摘要:

The neutron probe method forin situmeasurement of field capacity was applied to ferrallitic soils on the Kossou Lakeside slope (Ivory coast). For better utilisation of the natural resources, a study was conducted to determine the influence of the lake on the availability of soil water to plants along the lakeside slope. Two methods, one gravimetric and the other neutronic, were used to evaluate soil water content and its variation with time. Five access tubes were placed along the slope and were monitored during the study. The infiltration rate determined at three of the measuring sites was higher in the top soil layers than in the deeper soil layers. Drainage and redistribution data show a juxtaposition of two infiltration kinetics, the first being exponential and the second linear. The extrapolation of the second kinetic (slow) to the start of drainage gave, for the first 600 mm of soil, field capacities of 154, 184 and 163 mm for sites T1, T3 and T5 respectively. These differences were specifically related to the porosity of the sites under study. An analysis of the soil water profiles showed that the soil moisture near the lake was always higher than the permanent wilting point. The influence of the lake was not apparent during the long rainy season because of the steady decline of the water table. The water availability then depended upon the rainfall distribution and the specific characteristics of each of the sites, especially soil texture and structure. A linear relationship was found between soil moisture estimated by the neutronic and the gravimetric methods with correlation coefficients ranging from 0.80 to 0.96. The data also showed that the neutron probe method did not systematically underestimate the soil moisture of the top layers. This response seemed to be associated with the fraction of coarse sand. As soil moisture increased, data from the neutron probe method converged toward the gravimetric data regardless of the site.

ISSN:0262-6667    

DOI:10.1080/02626669409492727

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Helium has several characteristics which make it attractive for use as a tracer in hydrological studies. These include its inert nature, relatively high solubility in water (~ 1 %), low molecular diffusion in water, ready availability in commercial quantities, nontoxic nature, and low background atmospheric concentration. The use of helium as a tracer of water movement has become possible through the development of an instrument which takes advantage of the fact that at room temperature helium diffuses through a quartz glass membrane at a rate of three to four orders of magnitude greater than any other gas. This paper describes: (i) a set of experiments undertaken to compare breakthrough of helium with common salt (NaCl) tracer through laboratory sand columns; (ii) a set of groundwater tracing experiments conducted in a basaltic aquifer in Central O'ahur, Hawaii and (iii) two laboratory experiments undertaken to evaluate the applicability of helium instrumentation for the tracing of submerged plumes in open water conditions. The test results demonstrate that helium behaves as a conservative tracer during saturated flow through porous media. During unsaturated flow, exchange of helium with air entrained in the porous media reduces its usefulness. During submerged flow of a labelled plume, helium behaves like fluorescein in a relatively tranquil laboratory tank environment for hours but is gradually lost through the air-water interface, thus limiting the usefulness of helium in shallow plume tracing studies to short duration experiments.

ISSN:0262-6667    

DOI:10.1080/02626669409492728

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

For about two decades remote sensing (RS) data in the form of multi-spectral air photography, ground based weather radar as well as geostationary and polar orbiting satellite data have been available for use in hydrology. It is the intention of this paper to advocate the use of RS data in the field of hydrological modelling. It is shown that the main field of application of RS data in hydrological modelling lies in the meso-scale. The potential of RS in the framework of GIS is shown along with three examples. The first example shows the use of RS data for rainfall/runoff modelling in the lower meso-scale. A model was developed which used the high spatial resolution of Landsat polar orbiting satellites (30m × 30 m) for model parameter estimation. The second example shows the use of geostationary satellite data for the computation of long time series of monthly runoff values in the upper meso-scale. It was applied in West Africa for the purpose of water resources planning. In the third example, a water balance model in the upper meso-scale is presented which computes daily values for all the variables in the water balance equation along with an example of the model's application in the international Mosel River basin. Here also the detection of land use changes by multi-temporal satellite imagery and their impact on hydrological parameters is discussed. In this example, emphasis is put on the combination of RS data with other information, such as digital elevation models or digitized maps, all within the framework of GIS. In conclusion, not only the potential but also the limitations of the use of RS in hydrological modelling are discussed.

ISSN:0262-6667    

DOI:10.1080/02626669409492729

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A study was conducted to develop a computer model to simulate the spatial variability of field-measured saturated hydraulic conductivity (Ks) using Fourier series analysis.Ksmeasurements, bothin situand in the laboratory, were made at 150 and 300 mm depths at regular intervals of 4.6 m on two perpendicular transects crossing each other at the centre of a no-till field. Three Fourier series models, with a finite number of harmonics, were developed to simulate the variability inKsvalues. These models included the regular Fourier series model, the half-range Fourier series model with only cosine terms, and the half-range Fourier series model with only sine terms. Also, a test of significance was conducted with the first five and eight terms of the Fourier series models. This test indicated that with only five or eight terms model performances were not significantly different from each other at the 0.05 level. The overall results of this study indicated that spatial variability in theKsmeasurements made with both techniques, field and laboratory, can be represented successfully with half-range Fourier series with only cosine terms. Statistical analysis of predicted and observedKsvalues indicated that the two sets were not significantly different from each other at the 0.05 level.

ISSN:0262-6667    

DOI:10.1080/02626669409492730

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Two problems are addressed which arise when using monthly water balance models as an aid to making decisions in water resources engineering: what is the influence of data errors on model performance, and what is the data length required in order to obtain reliable models? Two previously defined types of models are used: in PE type models the input series are precipitation and potential evapotranspiration; in P type models the only input is precipitation. The main conclusions are: (1) random errors in precipitation data, when great enough, affect model performance significantly; (2) systematic errors in precipitation data are less important for the estimation of river flow; and (3) a data length of 10 years is necessary and sufficient for a reliable calibration of monthly water balance models of humid basins.

ISSN:0262-6667    

DOI:10.1080/02626669409492731

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492732

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492733

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492734

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492735

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492726

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor