Quantifying the effects of three-dimensional subsurface heterogeneity on Hortonian runoff processes using a coupled numerical,stochastic approach     

Reed M. Maxwell  Stefan J. Kollet 《Advances in water resources》2008

The impact of three-dimensional subsurface heterogeneity in the saturated hydraulic conductivity on hillslope runoff generated by excess infiltration (so-called Hortonian runoff) is examined. A fully coupled, parallel subsurface–overland flow model is used to simulate runoff from an idealized hillslope. Ensembles of correlated, Gaussian random fields of saturated hydraulic conductivity are used to create uncertainty in spatial structure. A large number of cases are simulated in a parametric manner with the variance of the hydraulic conductivity varied over orders of magnitude. These cases include rainfall rates above, equal and below the geometric mean of the hydraulic conductivity distribution. These cases are also compared to theoretical representations of runoff production based on simple assumptions regarding (1) the rainfall rate and the value of hydraulic conductivity in the surface cell using a spatially-indiscriminant approach; and (2) a percolation-theory type approach to incorporate so-called runon. Simulations to test the ergodicity of hydraulic conductivity on hillslope runoff are also performed. Results show that three-dimensional stochastic representations of the subsurface hydraulic conductivity can create shallow perching, which has an important effect on runoff behavior that is different than previous two-dimensional analyses. The simple theories are shown to be very poor predictors of the fraction of saturated area that might runoff due to excess infiltration. It is also shown that ergodicity is reached only for a large number of integral scales (∼30) and not achieved for cases where the rainfall rate is less than the geometric mean of the saturated hydraulic conductivity.  相似文献   

An assessment of ancient DNA preservation in Holocene–Pleistocene fossil bone excavated from the world heritage Naracoorte Caves,South Australia          下载免费PDF全文

Alicia Grealy  Amy Macken  Morten E. Allentoft  Nicolas J. Rawlence  Elizabeth Reed  Michael Bunce 《第四纪科学杂志》2016,31(1):33-45

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THE YIELD STRENGTH OF METEORITIC IRON     

Reed Knox 《Meteoritics & planetary science》1970,5(2):63-74

The compressive yield strength was determined on three meteorites using specimens 4 mm and 8 mm in length and strain magnifications of 10,000 and 2000 respectively, with an apparatus developed for testing small specimens of biological hard tissue. The flow stresses required to produce 0.2% plastic strain in a recrystallized Cañon Diablo specimen, in the Odessa octahedrite, and in the metal phase of a Brenham were 62.9 K psi, 46.6 K psi, and 62.7 K psi respectively. The flow stress of Cañon Diablo after heating in a vacuum for one hour at 871 °C and furnace cooling was 60.0 K psi. The microstructure and grain size of the heat treated specimen was virtually that of the untreated meteorite. Plastic deformation of the Odessa specimen produced wavy slip lines in kamacite on a previously polished and etched surface. Slip lines also developed in taenite and cracks occurred in the phosphide phase.  相似文献   

Age and progression of volcanism, Wrangell volcanic field, Alaska     

D H Richter  J G Smith  M A Lanphere  G B Dalrymple  B L Reed  Nora Shew 《Bulletin of Volcanology》1991,53(1):29-44

The Wrangell volcanic field covers more than 10 000 km² in southern Alaska and extends uninterrupted into northwest. Yukon Territory. Lavas in the field exhibit medium-K, calc-alkaline affinities, typical of continental volcanic arcs along convergent plate margins. Eleven major eruptive centers are recognized in the Alaskan part of the field. More than 90 K-Ar age determinations in the field show a northwesterly progression of eruptive activity from 26 Ma, near the Alaska-Yukon border, to about 0.2 Ma at the northwest end of the field. A few age determinations in the southeast extension of the field in Yukon Territory, Canada, range from 11 to 25 Ma. The ages indicate that the progression of volcanism in the Alaska part of the field increased from about 0.8 km/Ma, at 25 Ma, to more than 20 km/MA during the past 2 Ma. The progression of volcanic activity and its increased rate of migration with time is attributed to changes in the rate and angle of Pacific plate convergence and the progressive decoupling of the Yakutat terrane from North America. Subduction of Yakutat terrane-Pacific plate and Wrangell volcanic activity ceased about 200 000 years age when Pacific plate motion was taken up by strike-slip faulting and thrusting.  相似文献   

Oil spill fishery impact assessment model: Sensitivity to spill location and timing     

Malcolm L. Spaulding  Mark Reed  Eric Anderson  Tatsusaburo Isaji  J.Craig Swanson  Saul B. Saila  Ernesto Lorda  Henry Walker 《Estuarine, Coastal and Shelf Science》1985,20(1):41-53

An oil spill fishery impact assessment model system has been applied to the Georges Bank-Gulf of Maine region to assess the sensitivity of probable impact on several key fisheries to spill location and timing. Simulations of the impact on the fishery of tanker spills (20 million gallons released over 5 days), at two separate locations for each season of the year, and blowout spills (68 million gallons released over 30 days) at one location, with monthly releases and at six other locations with seasonal spills have been studied. Atlantic cod has been employed as the principal fish species throughout the simulations. Impacts on Atlantic herring and haddock have also been investigated for selected cases. All spill sites are located on Georges Bank with the majority in the general region of OCS leasing activity.The results of these simulations suggest a complex interaction among spill location and timing, the spatial and temporal distribution of spawning, the population dynamics of the species under study, and the hydrodynamics of the area. For the species studied, spills occurring during the winter and spring have the largest impact with cod being the most heavily impacted followed by haddock and herring. In all cases, the maximum cumulative loss to the fishery of a one time spill event never exceeded 25% of the annual catch with the exact value depending on the number of ichthyoplankton impacted by the spill and the compensatory dynamics of the population.  相似文献   

The Bawku LL5 Chondrite     

S. J. B. Reed  G. A. Chinner 《Meteoritics & planetary science》1995,30(4):468-469

Abstract— A meteorite fall was observed on 1989 December 29 in the vicinity of Bawku, North Ghana (11°05′N, 0°11′W). Two fragments (59 and 1498 g) of a stony meteorite were subsequently recovered. This is classified as an LL5 monomict breccia of shock category S2. The olivine and pyroxene compositions are Fa_26.8 and Fs_22.6 respectively.  相似文献   

Development and testing of a contamination potential mapping system for a portion of the General Separations Area, Savannah River Site, South Carolina     

J. M. Rine  R. C. Berg  J. M. Shafer  E. R. Covington  J. K. Reed  C. B. Bennett  J. E. Trudnak 《Environmental Geology》1998,35(4):263-277

 A methodology was developed to evaluate and map the contamination potential or aquifer sensitivity of the upper groundwater flow system of a portion of the General Separations Area (GSA) at the Department of Energy's Savannah River Site (SRS) in South Carolina. A Geographic Information System (GIS) was used to integrate diverse subsurface geologic data, soils data, and hydrology utilizing a stack-unit mapping approach to construct mapping layers. This is the first time that such an approach has been used to delineate the hydrogeology of a coastal plain environment. Unit surface elevation maps were constructed for the tops of six Tertiary units derived from over 200 boring logs. Thickness or isopach maps were created for five hydrogeologic units by differencing top and basal surface elevations. The geologic stack-unit map was created by stacking the five isopach maps and adding codes for each stack-unit polygon. Stacked-units were rated according to their hydrogeologic properties and ranked using a logarithmic approach (utility theory) to establish a contamination potential index. Colors were assigned to help display relative importance of stacked-units in preventing or promoting transport of contaminants. The sensitivity assessment included the effects of surface soils on contaminants which are particularly important for evaluating potential effects from surface spills. Hydrogeologic/hydrologic factors did not exhibit sufficient spatial variation to warrant incorporation into contamination potential assessment. Development of this contamination potential mapping system provides a useful tool for site planners, environmental scientists, and regulatory agencies. Received: 1 April 1997 · Accepted: 4 November 1997  相似文献   

The magnetic effects of brecciation and shock in meteorites: III. The achondrites     

Aviva Brecher  Miriam Fuhrman  Judy Stein 《Earth, Moon, and Planets》1979,20(3):265-279

We present results of a magnetic survey of achondritic meteorites, representing the aubrites (A), diogenites (D), Irowardites (H), and eucrites (E) groups and relate their magnetic behavior to respective class characteristics and models of origin.Magnetic susceptibility (x) values cluster well within each group and decrease systematically between groups (from 2 to 0.1×10^–3GOe^–1 cm^–3), with the average metal contents, (from 1 to <0.1 wt%) in the above order. The natural remanent magnetization (NRM) values range broadly within each group, but group averages decrease roughly as above. However, the considerable within-sample and intra-group variability in NRM level and its demagnetization characteristics attest to inhomogeneous and localized brecciation effects. Although petrological-chemical studies resolve a primary component of magmatic differentiation on the planetoid of origin, no clear magnetic record of such event has been preserved. The magnetization of achondrites is mainly the product of their complex, multi-stage impact brecciation and metamorphism history, in accord with other lines of evidence.The magnetic behavior of achondrites is remarkably similar to that characteristic of lunar breccias and impact-melt rocks and reinforces their analogous mode of genesis, as brought out by chemical and petrographic analyses.  相似文献   

History of Boulder 1 at Station 2, Apollo 17 based on trace element interrelationships     

Stanka Jovanovic  George W. Reed Jr. 《Earth, Moon, and Planets》1975,14(3-4):385-393

Correlations among the trace and minor element pairs Cl and Br, Cl and P₂O₅, and Ru and Os, present in parent igneous rocks, generally survived the processes of boulder breccia formation. Fractions of the Cl, Br, and Hg that are mobilized by water leaching and/or volatilization at moderate temperatures (?450°C) place constraints on the thermal history of Boulder 1 and its component breccias. Since, and possibly during, consolidation, the boulder has probably not been subjected to temperatures of ?450°C. The parent rocks of the Apollo 17 boulder and breccia samples studied could have been derived from two initial magmas. Boulder 1, Station 2 gray competent breccias 72255 and 72275 Clast #2 appear to be genetically unrelated to gray competent breccia and anorthositic material 72215, or to light friable breccia 72275; they do appear to be related to samples 72395 (Boulder 2) and 76315 (Station 6 boulder). Vapor clouds from apparently external sources permeated the source regions of the boulders.  相似文献   

Facilitating Co-Production of Transdisciplinary Knowledge for Sustainability: Working with Canadian Biosphere Reserve Practitioners     

Maureen G. Reed  Paivi Abernethy 《社会与自然资源》2018,31(1):39-56

Sustainability scientists argue that diverse knowledge holders should work together in social learning processes to co-produce knowledge in support of sustainability. Yet, how to co-produce such knowledge remains unexplored. A multi-year, national knowledge sharing partnership among Canadian biosphere reserve practitioners, academic researchers and policy advisors revealed that a skilled facilitator was necessary for successful knowledge co-production. We draw attention to the multiple barriers to learning and knowledge co-production, and to the skills required of the facilitator to address them. The facilitator helped draw together local and formalized western knowledge systems (weaving) and diffuse innovations across local sites (out-scaling) and between local sites and the broader program network (up-scaling). Our experience reveals that simply bringing parties together will not generate transformative change for sustainability. Rather, multi-lateral facilitators are needed to ensure deliberate and managed interventions and to institutionalize learning across a diverse collective.  相似文献