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451.
452.
Pervaiz Sikandar Allah Bakhsh Muhammad Arshad Tariq Rana 《Environmental Earth Sciences》2010,60(5):1113-1129
A geoelectrical resistivity survey using vertical electrical sounding (VES) was conducted at Chaj Doab (land between rivers
Jhelum and Chenab, Pakistan) and Rachna Doab (land between rivers Chenab and Ravi, Pakistan), with the objective of investigating
groundwater conditions. A total of 90 sites were selected with 43 sites in Chaj and 47 sites in Rachna Doabs. The resistivity
meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the VES data by employing a Schlumberger electrode configuration,
with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field
data were interpreted using the Interpex IX1D computer software and the resistivity versus depth models for each location
was estimated. The outputs of subsurface layers with resistivities and thickness presented in contour maps and 3-D views by
using SURFER software were created. A total of 102 groundwater samples from nearby hydrowells at different depths were collected
to develop a correlation between the aquifer resistivity of VES and the electrical conductivity (EC) of the groundwater and
to confirm the resulted geophysical resistivity models. From the correlation developed, it was observed that the groundwater
salinity in the aquifer may be considered low and so safe for irrigation if resistivity >45 Ω m, and marginally fit for irrigation
having resistivity between 25 and 45 Ω m. The study area has resistivities from 3.9 to 2,222 Ω m at the top of the unsaturated
layer, between 1.21 and 171 Ω m, in the shallow aquifers, and 0.14–152 Ω m in the deep aquifers of the study area. The results
indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers. 相似文献
453.
Water Resources - Hydrological runoff prediction in a reliable and precise manner contributes significantly to the optimal management of hydropower resources. Considering the importance of runoff... 相似文献
454.
Stephan Schulz Rike Becker Juan Carlos Richard-Cerda Muhammad Usman Tim aus der Beek Ralf Merz Christoph Schüth 《水文研究》2021,35(3):e14077
Information on water balance components such as evapotranspiration and groundwater recharge are crucial for water management. Due to differences in physical conditions, but also due to limited budgets, there is not one universal best practice, but a wide range of different methods with specific advantages and disadvantages. In this study, we propose an approach to quantify actual evapotranspiration, groundwater recharge and water inflow, i.e. precipitation and irrigation, that considers the specific conditions of irrigated agriculture in warm, arid environments. This approach does not require direct measurements of precipitation or irrigation quantities and is therefore suitable for sites with an uncertain data basis. For this purpose, we combine soil moisture and energy balance monitoring, remote sensing data analysis and numerical modelling using Hydrus. Energy balance data and routine weather data serve to estimate ET0. Surface reflectance data from satellite images (Sentinel-2) are used to derive leaf area indices, which help to partition ET0 into energy limited evaporation and transpiration. Subsequently, first approximations of water inflow are derived based on observed soil moisture changes. These inflow estimates are used in a series of forward simulations that produce initial estimates of drainage and ETact, which in turn help improve the estimate of water inflow. Finally, the improved inflow estimates are incorporated into the model and then a parameter optimization is performed using the observed soil moisture as the reference figure. Forward simulations with calibrated soil parameters result in final estimates for ETact and groundwater recharge. The presented method is applied to an agricultural test site with a crop rotation of cotton and wheat in Punjab, Pakistan. The final model results, with an RMSE of 2.2% in volumetric water content, suggest a cumulative ETact and groundwater recharge of 769 and 297 mm over a period of 281 days, respectively. The total estimated water inflow accounts for 946 mm, of which 77% originates from irrigation. 相似文献
455.
A new Local Ocean Tide Model, has been produced for the Exclusive Economic Zone (EEZ) of Malaysia, which incorporates some of the latest TOPEX/POSEIDON data for the years 1992 to 1998. Local tide gauge data are used as a comparison, along with another leading Global Ocean Tide Model, Ori96. The leading diurnal and semidiurnal constituents M2, S2, N2, K1, O1, P1 and Q1 are reproduced using TOPEX/POSEIDON Sea Surface Heights (SSH) in a response analysis type least squares derivation following Munk and Cartwright (1966). 相似文献
456.
Population pressure, agricultural intensification and changes in rural systems in Bangladesh 总被引:1,自引:0,他引:1
Abu Muhammad Shajaat Ali 《Geoforum》2007,38(4):720-738
Sustainable agricultural growth is the key to rural system changes that include changes in rural bio-physical environment, economic infrastructure and social conditions. The present study has examined the temporal changes in 18 selected indicators of rural systems in Bangladesh during the period 1975-2000, and explored the influences of demographic, market forces, environmental, institutional and technological factors inducing and mediating such changes. An analysis of 64 district level published census data showed significant increase in agricultural intensity, cropping patterns, land productivity and farm income; decline in labor and technological productivities; and major improvement in rural housing, economic and social conditions during this period. Spatially, major agricultural growth and rural development were observed in districts with high population density, less constrained environments, and better access to markets, irrigation canals, and capital loans. 相似文献
457.
Muhammad Khalifa Nadir Ahmed Elagib Bashir Mohammed Ahmed Lars Ribbe Karl Schneider 《水文科学杂志》2020,65(Z3):153-168
ABSTRACTUnderstanding the human–water–food–climate nexus is central to achieving sustainable intensification (SI) in agriculture. This research uses a socio-hydrological approach to understand the underpinning for implementing SI in the Gezira Irrigation Scheme, Sudan, by integrating vegetation indices derived from remote sensing, ancillary, gridded soil and precipitation data, supplemented by interviews with 393 farmers. The productivity gap was estimated as the difference between the potential and actual productivities. Based upon data on farmers’ socio-economic status and field practices, a regression tree model was built to determine the factors that control the sorghum yield. The model revealed that the financial status of farmers and access to water are the most influential factors on sorghum yield. A conceptual framework that elucidates SI and its bi-directional feedback to the environment, society and the economy is proposed. Implementing SI in the scheme has implications on water and food security in Sudan and beyond its borders. 相似文献
458.
Karez is an indigenous method of irrigation in which groundwater is tapped by a tunnel. After running for some distance the tunnel comes out in the open and the water is conducted to the command area. Karez irrigation is practised in 22 countries from China to Chile including Pakistan. In Pakistan it is confined to the province of Balochistan which has a tribal society.Karez is an old and stable irrigation system of Pakistan. It is a community enterprise managed by tribal tradition and run by social control. Spacing of the karez, their types, life, length, discharge, land development and allocation, water distribution and management are important aspects of karez irrigation which have been discussed in this paper. Differences in karez maintenance and management produced by differences in tradition and customs of various tribes inhabiting Balochistan are brought out. Furthermore recent changes in Karez irrigation caused by changes in the socio-economic conditions are also analysed. 相似文献
459.
The stable hydrogen isotopic compositions (δD) of selected aliphatic hydrocarbons (n-alkanes and isoprenoids) in eight crude oils of similar source and thermal maturity from the Upper Indus Basin (Pakistan) were measured. The oils are derived from a source rock deposited in a shallow marine environment. The low level of biodegradation under natural reservoir conditions was established on the basis of biomarker and aromatic hydrocarbon distributions. A plot of pristane/n-C17 alkane (Pr/n-C17) and/or phytane/n-C18 alkane (Ph/n-C18) ratios against American Petroleum Institute (API) gravity shows an inverse correlation. High Pr/n-C17 and Ph/n-C18 values and low API gravity values in some of the oils are consistent with relatively low levels of biodegradation. For the same oils, δD values for the n-alkanes relative to the isoprenoids are enriched in deuterium (D). The data are consistent with the removal of D-depleted low molecular weight (LMW) n-alkanes (C14–C22) from the oils. The δD values of isoprenoids do not change with progressive biodegradation and are similar for all the samples. The average D enrichment for n-alkanes with respect to the isoprenoids is found to be as much as 35‰ for the most biodegraded sample. For example, the moderately biodegraded oils show an unresolved complex mixture (UCM), loss of LMW n-alkanes (<C15) and moderate changes in the alkyl naphthalene distributions. The relative susceptibility of alkyl naphthalenes at low levels of biodegradation is discussed. The alkyl naphthalene biodegradation ratios were determined to assess the effect of biodegradation. The dimethyl, trimethyl and tetramethyl naphthalene biodegradation ratios show significant differences with increasing extent of biodegradation. 相似文献
460.
Muhammad Asif Robert Alexander Tahira Fazeelat Kieran Pierce 《Organic Geochemistry》2009,40(8):895-901
Sediment extracts and crude oils have been shown to contain methyl substituted biphenyls and dibenzothiophenes, with isomer distributions suggesting a geochemical relationship between the two compound classes. Laboratory simulation experiments have shown that carbon catalyses the reaction between surface adsorbed sulfur and biphenyl to form dibenzothiophene. Similarly, the methyl substituted biphenyls reacted to yield corresponding methyl dibenzothiophenes. We suggest that the widespread distribution of dibenzothiophene and alkylated dibenzothiophenes in sediments and crude oils is the result of a catalytic reaction of biphenyl ring systems and surface-adsorbed sulfur on the surface of carbonaceous material. 相似文献