Salinity trends in Louisiana estuaries

If long-term trends in the character of the estuarine salinity field are contributing to land-loss in coastal Louisiana, then evidence of the presence of these trends may exist in historical salinity records. Nonparametric tests for the presence of a trend in the time series of various salinity statistics were performed. The results appear to be strongly influenced by climatological variations of decadal scale. Statistically significant trends were found at many stations. Both increasing and decreasing trends occurred with no apparent underlying spatial pattern. The observed changes during the time covered by the available records were generally too small to be lethal to the dominant marsh plants.     

Core Jamming in Unconsolidated Formations

Geotechnical and Geological Engineering - In coring operations, core jamming is a permanent concern, taking place when the rock core sample becomes stuck within the inner core barrel, thus...     

Polycyclic aromatic hydrocarbons in dated sediments from Green Bay and Lake Michigan

Sediment cores from two locations in Green Bay and two in lake Michigan were analyzed for 12 polycyclic aromatic hydrocarbons (PAHs), loss-on-ignition (LOI),²¹⁰Pb,¹³⁷Cs, and⁷Be to study differences in deposition patterns between the freshwater estuary Green Bay, with several local sources, and the open Lake Michigan, dominated by atmospheric inputs. We found that the remote sites receive relatively less high-molecular weight PAHs such as ideno(1,2,3-cd)pyrene and dibenz(ah)anthracene and are more depleted in anthracene and pyrene. This may be related to a low Henry’s law constant for the high molecular compounds and to selective photo-oxidation of anthracene and pyrene during transport. While sedimentation rates are higher in Green Bay than in the open lake, the PAH levels are generally comparable (0.3–8.5 μg g^?1) in the two areas. However, the highest PAH levels are found in a core from Green Bay (GB88G). The two Green Bay cores have total PAH concentration maxima in 1985, which appear to be related to the combustion of petroleum. Also, one Green Bay core (GB88G) and the two from Lake Michigan exhibit PAH maxima in the early 1950s in agreement with observations from other study areas. There is a significant correlation between total PAH and LOI, and thus total organic carbon, for the Green Bay cores, but little or no such correlation for the Lake Michigan cores. This may indicate that PAHs in Green Bay are effectively scavenged by settling detritus.     

Origin of the sedimentary deposits of the Naracoorte Caves, South Australia

The origin of the sediments located in the Naracoorte Caves (South Australia) was investigated via the analysis of strontium isotope ratios (⁸⁷Sr/⁸⁶Sr), elemental geochemistry, and mineralogy. Sedimentary deposits located in Robertson, Wet, Blanche and several other chambers in Victoria Cave are all variable mixes of fine sand and coarse silts, which display similar and consistent strontium isotope ratios (0.717–0.725). This suggests that over the 400 ka time frame that these deposits span there has been minimal variation in the source of the clastic sediments. Increased strontium concentrations for these cave sediments correspond with increasing silt content, yet there is no correlation between ⁸⁷Sr/⁸⁶Sr ratios and silt content. This implies that the silt-sized component of the sediments is the main contributor of strontium to the cave sediments. Comparisons of ⁸⁷Sr/⁸⁶Sr with regional surficial deposits show a significant correlation between the cave sediments (avg: 0.7228; n = 27), the fine silt lunettes of the Bool Lagoon area (avg: 0.7224; n = 4), the sandy A horizons of the Coonawarra Red Brown Earths (RBEs; avg: 0.726; n = 5), and Holocene age podsolic sand deposits (0.723). These data suggest that there has been substantial flux from this group of deposits to the caves, as would be expected considering prevailing winds. This relationship is further supported by a strong correlation between many trace elements, including Ti, Zr, Ce, and Y; however, variations in clay mineralogy suggest that the fine silt-dominated lunettes and Padthaway RBEs were not significant contributors to the cave deposits. Hence, the detritus entering the caves was more than likely from areas proximal to the cave entrance and was dominated by medium grain-sized materials. Major regional deposits, including the coarser-grained, calcite-rich Bridgewater Formation sands, basalts from the lower SE, Padthaway Horst granites, Gambier limestone, and metamorphics from the Adelaide geosyncline show minimal correlation in ⁸⁷Sr/⁸⁶Sr ratios, elemental geochemistry, and mineralogy with the cave sediments, and are discounted as significant sources. In comparison, ⁸⁷Sr/⁸⁶Sr ratios for the Coorong silty sands (0.717–0.724), Lower Murray sands (0.727–0.730), and the medium size silt component of the Murray–Darling River system (0.71–0.72), compare favourably with the cave sediments. This relationship is further supported by similarities in elemental chemistry and mineralogy. Thus, much of the strontium-rich silt that is now located in the Naracoorte Cave sediments likely originated from the Murray–Darling basin. Over time, this material has been transported to the SE of South Australia, where it mixed with the medium sand component of the regressive dune ridge sequence, locally derived organic matter, limestone fragments, and fossil material to produce the unique deposits that we see evident in many of the chambers of the Naracoorte Cave system today.     

Correction of the Buckingham–Darcy Law for flow of high strength salts in variably saturated porous media

The Buckingham–Darcy Law is used to describe fluid flow in unsaturated porous media at low Reynolds number. In order to provide a priori corrections to this law, a process thermodynamic approach is utilized to ascertain the functional dependence. Using this knowledge, corrections to the hydraulic conductivity coefficient are proposed and compared with available data. The proposed corrections substantially predict the observed behavior of flow of high concentration (saturated) sodium chloride solutions in porous media. During the derivation, physical principles consistent with the thermodynamics of the system were utilized. A review of these principles and their results provides an alternative form of the generalized Gibbs–Duhem Relation for continuous processes, indicating that the identical equivalence to zero is unlikely to occur for dissipative processes. Further, the postulated Gibbs and Gibbs–Duhem Relations indicate that special differential operators need to be used for continuous processes rather than the usual use of a generic differential.     

Tidal and subtidal water volume exchange in an estuarine system

Estuarine water movements occur over a broad range of time scales. In this study, moored current meter data were used to investigate water volume exchange in the tidal passes of Lake Pontchartrain, Louisiana on the tidal and subtidal time scales. A calibration technique, employing cross-channel measurements of water velocity, was used to calibrate the moored current meters, thus allowing for calculation of volume flow over a 35-day period. The local diurnal tide accounted for 50% of the total volume exchange, the rest being due to subtidal events (frontal passage). This subtidal exchange occurs primarily as large-scale events characterized by volume fluxes up to six times greater than the normal tidal prism. Neglecting this subtidal component in the determination of the volume fluxes for a system such as Lake Pontchartrain, could result in substantial underestimation (by as much as 50%) of these volume and their corresponding material fluxes.     

Lessons Learned from the 2011 Great East Japan Tsunami: Performance of Tsunami Countermeasures, Coastal Buildings, and Tsunami Evacuation in Japan

In 2011, Japan was hit by a tsunami that was generated by the greatest earthquake in its history. The first tsunami warning was announced 3 min after the earthquake, as is normal, but failed to estimate the actual tsunami height. Most of the structural countermeasures were not designed for the huge tsunami that was generated by the magnitude M = 9.0 earthquake; as a result, many were destroyed and did not stop the tsunami. These structures included breakwaters, seawalls, water gates, and control forests. In this paper we discuss the performance of these countermeasures, and the mechanisms by which they were damaged; we also discuss damage to residential houses, commercial and public buildings, and evacuation buildings. Some topics regarding tsunami awareness and mitigation are discussed. The failures of structural defenses are a reminder that structural (hard) measures alone were not sufficient to protect people and buildings from a major disaster such as this. These defenses might be able to reduce the impact but should be designed so that they can survive even if the tsunami flows over them. Coastal residents should also understand the function and limit of the hard measures. For this purpose, non-structural (soft) measures, for example experience and awareness, are very important for promoting rapid evacuation in the event of a tsunami. An adequate communication system for tsunami warning messages and more evacuation shelters with evacuation routes in good condition might support a safe evacuation process. The combination of both hard and soft measures is very important for reducing the loss caused by a major tsunami. This tsunami has taught us that natural disasters can occur repeatedly and that their scale is sometimes larger than expected.     

Explication de décrues anormales par modèles analogiques de réservoirs

Résumé

Des modèles analogiques de réservoirs ont été élaborés à partir de l'analyse de débits de décrue de deux sources karstiques. La première source est caractérisée par une linéarité entre le débit et le temps; la seconde l'est par une loi en puissance. Pour les deux sources, il n'y a pas linéarité entre le volume d'eau souterraine stocké et le débit de la source pour un même temps. Les modèles analogiques élaborés sont constitués d'une association verticale en série de réservoirs. Pour la première source, il s'agit de réservoirs à parois verticales uniquement. Pour la seconde, il s'agit de réservoirs à parois verticales et d'un réservoir dont la géométrie des parois suit une loi en puissance à dimension non entière. La plausibilité et la reproductibilité des modèles analogiques proposés ont été validées en fonction des données disponibles. Il a été démontré que le cas de réservoirs linéaires en milieu karstique est un cas très particulier. Il correspond à des réservoirs à géométrie hyperbolique ou à des réservoirs à parois verticales à filtre poreux.

Editeur Z.W. Kundzewicz

Citation Carlier, E., Zouhri, L. et Shahrour, I., 2012. Explication de décrues anormales par modèles analogiques de réservoirs. Hydrological Sciences Journal, 57 (5), 913–927.     

Drivers of national climate policy

Patterns of national climate policy performance and their implications for the geopolitics of climate change are examined. An overview of levels of emissions performance across countries is first provided. Substantial changes in emissions trends over time are documented, notably with GHG emissions trajectories, which are shaped less and less by the developed/developing country divide. Various patterns of policy convergence and divergence in the types of policies states implement are then surveyed. Four broad types of explanation that may account for these trends are then explored: (1) variation in the institutional form of country-level governance regimes, (2) patterns of dependence on fossil fuel energy, (3) broad systemic differences among states (specifically in their population densities, carbon intensity, and per capita incomes, and (4) variations in the traditions of economic intervention by states. The article contributes to the growing body of work on comparative climate policy, and provides a first attempt at exploring the comparative politics of instrument choice. The analysis challenges the continued importance of a North–South divide for the future of climate policy, thus reinforcing a sense of the ‘new geopolitics’ of climate change. Some of the implications of the analysis for debates about the form of future international agreement on mitigation policy are also explored.

Policy relevance

The article contributes to the understanding of the variety of institutional conditions under which policy makers develop policy and thus the constraints and opportunities for the design of international agreements under these conditions.