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51.
Kirsten M. Menking Roger Y. Anderson Nabil G. Shafike Kamran H. Syed Bruce D. Allen 《Quaternary Research》2004,62(3):174-288
Well-preserved shorelines in Estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin's hydrologic balance for the purpose of estimating regional precipitation during the late Pleistocene. Estimates have ranged from 86% to 150% of modern, the disparity largely the result of assumptions about past temperatures. In this study, we use an array of models for surface-water runoff, groundwater flow, and lake energy balance to examine previously proposed scenarios for late Pleistocene climate. Constraints imposed by geologic evidence of past lake levels indicate that precipitation for the Last Glacial Maximum (LGM) may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15% of annual precipitation during these episodes. 相似文献
52.
B.S. Sukhija D.V. Reddy P. Nagabhushanam Syed Hussain V.Y. Giri 《Hydrogeology Journal》1996,4(2):70-88
In order to mine lignite from the Neyveli opencast mines, about 200 km south of Madras, India, the Neyveli aquifer has been undergoing depressurisation continuously for almost three decades. To gain insight into the aquifer hydrodynamics, environmental-isotope and chloride measurements on selected groundwater samples were initiated two decades ago, and detailed studies were undertaken during 1985–91. This article demonstrates the effect of large-scale groundwater withdrawals on the hydrologic regime and the effects on environmental chloride and isotopic distributions. A feature common to both the radiocarbon and chloride data of 1991 is their marked variation in a small area between the recharge zone and the mine area where pumping is concentrated. Furthermore, an excellent correlation exists between the temporal increase in the apparent radiocarbon ages of groundwater sampled in 1991 and 1985 and the corresponding lowering of potentiometric levels. Isochlors based on 1991 and 1985 data also indicate a changed hydrologic regime. In certain areas, heavy withdrawals have resulted in increased groundwater salinity. 相似文献
53.
Study of groundwater recharge processes is vital for quantification of total natural recharge to the aquifers. One of the
recharge processes demonstrated earlier by tracer experiments in the unsaturated zone is that of piston flow movement of soil
moisture. Based on this recharge process, environmental tritium, chloride and injected tritium studies have been carried out
extensively in various geological environs of India. The purpose of this paper is to evaluate the validity of the piston flow
concept in different geological environs viz. consolidated fractured and weathered granites, semi-consolidated sandstones
and unconsolidated alluvial tracts, and quantify the contribution from this process as well as that from the preferential
flow mechanism using different tracers. Analysis of tracer data demonstrates that the preferential flow recharge process contributes
very significantly (an average of 75% of total recharge) in the case of fractured granites and is important (an average of
33% of total recharge) for semi-consolidated sandstones, whereas the preferential flow recharge component is minimal in unconsolidated
alluvial tracts (piston flow model is applicable). These findings necessitate re-evaluation of the total natural recharge
potential of the above mentioned geological environs in view of the significant preferential flow recharge that is evidenced
and estimated.
Electronic Publication 相似文献
54.
55.
Geospatial presentation of habitat has become a key issue for planning conservation and management of any ecosystem. Hokersar wetland, one of the best resorts of migratory waterfowl in Kashmir, is under anthropogenic pressure and siltation due to floods. This has resulted in the degradation and change in the habitat quality of varied aquatic flora and fauna. Moreover, the seasonal changes affect the water level and land cover characteristics of the landscape. In the present study temporal mapping of the wetland has been carried out using the data sets for the autumn and spring seasons to assess the land cove/land use dynamics. The temporal change analysis, in the urban sprawl and the wetland, has been carried out to assess the rate of changes in the wetland and its environs. The wetland initially comprised of patch of marshy waterfowl habitat with some open water bodies. It has been fragmented into a large number of land uses because of anthropogenic activities. The increase in the settlement has been observed proportionate to the rate of fragmentation in the wetland. This study has created an information base, which will help to design conservation schemes for long term maintenance of the wetland. 相似文献
56.
Seismic imaging is an important step for imaging the subsurface structures of the Earth. One of the attractive domains for seismic imaging is explicit frequency–space (f – x) prestack depth migration. So far, this domain focused on migrating seismic data in acoustic media, but very little work assumed visco‐acoustic media. In reality, seismic exploration data amplitudes suffer from attenuation. To tackle the problem of attenuation, new operators are required, which compensates for it. We propose the weighted L 1 ‐error minimisation technique to design visco‐acoustic f – x wavefield extrapolators. The L 1 ‐error wavenumber responses provide superior extrapolator designs as compared with the previously designed equiripple L 4 ‐norm and L∞‐norm extrapolation wavenumber responses. To verify the new compensating designs, prestack depth migration is performed on the challenging Marmousi model dataset. A reference migrated section is obtained using non‐compensating f – x extrapolators on an acoustic dataset. Then, both compensating and non‐compensating extrapolators are applied to a visco‐acoustic dataset, and both migrated sections are then compared. The final images show that the proposed weighted L 1 ‐error method enhances the resolution and results in practically stable images. 相似文献
57.
Ijaz Ahmad Ahmad Zulfiqar Lisa Mona Mahmood Syed Amer Ali Asad Rehman Obaid Ur 《Water Resources》2019,46(6):894-909
Water Resources - Snow cover dynamics play an important role in the hydrological characteristics of Upper Indus Basin (UIB) of Pakistan in terms of seasonal accumulation and depletions. The current... 相似文献
58.
Thick forest cover and poor infrastructures are the major hindrances for detailed lithologic mapping in an inaccessible montane landscape. To overcome these limitations, we utilize a Landsat 5 TM image to map lithology using vegetation and drainage pattern as an indicator of underlying rock types in a heavily forested region of the Chittagong Hill Tracts area located in southeastern Bangladesh. We use supervised and unsupervised classifiers for a vegetation-based approach while on-screen digitization is used for drainage patterns-based mapping. Field observations were used for mapping lithology and evaluating accuracy. Overall, our results agree well with the current geologic map and improve it by providing a more spatially detailed distribution of the sandstone and shale. The performances of all approaches are good at the inner and outer flanks of anticlines located in the study area while the drainage pattern mapping performs best at the mid-flank area. 相似文献
59.
Communicating human health risks associated with disinfection by-products in drinking water supplies: a fuzzy-based approach 总被引:1,自引:2,他引:1
Rehan Sadiq Manuel J. Rodriguez Syed A. Imran Homayoun Najjaran 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):341-353
Chlorine used for the disinfection of water supplies can react with naturally occurring organic compounds and form potentially
harmful disinfection by-products (DBPs). A risk index for two regulated groups of chlorinated DBPs—trihalomethanes (THMs)
and haloacetic acids (HAAs), using fuzzy C-means (FCM) clustering algorithm and fuzzy rule-based modeling is proposed for risk communication. The proposed index evaluates
the cancer and non-cancer risks individually for THMs and HAAs using the FCM algorithm. Subsequently, two different fuzzy
rule-bases were used to evaluate the overall risk-index based on cancer and non-cancer risks. The overall risk-index will
provide drinking water utilities with an effective communication tool for communicating aggregated water quality compliance.
Simulated DBP occurrence data obtained from the City of Quebec, Canada, is used to demonstrate the application of this methodology. 相似文献
60.
Prerona Das Abhijit Mukherjee Syed Aaquib Hussain Md. Shahid Jamal Kousik Das Ashok Shaw Mrinal K. Layek Probal Sengupta 《水文研究》2021,35(1):e14002
Groundwater depletion has been an emerging crisis in recent years, especially in highly urbanized areas as a result of unregulated exploitation, thus leaving behind an insufficient volume of usable freshwater. Presently Ganges river basin, the sixth largest prolific fluvial system and sustaining a huge population in South Asia, is witnessed to face (i) aquifer vulnerability through surface waterborne pollutant and (ii) groundwater stress due to summer drying of river as a result of indiscriminate groundwater abstraction. The present study focuses on a detailed sub-hourly to seasonally varying interaction study and flux quantification between river Ganges and groundwater in the Indian subcontinent which is one of the first documentations done on a drying perennial river system that feeds an enormous population. Contributing parameters to the total discharge of a river at its middle course on both temporal and spatial scale is estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ18O and δ2H) and electrical conductivity data. Results from this model report groundwater discharge in river to be the highest in pre-monsoon, that is, 30%, whereas, during post-monsoon the contribution lowers to 25%; on the contrary, during peak monsoon, the flow direction reverses thus recharging the groundwater which is also justified using annual piezometric hydrographs of both river water and groundwater. River water-groundwater interaction also shows quantitative variability depending on river morphometry. The current study also provides insight on aquifer vulnerability as a result of pollutant mixing through interaction and plausible attempts towards groundwater management. The present study is one of the first in South Asian countries that provides temporally and spatially variable detailed quantification of baseflow and estimates contributing parameters to the river for a drying mega fluvial system. 相似文献