Predicting evaporation from mountain streams     

Andras Janos Szeitz  Robert Daniel Moore 《水文研究》2020,34(22):4262-4279

Evaporation can be an important control on stream temperature, particularly in summer when it acts to limit daily maximum stream temperature. Evaporation from streams is usually modelled with the use of a wind function that includes empirically derived coefficients. A small number of studies derived wind functions for individual streams; the fitted parameters varied substantially among sites. In this study, stream evaporation and above-stream meteorological conditions (at 0.5 and 1.5 m above the water surface) were measured at nine mountain streams in southwestern British Columbia, Canada, covering a range of stream widths, temperatures, and riparian vegetation. Evaporation was measured on 20 site-days in total, at approximately hourly intervals, using nine floating evaporation pans distributed across the channels. The wind function was fit using mixed-effects models to account for among-stream variability in the parameters. The fixed-effects parameters were tested using leave-one-site-out cross-validation. The model based on 0.5 m measurements provided improved model performance compared to that based on 1.5 m values, with RMSE of 0.0162 and 0.0187 mm h⁻¹, respectively, relative to a mean evaporation rate of 0.06 mm h⁻¹. Inclusion of atmospheric stability and canopy openness as predictors improved model performance when using the 1.5 m meteorological measurements, with minimal improvement when based on 0.5 m measurements. Of the wind functions reported in the literature, two performed reasonably while five others exhibited substantial bias.  相似文献   

Bridge Monitoring and Performance Evaluation     

Timothy O. Lawrence  Chad T. Ritter  Janos Gergely 《Geotechnical and Geological Engineering》2011,29(5):919-926

Over fifty percent of our nation’s 560,000-plus bridges are obsolete or structurally deficient. To upgrade or replace these structures would require a serious budget. In order to shorten this list of bridges and to improve their ratings, state DOTs are investigating new repair techniques and better performance evaluation tools in order to implement the new drive to sustainability within the infrastructure. The research presented herein focused on the evaluation of current US bridge analysis and rating procedures for the North Carolina Department of Transportation (NCDOT). To evaluate these procedures, several bridges were rated with commercially available software and a newly developed spreadsheet program. In parallel, the bridges were also load tested for comparison, from which, it was concluded that the NCDOT’s bridge rating software directly follows the latest AASHTO requirements. The experimental results, however, also proved that the bridges had significant strength reserves associated to several factors, such as, girder/deck composite action, impact and distribution factors, material strength, and contribution of non-structural elements. In this research, a simplified bridge testing protocol was developed from which it was concluded, that a relatively simple instrumentation setup could be effective in the load rating of bridges through testing. The data gathered through these instruments provide vital performance data for normal traffic conditions, as well as during extreme loading conditions and evacuations, which could lead to less restrictive load ratings and removal of the structurally deficient classification, yielding a more sustainable structure.  相似文献   

Mapping mean annual groundwater recharge in the Nebraska Sand Hills, USA   总被引：2，自引：1，他引：1  

Jozsef Szilagyi  Vitaly A. Zlotnik  John B. Gates  Janos Jozsa 《Hydrogeology Journal》2011,19(8):1503-1513

Mean annual recharge in the Sand Hills of Nebraska (USA) over the 2000?C2009 period was estimated at a 1-km spatial resolution as the difference of mean annual precipitation (P) and evapotranspiration (ET). Monthly P values came from the PRISM dataset, while monthly ET values were derived from linear transformations of the MODIS daytime land-surface temperature values into pixel ET rates with the help of ancillary atmospheric data (air temperature, humidity, and global radiation). The study area receives about 73?mm of recharge (with an error bound of ±73?mm) annually, which is about 14?±?14% of the regional mean annual P value of 533?mm. The largest recharge rates (about 200?±?85?mm or 30?±?12% of P) occur in the south-eastern part of the Sand Hills due to smoother terrain and more abundant precipitation (around 700?mm), while recharge is the smallest (about 40?±?59?mm or 10?±?14% of P) in the western part, where annual precipitation is only about 420?mm. Typically, lakes, wetlands, wet inter-dunal valleys, rivers, irrigated crops (except in the south-eastern region) and certain parts of afforested areas in the south-central portion of the study area act as discharge areas for groundwater.  相似文献   

Analytical solutions for co- and counter-current imbibition of sorbing, dispersive solutes in immiscible two-phase flow     

Karen Sophie Schmid  Sebastian Geiger  Kenneth Stuart Sorbie 《Computational Geosciences》2012,16(2):351-366

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XAFS characterization of the structural site of Yb in synthetic pyrope and grossular garnets     

S. Quartieri  G. Antonioli  C. A. Geiger  G. Artioli  P. P. Lottici 《Physics and Chemistry of Minerals》1999,26(3):251-256

The incorporation and site preference of minor amounts (about 1 wt%) of Yb³⁺ in synthetic pyrope (Mg₃Al₂Si₃O₁₂) and grossular (Ca₃Al₂Si₃O₁₂) garnet were studied by X-ray Absorption Fine-Structure (XAFS) Spectroscopy. The measurements, performed in the temperature range 77–343 K at both Yb L_I- and L_III-edges, demonstrate that Yb³⁺ enters the garnet structure and is located in the dodecahedral site in both samples. The coordination environment of Yb³⁺ in the two samples was compared to that of the X-site cation in end-member synthetic pyrope and grossular and in Yb₃Al₅O₁₂ as determined by single-crystal X-ray diffraction. The local geometry around Yb³⁺ is different from that of Mg and Ca in the bulk of the garnet, and also from that of Yb³⁺ in Yb₃Al₅O₁₂. Τhe XAFS results indicate that, (1) structural relaxation occurs around Yb³⁺ in the garnet structure; (2) the host garnet matrix exerts a major structural control on the incorporation of Yb³⁺, and (3) minor amounts of Yb³⁺ in garnet are located in structural sites and not in ill-defined defects. Received: 15 January 1998/ Revised, accepted: 21 July 1998  相似文献   

Evaluating the Potential of an Airborne Laser-scanning System for Measuring Volume Changes of Glaciers     

Etienne Favey  Alain Geiger  G. Hilmar Gudmundsson  & Aloysius Wehr 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):555-561

Airborne laser scanning (ALS) is well suited for the production of digital elevation models (DEM), and can, in contrast to photographic methods, be used to acquire a DEM independently of surface texture and external light sources. ALS thus serves as a tool to generate DEMs of firn areas where photogram- metric methods often fail.
The potential of an integrated ALS system – comprising a laser scanner, precise differential global positioning system, and a gyro platform – for DEM generation of firn areas is currently being assessed. The Unteraargletscher, Bernese Alps, Switzerland, has been chosen as a test site. As part of a pilot project aimed at determining the mass balance distribution of that glacier without the use of in situ information, ALS measurements were conducted in autumn 1997. The DEM derived from laser measurements is extremely sensitive to the position and attitude of the aircraft. Currently the main work focuses on assessing and improving the system's accuracy by error modelling and by the development of error-correction algorithms.
Preliminary results from Unteraargletscher are presented, and the potential of this method for the generation of DEMs of firn areas is discussed.  相似文献   

Mineralogy,chemistry, and noble gas contents of Adzhi-Bogdo– an LL3–6 chondritic breccia with L-chondritic and granitoidal clasts     

A. Bischoff  T. Geiger  H. Palme  B. Spettel  L. Schultz  P. Scherer  J. Schlüter  J. Lkhamsuren 《Meteoritics & planetary science》1993,28(4):570-578

Abstract— Adzhi-Bogdo is an ordinary chondrite regolith breccia (LL3–6) which fell on 1949 October 30 in Gobi Altay, Mongolia. The rock consists of submm- to cm-sized fragments embedded in a fine-grained clastic matrix. The polymict breccia contains various types of clasts, some of which must be of foreign origin. Components of the breccia include chondrules, melt rock clasts (some of which are K-rich), highly recrystallized rock fragments (“granulites”), breccia clasts, pyroxene-rich fragments with achondritic textures, and alkali-granitoids. The composition of olivine in most fragments is in the range of LL-chondrites. However, olivine in some components has significantly lower fayalite contents, characteristic of L-chondrites. The bulk meteorite is very weakly shocked (S2). Based on the bulk chemical composition, Adzhi-Bogdo is an ordinary chondrite. The concentrations of Fe and Ni are somewhat intermediate between L- and LL-chondrites. The contents of solar gases indicate that Adzhi-Bogdo is a regolith breccia. Most of the solar He and probably a part of the solar Ne of Adzhi-Bogdo has been lost. It is suggested that Adzhi-Bogdo experienced an (impact-induced) thermal event early in its history, because most of the radiogenic ⁴⁰Ar is retained.  相似文献   

Distribution of brine in grain boundaries during static recrystallization in wet, synthetic halite: insight from broad ion beam sectioning and SEM observation at cryogenic temperature     

Guillaume Desbois  Janos L. Urai  Peter A. Kukla  Uwe Wollenberg  Fabián Pérez-Willard  Zsolt Radí  Sandor Riholm 《Contributions to Mineralogy and Petrology》2012,163(1):19-31

We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films (<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes. First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration. Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine. When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid grain boundaries without resolvable brine films.  相似文献   

Biological Assessment of Eastern Oysters (Crassostrea virginica) Inhabiting Reef,Mangrove, Seawall,and Restoration Substrates     

Michael Drexler  Melanie L. Parker  Stephen P. Geiger  William S. Arnold  Pamela Hallock 《Estuaries and Coasts》2014,37(4):962-972

The eastern oyster, Crassostrea virginica, plays an essential functional role in many estuarine ecosystems on the east and Gulf coasts of the USA. Oysters form biogenic reefs but also live on alternative intertidal substrates such as artificial surfaces and mangrove prop roots. The hypothesis tested in this study was that non-reef-dwelling oysters (i.e., those inhabiting mangrove, seawall, or restoration substrates) were similar to their reef-dwelling counterparts based upon a suite of biological parameters. The study was carried out at six sites in three zones in Tampa Bay on the west coast of Florida using monthly samples collected from October 2008–September 2009. The timing of gametogenesis and spawning, fecundity, and juvenile recruitment were the same for oysters in all four habitats. Oyster size (measured as shell height), density, and Perkinsus marinus infection intensity and prevalence varied among habitats. This study indicates that oysters on mangroves, seawalls, and oyster restoration substrates contribute larvae, habitats for other species, and likely other ecosystem benefits similar to those of intertidal oyster reefs in Tampa Bay. Oysters from alternative intertidal substrates should be included in any system wide studies of oyster abundance, clearance rates, and the provision of alternate habitats, especially in highly developed estuaries.  相似文献   

Evolution of fault zones in carbonates with mechanical stratigraphy – Insights from scale models using layered cohesive powder     

Heijn W. van Gent  Marc Holland  Janos L. Urai  Ramon Loosveld 《Journal of Structural Geology》2010,32(9):1375-1391

We present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones, using cohesive hemihydrate powder (CaSO₄·½H₂O). The evolution of these dilatant fault zones involves a range of processes such as fragmentation, gravity-driven breccia transport and the formation of dilatant jogs. To allow scaling to natural prototypes, extensive material characterisation was done. This showed that tensile strength and cohesion depend on the state of compaction, whereas the friction angle remains approximately constant. In our models, tensile strength of the hemihydrate increases with depth from 9 to 50 Pa, while cohesion increases from 40 to 250 Pa. We studied homogeneous and layered material sequences, using sand as a relatively weak layer and hemihydrate/graphite mixtures as a slightly stronger layer. Deformation was analyzed by time-lapse photography and Particle Image Velocimetry (PIV) to calculate the evolution of the displacement field. With PIV the initial, predominantly elastic deformation and progressive localization of deformation are observed in detail. We observed near-vertical opening-mode fractures near the surface. With increasing depth, dilational shear faults were dominant, with releasing jogs forming at fault-dip variations. A transition to non-dilatant shear faults was observed near the bottom of the model. In models with mechanical stratigraphy, fault zones are more complex. The inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation.  相似文献