Flood forecasting in large rivers with data-driven models   总被引：1，自引：1，他引：0  

Phuoc Khac-Tien Nguyen  Lloyd Hock-Chye Chua  Lam Hung Son 《Natural Hazards》2014,71(1):767-784

Results from the application of adaptive neuro-fuzzy inference system (ANFIS) to forecast water levels at 3 stations along the mainstream of the Lower Mekong River are reported in this paper. The study investigated the effects of including water levels from upstream stations and tributaries, and rainfall as inputs to ANFIS models developed for the 3 stations. When upstream water levels in the mainstream were used as input, improvements to forecasts were realized only when the water levels from 1 or at most 2 upstream stations were included. This is because when there are significant contributions of flow from the tributaries, the correlation between the water levels in the upstream stations and stations of interest decreases, limiting the effectiveness of including water levels from upstream stations as inputs. In addition, only improvements at short lead times were achieved. Including the water level from the tributaries did not significantly improve forecast results. This is attributed mainly to the fact that the flow contributions represented by the tributaries may not be significant enough, given that there could be large volume of flow discharging directly from the catchments which are ungauged, into the mainstream. The largest improvement for 1-day forecasts was obtained for Kratie station where lateral flow contribution was 17 %, the highest for the 3 stations considered. The inclusion of rainfall as input resulted in significant improvements to long-term forecasts. For Thakhek, where rainfall is most significant, the persistence index and coefficient of efficiency for 5-lead-day forecasts improved from 0.17 to 0.44 and 0.89 to 0.93, respectively, whereas the root mean square error decreased from 0.83 to 0.69 m.  相似文献   

Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens     

R.S. Cutting  V.S. Coker  J.W. Fellowes  J.R. Lloyd  D.J. Vaughan 《Geochimica et cosmochimica acta》2009,73(14):4004-6858

The biologically-mediated reduction of synthetic samples of the Fe(III)-bearing minerals hematite, goethite, lepidocrocite, feroxhyte, ford ferrihydrite, akaganeite and schwertmannite by Geobacter sulfurreducens has been investigated using microbiological techniques in conjunction with X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). This combination of approaches offers unique insights into the influence of subtle variations in the crystallinity of a given mineral on biogeochemical processes, and has highlighted the importance of (oxyhydr)oxide crystallite morphology in determining the changes occurring in a given mineral phase. Problems arising from normalising the biological Fe(III) reduction rates relative to the specific surface areas of the starting materials are also highlighted. These problems are caused primarily by particle aggregation, and compounded when using spectrophotometric assays to monitor reduction. For example, the initial rates of Fe(III) reduction observed for two synthetic feroxyhytes with different crystallinities (as shown by XRD and TEM studies) but almost identical surface areas, differ substantially. Both microbiological and high-resolution TEM studies show that hematite and goethite are susceptible to limited amounts of Fe(III) reduction, as evidenced by the accumulation of Fe(II) during incubation with G. sulfurreducens and the growth of nodular structures on crystalline goethite laths during incubation. Lepidocrocite and akaganeite readily transform into mixtures of magnetite and goethite, and XRD data indicate that the proportion of magnetite increases within the transformation products as the crystallinity of the starting material decreases. The presence of anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle increases both the initial rate and longer term extent of biological Fe(III) reduction for all of the synthetic minerals examined. High-resolution XPS indicates subtle but measurable differences in the Fe(III):Fe(II) ratios at the mineral surfaces following extended incubation. For example, for a poorly crystalline schwertmannite, deconvolution of the Fe2p_3/2 peak suggests that the Fe(III):Fe(II) ratio of the near-surface regions varies from 1.0 in the starting material to 0.9 following 144 h of incubation with G.sulfurreducens, and to 0.75 following the same incubation period in the presence of 10 μM AQDS. These results have important implications for the biogeochemical cycling of iron.  相似文献   

Mineralogical control of rare earth elements in acid sulfate soils     

Susan A. Welch  Andrew G. Christy  Lloyd Isaacson  Dirk Kirste 《Geochimica et cosmochimica acta》2009,73(1):44-177

Major, trace and rare earth element concentrations were measured in porewater, surface water and sediments at an acid sulfate soil site. The concentrations of La and Ce in porewater are up to 1-3 ppm. There is a strong correlation between REE concentration and acidity, except that the maximum concentrations were consistently found below the horizon of maximum acidity, associated with an increase in pH (to ca. 4) and change in mineralogy from jarosite-dominated to goethite-dominated mottles. Jarosite replacement by goethite is as expected with the rise in pH, which in turn is due to the occurrence of a fossil shell bed just below. The rare earth element patterns in the porewaters are enriched in the MREE with respect to Post-Archaean Australian Shale (PAAS). Measurements and calculations show that this is in accord with experiments on low-degree partial dissolution of jarosite, even when the jarosite itself is highly enriched in LREE. There is a clear fractionation in the patterns between the clay-rich soil matrix, which is slightly depleted in the LREE when normalized to PAAS (La/Yb_PAAS ∼0.5), and the secondary mineral phase jarosite, which is enriched in the LREE (La/Yb_PAAS = 15-50). The REE pattern in the porewater changes with the transition from jarosite- to goethite-rich mottles, becoming relatively more enriched in the LREE compared to the HREE, which is consistent with the incongruent dissolution of jarosite to form goethite and the release of greater amounts of jarosite REE to solution, including proportionately more of the jarosite-compatible LREE.Maximum surface water REE concentrations in acidic water were 100-200 ppb La and Ce. REE patterns in surface water were very similar to the porewater transition zone, enriched in the MREE, but asymmetric, relatively enriched in the LREE compared to the HREE.  相似文献   

Centimeter-Level Positioning of a U. S. Coast Guard Buoy Tender   总被引：1，自引：1，他引：0  

David B. Zilkoski  J. Don D'Onofrio  Rudolf J. Fury  Curtis L. Smith  Lloyd C. Huff  Barry J. Gallagher 《GPS Solutions》1999,3(2):53-65

With the availability of high-accuracy, differential global positioning system (GPS) results in real-time, there is a new opportunity to use GPS to accurately measure a marine vessel's dynamic draft (settlement and squat) and 3D attitude (roll, pitch, and heading). The National Geodetic Survey (NGS) and the Coast Survey (CS), offices of the National Ocean Service (NOS), National Oceanic and Atmospheric Administration (NOAA), propose to transfer this technology to the shipping industry. The overall goal of this project is to provide the position of a vessel's keel in real time to within 10 cm (about 4 inches) relative to the bottom of the shipping channel. In support of this phase of the project, there were three meetings hosted by the Port of Oakland, California and NOS to discuss the real-time positioning of vessels project. On December 3 and 4, 1996, CS, NGS, Trimble Navigation Ltd., and the U. S. Coast Guard (USCG) performed GPS tests on a USCG buoy-tender ship. GPS data were used to compute the vessel's dynamic draft and 3D attitude. During the test, five receivers continually collected data; one receiver was located at a base station on the USCG pier on Yerba Buena Island, and four were on the ship: two on the stern and two on the bow. CS installed a TSS-335B vertical reference unit (to measure heave, pitch, and roll) in the engine room of the ship. NOS processed the GPS data and computed the vessel's dynamic draft and 3D attitude. The results indicate that the linear equivalent to the vessel's dynamic draft and 3D attitude were accurate to the 10-cm level using GPS. It was also demonstrated how a ship can be used to measure local water-level changes and actual water-level values everywhere it travels. ? 1999 John Wiley & Sons, Inc.  相似文献   

Wave-tide interaction modulates nearshore wave height     

Lewis  Matt J.  Palmer  Tamsin  Hashemi  Resa  Robins  Peter  Saulter  Andrew  Brown  Jenny  Lewis  Huw  Neill  Simon 《Ocean Dynamics》2019,69(3):367-384

Ocean Dynamics - The combined hazard of large waves occurring at an extreme high water could increase the risk of coastal flooding. Wave-tide interaction processes are known to modulate the wave...  相似文献   

URBAN COGNITIVE MAPS: COMPUTATION AND STRUCTURE     

Robert Lloyd  Hartwell Hooper 《The Professional geographer》1991,43(1):15-28

Geographic research has not focused on the information we encode into our memories about the characteristics of locations. The accuracy of information encoded in urban cognitive maps, how information varies among individuals, and the structure of the information were studied. Experimental results indicated subjects were more accurate and consistent for socio-economic than for life-cycle characteristics. Some characteristics of the population in a neighborhood, such as race and income, may be more visible and easier to encode through direct contact than other less visible characteristics such as age. A theoretical argument is made that characteristics not encoded for locations can possibly be computed through their covariation with known characteristics.  相似文献   

The hydrodynamics of bipolar explosions     

H. M. Lloyd  T. J. O'Brien  M. F. Bode  F. D. Kahn 《Astrophysics and Space Science》1994,216(1-2):161-166

Bipolarity is a common feature in the outbursts of classical, recurrent and symbiotic novae. In this paper, we present the results of numerical calculations of bipolar explosions in which two parcels of gas are ejected at highly supersonic and oppositely directed velocities into a cold surrounding medium. The calculations demonstrate the formation of a dense ring of shocked material in the plane normal to the line of ejection, due to the interaction of two bowshocks. Observational candidates for this hydrodynamic phenomenon are discussed.This author is supported by the SERC.  相似文献   

Atmospheric structure in the lower thermosphere     

K. H. Lloyd  L. M. Sheppard 《Planetary and Space Science》1965,13(12):1313

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Climatic change,orography and geostrophic motion     

Dr. Huw C. Davies 《Theoretical and Applied Climatology》1975,23(1-2):1-12

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Mind mapping as an interactive tool for engaging complex geographical issues     

David Lloyd  Bill Boyd  Kristin Den Exter 《New Zealand geographer》2010,66(3):181-188

Students and communities engaging with complex geographical issues require tools to assist them structure and contextualise data. This paper examines the use of mind mapping as a tool in geographical education. Case studies are presented from a sample of undergraduate and cross-cultural educational settings demonstrating the use of mind mapping in communication, analysis and problem solving. In critiquing this educational tool, we conclude that mind mapping is particularly effective with communities whose cultures are strong on visual communication but weaker on written communication and in cross-cultural situations where use of written English would disadvantage learners.  相似文献