Application of kinematic wave theory for predicting flash flood hazards on coupled alluvial fan–piedmont plain landforms

A rainstorm that caused a severe flash flood on the piedmont plain at the toe positions of two alluvial fans located to the west of the Organ Mountains in Dona Ana County, New Mexico, USA, is analysed. The space–time distributions of rainfall are evaluated from the Next Generation Weather Radar (NEXRAD) and overland flow is modelled as kinematic wave. The spatial distribution of rainfall shows a topographic control. The greatest rainfall depth, duration, and intensity occurred at the higher elevation mountain slopes and decreased with decreasing elevation from the alluvial fans to the piedmont plain. The alluvial fan–piedmont plain system is modelled by coupling divergent and rectangular overland flow planes. Explicit finite difference approximations, hybridized with the analytical method of characteristics, are made to the kinematic wave equations to account for the spatial and temporal distribution of the rainfall and variable boundary conditions. Simulation results indicate that sheet‐flow floodwater elevations rise (1) in a nonlinear fashion from the apex to toe positions of the alluvial fans, and (2) near linearly from the toe positions of the alluvial fans onto the piedmont plains with the formation of kinematic shocks near the middle to the upstream end of the plane at times between the initiation of the rainstorm and the time of concentration of the plane. Thus, the maximum flooding occurs at the middle or upstream sections of the piedmont plains regardless of the pattern of space–time variability of rainfall. These results are in agreement with observed geomorphologic features suggesting that piedmont plains are naturally flood‐prone areas. This case study demonstrates that flood hazards on piedmont plains can exceed those on alluvial fans. The models presented in this study suggest that the flood hazard zones on coupled alluvial fan–piedmont plain landforms should be delineated transverse to the flow directions, as opposed to the flood hazard zones with boundaries in the longitudinal direction of the axis of an alluvial fan. Copyright © 2003 John Wiley & Sons, Ltd.     

CMBEAR: Python-Based Recharge Estimator Using the Chloride Mass Balance Method in Australia

The chloride mass balance (CMB) method is widely used to estimate long-term rates of groundwater recharge. In regions where surface water runoff is negligible, recharge can be estimated using measurements of chloride concentrations of groundwater and precipitation, and an estimate of long-term average rainfall. This paper presents the Chloride Mass Balance Estimator of Australian Recharge (CMBEAR), a Jupyter (Python) Notebook that is set up to rapidly apply the CMB method using gridded maps of chloride deposition rates across the Australian continent. For an Australian context, the chloride deposition rate and rainfall maps have been provided. Thus, CMBEAR requires only a spreadsheet with the groundwater chloride concentration, the latitude and longitude of the sample location, and some simple user inputs. CMBEAR may be easily applied in other regions, providing that a gridded chloride deposition map is available. Recharge estimates from CMBEAR are compared against published applications of the CMB method. CMBEAR is also applied to a large dataset from the Northern Territory and is used to produce a gridded map of recharge for western Victoria. CMBEAR provides a reproducible and straightforward approach to apply the CMB method to estimate groundwater recharge.     

3D seismic technology: the geological 'Hubble'

The proliferation of three‐dimensional (3D) seismic technology is one of the most exciting developments in the Earth Sciences over the past century. 3D reflection seismic data provide interpreters with the ability to map structures and stratigraphic features in 3D detail to a resolution of a few tens of metres over thousands of square kilometres. It is a geological ‘Hubble’, whose resolving power has already yielded some fascinating (and surprising) insights and will continue to provide a major stimulus for research into geological processes and products for many decades to come. Academic and other research institutions have a major role to play in the use of this data by exploiting the enormous volume of geological information contained in 3D seismic surveys. This paper reviews some of the recent advances in basin analysis made using the medium of 3D seismic data, focusing on the fields of structural and sedimentary geology, fluid–rock interactions and igneous geology. It is noted that the increased resolution of the 3D seismic method provided the essential catalyst necessary to stimulate novel observations and discover new geological structures such as mud diapir feeders, km‐long gas blow‐out pipes, giant pockmarks and sandstone intrusions, and to capture the spatial variability of diagenetic fronts. The UKs first impact crater was also discovered using 3D seismic data. The potential for future developments in this field of geophysical interpretation is considerable, and we anticipate that new discoveries will be made in many years to come.     

Evaluation of Vapor Intrusion Risk from Ethylene Dibromide Using the Vertical Screening Distance Approach

Vapor intrusion (VI) occurs when volatile contaminants in the subsurface migrate through the vadose zone into overlying buildings. The 2015 U.S. EPA petroleum VI guidance recommends that additional investigation of the VI risk from gasoline hydrocarbons at the underground storage tank (UST) sites is not necessary where the vertical distance between a building and a vapor source exceeds a recommended vertical screening distance. However, due to the lack of soil-gas data on the attenuation of ethylene dibromide (EDB), additional VI investigations to evaluate VI risk from EDB are recommended at UST sites with leaded gasoline releases containing EDB. We analyzed soil-gas and groundwater concentrations of EDB from eight petroleum UST sites using a new analytical method with soil-gas detection limit <0.16 μg/m³ EDB (VI screening level at the 10⁻⁶ risk level). The analysis included (1) assessing the frequency of EDB detections ≤0.16 μg/m³ at various vertical separation distances and (2) predicting vertical screening distances for EDB using the U.S. EPA PVIScreen model for different soil types in the vadose zone above dissolved-phase and LNAPL sources. Ranges of estimated aerobic biodegradation rate constants for EDB, air exchange rates for residential buildings, and source vapor concentrations for other constituents were combined with conservative estimates of EDB source concentrations as model inputs. Concentrations of EDB in soil-gas indicated that the U.S. EPA recommended vertical screening distances are protective of VI risk from EDB. Conversely, vertical screening distances predicted by modeling were >6 ft (1.8 m) for sites with sand and loam soil above dissolved phase sources and >15 ft (4.6 m) for sites with sand soil above LNAPL sources. This predicted dependence on the vapor source type and soil type in the vadose zone highlights the importance of soil characterization for VI screening at sites with EDB sources.     

Neil Smith, 1954–2012: “The Future is Indeed Radically Open”

Investors in single-family residential properties have played a crucial role in the United States foreclosure crisis. In this paper, we analyze investor behavior in the diverse urban housing market of Fulton County, Georgia. We examine the composition of buyers of lender-owned properties at two different stages of the foreclosure crisis, and analyze the intrametropolitan geography of investment. Results indicate that large-scale investors are most active in low-value housing submarkets with high poverty and vacancy rates.     

Probabilistic assessment of wildfire hazard and municipal watershed exposure

The occurrence of wildfires within municipal watersheds can result in significant impacts to water quality and ultimately human health and safety. In this paper, we illustrate the application of geospatial analysis and burn probability modeling to assess the exposure of municipal watersheds to wildfire. Our assessment of wildfire exposure consists of two primary components: (1) wildfire hazard, which we characterize with burn probability, fireline intensity, and a composite index, and (2) geospatial intersection of watershed polygons with spatially resolved wildfire hazard metrics. This effort enhances investigation into spatial patterns of fire occurrence and behavior and enables quantitative comparisons of exposure across watersheds on the basis of a novel, integrated measure of wildfire hazard. As a case study, we consider the municipal watersheds located on the Beaverhead-Deerlodge National Forest (BDNF) in Montana, United States. We present simulation results to highlight exposure across watersheds and generally demonstrate vast differences in fire likelihood, fire behavior, and expected area burned among the analyzed municipal watersheds. We describe how this information can be incorporated into risk-based strategic fuels management planning and across the broader wildfire management spectrum. To conclude, we discuss strengths and limitations of our approach and offer potential future expansions.     

Alice Springs age shear zones from the southeastern Reynolds Range,central Australia

The southeast Reynolds Range, central Australia, is cut by steep northwest‐trending shear zones that are up to hundreds of metres wide and several kilometres long. Amphibolite‐facies shear zones cut metapelites, while greenschist‐facies shear zones cut metagranites. Rb–Sr and ⁴⁰Ar–³⁹Ar data suggest that both sets of shear zones formed in the 400–300 Ma Alice Springs Orogeny, with the sheared granites yielding well‐constrained ⁴⁰Ar–³⁹Ar ages of ca 334 Ma. These data imply that the shear zones represent a distinct tectonic episode in this terrain, and were not formed during cooling from the ca 1.6 Ga regional metamorphism. A general correlation between regional metamorphic grade and the grade of Alice Springs structures implies a similar distribution of heat sources for the two events. This may be most consistent with both phases of metamorphism being caused by the burial of anomalously radiogenic heat‐producing granites. The sheared rocks commonly have undergone metasomatism implying that the shear zones were conduits of fluid flow during Alice Springs times.     

A subsurface evacuation model for submarine slope failure

Analysis of three-dimensional (3D) seismic reflection data from the Norwegian continental margin provides an insight into an unusual, buried submarine slope failure, which occurred adjacent to the later Holocene-age Storegga Slide. The identified failure, informally named the 'South Vøring Slide' (SVS), occurs in fine-grained hemipelagic and contourite sediments on a slope of 0.5°, and is characterised by a deformed seismic facies unit consisting of closely spaced pyramidal blocks and ridges bound by small normal faults striking perpendicular to the slope. The SVS contrasts with other previously described submarine slope failures in that it cannot be explained by a retrogressive model. The defining characteristic is the high relative volume loss. The area affected by sliding has thinned by some 40%, seen in combination with very modest extension in the translation direction, with line length balancing yielding an extension value of only 4.5%. The volume loss is explained by the mobilisation of an approximately 40 m thick interval at the lower part of the unit and its removal from beneath a thin overburden, which subsequently underwent extensional fragmentation. Evidence for the mobilisation of a thick fine-grained interval in the development of a submarine slope failure from a continental margin setting may have implications for the origins of other large-scale slope failures on the Norwegian margin and other glacially influenced margins worldwide.