共查询到10条相似文献，搜索用时 323 毫秒
1.
Alan L. Flint Lorraine E. Flint Edward M. Kwicklis June T. Fabryka-Martin Gudmundur S. Bodvarsson 《Hydrogeology Journal》2002,10(1):180-204
Obtaining values of net infiltration, groundwater travel time, and recharge is necessary at the Yucca Mountain site, Nevada,
USA, in order to evaluate the expected performance of a potential repository as a containment system for high-level radioactive
waste. However, the geologic complexities of this site, its low precipitation and net infiltration, with numerous mechanisms
operating simultaneously to move water through the system, provide many challenges for the estimation of the spatial distribution
of recharge. A variety of methods appropriate for arid environments has been applied, including water-balance techniques,
calculations using Darcy's law in the unsaturated zone, a soil-physics method applied to neutron-hole water-content data,
inverse modeling of thermal profiles in boreholes extending through the thick unsaturated zone, chloride mass balance, atmospheric
radionuclides, and empirical approaches. These methods indicate that near-surface infiltration rates at Yucca Mountain are
highly variable in time and space, with local (point) values ranging from zero to several hundred millimeters per year. Spatially
distributed net-infiltration values average 5 mm/year, with the highest values approaching 20 mm/year near Yucca Crest. Site-scale
recharge estimates range from less than 1 to about 12 mm/year. These results have been incorporated into a site-scale model
that has been calibrated using these data sets that reflect infiltration processes acting on highly variable temporal and
spatial scales. The modeling study predicts highly non-uniform recharge at the water table, distributed significantly differently
from the non-uniform infiltration pattern at the surface.
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2.
Using groundwater levels to estimate recharge 总被引：24，自引：4，他引：24
Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different
approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data.
The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of
specific yield and changes in water levels over time. Advantages of this approach include its simplicity and an insensitivity
to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate
to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the
method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described. The theory
underlying the methods is explained. Examples from the literature are used to illustrate applications of the different methods.
Electronic Publication 相似文献
3.
Thomas J. Jackson 《Hydrogeology Journal》2002,10(1):40-51
Remote sensing provides information on the land surface. Therefore, linkages must be established if these data are to be
used in groundwater and recharge analyses. Keys to this process are the use of remote sensing techniques that provide information
on soil moisture and water-balance models that tie these observations to the recharge. Microwave remote sensing techniques
are used to map the spatial domain of surface soil moisture and to monitor its temporal dynamics, information that cannot
be measured using other techniques. The physical basis of this approach is presented with examples of how microwave remote
sensing is utilized in groundwater recharge and related studies.
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4.
Moisture samples obtained from unsaturated-zone profiles in sands from northern Nigeria were used to obtain recharge estimates
using the chloride (Cl) mass-balance method and to produce records of past recharge and climatic events. Recharge rates range
from 14–49 mm/year, on the basis of unsaturated-zone Cl values and rainfall chemistry measured over eight years at three local
stations. The unsaturated-zone results also provide a record of the changing recharge and climatic events of the past 80 years;
this record compares quite well with modelling results using precipitation data from Maiduguri, especially for the late 20th-century
period of drought. The best fit for the model is made, however, by using a lower mean rainfall Cl (0.65 mg/l) than that obtained
from the mean of the field results (1.77 mg/l Cl). This result implies that the measured rainfall Cl probably overestimates
the depositional flux of Cl, although the lower value is comparable to the minimum of the measured rainfall Cl values (0.6 mg/l
Cl). Recharge estimates made using these lower Cl values range from 16–30 mm/year. The spatial variability was then determined
using results from 360 regional shallow wells over 18,000 km2.
Using the revised rainfall estimate, the Cl balance indicates a value of 43 mm for the regional recharge, suggesting that
either additional preferential flow is taking place over and above that from the vadose one, or that the regional recharge
represents inputs from earlier wetter periods. These recharge estimates compare favourably with those from hydraulic modelling
in the same area and suggest that the recharge rates are much higher than values previously published for this area. High
nitrate (NO3) concentrations (NO3-N>Cl) preserved under aerobic conditions in the vadose zone reflect secondary enrichment from N-fixing vegetation, as occurs
elsewhere in the Sahel.
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5.
Groundwater recharge: an overview of processes and challenges 总被引：11，自引：13，他引：11
Since the mid-1980s, a relative explosion of groundwater-recharge studies has been reported in the literature. It is therefore
relevant to assess what is now known and to offer further guidance to practitioners involved in water-resource development.
The paper summarizes current understanding of recharge processes, identifies recurring recharge-evaluation problems, and reports
on some recent advances in estimation techniques. Emphasis is accorded to (semi-)arid regions because the need for information
is greatest in those areas – groundwater is often the only water source, is vulnerable to contamination, and is prone to depletion.
Few studies deal explicitly with groundwater recharge in temperate and humid zones, because recharge is normally included
in regional groundwater investigations as one component of the water balance. The resolution of regional water-balance studies
in (semi-)arid areas is, in contrast, often too low to quantify the limited recharge component with sufficient precision.
Despite the numerous studies, determination of recharge fluxes in (semi-)arid regions remains fraught with uncertainty. Multiple
tracer approaches probably offer the best potential for reliable results in local studies that require 'at-point' information.
However, many investigations indicate that these approaches are not straightforward, because in some cases preferential flow
contributes as much as 90% of the estimated total recharge. Tracer results (e.g. Cl–, 3H) must therefore be interpreted with care in areas with multi-modal flow in the vadose zone. Moreover, accurate estimation
of total chloride deposition is essential, and tritium may be influenced by vapour transport at low flux rates. In addition,
paleoclimatic and paleohydrological conditions may cause discrepancies between measured actual processes and calculated long-term
averages.
The frequently studied issues of localized recharge and spatial variability need not be a problem if concern is with regional estimates. The key for practitioners is
the project objective, which dictates whether 'at-point' or area-/groundwater-based estimation methods are appropriate. Many
indirect (wadi) recharge studies reported in the literature are site specific; the relationship between 'at point' hydraulic properties
and channel-reach losses demands further investigation.
Electronic Publication 相似文献
6.
A comparison of recharge rates in aquifers of the United States based on groundwater-age data 总被引：3，自引：1，他引：2
P. B. McMahon L. N. Plummer J. K. B?hlke S. D. Shapiro S. R. Hinkle 《Hydrogeology Journal》2011,19(4):779-800
An overview is presented of existing groundwater-age data and their implications for assessing rates and timescales of recharge in selected unconfined aquifer systems of the United States. Apparent age distributions in aquifers determined from chlorofluorocarbon, sulfur hexafluoride, tritium/helium-3, and radiocarbon measurements from 565 wells in 45 networks were used to calculate groundwater recharge rates. Timescales of recharge were defined by 1,873 distributed tritium measurements and 102 radiocarbon measurements from 27 well networks. Recharge rates ranged from?<?10 to 1,200?mm/yr in selected aquifers on the basis of measured vertical age distributions and assuming exponential age gradients. On a regional basis, recharge rates based on tracers of young groundwater exhibited a significant inverse correlation with mean annual air temperature and a significant positive correlation with mean annual precipitation. Comparison of recharge derived from groundwater ages with recharge derived from stream base-flow evaluation showed similar overall patterns but substantial local differences. Results from this compilation demonstrate that age-based recharge estimates can provide useful insights into spatial and temporal variability in recharge at a national scale and factors controlling that variability. Local age-based recharge estimates provide empirical data and process information that are needed for testing and improving more spatially complete model-based methods. 相似文献
7.
The cumulative storage accumulation curve (CSAC) is a tool for saturated-volume fluctuation (SVF) analysis of transient recharge
to shallow phreatic aquifers discharging only to springs. The method assumes that little underflow or phreatic evapotranspiration
occurs. The CSAC is a modified water-table hydrograph that distinguishes storage increase caused by recharge from loss due
to springflow-induced recession. Required for the analysis are water-table fluctuations at a single representative location
within the catchment of a single spring and either direct measurements or robust interpolations of springflows at different
aquifer stages. The method employs empirical manipulation of head observations, varying spring catchment area to minimize
CSAC water-level changes in late portions of long recessions. Results include volumetric estimates of recharge integrated
over individual events and instantaneous rates of recharge to the water table, at the temporal resolution of the water-level
sampling interval. The analysis may also yield physically realistic information on spring catchment and recharge focusing.
In a test case in West Virginia, USA, recharge estimates by this technique were consistent with integrated springflow time
series but greater than estimates based on potential evapotranspiration. Results give insight into dynamic recharge behavior
over time as well as an indication of recharge catchment size.
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8.
A catchment water balance model for estimating groundwater recharge in arid and semiarid regions of south-east Iran 总被引：1，自引：0，他引：1
This paper presents a new model of the rainfall-runoff-groundwater flow processes applicable to semiarid and arid catchments
in south-east Iran. The main purpose of the model is to assess the groundwater recharge to aquifers in these catchments. The
model takes into account main recharge mechanisms in the region, including subsurface flow in the valley alluvium in mountainous
areas and recharge from the bed of ephemeral rivers. It deals with the effects of spatial variation in the hydrological processes
by dividing the catchment into regions of broad hydrologic similarity named as highland, intermediate and aquifer areas. The
model is based on the concept of routing precipitation within and through the catchment. The model has been applied to the
Zahedan catchment and the results indicate that the groundwater level estimated by the recharge model generally is in agreement
with the behaviour of groundwater levels in observation wells. The sensitivity analysis indicates that when the rainfall in
the aquifer area is used to replace the values recorded in the intermediate area and the highland area, the recharge estimates
are reduced by 42-87%. This result supports the division of the catchment into different zones of hydrological similarity
to account for spatial variability of hydrological processes.
Electronic Publication 相似文献
9.
Artificial recharge of groundwater: hydrogeology and engineering 总被引：25，自引：4，他引：25
Herman Bouwer 《Hydrogeology Journal》2002,10(1):121-142
Artificial recharge of groundwater is achieved by putting surface water in basins, furrows, ditches, or other facilities
where it infiltrates into the soil and moves downward to recharge aquifers. Artificial recharge is increasingly used for short-
or long-term underground storage, where it has several advantages over surface storage, and in water reuse. Artificial recharge
requires permeable surface soils. Where these are not available, trenches or shafts in the unsaturated zone can be used, or
water can be directly injected into aquifers through wells. To design a system for artificial recharge of groundwater, infiltration
rates of the soil must be determined and the unsaturated zone between land surface and the aquifer must be checked for adequate
permeability and absence of polluted areas. The aquifer should be sufficiently transmissive to avoid excessive buildup of
groundwater mounds. Knowledge of these conditions requires field investigations and, if no fatal flaws are detected, test
basins to predict system performance. Water-quality issues must be evaluated, especially with respect to formation of clogging
layers on basin bottoms or other infiltration surfaces, and to geochemical reactions in the aquifer. Clogging layers are managed
by desilting or other pretreatment of the water, and by remedial techniques in the infiltration system, such as drying, scraping,
disking, ripping, or other tillage. Recharge wells should be pumped periodically to backwash clogging layers. Electronic supplementary
material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s10040-001-0182-4.
Electronic Publication 相似文献
10.
Methodology for groundwater recharge assessment in carbonate aquifers: application to pilot sites in southern Spain 总被引：1，自引：0，他引：1
B. Andreo J. Vías J. J. Durán P. Jiménez J. A. López-Geta F. Carrasco 《Hydrogeology Journal》2008,16(5):911-925
Aquifer recharge can be determined by conventional methods such as hydrodynamic or hydrologic balance calculations, or numerical, hydrochemical or isotopic models. Such methods are usually developed with respect to detrital aquifers and are then used on carbonate aquifers without taking into consideration their hydrogeological particularities. Moreover, such methods are not always easy to apply, sometimes requiring data that are not available. Neither do they enable determination of the spatial distribution of the recharge. For eight regions in southern Spain, the APLIS method has been used to estimate the mean annual recharge in carbonate aquifers, expressed as a percentage of precipitation, based on the variables altitude, slope, lithology, infiltration landform, and soil type. The aquifers are representative of a broad range of climatic and geologic conditions. Maps of the above variables have been drawn for each aquifer, using a geographic information system; thus they can be superimposed to obtain the mean value and spatial distribution of the recharge. The recharge values for the eight aquifers are similar to those previously calculated by conventional methods and confirmed by discharge values, which corroborates the validity of the method. 相似文献