A non-traditional approach to the analysis of flood hazard for dams     

Zoran Micovic  Desmond N. D. Hartford  Melvin G. Schaefer  Bruce L. Barker 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(2):559-581

The traditional and still prevailing approach to characterization of flood hazards to dams is the inflow design flood (IDF). The IDF, defined either deterministically or probabilistically, is necessary for sizing a dam, its discharge facilities and reservoir storage. However, within the dam safety risk informed decision framework, the IDF does not carry much relevance, no matter how accurately it is characterized. In many cases, the probability of the reservoir inflow tells us little about the probability of dam overtopping. Typically, the reservoir inflow and its associated probability of occurrence is modified by the interplay of a number of factors (reservoir storage, reservoir operating rules and various operational faults and natural disturbances) on its way to becoming the reservoir outflow and corresponding peak level—the two parameters that represent hydrologic hazard acting upon the dam. To properly manage flood risk, it is essential to change approach to flood hazard analysis for dam safety from the currently prevailing focus on reservoir inflows and instead focus on reservoir outflows and corresponding reservoir levels. To demonstrate these points, this paper presents stochastic simulation of floods on a cascade system of three dams and shows progression from exceedance probabilities of reservoir inflow to exceedance probabilities of peak reservoir level depending on initial reservoir level, storage availability, reservoir operating rules and availability of discharge facilities on demand. The results show that the dam overtopping is more likely to be caused by a combination of a smaller flood and a system component failure than by an extreme flood on its own.  相似文献   

How processing digital elevation models can affect simulated water budgets   总被引：1，自引：0，他引：1  

Kuniansky EL  Lowery MA  Campbell BG 《Ground water》2009,47(1):97-107

For regional models, the shallow water table surface is often used as a source/sink boundary condition, as model grid scale precludes simulation of the water table aquifer. This approach is appropriate when the water table surface is relatively stationary. Since water table surface maps are not readily available, the elevation of the water table used in model cells is estimated via a two-step process. First, a regression equation is developed using existing land and water table elevations from wells in the area. This equation is then used to predict the water table surface for each model cell using land surface elevation available from digital elevation models (DEM). Two methods of processing DEM for estimating the land surface for each cell are commonly used (value nearest the cell centroid or mean value in the cell). This article demonstrates how these two methods of DEM processing can affect the simulated water budget. For the example presented, approximately 20% more total flow through the aquifer system is simulated if the centroid value rather than the mean value is used. This is due to the one-third greater average ground water gradients associated with the centroid value than the mean value. The results will vary depending on the particular model area topography and cell size. The use of the mean DEM value in each model cell will result in a more conservative water budget and is more appropriate because the model cell water table value should be representative of the entire cell area, not the centroid of the model cell.  相似文献   

Measuring and monitoring persistent organic pollutants in the context of risk assessment   总被引：3，自引：0，他引：3  

Wu RS  Chan AK  Richardson BJ  Au DW  Fang JK  Lam PK  Giesy JP 《Marine pollution bulletin》2008,57(6-12):236-244

Due to growing concerns regarding persistent organic pollutants (POPs) in the environment, extensive studies and monitoring programs have been carried out in the last two decades to determine their concentrations in water, sediment, and more recently, in biota. An extensive review and analysis of the existing literature shows that whilst the vast majority of these efforts either attempt to compare (a) spatial changes (to identify "hot spots"), or (b) temporal changes to detect deterioration/improvement occurring in the environment, most studies could not provide sufficient statistical power to estimate concentrations of POPs in the environment and detect spatial and temporal changes. Despite various national POPs standards having been established, there has been a surprising paucity of emphasis in establishing accurate threshold concentrations that indicate potential significant threats to ecosystems and public health. Although most monitoring programs attempt to check compliance through reference to certain "environmental quality objectives", it should be pointed out that many of these established standards are typically associated with a large degree of uncertainty and rely on a large number of assumptions, some of which may be arbitrary. Non-compliance should trigger concern, so that the problem can be tracked down and rectified, but non-compliance must not be interpreted in a simplistic and mechanical way. Contaminants occurring in the physical environment may not necessarily be biologically available, and even when they are bioavailable, they may not necessarily elicit adverse biological effects at the individual or population levels. As such, we here argue that routine monitoring and reporting of abiotic and biotic POPs concentrations could be of limited use, unless such data can be related directly to the assessment of public health and ecological risks. Risk can be inferred from the ratio of predicted environmental concentration (PEC) and the predicted no effect concentration (PNEC). Currently, the paucity of data does not allow accurate estimation of PNEC, and future endeavors should therefore, be devoted to determine the threshold concentrations of POPs that can cause undesirable biological effects on sensitive receivers and important biological components in the receiving environment (e.g. keystone species, populations with high energy flow values, etc.), to enable derivation of PNECs based on solid scientific evidence and reduce uncertainty. Using the threshold body burden of POPs required to elicit damages of lysosomal integrity in the green mussel (Perna virvidis) as an example, we illustrate how measurement of POPs in body tissue could be used in predicting environmental risk in a meaningful way.  相似文献   

Generalized dual porosity: A numerical method for representing spatially variable sub-grid scale processes     

George A. Zyvoloski  Bruce A. Robinson  Hari S. Viswanathan 《Advances in water resources》2008

A generalized dual porosity method (GDPM) has been developed to incorporate sub-grid scale heterogeneity into large-scale flow and transport simulations. The method is spatially variable in the sense that the method can be applied with different levels of resolution for different spatial nodes in the simulation. The method utilizes the nodal connectivity structure and linear equation solvers of unstructured grids like those used in the finite element method, and can be applied to any problem without externally modifying the numerical grid. The algorithm scales linearly in CPU time and storage with the number of GDPM nodes. We demonstrate the utility and computational efficiency of the technique with two verification problems and an example problem of a field site.  相似文献   

Antioxidant responses to polycyclic aromatic hydrocarbons and organochlorine pesticides in green-lipped mussels (Perna viridis): do mussels "integrate" biomarker responses?   总被引：1，自引：0，他引：1  

Richardson BJ  Mak E  De Luca-Abbott SB  Martin M  McClellan K  Lam PK 《Marine pollution bulletin》2008,57(6-12):503-514

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCs) are generally present in the marine environment in complex mixtures. The ecotoxicological nature of contaminant interactions, however, is poorly understood, with most scientific observations derived from single contaminant exposure experiments. The objective of this experiment was to examine dose-response relationships between antioxidant parameters and body contaminant levels in mussels exposed to different exposure regimes under laboratory conditions. Accordingly, the green-lipped mussel, Perna viridis, was challenged with a mixture of PAHs (anthracene, fluoranthene, pyrene, benzo[a]pyrene) and OC pesticides (alpha-HCH, aldrin, dieldrin, p,p'-DDT) over a 4 week period. Contaminants were delivered under four different dosing regimes, with all treatments receiving the same total contaminant load by the end of the exposure period. Antioxidant biomarkers were measured after 1, 2, 3 and 4 weeks, including glutathione (GSH), gluathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and lipid peroxidase (LPO). GST and CAT were induced in hepatic tissues in most of the exposure regimes, with the majority of significant induction occurring in a constant exposure regime and a two-step alternate exposure regime. Significant differences among exposure regimes were detected in the body burden of contaminants after 28 days. Hepatic CAT and GSH are proposed as potentially useful biomarkers as they showed good correlation with target contaminants and were not readily affected by different dosing patterns.  相似文献   

Organochlorine contaminants in the muscle of striped bass illegally harvested from shad gill nets in the Hudson River Estuary     

Deshpande AD  Doyle SA  Dockum BW  Tesolin-Gee A 《Marine pollution bulletin》2008,56(12):2088-2093

  相似文献   

Antioxidant responses to polycyclic aromatic hydrocarbons and organochlorine pesticides in green-lipped mussels (Perna viridis): Do mussels “integrate” biomarker responses?     

Bruce J. Richardson  Eva Mak  Sharon B. De Luca-Abbott  Michael Martin  Katherine McClellan  Paul K.S. Lam 《Marine pollution bulletin》2008,57(6-12):503

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCs) are generally present in the marine environment in complex mixtures. The ecotoxicological nature of contaminant interactions, however, is poorly understood, with most scientific observations derived from single contaminant exposure experiments. The objective of this experiment was to examine dose-response relationships between antioxidant parameters and body contaminant levels in mussels exposed to different exposure regimes under laboratory conditions. Accordingly, the green-lipped mussel, Perna viridis, was challenged with a mixture of PAHs (anthracene, fluoranthene, pyrene, benzo[a]pyrene) and OC pesticides (α-HCH, aldrin, dieldrin, p,p′-DDT) over a 4 week period. Contaminants were delivered under four different dosing regimes, with all treatments receiving the same total contaminant load by the end of the exposure period. Antioxidant biomarkers were measured after 1, 2, 3 and 4 weeks, including glutathione (GSH), gluathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and lipid peroxidase (LPO). GST and CAT were induced in hepatic tissues in most of the exposure regimes, with the majority of significant induction occurring in a constant exposure regime and a two-step alternate exposure regime. Significant differences among exposure regimes were detected in the body burden of contaminants after 28 days. Hepatic CAT and GSH are proposed as potentially useful biomarkers as they showed good correlation with target contaminants and were not readily affected by different dosing patterns.  相似文献   

Towards a HPC Framework for Integrated Processing of Geographical Data: Encapsulating the Complexity of Parallel Algorithms   总被引：5，自引：0，他引：5  

Michael J. Mineter  Steve Dowers  & Bruce M. Gittings 《Transactions in GIS》2000,4(3):245-261

High-performance computing (HPC) techniques are still considered an esoteric research branch of GI processing. They are complex to use, deterring both academic modellers and commercial software developers. Yet the use of many environmental models is constrained by computation times. Furthermore, as remote sensing, environmental modelling and GIS converge, so the need for parallel computing becomes more apparent. Several case studies, parallelising the processing of raster, grid and vector-topology, demonstrate that scope exists for encapsulating the complexity of the parallelism in software frameworks, with strategies of spatial decomposition into sub-areas maximising the re-use of code from sequential algorithms. We show that parallel software frameworks can speed both the development and the execution of new applications. Based upon these case studies, the parallelisation of both interpolation and modelling in one software system is considered, with reference to pest infestation models, using both task and data parallelism. We discuss some of the requirements of a parallel software framework to underpin the integrated analysis of geographical data and environmental models.  相似文献   

Lyα imaging of a very luminous z = 2.3 starburst galaxy with WFPC2     

Nathan Roche  James Lowenthal  Bruce Woodgate 《Monthly notices of the Royal Astronomical Society》2000,317(4):937-951

  相似文献   

Concentrations of Persistent Organic Pollutants in Surface Sediments of the Mudflat and Mangroves at Mai Po Marshes Nature Reserve, Hong Kong   总被引：4，自引：0，他引：4  

Gene J. Zheng  Michael H. W. Lam  Paul K. S. Lam  Bruce J. Richardson  Ben K. W. Man  Ashley M. Y. Li 《Marine pollution bulletin》2000,40(12):1210-1214

  相似文献