| dc.description.abstract | The Koster Islands consists of two archipelago islands situated west of Strömstad, on the westcoast
of Sweden. A popular tourist destination, the islands’ population can rise to over 6 000
on a hot summer day, in contrast to the approximate 330 permanent residents. Water
resources on the islands are scarce, resulting in substandard groundwater quality and quantity
for the islands’ mainly private wells. The problems become particularly pronounced during
the summer season, where high temperatures and vegetative activity along with increased
population exerts extra pressure on the water supply. Due to the popularity of the destination,
demand is high to further exploit the islands, such as building new permanent residences,
holiday homes or extensions, which also leads to an increased interest in establishing new
private wells. Establishing a new private well on the Koster Islands requires a permit from the
municipality of Strömstad. The permit is issued by the Environmental and Construction
Department of the municipality, which is restrictive in issuing permits due to the sensitive
groundwater situation. The department finds the given directives on how these situations
should be handled are subpar and seeks suitable methods to determine the propriety of the
new well location in order to prevent the already established wells getting affected.
This thesis aims to research what accurate methods are available to determine the radius of
influence, i.e. the width of the cone of depression resulting in the groundwater after pumping,
based on data easily available in maps of soil types and depths. The thesis was conducted by
literary studies, an interview with a representative of the Strömstad municipality, and
applications of four found methods in a case study based on six modelled wells on the islands.
As the work progressed, it became apparent that all methods available in the literature
required some sort of field work to determine certain parameters, the hydraulic conductivity
in particular. Four methods were applied with selected parameters on six modelled wells. The
wells were modelled in two different soil types and three different soil depths. All of the
methods required the hydraulic conductivity to be known, but it was found that only an
approximate value can be used if no form of field testing has taken place. Instead, literature
provides a range of possible hydraulic conductivities for each soil type, which was used in the
calculations. The radius of influence was calculated for each well, making calculations
displaying the resulting variation in radius when the hydraulic conductivity is unknown. To
visualise the change in radius of influence which occurs when the water table drops naturally,
calculations were made based on two different groundwater levels. The results from the
modelling shows that there are no efficient methods of determining the radius of influence of
a dug well based on only information reacquired from literature and map data as the large
range of the hydraulic conductivity in turn leads to a large range in radius of influence. It is
thus of importance to perform an extensive hydrogeological survey to determine the locationdependent
parameters. The thesis also shows that there is a demand for clearer directives in
how handling of similar groundwater problems should be done and that further research is
necessary in order to find efficient alternatives to determine the radius of influence of a well. | sv |
