摘要:

An analytical study of major cations and anions of the glacier fed Alaknanda River and its tributaries has been carried out to assess the weathering and geochemical processes in the high altitude river basin. The Alaknanda and its tributaries were sampled during pre-monsoon (June 1992) and post-monsoon (October 1992) season for the present hydrogeochemical study. Calcium and magnesium are the major cations, accounting for 85% of the total cations. Among the anions, bicarbonate is the most dominant (78%) with minor contribution from sulphate (19%) and chloride (3%). The average (Ca+Mg)/HCO3equivalent ratio of 1.2, a relatively high contribution of (Ca+Mg) to the total cations (TZ+) and high (Ca+Mg)/(Na+K) ratio indicate that the carbonate weathering could be the primary source of the major ions to these waters. Wide seasonal and spatial variations are observed in the total dissolved solids (TDS) and total suspended matter (TSM) concentration in the Alaknanda river basin. The chemical denudation rate of Alaknanda is 133 t km−2year−1, nearly double that of the Ganga river basin and three times the world average. The sediment erosion rate of the basin is 356 t km−2year−1, double that of the world physical denudation rate. The high rates of denudation are attributed to high relief, intense monsoon rainfall, landslides and glacial erosion in the Himalaya.

ISSN:0262-6667    

DOI:10.1080/02626669809492181

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Ganges, Brahmaputra and Meghna (GBM) river basins occupy about 1.75 x 106km2of the Himalayan region. More than half a billion people in Nepal, India, Bhutan and Bangladesh are directly or indirectly dependent on the water resources of the GBM rivers. These river basins are characterized by diversified climatic patterns. Analyses of trends and persistence in precipitation over these river basins are necessary for sound water resources planning. Time series of annual precipitation for each of the 16 meteorological subdivisions covering the three river basins were examined for trends using the Mann-Kendall rank statistic, Student's t-test and regression analysis, and for persistence using first order autocorrelation analysis. Results indicate that precipitation in the Ganges basin is by-and-large stable. Precipitation in one subdivision in the Brahmaputra bassin shows a decreasing trend and another shows an increasing trend. One of the three subdivisions in the Meghna basin shows a decreasing trend while another shows an increasing trend. Markovian persistence is not present in the precipitation series in the Ganges basin but it is present in two common subdivisions in the Brahmaputra and Meghna basins.

ISSN:0262-6667    

DOI:10.1080/02626669809492182

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Simple analytical calculations of groundwater flow around wells usually employ the Thiem well formula for steady calculations and the Theis formula for transient calculations. The superposition principle can be used with both formulas and even for combinations of both formulas. It is generally assumed that flow converges to a steady state when the boundary conditions remain constant for a long time. However, the heads in Theis's formula do not converge to steady heads for large times, although the (specific) discharges do converge to those of the steady Thiem well. This undesirable behaviour of the Theis solution can be compensated by means of a new function: the ring well. The ring well is a combination of Theis's well and Glover's well (solution for a transient well in a circular island). A second function, uniform recharge during a time interval, is needed to assure that the heads converge at a specific level. The functions also allow an analytical transition with Theis wells between any two steady states consisting of Thiem wells. The functions do not have a wide range of practical applications but they increase insight into the relationship between the two main functions in groundwater flow.

ISSN:0262-6667    

DOI:10.1080/02626669809492183

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The snow and rain in the Himalayas are the main sources of supply for the rivers in the Indo-Gangetic plains. Irrigation, hydropower generation, and water supply are very much dependent on the availability of water in the Himalaya rivers. Mathematical models serve as important aids for the estimation of water availability in rivers. In the present study the SLURP watershed model is applied to a rainfed area of the Satluj catchment located in the western Himalayas, India. The SLURP model developed at NHRI, Canada, is a distributed conceptual model which simulates the behaviour of a watershed by carrying out vertical water balances for each element of a matrix of landcovers and subareas of a watershed and then routing the resulting runoff between subareas. The ILWIS geographic information system was used to prepare the input data required for SLURP and land use data were obtained from the IRS satellite LISS II visible and near infrared sensors. The simulated flows at the Bhakhra Dam outlet of the Satluj catchment were computed and found to compare well with the observed flows.

ISSN:0262-6667    

DOI:10.1080/02626669809492184

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Control of summer river temperature is needed for maintaining water temperature standards to protect aquatic biota and wildlife habitats. Given the fact that instream discharge, among meteorological and hydrological factors, may be the only one that can be practically managed, is it feasible to moderate summer river temperature through reservoir and streamflow regulations? An analysis is conducted to quantify the effects of the magnitude of instream flow on summer river temperature with weather as a reference. Relationships between water temperature and river discharge or flow depth are developed using a simplified model and adopting the concept of equilibrium temperature and bulk surface heat exchange coefficient. The relationships are validated against continuous 5-year field measurements at the central Platte River, Nebraska, USA. It was found that the variation of daily maximum water temperature with flow was stronger than that of daily mean. A critical discharge was obtained, which divides dramatic drop and slow variation in river temperature values. The existence of the critical discharge makes it possible to reduce or minimize the occurrence of daily maximum water temperature exceeding a standard at a river reach by increasing discharge to an achievable level. This study advances understanding of impacts of instream flow on summer river temperature and provides information useful in proper planning and design of reservoir operations and streamflow management.

ISSN:0262-6667    

DOI:10.1080/02626669809492185

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

La pluie en zone soudano-sahélienne se caractérise par une variabilité spatio-temporelle qui doit être prise en compte pour l'estimation de la pluie spatiale. Il est proposé une approche qui tente d'intégrer cette caractéristique. Le mode de calcul s'appuie dans une première phase sur une discrétisation spatiale du domaine en mailles carrées emboîtées de tailles variables pour délimiter les aires d'influence. Ensuite, la pluie spatiale d'un poste s'estime en fonction des enregistrements ponctuels au niveau dudit poste et de ceux des stations voisines, suivant des critères basés sur les conditions climatiques de la région. Les résultats d'un exemple d'application au bassin versant du Massili (Burkina Faso) sont présentés.

ISSN:0262-6667    

DOI:10.1080/02626669809492186

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

L'Afrique de l'Ouest non sahélienne a connu autour des années 1970 une variabilité du régime pluviométrique. Pour étudier cette variabilité, des séries chronologiques de totaux précipités, de durées des saisons des pluies, de hauteurs de pluie en saison sèche de nombres de jours de pluie ont été constitués au pas de temps annuel entre 1950 et 1989, soumises à plusieurs tests statistiques de détection de rupture. Pour caractériser la variation spatio-temporelle du phénomène étudié, les résultats des tests ont été traités par des analyses des correspondances multiples. II ressort qu'une modification du régime pluviométrique s'est manifestée dès 1966 essentiellement au Sénégal et en Guinée Bissau, puis en Guinée Conakry, au Mali, au Burkina Faso et au nord du Bénin. La façon dont la Côte d'Ivoire, le Togo et le sud du Bénin ont été atteints s'est révélée beaucoup plus variable. Le Cameroun et la République Centrafricaine n'ont été que très faiblement ou pas du tout touchés.

ISSN:0262-6667    

DOI:10.1080/02626669809492187

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Dans les zones arides et semi-arides d'Afrique de l'Ouest et Centrale, la notion de précarité de la ressource en eau n'est pas récente. Cependant, la sécheresse qui affecte les régions tropicales africaines depuis les deux dernières décennies présente tout à la fois une sévérité, une persistance et une extension remarquables. Les séries pluviométriques annuelles enregistrées sur de longues durées sur un ensemble de stations couvrant l'Afrique de l'Ouest et Centrale non sahélienne (du Sénégal à la Centrafrique) ont permis d'étudier l'évolution spatio-temporelle de la pluviométrie dans cette région. Les résultats montrent l'alternance de périodes sèches et humides depuis le début du vingtième siècle. La sécheresse actuelle n'a pas connu d'équivalent, ni en durée, ni en intensité, sur l'ensemble de la période étudiée. Une étude statistique, confirmée par des représentations cartographiques de ces différentes périodes met cependant en évidence le caractère fortement hétérogène du phénomène dans l'espace.

ISSN:0262-6667    

DOI:10.1080/02626669809492188

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The use of remote sensing information in operational hydrology is relatively limited, but specific examples can be cited for determining precipitation, soil moisture, groundwater, snow, surface water and basin characteristics. The application of remote sensing in hydrology can be termed operational if at least one of two conditions are met: (a) the application produces an output on a regular basis, or (b) the remote sensing data are used regularly on a continuing basis as part of a procedure to solve a problem or make decisions. When surveying the various operational applications, simple approaches and simple remote sensing data sets are the most successful. In the data-sparse developing countries, many operational remote sensing approaches exist (out of necessity) that may not be needed in developed countries because of existing data networks. To increase the use of remote sensing in operational hydrology in developed countries, pilot projects need to be increased and information services must be improved. Increased utilization of GIS to combine remote sensing with other information will promote new products and applications. End user training must be improved by focusing on satellite data processing and manipulation. In developing countries the same improvements are needed plus some more basic ones. There is a need for international monetary assistance to establish long-term remote sensing data, improved database systems and image processing capabilities. There is also the need to set up innovative regional training centres throughout the developing world.

ISSN:0262-6667    

DOI:10.1080/02626669809492189

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669809492190

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor