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41.
Regional source tsunamis pose a potentially devastating hazard to communities and infrastructure on the New Zealand coast. But major events are very uncommon. This dichotomy of infrequent but potentially devastating hazards makes realistic assessment of the risk challenging. Here, we describe a method to determine a probabilistic assessment of the tsunami hazard by regional source tsunamis with an “Average Recurrence Interval” of 2,500-years. The method is applied to the east Auckland region of New Zealand. From an assessment of potential regional tsunamigenic events over 100,000 years, the inundation of the Auckland region from the worst 100 events is modelled using a hydrodynamic model and probabilistic inundation depths on a 2,500-year time scale were determined. Tidal effects on the potential inundation were included by coupling the predicted wave heights with the probability density function of tidal heights at the inundation site. Results show that the more exposed northern section of the east coast and outer islands in the Hauraki Gulf face the greatest hazard from regional tsunamis in the Auckland region. Incorporating tidal effects into predictions of inundation reduced the predicted hazard compared to modelling all the tsunamis arriving at high tide giving a more accurate hazard assessment on the specified time scale. This study presents the first probabilistic analysis of dynamic modelling of tsunami inundation for the New Zealand coast and as such provides the most comprehensive assessment of tsunami inundation of the Auckland region from regional source tsunamis available to date. 相似文献
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43.
Bradley W. Lane 《Journal of Geographical Systems》2011,13(2):147-171
Rail transit continues to be a popular alternative for cities as a tool for alleviating automobile congestion and for redeveloping
areas into transit and pedestrian-friendly environments. Ideally, rail transit will draw trips away from cars, but the quantitative
work that tests this notion has often been either case studies of neighborhoods, in which conclusions are tough to generalize,
or citywide comparisons where important spatial variation is lost in aggregation. This study seeks to narrow this gap in the
research by using multivariate analysis of covariance to isolate the effect of covariates and cities on changes in work trip
mode choice at the traffic analysis zone (TAZ) level for nine cities between 1990 and 2000. The results suggest differences
by city in the change at the TAZ level of the proportion of people driving alone and taking transit. Increases in transit
usage were associated with cities that built rail transit, while increases in automobile commuting and decreases in transit
usage were associated with cities that did not. 相似文献
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45.
A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India 总被引:1,自引:1,他引:0
Jayalakshmi Devi Oinam AL. Ramanathan Anurag Linda Gurmeet Singh 《Environmental Earth Sciences》2011,62(6):1183-1195
The presence of arsenic (As) in groundwater and its effect on human health has become an issue of serious concern in recent
years. The present study assessed the groundwater quality of the Bishnupur District, Manipur, with respect to drinking water
standards. Higher concentrations of pH, iron and phosphate were observed at several locations. Phosphate and iron levels were
highest in the pre-monsoon, followed by monsoon and post-monsoon seasons. The arsenic concentrations were highest during post-monsoon
(1–200 μg L−1) as compared to pre-monsoon (1–108 μg L−1) and monsoon (2–99 μg L−1). Kwakta and Ngakhalawai show higher levels of arsenic concentration as compared to the prescribed World Health Organization
(WHO) and Bureau of Indian Standards (BIS) norms. Arsenic showed a strong positive correlation with phosphate and negative
correlation with sulphate, suggesting a partial influence of anthropogenic sources. The study suggests that the Bishnupur
area has an arsenic contamination problem, which is expected to increase in the near future. 相似文献
46.
Intensive field monitoring of a reach of upland gravel‐bed river illustrates the temporal and spatial variability of in‐channel sedimentation. Over the six‐year monitoring period, the mean bed level in the channel has risen by 0·17 m with a maximum bed level rise of 0·5 m noted at one location over a five month winter period. These rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2·6 times and overbank flow time increasing by 12·8 hours. This work raises the profile of coarse sediment transfer in the design and operation of river management, specifically engineering schemes. It emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic. Exploration of the sediment supply and transfer system can explain patterns of channel sedimentation. The complex spatial, seasonal and annual variability in sediment supply and transfer raise uncertainties into the system's response to potential changes in climate and land‐use. Thus, there is a demand for schemes that monitor coarse sediment transfer and channel response. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
47.
M. R. Zapatero Osorio E. L. Martín B. F. Lane Ya. Pavlenko H. Bouy I. Baraffe G. Basri 《Astronomische Nachrichten》2005,326(10):848-851
GJ 569Bab is the first brown dwarf binary for which the mass of each component has been derived by solving the astrometric and spectroscopic orbit of the pair, i.e., independently of any theoretical assumption. This allows us to test the predictions of the various evolutionary models available in the literature. Particularly interesting are the predictions of lithium depletion for the mass (0.08–0.05M⊙) and likely age (300–800 Myr) of the substellar components. High‐resolution optical spectra of GJ 569B (the pair is not resolved) obtained with HIRES at the Keck telescope show that there has been significant lithium depletion in both components. We will compare these results to state‐of‐the‐art theoretical calculations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
48.
We studied the macroinvertebrate fauna of a rocky shore in the freshwater tidal Hudson River during 1992–1994, the early years of the zebra mussel (Dreissena polymorpha) invasion. The macroinvertebrate community was numerically dominated by chironomids, nematodes, oligochaetes, gastropods, zebra mussels, and planarian flatworms. The community was a mixture of species typical of stony warm water rivers and lake shores, freshwater generalists, and semiterrestrial species. Overall macroinvertebrate densities were moderate to low (2,800–14,600 m−2). Density was a strong function of season and elevation, with consistently low densities in the early spring and in the intertidal zone. This pattern suggests that physical harshness (alternating submergence and desiccation;ice and low temperatures) limits the distribution of invertebrates at this site. Zebra mussels occurred at our study site chiefly below the low tide mark, but only at moderate abundance (usually <1,000 m−2). A weak correlation between the densities of zebra mussels and those of other macroinvertebrates nonetheless suggests that the zebra mussel invasion may have affected community structure. 相似文献
49.
Since 1991, Mississippi River water has been diverted at Caernarvon, Louisiana, into Breton Sound estuary. Breton Sound estuary encompasses 1100 km2 of fresh and brackish, rapidly subsiding wetlands. Nitrite + nitrate, total Kjeldahl nitrogen, ammonium, total phosphorus, total suspended sediments, and salinity concentrations were monitored at seven locations in Breton Sound from 1988 to 1994. Statistical analysis of the data indicated decreased total Kjeldahl nitrogen with associated decrease in total nitrogen, and decreased salinity concentrations in the estuary due to the diversion. Spring and summer water quality transects indicated rapid reduction of nitrite + nitrate and total suspended sediment concentration as diverted Mississippi River water entered the estuary, suggesting near complete assimilation of these constituents by the ecosystem. Loading rates of nitrite + nitrate (5.6–13.4 g m−2 yr−1), total nitrogen (8.9–23.4 g m−2 yr−1), and total phosphorus (0.9–2.0 g m−2 yr−1) were calculated along with removal efficiencies for these constituents (nitrite + nitrate 88–97%; total nitrogen 32–57%; total phosphorus 0–46%). The low impact of the diversion on water quality in the Breton Sound estuary, along with assimilation of TSS over a very short distance, suggests that more water may be introduced into the estuary without detrimental affects. This would be necessary if freshwater diversions are to be used to distribute nitrients and sediments into the lower reaches of the estuary, in an effort to compensate for relative sea-level rise, and reverse the current trend of rapid loss of wetlands in coastal Louisiana. 相似文献
50.