| 1. |
- Haridy, SA, et al.
(författare)
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Estimation of LNAPL saturation in fine sand using time-domain reflectometry
- 2004
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 49:6, s. 987-1000
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Tidskriftsartikel (refereegranskat)abstract
- Recently, substantial progress has been made in detection and observation of non-aqueous phase liquids (NAPLs) in the subsurface using different experimental techniques. However, there is still a lack of appropriate direct methods to measure the saturation of NAPL theta(NAPL)). This paper provides a guide for estimating theta(NAPL) and water content (theta(a)) in unsaturated and saturated sand based on direct measurements of soil dielectric constant (K-a) and electrical conductivity (sigma(a)) using time domain reflectometry (TDR). The results show that the previously used dielectric mixing model fails to predict, theta(NAPL) in the case of a four-phase system. A new methodology is suggested and exemplified by showing that the measured K-a gives accurate estimation of theta(NAPL) for a three-phase system while in a four-phase system, both sigma(a) and K-a need to be measured. The results show that using the suggested methodology, accurate predictions of theta(w) (R-2 = 0.9998) and theta(NAPL) lower than 0.20 m(3) m(-3) (average R-2 = 0.9756) are possible.
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| 2. |
- Persson, Magnus, et al.
(författare)
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Solute transport and water content measurements in clay soils using time domain reflectometry
- 2000
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 45:6, s. 833-847
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Tidskriftsartikel (refereegranskat)abstract
- Clayey and saline soils have been shown to be problematic for time domain reflectometry (TDR) measurements. This study presents some of these problems and discusses solutions to them. Thirteen solute transport experiments were carried out in three undisturbed soil columns of swelling clay soil from Tunisia, labelled S1, S2, and S3 respectively. The columns were collected at three different physiographical regions within a catchment. Water fluxes ranged from 1.2 to 7.2 cm day(-1). The large solute transport heterogeneity and large tailing indicated that preferential flow was most pronounced in SI. The preferential flow took place in voids between structural elements and in wormholes. In S3, preferential flow was also evident, but not to the same extent as in S1. In S2, the solute transport was more uniform with little preferential flow. The heterogeneity of the solute transport increased with the water flux in S1 and to a smaller extent in S3, whereas it remained constant in S2. In a previous dye experiment in the field, preferential flow in cracks was observed at those sites where SI and S3 were collected. In the column experiments, preferential flow in these cracks was less due to the higher initial water content compared to the dye experiments, indicating that the desiccation cracks were closed by the swelling clay.
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| 3. |
- Persson, Magnus, et al.
(författare)
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Utilisation de réseaux de neurones pour l'étalonnage de mesures par réflectométrie en domaine temporel
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:3, s. 389-398
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Tidskriftsartikel (refereegranskat)abstract
- Time-domain reflectometry (TDR) is an electromagnetic technique for measurements of water and solute transport in soils. The relationship between the TDR-measured dielectric constant (Ka) and bulk soil electrical conductivity ([sgrave]a) to water content (θW) and solute concentration is difficult to describe physically due to the complex dielectric response of wet soil. This has led to the development of mostly empirical calibration models. In the present study, artificial neural networks (ANNs) are utilized for calculations of θw and soil solution electrical conductivity ([sgrave]w) from TDR-measured Ka and [sgrave]a in sand. The ANN model performance is compared to other existing models. The results show that the ANN performs consistently better than all other models, suggesting the suitability of ANNs for accurate TDR calibrations.
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| 4. |
- Singh, P, et al.
(författare)
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Effect of warmer climate on the depletion of snowcovered area in the Satluj basin in the western Himalayan region
- 2003
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 48:3, s. 413-425
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Tidskriftsartikel (refereegranskat)abstract
- The effect of warmer climate on the depletion of snow-covered area has been evaluated for the Satluj River basin located in the western Himalayan region in India. Snowmelt runoff contributes substantially to the annual streamflow of this river. In order to study the impact of three warming scenarios (T+1, T+2 and T+3degreesC), more than 160 new snow depletion curves were prepared for different elevation zones of the basin over a study period of nine years (1985/86-1990/91 and 1996/97-1998/99). For each zone, the relationship between the cumulative melt and snow-covered area was established and used to obtain the snow depletion curves under warmer climate. Projected snow depletion curves at the basin scale were derived by synthesizing the effect of warming for all zones. Warmer climatic conditions accelerate the melting of snow resulting in faster disappearance of seasonal snow cover from the basin. For the study basin, acceleration in depletion of snow-covered area is computed to be 20, 31 and 40 days for T+1, T+2 and T+3degreesC scenarios, respectively, by the end of the ablation season. The impact of warmer climate on accelerating the depletion of snow-covered area is found to be higher in the early and late parts of the ablation season. The consequences of faster disappearance of snow from the basin are discussed in terms of the hydrology and climatology of the basin.
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| 5. |
- Sivakumar, Bellie, et al.
(författare)
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Monthly runoff prediction using phase-space reconstruction
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:3, s. 377-387
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear prediction method, developed based on the ideas gained from deterministic chaos theory, is employed: (a) to predict monthly runoff; and (b) to detect the possible presence of chaos in runoff dynamics. The method first reconstructs the single-dimensional (or variable) runoff series in a multi-dimensional phase space to represent its dynamics, and then uses a local polynomial approach to make predictions. Monthly runoff series observed at the Coaracy Nunes/Araguari River basin in northern Brazil is studied. The predictions are found to be in close agreement with the observed runoff, with high correlation coefficient and coefficient of efficiency values, indicating the suitability of the nonlinear prediction method for predicting the runoff dynamics. The results also reveal the presence of low-dimensional chaos in the runoff dynamics, when an inverse approach is adopted for identification, as: (a) an optimal embedding dimension exists, and (b) the prediction accuracy decreases with an increase in prediction lead lime.
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| 6. |
- Sivakumar, B., et al.
(författare)
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Preuve de l’0existence de chaos dans le processus pluie-débit
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:1, s. 131-145
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Tidskriftsartikel (refereegranskat)abstract
- The transformation of rainfall into runoff is one of the most important processes in hydrology. In the past few decades, a wide variety of automated or computer-based approaches have been applied to model this process. However, many such approaches have an important limitation in that they treat the rainfall-runoff process as a realization of only a few parameters of linear relationships rather than the process as a whole. What is required, therefore, is an approach that can capture not only the overall appearance but also the intricate details of the nonlinear behaviour of the process. The purpose of this study is to investigate the possibility of understanding the dynamics of the rainfall-runoff process from a new perspective, as a chaotic process. The possible existence of chaotic behaviour in the rainfall-runoff process is studied by investigating the rainfall and runoff time series: (a) separately; and (b) jointly (using the runoff coefficient). Monthly rainfall and runoff observed over a period of 131 years (January 1807-December 1937) at the Göta River basin in the south of Sweden are analysed. The correlation dimension method is employed to identify the presence of chaos. The correlation dimensions obtained for the rainfall and runoff time series are 6.4 and 5.5, respectively. The finite dimensions obtained for the rainfall and runoff time series indicate the possible existence of chaos in these processes, implying that the joint rainfall-runoff process might also exhibit chaotic behaviour. The correlation dimension of about 7.8 obtained for the runoff coefficient also indicates the possible presence of chaos and supports the above results.
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| 7. |
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| 8. |
- Vassiljev, A, et al.
(författare)
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A dual-porosity model for nitrogen leaching from a watershed
- 2004
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 49:2, s. 313-322
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Tidskriftsartikel (refereegranskat)abstract
- The MASONW (MACRO + SOILN + Watershed) model describing nitrogen leaching in watersheds was developed and tested. The model is based on the MACRO and SOILN models. The dual-porosity model MACRO simulates water flow on the field scale. The SOILN model describes turnover and leaching of nitrogen. Two main features of a watershed have been added into these two models: (a) the existence of a river system, and (b) variable thickness of the aeration zone within a watershed. Good agreement between the output of the MASONW model and observed data for water discharge and nitrate concentrations were achieved in the Odense watershed (496 km2) in Denmark.
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| 9. |
- Wang, XP, et al.
(författare)
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Water balance change for a re-vegetated xerophyte shrub area
- 2004
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 49:2, s. 283-295
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Tidskriftsartikel (refereegranskat)abstract
- Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990-1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 rum or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that revegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/ groundwater needs of local populations.
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| 10. |
- Wilk, Julie, 1962-, et al.
(författare)
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Calibrating a rainfall-runoff model for a catchment with limited data
- 2002
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 47:1, s. 3-17
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Tidskriftsartikel (refereegranskat)abstract
- A rainfall-runoff model has been established to simulate streamflow in a regulated catchment in southern India, where data were limited in relation to the basin's complexity. Within the basin is a network of hydropower reservoirs and tunnels that complicate the relationships between observed and natural flows. The basin is affected by two monsoons that dominate in different areas and can only be quantified through a relatively sparse raingauge network. These characteristics combine to make it difficult to satisfactorily define the spatial distribution of rainfall inputs to the basin. After critically assessing the data that were found to be inconsistent and unrepresentative, various assumptions about the operation of the system were tested. Despite incomplete streamflow data and the complex hydropower system, the limiting factor affecting successful simulations of streamflow at the basin outlet was the uncertain representativeness of the calculated areal rainfall. The final outcome is a model, which despite shortcomings, is considered to be a useful water resources management tool that provides a sound basis for further studies.
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