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Tracing water movement in the capillary fringe

Pojmark, Pontus LU (2011) VVR820 20102
Division of Water Resources Engineering
Abstract
The capillary fringe is a small zone on top of the ground water table where a low capillary tension keeps soil pores with water up to a certain level. Normally, calculations in hydrogeology consider that the capillary fringe only has vertical movement like the unsaturated zone in comparison to the ground water zone, which only has horizontal movement. Today’s usage of pollutants in the environment is a threat to a clean groundwater supply. It is therefore of interest to study the movement in the capillary fringe since the pollutants must pass it before contaminating the ground water.

This master thesis will describe experiments and observations of the movement of a dye tracer when it is passing the capillary fringe. The movement will be... (More)
The capillary fringe is a small zone on top of the ground water table where a low capillary tension keeps soil pores with water up to a certain level. Normally, calculations in hydrogeology consider that the capillary fringe only has vertical movement like the unsaturated zone in comparison to the ground water zone, which only has horizontal movement. Today’s usage of pollutants in the environment is a threat to a clean groundwater supply. It is therefore of interest to study the movement in the capillary fringe since the pollutants must pass it before contaminating the ground water.

This master thesis will describe experiments and observations of the movement of a dye tracer when it is passing the capillary fringe. The movement will be observed with both image analysis and resistivity measurements to determine the flow path of the dye. The aim of the study is to find if there is horizontal movement in the capillary fringe, and try to see how it is affected by different gradients of the saturated zone.

To be able to conduct experiments on the movement in the capillary fringe a special aquarium with access to control the water level and gradient of the saturated zone is used. A Brilliant Blue dye is inserted into the sand and the movement of the dye is observed with both resistivity- and image analysis to obtain the flow path. The images for the image analysis are converted using Adobe Photoshop into black and white images and put in a template created in Adobe Illustrator showing the levels of the saturated zone and the capillary fringe. The resistivity is measured before the experiment begins to obtain the background resistivity in the aquarium. The background resistivity value is removed from the resistivity values collected during the experiment, and the presented resistivity images show only the change of resistivity in the experiment at the investigated time.

The experiments are done with three different gradients on the saturated zone to see if there is a difference in the flow path dependent on the gradient. The investigated gradients are 0.48, 0.90 and 1.79 degrees.

The result of the image analysis shows a large horizontal movement in the capillary fringe, and the horizontal speed is increasing with a steeper gradient.

The resistivity images show a similar movement as the image analysis but results are only reliable in the beginning of the experiment when the dye tracer travels in the part where resistivity data is obtained. It is recommended that in future studies the resistivity model should be changed to one with more data measurements. (Less)
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author
Pojmark, Pontus LU
supervisor
organization
course
VVR820 20102
year
type
H3 - Professional qualifications (4 Years - )
subject
report number
11/5005
ISSN
1101-9824
language
English
id
2213116
date added to LUP
2011-11-23 09:20:28
date last changed
2011-11-23 09:33:40
@misc{2213116,
  abstract     = {The capillary fringe is a small zone on top of the ground water table where a low capillary tension keeps soil pores with water up to a certain level. Normally, calculations in hydrogeology consider that the capillary fringe only has vertical movement like the unsaturated zone in comparison to the ground water zone, which only has horizontal movement. Today’s usage of pollutants in the environment is a threat to a clean groundwater supply. It is therefore of interest to study the movement in the capillary fringe since the pollutants must pass it before contaminating the ground water.

This master thesis will describe experiments and observations of the movement of a dye tracer when it is passing the capillary fringe. The movement will be observed with both image analysis and resistivity measurements to determine the flow path of the dye. The aim of the study is to find if there is horizontal movement in the capillary fringe, and try to see how it is affected by different gradients of the saturated zone.

To be able to conduct experiments on the movement in the capillary fringe a special aquarium with access to control the water level and gradient of the saturated zone is used. A Brilliant Blue dye is inserted into the sand and the movement of the dye is observed with both resistivity- and image analysis to obtain the flow path. The images for the image analysis are converted using Adobe Photoshop into black and white images and put in a template created in Adobe Illustrator showing the levels of the saturated zone and the capillary fringe. The resistivity is measured before the experiment begins to obtain the background resistivity in the aquarium. The background resistivity value is removed from the resistivity values collected during the experiment, and the presented resistivity images show only the change of resistivity in the experiment at the investigated time.  

The experiments are done with three different gradients on the saturated zone to see if there is a difference in the flow path dependent on the gradient. The investigated gradients are 0.48, 0.90 and 1.79 degrees. 

The result of the image analysis shows a large horizontal movement in the capillary fringe, and the horizontal speed is increasing with a steeper gradient. 

The resistivity images show a similar movement as the image analysis but results are only reliable in the beginning of the experiment when the dye tracer travels in the part where resistivity data is obtained. It is recommended that in future studies the resistivity model should be changed to one with more data measurements.},
  author       = {Pojmark, Pontus},
  issn         = {1101-9824},
  language     = {eng},
  note         = {Student Paper},
  title        = {Tracing water movement in the capillary fringe},
  year         = {2011},
}