Geologic influences on fluvial hydrology and bedload transport in small mountainous watersheds,Northern New Mexico,U.S.A.     

Keith I. Kelson  Stephen G. Wells 《地球表面变化过程与地形》1989,14(8):671-690

Discharge characteristics in six adjacent mountainous watersheds in northern New Mexico, U.S.A., vary substantially between basins underlain by different lithologies. Relatively resistant gneisses and granites underlie two basins (drainage areas: 43 and 94 km²) that have high unit discharge (0·010 to 0·14 m³s^?1 km^?2), high bankfull discharge, and sustained high discharge. Less resistant sandstones and shales underlie four basins (drainage areas: 96 to 215 km²) that have relatively low unit discharge (0·001 to 0·005 m³s^?1 km^?2), relatively low bankfull discharge, and peak discharges that are not sustained as long as those in the crystalline terrane. Analysis of snowmelt-runoff water budgets suggests that three factors control hydrologic conditions in the basins. First, area-elevation distributions appear to control the timing and amounts of water input. These distributions probably reflect the erosional resistance of the different lithologies. Second, lithology appears to control runoff production in areas having minor amounts of storage. Third, glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases. The amount of return flow released by glacial deposits, however, is probably controlled by the permeability of underlying bedrock. Therefore it appears that the duration, timing, and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology. Stream power and shear stress estimates derived from bankfull discharge and bed-material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane. It appears that source-area lithology, by controlling discharge production, also influences stream power, bedload transport capabilities, and therefore total amounts of bedload transport.  相似文献   

Extracting Holocene paleohydrology and paleoclimatology information from modern extreme flood events: An example from southern California     

Yehouda Enzel  Stephen G. Wells 《Geomorphology》1997,19(3-4)

The extraction of paleohydrological and paleoclimatological information from a modern hydrological system, shown to represent unique and extreme hydroclimatological conditions, is illustrated by an example from the Mojave River drainage basin in southern California. The Mojave River allows only the most extreme floods to reach its terminal basin in the Silver Lake playa and to form ephemeral lakes. All the other floods are lost by transmission into the alluvial aquifer along its 200 km channel. This filtering out of regular floods by the river provides an essential tool in establishing a physical link between atmospheric and hydrologic conditions. We demonstrate such a link between anomalous, present-day atmospheric circulation patterns over the North Pacific Ocean, extreme storms in southern California that produced the heaviest precipitation on record, the largest floods of record in the Mojave River watershed, and ephemeral lakes in its terminal playa. This physical link determines the possible cause of the formations of perennial, short-duration, shallow lakes in Silver Lake playa during the late Holocene and characterizes the hydroclimatic conditions that prevailed during these lacustrine episodes. Hydrological simulations of this river and its filtering character demonstrate that these lakes could have formed only if the most extreme modern storms and floods were more frequent in at least an order of magnitude during specific time episodes. We conclude that such extreme hydroclimatic conditions occurred more frequent in past episodes during which the Holocene lakes formed. In turn, this conclusion indicates that the cause of these storms and floods, i.e. the anomalous atmospheric circulation pattern, must have been more frequent. This research outlines a way to extract information on Holocene climates in hydrologic settings that demonstrate a unique cause and effect relationship.  相似文献   

Weathering rates of sandstone in a semi-arid environment (Hunter Valley,Australia)   总被引：1，自引：0，他引：1  

Tony Wells  Greg Hancock  John Fryer 《Environmental Geology》2008,54(5):1047-1057

The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years. This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region. Of the four processes examined, only the freeze–thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region.  相似文献   

Titius-bode series galaxy group red shift differences calculated from roots of the bessel equation     

Daniel R. Wells 《Astrophysics and Space Science》1995,227(1-2):255-263

It has been shown in detail by Wells (Wells, 1986) that the Bode numbers and measured velocity ratios of the planets are accurately predicted by the eigenvalues of the Euler-Lagrange equations resulting from the variation of the free energy of the generic plasma that formed the Sun and planets. This theory is reviewed and extended to show that the equations make accurate predictions for all the major planets out to and including Pluto. The semimajor axes and velocity ratios of Pluto and Neptune are predicted exactly. The Bode numbers are shown in Table I to correspond to the roots of the first-order Bessel functions. The extrema of the roots of the zeroth-order Bessel function predict the ratios of the measured planetary velocities almost without error for the outer planets. Both sets of roots correspond to the same eigenvalue solution of the forcefree equation. The eigenvalues are set by the initial energy input to the plasma nebula. Both the Titius-Bode series and Kepler's harmonic law are predicted by the relaxed state solution of the free-energy equation for the generic plasma that formed the Sun and planets. Newton's law of gravitation is not used in the calculations. The solution makes exact predictions for the outer planets where the Titius-Bode series fails completely.The work of Arp (Arp, 1985) adds to the growing body of observable evidence of objects which appear to be attached to galaxies or galaxy systems but display red shifts, sometimes quite large, differing from those of the associated galaxies. Adding to the mystery and confusion are a series of objects that have quantized red shifts.It is widely recognized that the history of these objects involves extremely high energy processes. The solutions of the equations of the relaxed state of the resulting high energy plasmas is discussed and it is shown that the predictions of red shift frequencies are quantized and agree numerically with many of the quantized shifts reported by Arp and Sulentic.  相似文献   

A model of tidal flushing of an estuary by dipole formation     

Mathew G. Wells  Gert-Jan F. van Heijst 《Dynamics of Atmospheres and Oceans》2003,37(3):223-244

We discuss a laboratory model of the flushing and mixing between a bay and a sea connected by a narrow channel. Tidal changes in water elevation lead to periodic flow in and out of the bay through the narrow channel. Due to flow separation there is an asymmetry between the flow entering and leaving the channel on different phases of the tide. A consequence of this asymmetry is that every tidal cycle a fraction of fluid is not returned through the channel, so that a passive tracer in the bay is successively flushed away. We consider what happens when the creation of vorticity in the channel leads to the formation of a dipole that can propagate away from the returning flow of the later phase of the tide. When the dimensionless ratio of maximum channel velocity U, width of channel W and tidal period T is such that W/UT<0.13, we find that dipoles can propagate away from the source region without being drawn back into the sink. This process leads to a larger exchange of water between the estuary and sea, than the classical model of tidal flushing by the jet-sink asymmetry of [Stommel, H., Farmer, H. G., 1952. On the nature of estuarine circulation WHOI Tech. Rep. 52–88, 131].  相似文献   

A three-dimensional hydrodynamic model of estuarine circulation with an application to Southampton Water, UK     

Anne Levasseur  Lei Shi  Neil C. Wells  Duncan A. Purdie  Boris A. Kelly-Gerreyn   《Estuarine, Coastal and Shelf Science》2007,73(3-4):753-767

A three-dimensional hydrodynamic model has been developed to simulate water mass circulation in estuarine systems. This model is based on the primitive equation in Cartesian coordinates with a terrain-following structure, coupled with a Mellor–Yamada 2.5 turbulence scheme. A fractional-step method is applied and the subset of equations is solved with finite volume and finite element methods. A dry–wet process simulates the presence of the tidal flat at low water. River inputs are introduced using a point-source method. The model was applied to a partially mixed, macrotidal, temperate estuary: Southampton Water, UK. The model is validated by comparisons with sea surface elevation, ADCP measurements and salinity data collected in 2001. The mean spring range 2(M₂ + S₂) and the mean neap range 2(M₂ − S₂) are modelled with an error relative to observation of 12 and 16%, respectively. The unique tidal regime of the system with the presence of the ‘young flood stand’ corresponding to the slackening conditions occurring at mid flood and ‘double high water’ corresponding to an extension of the slackening conditions at high tide is accurately reproduced in the model. The dynamics of the modelled mean surface and bottom velocity closely match the ADCP measurements during neap tides (rms of the difference is 0.09 and 0.01 m s⁻¹ at the bottom and at the surface, respectively), whereas at spring the difference is greater (rms of the difference is 0.25 and 0.20 m s⁻¹ at bottom and surface, respectively). The spatial and temporal variation of the degree of stratification as indicated by salinity distributions compares well with observations.  相似文献   

Proposing a coordinated environmental effects monitoring (EEM) program structure for the offshore petroleum industry,Nova Scotia,Canada     

K.J. Curran  P.G. Wells  A.J. Potter 《Marine Policy》2006

Environmental effects monitoring (EEM) identifies, quantifies, and compares predicted environmental impacts of a proposed industrial project to those observed after the project has been developed. Several EEM program structures exist, while the structure used by Environment Canada to monitor impacts of the pulp and paper industry has proven to be effective. The aim of this study is to provoke discussion on the development of an effective and coordinated petroleum EEM program structure for the offshore of Nova Scotia, Canada. A structure that supports development of a national EEM program for the petroleum industry is then proposed. Advantages of a coordinated EEM program structure include: (1) reduced cost of the EEM; (2) fewer gaps and less overlapping of responsibilities; (3) fewer calculated risks to the marine environment; and (4) improved environmental safeguards.  相似文献   

Storm-induced fine-sediment transport,west coast of south Korea     

John T. Wells  Y. A. Park  J. H. Choi 《Geo-Marine Letters》1984,4(3-4):177-180

Archived data, together with field observations collected between 1980 and 1982 off the west coast of Korea, suggest that the onset of winter monsoon winds in late fall initiates a residual southward flow that potentially carries large volumes of resuspended bottom sediments into the Korea Strait. During the calm conditions of summer, muds are replenished by high river discharges and reform the band of soft material, which characteristically occurs as a series of mudflats near the coast. Thus, these mudflats serve as a temporary storage facility during summer accumulation and as a source during winter erosion.  相似文献   

The teaching of geology in schools: Report of a discussion held on 5th April, 1946     

Vernon Wilson  Francis Jones  J.I. Platt  G. Van Praagh  A.E. Trueman  M.E. Tomlinson  M.M. Sweeting  S.G. Harries  F.E. Clegg  A.G. Lowndes  K.A. Joysey  F.J. North  H.E. Dudley  R.O. Jones  A.K. Wells  L.J. Chubb  W.B. West  H.J.W. Brown  A.H. Gunner 《Proceedings of the Geologists' Association. Geologists' Association》1947,58(1):1-44

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A study of the pebble beds in the Lower Greensand in East Surrey and West Kent     

A.K. Wells  F. Gossling 《Proceedings of the Geologists' Association. Geologists' Association》1947,58(3):194-IN4

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