摘要:

On the basis of the degree of mineralization, the groundwater of Apan-Tochac sub-basin may be considered as fresh (TDS < 500 ppm). However, chlorination is necessary to make it fit for human consumption. Major ion analyses of over 235 water samples reveal a striking relationship between hydrochemical evolution and the groundwater flow system. A high content of total dissolved solids, and low values of the Ca:Mg ratio are present in wells located on the plain (discharge zone), whereas opposite conditions are associated with wells located in higher regions (recharge zone). Statistical data analysis using the method of principal components allowed to differentiation of two hydrochemical families: (a) low mineralization corresponding to the recharge zone, and (b) high mineralization corresponding to the discharge zone. Waters of the Ca + Mg + HCO3, and Na + Mg + HCO3hydrochemical fades are present and the former is dominant. The water is slightly alkaline, having slight problems of salinity during the year owing mainly to Ca2+HCO3−and Na+Cl−salts. The hydrochemistry of the groundwater reflects the pattern of local groundwater flow for this sub-basin.

ISSN:0262-6667    

DOI:10.1080/02626669809492165

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two types of monthly water balance models at basin scale are used: PE models use precipitation and potential evapotranspiration (PET) as their observed input data, whereas P models need only precipitation. Calibration proceeds by comparing model runoff and observed runoff. Calibration is entirely automatic with the exclusion of subjective elements. All models differ only by their actual evapotranspiration equations. PE models from previous papers are generalized essentially by replacing the constant evapotranspiration parameter by a periodic one, thus increasing the number of parameters by two (a “parameter” is an unknown constant to be estimated, and which is a characteristic of the river basin to be described). P models use a periodic “driving force”, which is intended to represent periodicity of hydrological phenomena, normally originating in the (unavailable) PET time series. These eight PE models and three P models are then applied to 55 river basins in 10 countries with widely diverging climates and soil conditions. A marked improvement of model performance in about one third of the basins is due to the introduction of the above mentioned periodic functions. Even when PET data are available it is sometimes useful to consider P models. P models scarcely perform less well than PE models. An engineer, wanting to try out as few models as possible on a given river basin, can restrict his attention to the optimization of two or three models. The paper is an extension of a long effort towards monthly water balance models, and is believed to give a solution in most circumstances.

ISSN:0262-6667    

DOI:10.1080/02626669809492166

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The main contributors of high nitrate concentrations in the groundwater of the Vamsadhara River basin are the point sources associated with livestock barns while the seasonal variations in nitrate (NO3) concentrations are attributed to the prevailing hydrogeological conditions. The observed increase in nitrate under rising water level conditions, contradicting an expected decrease due to dilution by rainwater, is believed to be caused by the contribution of NO3from the clayey soil. The processes of sorption, retention and slow denitrification in clay are probably responsible for the contribution of nitrate to the groundwater in the post-monsoon season. The positive linear relationship between chloride and nitrate is in agreement with the similarities in behaviour of these ions in the clayey formations.

ISSN:0262-6667    

DOI:10.1080/02626669809492167

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Deployment of sediment traps over a 12-month period has enabled investigation of the lateral variability of overbank deposition rates and particle size composition of deposited sediment across a frequently inundated flood plain section of the River Culm, southeast Devon, UK. Although a general exponential decrease in deposition rate and grain size with distance from the channel occurs, significant deviations from these trends are associated with the microtopography of the flood plain and secondary flow routes and, in particular, with ditches. The coarsest material and the greatest variability in deposition rates occur within a few metres of the channel. Similar trends are evident for mean particle size, percentage silt and clay, arithmetic sorting and skewness. These parameters also display substantial variation at the distal margins of the flood plain due to the presence of drainage ditches.

ISSN:0262-6667    

DOI:10.1080/02626669809492168

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Discharge data available for assessing surface water resources in the country are limited. A regional method is derived for assessing surface water resources with the limited data sets for two basin systems in the country. The regression equations derived have a better fit in the more humid part of the country than the less humid part. The results of the assessment are presented for water resources planning and development.

ISSN:0262-6667    

DOI:10.1080/02626669809492169

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Cette étude présente l'application du modèle déterministe de simulations hydrologiques CEQUEAU pour la reconstitution des débits moyens journaliers et mensuels de quatre stations hydrométriques du bassin versant de l'oued Miliane (Tunisie) ainsi que les niveaux moyens journaliers dans le barrage Bir Mcherga. Le modèle a été calibré avec les données de trois années d'observation (de 1972/73 à 1974/75). Durant cette période, les débits moyens journaliers sont reconstitués avec des coefficients de Nash variant de 0.88 à 0,97 et des écarts relatifs qui varient entre −2.3% et −4.7%. Pour les débits de pointe les biais sont plus élevés. L'analyse des séries résiduelles a montré que les résidus sont homogènes et temporellement dépendants mais les résidus des différents stations sont indépendants. Durant la période de validation (de 1975/76 à 1976/77), les coefficients de corrélation et de Nash se sont dégradés pour les deux stations restées en fonctionnement (0.71 et 0.89). Les biais obtenus varient entre −3.7% et +5.5%.

ISSN:0262-6667    

DOI:10.1080/02626669809492170

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In semiarid regions, periods of one to several consecutive months of scarcity of precipitation or low flow rates in rivers and streams frequently occur. In these regions, scarce precipitation considerably affects grazing activities on rangelands, irrigation agriculture, and flora and fauna of surface stream environments. This paper is concerned with estimating probabilities of occurrence for such events and associated risks by using statistical information provided by monthly precipitation and streamflow series. Conventional return period and risk concepts as customarily used in hydrology are applied, and events of interest such as meteorological droughts are considered by using monthly precipitation as a time-related series of supply, thereafter addressing hydrological droughts in terms of streamflow supply. For these two kinds of events, periodic situations of time-independent phenomena are considered for the case of precipitation, with time-dependent phenomena considered for streamflows. The method is applied to the semiarid portion of Chile to calculate probabilities of occurrence of specific numbers of consecutive months with no significant precipitation, or flow rates insufficient to meet stream ecological needs.

ISSN:0262-6667    

DOI:10.1080/02626669809492171

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Long-term rainfall and streamflow records for the Moor House National Nature Reserve and sites close by in the northern Pennines are analysed in order to place observations made since 1991 as part of the UK Environmental Change Network (ECN) in context. Rainfall records for the Durham Observatory since 1880 and streamflow for the River Wear at Durham since 1958 provide a regional setting within which the upland records can be assessed. Since 1991, the most notable event has been the drought of the 1995 summer which followed one of the wettest winters on record. A strong tendency is noted for increased hydrological variability recently, with the contrast between winter and summer becoming more extreme, both for rainfall and runoff.

ISSN:0262-6667    

DOI:10.1080/02626669809492172

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents new calculations of Lake Victoria's water balance. Evaporation is estimated using both the Penman formula and the energy balance approach, and sensitivity studies are performed to determine the influence of input data on the estimates. Rainfall over the lake is estimated from catchment rainfall using a relationship between the two that was derived using satellite data. The results, using the reference period 1956–1978, indicate that mean annual rainfall over the lake is 1791 mm, compared to mean annual evaporation of 1551 mm. When compared with lake level changes, tributary inflow, and discharge during this period, there is a resultant imbalance of 19 mm. Adding this amount to the calculated evaporation, we are able to reproduce with great accuracy the lake level changes during the period 1956–1978 utilizing precipitation estimates of this study plus measured inflow and discharge. Sensitivity studies show that the discrepancy in the balance of 19 mm is considerably smaller than the error in evaporation calculations that can be introduced by uncertainties in the input data. Of particular concern is cloudiness. The diurnal cycle of cloudiness is quite different over the lake than at shoreline stations and the total cloud cover over the lake is probably lower than at these stations. A change from 50% cloudiness to 30% can increase evaporation by about 30%. Thus, this study underscores the need for adequate cloud data, sufficient to resolve the diurnal cycle, as well as direct estimates of lake rainfall in assessing the lake's water balance.

ISSN:0262-6667    

DOI:10.1080/02626669809492173

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669809492174

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor