Two-dimensional,high-resolution modeling of urban dam-break flooding: A case study of Baldwin Hills,California

Modeling of dam-break flooding in an urban residential area in southern California is presented. Modeling is performed using BreZo, an unstructured grid, Godunov-type, finite volume model that solves the shallow-water equations. The model uses terrain data from a 1.5 m Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) and contour data depicting the reservoir and breach geometry. A spatially distributed Manning coefficient based on a landcover classification derived from digital orthophotos and vector data (e.g., parcel outlines) is also used, and the interception of flow by storm drains is modeled with sink terms in the 2D continuity equation. The model is validated with flood extent and stream flow measurements, and a sensitivity analysis is completed to identify the necessary level of data and model complexity for accuracy purposes. Results show street depressions in the land surface should be resolved by the computational mesh for flood extent and stream flow accuracy. A ca. 5 m resolution mesh that spans streets by approximately 3 cells achieves a good balance between accuracy and computational effort. Results also show that heterogeneous resistance is important for stream flow accuracy, and the interception of overland flow by storm sewers is important for flood extent accuracy. The sensitivity of predictions to several additional factors such as the reservoir level, breach geometry and DTM source (LiDAR, National Elevation Data, Shuttle Radar Topography Mission Data) is also reported.     

Mercury flux to estuarine sediments, derived from Pb-210 and Cs-137 geochronologies (Guaratuba Bay, Brazil)

A sediment core from Guaratuba Bay was used to indicate possible Hg modifications to this coastal environment brought about by growing agricultural activity. Sedimentation rates were estimated to be 6.1 mm/year and 5.2 mm/year through 210Pb and 137Cs geochronologies, respectively. Mercury concentrations and organic matter ratios in the surface layers are greater than in the older sediments, supporting the hypothesis of anthropogenic enrichment. Results show that the Hg flux has raised more than twofold during the second half of the 20th century. These results point to the need for further studies to substantiate the hypothesis of anthropogenic enrichment and to quantify point sources of Hg to this estuary.     

The role of suspended sediments and phytoplankton in the partitioning and transport of silver in estuaries

Silver sorbs readily at low salinities to both phytoplankton and suspended sediments. As salinity increases, the degree of sorption decreases. Nearly 80% of silver sorbed to suspended sediments at low salinities will desorb at higher salinities, but desorption does not occur when silver is associated with phytoplankton. Thus, silver incorporation onto/into cellular material will increase the retention of silver within the estuary, reducing its rate of transport.     

Emplacement of massive deposits by sheet flow

Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross-laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning-energy flows, and that the parallel-laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open-channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non-dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel-laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes.     

Temporal and spatial patterns of trace elements in the Patuxent River: A whole watershed approach

Trace element distributions, partitioning, and speciation were examined at 15 sites in the Patuxent River watershed from May 1995 through October 1997 to determine possible sources of trace elements to the river and estuary, to examine the relationship of the trace element discharges to freshwater discharges as well as to land use and geographic region, to validate previous estimates of loadings to the river, and to provide baseline data for trace elements in the Patuxent River watershed and estuary. Six freshwater sites were examined, representing different basins and geographic provinces, and nine sites along the estuarine salinity gradient. Subregions within the watershed varied considerably in concentrations and areal yields for some elements. Concentrations of As, Cd, Ni, Pb, and Zn were elevated in the Coastal Plain sites compared to the Piedmont sites, while Cu and Hg were more evenly distributed. Cadmium, Cu, Hg, Ni, Pb, and Zn showed overall positive correlations with river flow while As and methylHg (meHg) showed negative correlations with river flow. Concentrations of trace elements in the estuarine portion of the river were generally low, and consistent with mixing between Patuxent River water with elevated concentrations and the lower concentrations of the Chesapeake Bay. Interesting features included a local Cd maximum in the low salinity region of the estuary, probably caused by desorption from suspended sediments, and a significant input of water containing high As concentrations from the Chesapeake Bay and from As being released from bottom sediments in summer. Comparisons between the estimated annual flux of trace elements and the estimates of suspected source terms (atmospheric deposition, urban runoff, and known point sources) suggest that, except for Hg, direct atmospheric deposition is small compared to fluvial loads. Current estimates of trace element inputs from point sources or from urban runoff are inadequate for comparison with other sources, because of inappropriate techniques and/or unacceptably high detection limits. A complete examination of trace element dynamics in the Patuxent River (and in other coastal systems) will require better data for these potential sources.     

Plane strain shear strength of unsaturated fiber-reinforced fine-grained soils

Acta Geotechnica - Discrete randomly distributed fibers are commonly used to improve the engineering characteristics of the soil and thus soil properties such as shear strength, compressibility,...     

Plagioclase breakdown and regeneration reactions in Grenville kyanite eclogite at Glenelg,NW Scotland

A rare type of eclogite at Glenelg contains finegrained, white streaks about 1 mm across consisting of kyanite-oligoclase ±quartz ±Kfeldspar. Garnet and omphacite bordering the streaks are relatively enriched in grossular and jadeite components respectively. The streaks are interpreted as former plagioclase which reacted with neighbouring garnet and omphacite during a period of shearing and compression. P-T conditions during the reaction are estimated as 740° C and 17 kbar. Subsequent reaction, manifest by narrow rims of oligoclase on kyanite, new growth of garnet and resorption of omphacite, is interpreted as an effect of near-isothermal decompression by about 2 kbar. The compressive phase is attributed to dextral transpression (oblique convergence) along the Grenville Front in Scotland.     

Meteoric lithification of catastrophic rockslide deposits: Diagenesis and significance

Deposits of catastrophic rockslides composed of lithologies rich in carbonate minerals may undergo precipitation of cements that can be used to proxy-date the rockslide event and/or subsequent geomorphic changes of the rockslide mass.In the Alps, localized to widespread lithification of post-Glacial rockslide deposits is observed in lithologies ranging from limestones and dolostones to metacarbonates to calcphyllites. Lithification of rockslide deposits to breccias may be localized to meteoric ‘runoff-shadows’ below larger boulders, or may comprise a layer of breccia or may affect a rockslide mass down its base. In addition, precipitation of cements and small stalactites may take place in megapores on boulder undersides. Cements found in rockslide deposits comprise skalenohedral calcite, prismatic calcite, blocky calcite, calcitic micrite and micropeloidal calcitic cement and, rarely, botryoidal aragonite. Initial cement formation probably is driven by meteoric dissolution–re-precipitation of (mini-) micritic abrasive rock powder generated by dynamic disintegration during the rockslide event. Preliminary ²³⁴U/²³⁰Th ages of rockslide cements support a concept that cementation starts immediately or early after a rockslide event. In rockslide deposits of calcphyllite with accessory pyrite, oxidation of pyrite probably also propels the process of carbonate dissolution–re-precipitation. Limestone-precipitating springs emerging from rockslide masses, and well-cemented talus slopes and fluvial conglomerates percolated by rockslide-derived groundwaters, indicate that rockslide deposits remain diagenetically active long after emplacement.     

Seeing the Forest for the Trees: A Bibliometric Analysis of Environmental and Resource Sociology

Abstract

Environmental sociology and the sociology of natural resources have become two established research areas in the United States with distinct institutional origins, research themes, and theoretical roots, as well as associated professional networks, journals, and conferences. Existing discussions of the relationships between the two subdisciplines are largely based on personal reflections and exploratory analyses. However, there is still not a clear understanding of the overall picture of interdisciplinary sociological research on human–nature interactions. In this study we conduct a comprehensive bibliometric analysis of 8027 articles published in 30 selected academic journals during 1985–2017. Findings of this research provide a more complete view of the intellectual landscape of environmental and resource sociology. Overall, the study produces an empirically-based characterization of environmental sociology and the sociology of natural resources in terms of coauthorship and citation networks, and highlights the need for more sustained synthesis across different knowledge domains.