When does spatial resolution become spurious in probabilistic flood inundation predictions?

Advances in remote sensing have enabled hydraulic models to run at fine scale resolutions, producing precise flood inundation predictions. However, running models at finer resolutions increase their computational expense, reducing the feasibility of running the multiple model realizations required to undertake uncertainty analysis. Furthermore, it is possible that precision gained by running fine scale models is smoothed out when treating models probabilistically. The aim of this paper is to determine the level of spatial complexity that is required when making probabilistic flood inundation predictions. The Imera basin, Sicily is used as a case study to assess how changing the spatial resolution of the hydraulic model LISFLOOD‐FP impacts on the skill of conditional probabilistic flood inundation maps given model parameter and boundary condition uncertainties. We find that model performance deteriorates at resolutions coarser than 50 m. This is predominantly caused by changes in flow pathways at coarser resolutions which lead to non‐stationarity in the optimum model parameters at different spatial resolutions. However, although it is still possible to produce probabilistic flood maps that contain a coherent outline of the flood extent at coarser resolutions, the reliability of these maps deteriorates at resolutions coarser than 100 m. Additionally, although the rejection of non‐behavioural models reduces the uncertainty in probabilistic flood maps the reliability of these maps is also reduced. Models with resolutions finer than 50 m offer little gain in performance yet are more than an order of magnitude computationally expensive which can become infeasible when undertaking probabilistic analysis. Furthermore, we show that using deterministic, high‐resolution flood maps can lead to a spurious precision that would be misleading and not representative of the overall uncertainties that are inherent in making inundation predictions. Copyright © 2015 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

Probabilistic seismic hazard assessment in SE-Spain based on macroseismic site histories

In many countries such as Spain earthquake databases still mainly comprise macroseismic data from felt effects. The full exploit of this information is of basic importance for seismic risk assessment and emergency planning, given the strict link between macroseismic intensity and damage. A probabilistic procedure specifically developed to handle macroseismic data, mostly relying on site information and seismogenic-source free, has been applied to evaluate seismic hazard in SE-Spain (Alicante-Murcia region). Present seismicity is moderate-low with largest magnitudes slightly over Mw5.0. The historical record includes very destructive earthquakes, maximum EMS98 intensities reaching IX–X and X in the nineteenth century (e.g., Torrevieja 1829 earthquake). Very recently, two events in the area on 11 May 2011 (Mw4.5, Mw5.2) killed nine people, injured 300, and produced important damage in the city of Lorca. Regional hazard maps for the area together with specific hazard curves at selected localities are obtained. Results are compared with the maximum observed intensities in the period 1300–2012, and with the values in the seismic hazard map from the Spanish Building Code in force. In general, the maximum felt intensity values are closer to the hazard values calculated for 2 % probability of exceedance in 50 years, using felt and expected intensity. The intensity-based probabilistic hazard maps obtained through the applied approach reduce the inherent smoothing of those based on standard probabilistic seismic hazard assessment approaches for the region, allowing identifying possible over- or sub-estimates of site hazard values, providing very valuable information for risk reduction strategies or for future updates of the building code hazard maps.     

Pro‐glacial lake sedimentation from jökulhlaups (GLOF), Blåmannsisen,northern Norway

Outburst floods from glacier‐dammed lakes are major events associated with glacier thinning and volume reduction. This paper investigates jökulhlaups emanating from the glacier‐dammed lake Øvre Messingmalmvatn at Rundvassbreen, an outlet glacier of the Blåmannsisen ice cap in northern Norway. Since 2001, the lake has several times been observed to drain suddenly, causing jökulhlaup outbursts into the pro‐glacial lake Rundvatnet. Varve analysis and lead‐210 (²¹⁰Pb) dating were used to date sediment cores taken from Rundvatnet. It was found that sedimentation from jökulhlaups is recognizable in the lake as distinct sand layers embedded in the varved silt‐clay sequence which represents the normal lake sedimentation. Sand fractions were carried in suspension because of the extreme hydraulic conditions of jökulhlaups. The thickest sand layer was deposited during the 2001 jökulhlaup which lasted three days and had a total volume of 40 ×10⁶ m³. Jökulhlaups were also recorded in 2005, 2007, 2009, and 2010; they each resulted in a sand layer. Annual sediment accumulation in Rundvatnet increased up to 10‐fold during the years with jökulhlaup outburst floods, from a normal value of 1–2 mm yr^?1 to 8–10 mm yr^?1. Five other jökulhlaups were identified from the 1910–1930 sedimentation interval, in addition to those observed in 2001–2010; there appear to have been none for 70 years during 1931–2000. Each jökulhlaup was preceded by a period when the glacier thinned to a critical volume and could no longer withstand the hydrostatic pressure of Øvre Messingmalmvatn; consequently a tunnel developed beneath the glacier, leading to a jökulhlaup. Statistical analyses of the correlations between the pro‐glacial sedimentation rate and temperature and precipitation suggested that although climate conditions are expected to influence sedimentation in the pro‐glacial catchment, a host of other interacting factors moderate the availability and delivery of sediment to the pro‐glacial system, making the processes responsible for changes in pro‐glacial sedimentation to remain uncertain. Copyright © 2014 John Wiley & Sons, Ltd.     

An Investigation of the Pressure Pulsing Reagent Delivery Approach

Pressure pulsing technology is an innovative method that has been developed with the aim of overcoming preferred flow paths associated with remediation techniques that rely on the injection of reagents. Numerical and field experiments were conducted to assess how pressure pulsing affects groundwater flow and solute transport during reagent injection. A series of field experiments were performed at two field sites where a monitoring network designed to capture the breakthrough of solutes delivered from an injection well was installed. Pressure pulsing and conventional injection methods were used at each site. One site was comprised of fine sand with low heterogeneity, while the other was moderately heterogeneous with discrete layers varying from fine sand to silt. The data suggest that breakthrough was more uniform for the pressure pulsing injections; however, this difference was minor and complicated by sorption of some of the tracers employed. The groundwater flow and solute transport modeling exercise simulated the rapid boundary pressure modulation that occurs in association with pressure pulsing. Two‐dimensional (2D) simulations revealed that repeated sudden onset of injection cessation produces brief periods of gradient reversal and the development of a mixing zone near the injection well. The spatial extents of this mixing zone were found to be highly dependent upon the hydraulic diffusivity of the medium, with medium heterogeneity and pulsing frequency playing secondary roles. Three‐dimensional (3D) numerical simulations were used to benchmark the observations from one of the field sites. The results from the modeling effort showed that solute breakthrough from a pressure pulsing injection is more dispersed relative to a conventional injection as a result of the mixing zone phenomenon; however, we were unable to directly observe this mixing zone using the instrumentation deployed at the two field sites.     

Camping impacts on vegetation and soil in a Hong Kong country park

The successful country parks programme in Hong Kong has attracted a heavy patronage and caused widespread degradation in recreational sites. Visitor impacts were studied in six camp sites representing three levels of use. Most changes in vegetation and soil, evaluated in absolute and relative terms, were statistically significant. Trampling resulted in loss of vegetation cover, and reduction in plant height and root biomass. Species composition shifted in response to increasing usage towards domination by a few trampling-resistant grasses (monocots) at the expense of sensitive woody dicots. The loss of vegetation and litter cover contributed to soil compaction, increases in bulk density, penetration resistance and bare soil cover, and decreases in void ratio and organic matter content. Structural damage led to reduction in water storage and infiltration rate. These effects have management implications with respect to the design and rehabilitation of sites to enhance durability and to relieve the excessive recreational burden.     

Geochronology of unconformity-related uranium deposits in the Athabasca Basin,Saskatchewan, Canada and their integration in the evolution of the basin

The importance of geochronology in the study of mineral deposits in general, and of unconformity-type uranium deposits in particular, resides in the possibility to situate the critical ore-related processes in the context of the evolution of the physical and chemical conditions in the studied area. The present paper gives the results of laser step heating ⁴⁰Ar/³⁹Ar dating of metamorphic host-rock minerals, pre-ore and syn-ore alteration clay minerals, and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) U/Pb dating of uraninite from a number of basement- and sediment-hosted unconformity-related deposits in the Athabasca Basin, Canada. Post-peak metamorphic cooling during the Trans-Hudson Orogen of rocks from the basement occurred at ca 1,750 Ma and gives a maximum age for the formation of the overlying Athabasca Basin. Pre-ore alteration occurred simultaneously in both basement- and sandstone-hosted mineralizations at ca 1,675 Ma, as indicated by the ⁴⁰Ar/³⁹Ar dating of pre-ore alteration illite and chlorite. The uranium mineralization age is ca 1,590 Ma, given by LA-ICP-MS U/Pb dating of uraninite and ⁴⁰Ar/³⁹Ar dating of syn-ore illite, and is the same throughout the basin and in both basement- and sandstone-hosted deposits. The mineralization event, older than previously proposed, as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far-field, continent-wide tectonic events such as the metamorphic events in Wyoming and the Mazatzal Orogeny (ca 1.6 to 1.5 Ga), the Berthoud Orogeny (ca 1.4 Ga), the emplacement of the McKenzie mafic dyke swarms (ca 1.27 Ga), the Grenville Orogeny (ca 1.15 to 1 Ga), and the assemblage and break-up of Rodinia (ca 1 to 0.85 Ga). The results of the present work underline the importance of basin evolution between ca 1.75 Ga (basin formation) and ca 1.59 Ga (ore deposition) for understanding the conditions necessary for the formation of unconformity-type uranium deposits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.