摘要:

The occurrence of fingered preferential flow depends on both flow and porous media characteristics. The boundary condition of unsaturated infiltration has been investigated to assess whether it produces unstable wetting in homogeneous coarse sands. Laboratory tracer experiments were conducted in two coarse sand materials; for each sand material two initial conditions of air dry and field capacity were considered. Results indicate that the commonly occurring process of nonponding rainfall can provoke fingered preferential flow in homogeneous sandy soils. This phenomenon is very predominant in dry as compared to wet initial conditions. Models of water flow and solute transport in uniform coarse soils should incorporate the effects of such fingered flow phenomenon.

ISSN:0262-6667    

DOI:10.1080/02626669509491387

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper first presents a duration-dependent hypothesis regarding the parameters of the two component extreme value (TCEV) distribution and proposes a simple model to obtain the rainfall depth-duration relationship both at ungauged sites and at short record gauged sites in the Sicilian region. Then, by using the annual maximum peak flood and the annual maximum mean daily discharge recorded in Sicily, a TCEV hierarchical regional procedure is developed. An empirical estimation criterion which links the mean annual flood with the watershed area, and a modified rational formula in which a mean runoff coefficient is introduced, are proposed. Finally, two relationships are established for estimating the mean runoff coefficient, making use of the permeable watershed area and the wooded area.

ISSN:0262-6667    

DOI:10.1080/02626669509491388

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The hydrological behaviour of a representative basin in Central Anatolia, Turkey, was studied by isotopic evaluation of water elements. Samples taken from precipitation, groundwater, subsurface water from the unsaturated zone, and streamflow were analysed for oxygen-18, deuterium and tritium to study quantitative aspects of various components of the streamflow. Eight storm events were used to determine the sources of the contributions to the flood hydrographs.

ISSN:0262-6667    

DOI:10.1080/02626669509491389

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper discusses how lognormal, Gumbel and log-Pearson type 3 distributions were eliminated as candidates for modelling at-site annual maximum discharge series in Bangladesh. Among candidate distributions, the generalized extreme value distribution best represented the statistical characteristics of observed data. Comparisons of distributions were based upon the root mean square deviation in fit, the probability plot correlation coefficient andL-moment ratio diagrams. The last method assesses whether a candidate distribution is capable of simulating the site-to-site variation in statistical characteristics that is present in observed flood samples.

ISSN:0262-6667    

DOI:10.1080/02626669509491390

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A sensitivity analysis was performed on a sediment-phosphate transport model by determining the phosphate sorption characteristics of separated size fractions and prepared size distributions of fine-grained (< 64 μm) river sediment typically transported in two southern Ontario streams. The Langmuir equation was used to quantify phosphate release from the sediment. Results of the study indicated that Langmuir coefficients determined separately for individual grain size fractions can be used to model sediment-phosphate interactions. Under laboratory conditions, output from the model provided conservative estimates of phosphate release/uptake from grain size distributions of sediment in fluvial systems. The study provides phosphate release data for use in models that estimate sediment-P losses from watersheds.

ISSN:0262-6667    

DOI:10.1080/02626669509491391

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Monthly mean data collected for a 90 year period (1901–1990) have been used to study long term water temperature trends at 10 river sites in Austria. Significant increases in monthly mean values were evident over the study period for seven river stations, but the magnitude of the rise varied from 0.47 to 1.26°C and its pattern was not uniform between catchments. River temperature trends for individual months also ranged from increases of >2.5°C, through no significant change, to decreases of >1.0°C. Rises in water temperature during the twentieth century appear to reflect, at least in part, the increasing impact of human activity on Austrian rivers. Progressive regulation of main rivers, such as the Danube and Inn, has resulted in strong increases in mean water temperatures during the low flow period of autumn but not in the summer months when high flows generally occur. Different trends were evident for sites closer to glacial runoff sources, for catchments containing a large proportion of lakes, and for stations influenced by point source discharges and other local factors. Rising mean water temperatures at the end of the study period were related more to the occurrence of mild winters than to the incidence of particularly hot summers.

ISSN:0262-6667    

DOI:10.1080/02626669509491392

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Hadejia-Nguru Wetlands produce agricultural, fishing and fuelwood benefits of upto 1277 Naira ha−1(N1 = US$22, October 1994), over five times the productivity of formal irrigation schemes. The wetlands play a vital role in aquifer recharge. The key is the annual wet season flooding of over 2000 km2in the 1960s and around 1500 km2in the 1970s. A water balance model, utilizing monthly hydrological and meteorological data simulates flood extent and groundwater storage within the wetlands. The model was operated between 1964 and 1987 and was calibrated using observed flood extents ranging from 50 to 3265 km2. Subsequently elements were added for dams and irrigation schemes. Results indicate that full implementation of all the schemes constructed or planned would cause flooding to be less than 375 km2for 60% of the time and groundwater storage to fall by over 5500 106m3. It is possible to define an operating regime for the basin's hydraulic structures which could provide artificial floods and enable a distribution of water between formal irrigation, small scale irrigators, the wetlands and downstream users. This regime would provide assured flooding, of around 1000 km2each year, and a reduced loss of groundwater storage. Such a sustainable development scheme could offset decades of piecemeal development and bring a philosophy which emphasizes water use throughout the basin not just in irrigation in the upper reaches.

ISSN:0262-6667    

DOI:10.1080/02626669509491393

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491394

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491395

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491397

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor