Numerical evaluation of pumping well transmissivity estimates in laterally heterogeneous formations

Transmissivity estimates derived from non-steady-state, single well, constant discharge, aquifer tests in laterally heterogeneous environments generally are questioned relative to their representativeness of aquifer conditions. Drawdown in pumping wells reflects the removal of water from storage in the aquifer and transient refraction of groundwater path-lines during the evolution of a non-symmetrical cone of depression. Simulations of single-well aquifer tests in aquifers with simple, arbitrary distributions of block heterogeneities suggest that transmissivity (T) values derived by the Cooper–Jacob (1946) method generally reflect volumetric, weighted mean T values of all of the heterogeneities contacted by the cone of depression at a particular time. This finding suggests that early-time drawdown data for single well aquifer tests reflect rapidly changing, volumetric, weighted mean T values proximal to the pumping well while late-time drawdown data reflect stabilized conditions and spatially averaged, volumetric weighted mean T out to a considerable distance from the pumping well.

---

Resume Los estimados de transmisividad derivados de estados no estables, pozos individuales, descarga constante, pruebas de acuíferos en ambientes heterogéneos laterales generalmente se cuestionan en cuanto a su representatividad de las conidiones de los acuíferos. La extracción de agua en pozos de bombeo refleja la extracción de agua del depósito en el acuífero y la refracción transitoria de líneas de trayectoria del agua subterránea durante la evolución de un cono no simétrico de depresión. Las simulaciones de pozos individuales, pruebas de acuíferos en acuíferos con distribuciones simples, arbitrarias de heterogeneidades de bloque sugieren que los valores de transmisividad (T) derivados por el método Cooper–Jacob (1946) generalmente reflejan valores medios volumétricos potenciales (weighted) de todas las heterogeneidades en contaco con el cono de la depresión en un momento particular. Este descubrimiento sugiere que los datos de extracción tempranos de pruebas de pozos individuales reflejan valores medios potenciales volumétricos que cambian rápidamente en la proximidad del pozo de bombeo mientras que los valores de extracción tardíos reflejan condiciones estabilizadas y medias potenciales volumétricas a una distancia considerable del pozo de bombeo.

---

Resumé Les estimés de transmissivité dérivés dessais de pompage en régime transitoire dans un seul puits contenu dans une formation latéralement hétérogène sont généralement questionable en ce qui concerne la représentativité des conditions de laquifère. Le rabattement dans les puits de pompage reflète lextraction deau provenant de lemmagasinement de laquifère et la réfraction en régime transitoire des lignes découlement durant lévolution dun cone de dépression non symétrique. Des simulations dessai de pompage dans un seul puits contenu dans un domaine avec des blocs hétérogènes distribués arbitrairement suggèrent que les valeurs de transmissivité obtenus avec la méthode dinterprétation de Cooper–Jacob (1946) sont généralement représentatifs du volume moyen pondéré de toutes les hétérogénéités en contact avec le cone de dépression à un temps particulier. Cette découverte suggère que les données de rabattement au début dun essai pour un seul puits reflètent un changement rapide des valeurs moyennes proximales pondérées tandis que le rabattement à un temps tardif reflète les conditions stabilisées et la moyenne spatiale jusquà une distance considérable du puits de pompage.

     

Chilean and Southeast Pacific paleoclimate variations during the last glacial cycle: directly correlated pollen and δO records from ODP Site 1234

Joint pollen and oxygen isotope data from Ocean Drilling Program Site 1234 in the southeast Pacific provide the first, continuous record of temperate South American vegetation and climate from the last 140 ka. Located at 36°S, 65 km offshore of Concepcion, Chile, Site 1234 monitors the climatic transition zone between northern semi-arid, summer dry-winter wet climate and southern year-round, rainy, cool temperate climate. Dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the Andean foothills. Down-hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest (characterized by grasses, herbs, ferns, and trees such as deciduous beech, Nothofagus obliqua), mesic Valdivian Evergreen Forest (including conifers such as the endangered Prumnopitys andina), and Subantarctic Evergreen Rainforest (comprised primarily of southern beech, N. dombeyi) reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds. During glacial intervals (MIS 2-4, and 6), rainforests and parkland dominated by Nothofagus moved northward into the region. At the MIS 6/5e transition, coeval with the rapid shift to lower isotopic values, rainforest vegetation was rapidly replaced by xeric plant communities associated with Mediterranean-type climate. An increased prominence of halophytic vegetation suggests that MIS 5e was more arid and possibly warmer than MIS 1. Although rainforest pollen rises again at the end of MIS 5e, lowland deciduous forest pollen persists through MIS 5d and 5c, into MIS 5b. Substantial millennial-scale variations occur in both interglacial and glacial regimes, attesting to the sensitivity of the southern westerly belt to climate change. Comparison of the cool, mesic N. dombeyi rainforest assemblage from Site 1234 with δ¹⁸O in the Byrd Ice core shows that on time scales longer than 10 ka, cool-moist conditions in central Chile were coherent with and occurred in phase with Antarctic cooling. This is also likely at millennial scales, although rainforest pollen lags Antarctic cooling with exponential response times of about 1000 years, which plausibly reflects the ecological response time to regional climate change.     

Linearly Organized Turbulence Structures Observed Over a Suburban Area by Dual-Doppler Lidar

Dual-Doppler lidar observations are used to investigate the structure and evolution of surface-layer flow over a suburban area. The observations were made during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City, U.S.A. in the summer of 2003. This study focuses specifically on a 10-h sequence of scan data beginning shortly after noon local time on 7 July 2003. During this period two coherent Doppler lidars performed overlapping low elevation angle sector scans upwind and south of Oklahoma City’s central business district. Radial velocity data from the two lidars are processed to reveal the structure and evolution of the horizontal velocity field in the surface layer throughout the afternoon and during the evening transition period. The retrieved velocity fields clearly show a tendency for turbulence structures to be elongated in the direction of the mean flow throughout the entire 10-h study period. In order to quantify the observed anisotropy and its dependence on stability, integral length scales are estimated directly from the spatially resolved velocity retrievals. As the flow became more stably stratified the characteristic cross-stream dimension of the linear structures decreased. The streamwise component was consistently more anisotropic than the cross-stream component, and both velocity components exhibited maximum anisotropy under neutral conditions. The ratio of the streamwise to cross-stream length scale was estimated to be about eight for the streamwise component, and four for the cross-stream component under neutral conditions.     

Hurricane Katrina storm surge delineation: implications for future storm surge forecasts and warnings

The storm surge in coastal Mississippi caused by Hurricane Katrina was unprecedented in the region. The height and geographic extent of the storm surge came as a surprise to many and exceeded pre-impact surge scenarios based on SLOSH models that were the basis for emergency preparedness and local land use decision-making. This paper explores the spatial accuracy of three interpolated storm surge surfaces derived from post-event reconnaissance data by comparing the interpolation results to a specific SLOSH run. The findings are used to suggest improvements in the calibration of existing pre-event storm surge models such as SLOSH. Finally, the paper provides some suggestions on an optimal surge forecast map that could enhance the communication of storm surge risks to the public.     

The impact of Greenland melt on local sea levels: a partially coupled analysis of dynamic and static equilibrium effects in idealized water-hosing experiments

Local sea level can deviate from mean global sea level because of both dynamic sea level (DSL) effects, resulting from oceanic and atmospheric circulation and temperature and salinity distributions, and changes in the static equilibrium (SE) sea level configuration, produced by the gravitational, elastic, and rotational effects of mass redistribution. Both effects will contribute to future sea level change. To compare their magnitude, we simulated the effects of Greenland Ice Sheet (GIS) melt by conducting idealized North Atlantic “water-hosing” experiments in a climate model unidirectionally coupled to a SE sea level model. At current rates of GIS melt, we find that geographic SE patterns should be challenging but possible to detect above dynamic variability. At higher melt rates, we find that DSL trends are strongest in the western North Atlantic, while SE effects will dominate in most of the ocean when melt exceeds ~20 cm equivalent sea level.     

Seismic stratigraphy records the deglacial history of Jakobshavn Isbræ, West Greenland

Jakobshavn Isbræ is one of the largest ice streams in the Greenland Ice Sheet, presently draining c. 6.5% of the Inland Ice. Here we present high‐resolution Chirp and Sparker sub‐bottom profiles from a seismic survey conducted just outside of the Jakobshavn Isfjord, which provides detailed insight into the glacimarine sedimentary history of the Jakobshavn ice stream during the Holocene. We observe acoustically stratified and homogeneous sediments that drape an irregular substratum and were deposited between ～10 and c. 7.6k cal a BP. The stratified lower units are interpreted as the product of ice‐proximal glacimarine sedimentation deposited rapidly when the grounded ice margin was located close to depositional basins on topographic highs. The upper acoustically homogenous units reflect suspension settling of fine‐grained material and gravitational flows that were extruded from an increasingly unstable ice margin as the ice retreated into the fjord. Proximity to the ice margin and bedrock topography were the dominant controls on sediment accumulation during deglaciation although the 8.2‐ka cooling event probably influenced the position of the ice margin at the fjord mouth. The post‐glacial sedimentary record is characterized by glacimarine and hemipelagic rainout with an increased ice‐rafted detritus fraction that records sedimentation following ice stream retreat into Jakobshavn Isfjord sometime after c. 7.8k cal a BP. Copyright © 2011 John Wiley & Sons, Ltd.     

Managing organizational change in an international scientific network: A study of ICES reform processes

Organizations involved in the governance of natural resources are challenged to adjust to the call for more holistic management approaches. This often necessitates organizational change. Here change processes in the International Council for the Exploration of the Sea (ICES) during the years 1998–2009 are investigated using semi-structured interviews combined with observations and review of documents. Several organizational reforms were implemented during the time period studied. The major drivers were the need to improve efficiency and a striving for better integration between different components within the organization. The reform processes were driven forward by individuals who navigated between opportunities and constrains embedded in the network structure of ICES. This required good leadership and communication skills. Broad consultations were important to ensure support within the ICES community. By increasing the understanding of the dynamics of change in organizations, which operate at the science–policy interface developments in desired directions can be facilitated.     

Influence of late Holocene hillslope processes and landforms on modern channel dynamics in upland watersheds of central Nevada

Stratigraphic, geomorphic, and paleoecological data were collected from upland watersheds in the Great Basin of central Nevada to assess the relationships between late Holocene climate change, hillslope processes and landforms, and modern channel dynamics. These data indicate that a shift to drier, warmer climatic conditions from approximately 2500 to 1300 YPB led to a complex set of geomorphic responses. The initial response was massive hillslope erosion and the simultaneous aggradation of both side-valley alluvial fans and the axial valley system. The final response was fan stabilization and axial channel incision as fine-grained sediments were winnowed from the hillslope sediment reservoirs, and sediment yield and runoff processes were altered. The primary geomorphic response to disturbance for approximately the past 1900 years has been channel entrenchment, suggesting that the evolutionary history of hillslopes has produced watersheds that are prone to incision. The magnitude of the most recent phase of channel entrenchment varies along the valley floor as a function of geomorphic position relative to side-valley alluvial fans. Radial fan profiles suggest that during fan building, fan deposits temporarily blocked the flow of sediment down the main stem of the valley, commonly creating a stepped longitudinal valley profile. Stream reaches located immediately upvalley of these fans are characterized by low gradients and alternating episodes of erosion and deposition. In contrast, reaches coincident with or immediately downstream of the fans exhibit higher gradients and limited valley floor deposition. Thus, modern channel dynamics and associated riparian ecosystems are strongly influenced by landforms created by depositional events that occurred approximately 2000 years ago.     

KRb ratios in Precambrian granulite terranes

Concentrations of potassium and rubidium are reported for 62 Precambrian shield whole-rock samples belonging to the pyroxene granulite facies of world-wide distribution. Compared with the Main Trend established by Shaw (1968) for igneous and quasi-igneous rocks of the upper crust, the high-grade metamorphic granulites exhibit a similar correlation but with a measurable depletion in Rb for a given K content. The Metamorphic Trend may be described by the equations: log₁₀ (ppm Rb) = 1.136 log₁₀ (per cent K) + 1.495 or ppm Rb = 31.28 (per cent K)^1.136. The square of the product moment correlation coefficient shows that 80 per cent of the variation in Rb is associated with variation in K.All suites studied have initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios less than 0.707. This low value argues against repeated extraction of Rb and K through time on a regional scale. Rather, the major depletion in these lithophile elements occurred in the early stages of crustal evolution.