarine groundwater discharge (SGD)-derived, shelf-scale nutrient inputs to the GBR. The total SGD was ∼10–15 times greater than average river inputs, with nearshore groundwater discharge accounting for ∼30% of this. Total SGD accounted for >30% of all known dissolved inorganic N and >60% of inorganic P inputs and exceeded regional river inputs. However, SGD was only a small proportion of the nutrients necessary to sustain primary productivity, suggesting that internal recycling processes still dominate the nutrient budget. With millions of dollars spent managing surface water nutrient inputs to reef systems globally, we argue for a shift in the focus of management to safeguard reefs from the impacts of excess nutrients.
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IJS, KILJ, NUK, PNG, UL, UM
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