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121.
In many countries groundwater resources are under-appreciated and, therefore, underutilizied; whereas, in some areas they are inappropriately exploited and, therefore, over-utilized. “Over utilization” can lead to depletion in quantity or a degradation in quality or both. Obstacles to effective management include: (1) lack of knowledge of basic principles of groundwater science among water planners, (2) in many, if not in most countries, ownership of groundwater is in the private domain with the result that codependence is unrecognized, and (3) a misunderstanding by water planners of the concepts of “overexploitation%rdquo; and conjunctive use. The economic, social, and hydrologic constraints and procedures for management for sustainable development of groundwater are significantly different from those for surface water because these differences result from such things as (1) groundwater development is not dependent on large scale collective projects (unlike the utilization of surface water that requires engineering structures for diverting, regulating and transporting water), (2) the activities of many different groups can affect the quality of water, and (3) users of groundwater often are not aware of their co-dependence on the groundwater heritage in which each participates. Hydrogeologists should try to identify those governmental policies that have a detrimental environmental effect, promote those policies that are beneficial, and demonstrate the need for a policy in matters where a policy is lacking. 相似文献
122.
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125.
P. C. Ram 《Astrophysics and Space Science》1991,175(1):119-123
An analysis of Hall and ion-slip current effects on the MHD free-convection flow of a partiallyionised gas past an infinite vertical porous plate in a rotating frame of reference is carried out. A strong magnetic field is applied perpendicular to the plate and the plate temperature oscillates in time about a constant non-zero mean. The problem has been solved for the velocity and temperature fields and the effects of
e
(the Hall parameter),
i
(the ion-slip parameter),E
r
(rotation parameter), and have been discussed and shown graphically. 相似文献
126.
Steven M. Nelson Eloise Kendy Karl W. Flessa J. Eliana Rodríguez-Burgueño Jorge Ramírez-Hernández Tomás E. Rivas-Salcedo 《水文研究》2020,34(22):4156-4174
The macrotidal Colorado River Delta at the northern end of the Gulf of California in Mexico is hydrologically complex. We review historical accounts, data, field notes and photographs to evaluate the hydrological processes active on the delta prior to the advent of upstream dams. We also employ satellite imagery as well as recent LIDAR data to illustrate the critical role played by headcut erosion in restoring the river's fluvial/tidewater connection during the 1979–1988 floods. Prior to human manipulation, the river's contribution of fresh water to the Gulf was periodically interrupted by natural overflowing, avulsing, and flooding into the sub-sea level Salton Sink on the north slope of the delta plain. River flow south towards the Gulf was also subject to occasional overflow into Laguna Salada, another sub-sea level basin. In the mid-20th century, the Delta was disconnected from its fluvial supply following installation of upstream dams and reservoirs. A tidal sediment obstruction developed in the estuary channel, forming a final barrier to fluvial connectivity. Release of Colorado River floodwaters into Mexico between 1979 and 1988 provided a natural experiment on the hydrological response of a long-disconnected macrotidal delta to restoration of fluvial supply. 相似文献
127.
Francisco Balocchi Neftali Flores José Luis Arumí Andrés Iroumé Don A. White Richard P. Silberstein Pablo Ramírez de Arellano 《水文研究》2021,35(6):e14182
In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long-term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient (α) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient (α) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south-central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ (p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference (p < 0.05) between these and Eucalyptus plantations. The recession constant is a well-established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate. 相似文献
128.
Natural Hazards - In recent years, floods have become one of the natural hazards that generate the greatest economic and human losses on the planet. As is well known, torrential rainfall events are... 相似文献
129.
Self-Similar and Self-Affine Properties of Two-Dimensional Fracture Patterns in Rocks 总被引:1,自引:0,他引:1
In this paper, we investigate the fractal properties of binary maps of rock fractures at different scales and different geological
types, as well as different families of fracture patterns obtained from a two-dimensional Laplacian growth model (LGM). From
these analyses we figure out which families of the LGM patterns match the structural properties of the fracture binary maps.
The LGM is defined in terms of a nonlinear map that depends on two parameters, λ and
\mathfraka\mathfrak{a}, that respectively define the area and shape of the elements of the aggregate that conforms the patterns. The fractal dimension
and roughness exponent of the LGM patterns are found to depend on
\mathfraka\mathfrak{a}, with
0 < \mathfrak a < 10<\mathfrak {a}<1. From a detailed statistical analysis of these patterns we found that the fractal dimensions of capacity, correlation and
information decrease monotonically as
\mathfraka\mathfrak{a} increases. We also found that the values of these three fractal dimensions tend to collapse on top of each other as
\mathfraka\lessapprox1\mathfrak{a}\lessapprox1. Remarkably, the fractal properties of rock fractures in the scales from millimeters up to a few meters appear to be well
represented by the fractal structure of the LGM families of patterns with
\mathfraka=0.15\mathfrak{a}=0.15 and 0.30, while the fractal properties of rock fractures in the scale of kilometers seems to be well represented by the LGM
family with
\mathfraka=0.90\mathfrak{a}=0.90. In addition, the three fractal dimension values of fracture binary maps in the scales from millimeters up to meters were
found to be different between them. Nonetheless, for fractures in the scale of kilometers, the values of the three fractal
dimensions are very close to each other as an indication of self-similar behavior. Analysis of the corrections to the scaling
of the roughness exponent, ζ, suggests that they are negligible for the LGM family of fracture patterns with
\mathfraka=0.9\mathfrak{a}=0.9. This finding points to a self-affine structure for this family of patterns. In fact, the calculated roughness exponent results
are in the range of values characteristic of rock fractures. 相似文献
130.
Gabriel Katul Chun-Ta Lai Karina Schfer Brani Vidakovic John Albertson David Ellsworth Ram Oren 《Advances in water resources》2001,24(9-10)
The variability in land surface heat (H), water vapor (LE), and CO2 (or net ecosystem exchange, NEE) fluxes was investigated at scales ranging from fractions of seconds to years using eddy-covariance flux measurements above a pine forest. Because these fluxes significantly vary at all these time scales and because large gaps in the record are unavoidable in such experiments, standard Fourier expansion methods for computing the spectral and cospectral statistical properties were not possible. Instead, orthonormal wavelet transformations
are proposed and used. The
are ideal at resolving process variability with respect to both scale and time and are able to isolate and remove the effects of missing data (or gaps) from spectral and cospectral calculations. Using the
spectra, we demonstrated unique aspects in three appropriate ranges of time scales: turbulent time scales (fractions of seconds to minutes), meteorological time scales (hour to weeks), and seasonal to interannual time scales corresponding to climate and vegetation dynamics. We have shown that: (1) existing turbulence theories describe the short time scales well, (2) coupled physiological and transport models (e.g. CANVEG) reproduce the wavelet spectral characteristics of all three land surface fluxes for meteorological time scales, and (3) seasonal dynamics in vegetation physiology and structure inject strong correlations between land surface fluxes and forcing variables at monthly to seasonal time scales. The broad implications of this study center on the possibility of developing low-dimensional models of land surface water, energy, and carbon exchange. If the bulk of the flux variability is dominated by a narrow band or bands of modes, and these modes “resonate” with key state and forcing variables, then low-dimensional models may relate these forcing and state variables to NEE and LE. 相似文献