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41.
Fractal models for predicting soil hydraulic properties: a review 总被引:33,自引:0,他引:33
Modern hydrological models require information on hydraulic conductivity and soil-water retention characteristics. The high cost and large spatial variability of measurements makes the prediction of these properties a viable alternative. Fractal models describe hierarchical systems and are suitable to model soil structure and soil hydraulic properties. Deterministic fractals are often used to model porous media in which scaling of mass, pore space, pore surface and the size-distribution of fragments are all characterized by a single fractal dimension. Experimental evidence shows fractal scaling of these properties between upper and lower limits of scale, but typically there is no coincidence in the values of the fractal dimensions characterizing different properties. This poses a problem in the evaluation of the contrasting approaches used to model soil-water retention and hydraulic conductivity. Fractal models of the soil-water retention curve that use a single fractal dimension often deviate from measurements at saturation and at dryness. More accurate models should consider scaling domains each characterized by a fractal dimension with different morphological interpretations. Models of unsaturated hydraulic conductivity incorporate fractal dimensions characterizing scaling of different properties including parameters representing connectivity. Further research is needed to clarify the morphological properties influencing the different scaling domains in the soil-water retention curve and unsaturated hydraulic conductivity. Methods to functionally characterize a porous medium using fractal approaches are likely to improve the predictability of soil hydraulic properties. 相似文献
42.
Edmund Penning-Rowsell 《GeoJournal》1997,43(3):247-262
A model is put forward to prescribe the processes and steps whereby governments can and should integrate their natural resources policies across the many different sectors involved. The model has developed from the analysis of policies for water resources, coastal zones and soil resources in OECD countries. Such a model can never be comprehensive but the one developed does help to pinpoint some of the reasons for the adverse impacts that occur where the appropriate institutional arrangements to promote policy integration are lacking. By stressing the links – or otherwise – between national policies and management practices on the ground it also highlights both the importance of having the appropriate data available to monitor policy integration, and the narrow range of policy instruments currently being deployed to minimise inter-sectoral conflict and thus to promote sustainable resources management. 相似文献
43.
Edmund J. Zolnik 《The Professional geographer》2007,59(3):365-377
Using a case study approach, this article explores the potential to increase public transit ridership via the expansion of Unlimited Access (UA) from a university‐ or employer‐based program to a community‐based program. UA partners universities or employers with regional transit organizations to provide free or discounted public transit service to students as well as employees and, potentially, to local community residents. A case study on the only known UA program failure highlights the importance of equitable cost attribution as well as stakeholder coordination and dedicated operations funds to the long‐term success of community‐based UA programs. 相似文献
44.
Edmund Penning-Rowsell Clare Johnson Sylvia Tunstall 《Global Environmental Change》2006,16(4):323-339
This paper evaluates policy accelerations after past flood crises in the UK (in 1947, 1953, 1998 and 2000) and explores their value as surrogates or metaphors for how governments might respond with policy changes to the local expressions of global climate and environmental change in the future. We find that these past policy change accelerations were, in general, not based on the development of new ideas but on bringing forward existing ideas that were already the subject of widespread professional or public discourse. We suggest, therefore, that we may be able to detect now, as ‘signals’ within current policy discourse, the embryos of the policy shifts that are likely to come about as part of any crisis-response adaptation to future climate change. If this is the case, then we believe that those with policy responsibilities now may be able to begin carefully and proactively to prepare the ground for such policy changes ahead of the crisis events that will alone trigger their acceleration and adoption. 相似文献
45.
Julian Bommer Robin Spence Mustafa Erdik Shigeko Tabuchi Nuray Aydinoglu Edmund Booth Domenico del Re Oliver Peterken 《Journal of Seismology》2002,6(3):431-446
Following the devastating Kocaeli and Düzce earthquakes of August andNovember 1999, the Turkish Government was faced with an enormousfinancial burden as a result of its statutory obligation to cover the full costsof rebuilding. In order to offset this liability in the future – which has hadan adverse effect on the Government's economic programme – acompulsory earthquake insurance scheme has been introduced for allhouseholders in Turkey. A key element for successful implementation ofthis novel and ambitious programme is the transfer of the earthquake riskabsorbed by the Turkish Catastrophe Insurance Pool (TCIP) to theinternational reinsurance market. An earthquake loss model, described inthis paper, has been developed for the TCIP to serve as a basis for thedecision-making process with respect to the pricing of its insurance policy,risk control, the purchase of reinsurance, and the transfer of seismic risk.Sample results of the loss calculations are presented. 相似文献
46.
M. Nafi Toksöz Anton M. Dainty Edmund Reiter Ru-Shan Wu 《Pure and Applied Geophysics》1988,128(1-2):81-100
The mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data, coda wavesRg attenuation, strong motion attenuation measurements in the northeast United States and Canada, and theoretical models. The frequency range 1–10 Hz has been studied. The relative contributions to attenuation of anelasticity of crustal rocks (constantQ), fluid flow and scattering are evaluated. Scattering is found to be strong with an albedoB
0=0.8–0.9 and a scattering extinction length of 17–32 km. The albedo is defined as the ratio of the total extinction length to the scattering extinction length. TheRg results indicate thatQ increases with depth in the upper kilometer or two of the crust, at least in New England. CodaQ appears to be equivalent to intrinsic (anelastic)Q and indicates that thisQ increases with frequency asQ=Q
o
f
n
, wheren is in the range of 0.2–0.9. The intrinsic attenuation in the crust can be explained by a high constantQ (500Q
o2000) and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks. A fluid-flow attenuation model gives a frequency dependence (QQ
o
f
0.5) similar to those determined from the analysis of coda waves of regional seismograms.Q is low near the surface and high in the body of the crust. 相似文献
47.
Edmund A. Jarzembowski B. Wang 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):673-676
Mayflies are very rare in the British fossil record. The first nymph to be found, Schistonotorum wallisi gen. et sp. nov., is described from the non-marine Lower Cretaceous of southeast England. This Early Barremian find is from the Upper Weald Clay Formation at Smokejacks brickworks, Surrey. It is preserved as an adpression in concretionary sideritic ironstone from the upper insect bed exposed in the northeast face of the pit. The palaeoecological significance of this record is discussed. 相似文献
48.
AbstractIn 2007, the Texas legislature created a program to identify environmental flow standards statewide through the coordinated efforts of scientific and stakeholder groups and rulemaking by the Texas Commission on Environmental Quality. To aid in this task, a Hydrology-based Environmental Flow Regime (HEFR) method was developed that combines a suite of user-customizable hydrologic statistics with an implementation framework. Following the concepts of the Natural Flow Paradigm, the methodology includes the separation of a long-term hydrograph into key flow components (e.g. subsistence, base, high-flow pulse and overbank) defined by the Texas Instream Flow Program. Seasonal, annual and inter-annual flow component statistics were then coupled with biology, water quality and geomorphology overlays, where available, and with implementation rules applied to example large-scale water supply projects to support development of environmental flow standards for use in water rights permit conditions. The HEFR methodology and resulting flow recommendations are compared to two contemporary in-stream flow studies and adopted environmental flow standards. Subsistence flows were fairly similar. Baseflows were in a similar range, but fewer than three seasonal levels have sometimes been specified in in-stream flow studies. Episodic events are quite different in terms of magnitude, frequency, duration and applicable number.
Editor D. Koutsoyiannis; Guest editor M. AcremanCitation Opdyke, D.R., Oborny, E.L., Vaugh, S.K., and Mayes, K.B., 2014. Texas environmental flow standards and the hydrology-based environmental flow regime methodology. Hydrological Sciences Journal, 59 (3–4), 820–830. 相似文献
49.
Edmund D. Gill 《地球表面变化过程与地形》1981,6(1):81-83
The development of honeycomb weathering on seawalls of non-marine Lower Cretaceous greywacke built in 1943 and 1949 shows that under certain conditions this type of tafoni is a significant factor in the retrogradation of rocky coasts. 相似文献