Welcome to this lecture on groundwater.
Almost 80% of all drinking water in Switzerland comes from groundwater,
either from groundwater water directly,
or from springs that are fed by the groundwater.
Globally 600 to 700 cubic kilometers of water are extracted each year.
This makes groundwater the most extracted raw material on Earth.
In Switzerland, the amount of groundwater extracted for
drinking water increased until the mid-1980s.
Since then it has decreased slightly due to water savings.
If we dig a hole in the ground,
at some point we reach the groundwater table.
Below the groundwater table,
all of the ports are filled with water.
Above the groundwater table,
some of the ports are filtered water,
other ports are filled with air.
Aquifers are material that not only store a lot of water,
but it also transmit water.
We do an experiment and we pour water
through different types of soils for example a clay soil,
a silt soil and a sand soil then we see that
the water flows very slowly through the clay and very quickly through the sand.
This means that sand is a good aquifer and clay is not.
The first person to study how the material of
aquifer affects groundwater flow was Henry Darcy.
He did experiments in the 1850s in order to understand
the water supply for the city of Dijon and the supply to its springs and fountains.
He did column experiments,
and in these column experiments he found what we now call Darcy's Law.
That is that the amount of flow shown here as Q
is dependent on the cross-sectional area of the column, A,
multiplied by the difference in height at the beginning of the column and
the end of the column divided by the length of the column.
This difference in the height at the beginning of the column and the end of the column,
divided by the length of the column is what we call the hydraulic gradient.
In addition, there is a proportionality constant.
This depends on the material.
We call this the hydraulic conductivity.
It describes how quickly water can move through the soil.
It's high for sands and very low for clay.
When we pump groundwater,
we can change the hydraulic gradient.
Initially the groundwater level is quite flat,
but then when we start pumping,
the groundwater level decreases and we create around the
well what we call a cone of depression; here gradient steeper.
We may also change the direction of flow.
Here we have a situation where water flows from the land to the river,
but then when we create a new well and start pumping from it,
we change the direction.
We now have water flowing from the river into our well.
In Switzerland, there are strict legal requirements around wells.
Each groundwater well it's protected by three different protection zones.
Protection zone one shown here in red protects the well it's usually fenced off.
Protection zone two is at least 100 meters long in the direction of flow.
Water stays in this protection zone usually for at least 10 days.
This is enough time to kill most microbial organisms.
Housing is not allowed in these protection zone.
In addition, there is protections zone three;
in this area no activities are allowed that may harm the groundwater.
Here we have a map of the protection zones for wells around Zurich.
We see in red the wells and the springs.
In blue, the different flow lines to watch these wells and springs.
In dark blue, protection zone one.
In light blue, protection two.
And in a very light color, protection zone three.
In this lecture we've talked about groundwater
and the importance of groundwater for drinking water in Switzerland.
In the next lectures we will talk about the different types of aquifers in Switzerland,
as well as how we measure groundwater levels.
We look forward to seeing you there.