The mayor of hetzles, franz schmidtlein (), has called for water conservation in the local gazette. The reason: due to the drought, the local spring only produces 2.8 liters per second. Schmidtlein expects that even after abundant rainfall, it will take three to four weeks for the spring to return to its normal water supply.
He calls it the dogger spring. With this, he also mentioned the geological cause, why hetzles and also other places in a similar position in front of the jura are currently in water shortage, if they are not connected to a water extraction from other rock layers.
In this country, jura dogger is the name for the middle rock layer of the jura, from which mountains such as the walberla and the hetzles are built up.
The lowest is a shale called lias, then a layer of clay separates it from the dogger, a sandstone. On top sits the malm, the typical weibe lime.
He, too, is separated by an impermeable layer of clay.
The rock layers can be thought of as a cake made of different layers of dough with a separating layer of cream in between. The "dough layers are the deposits of primeval seas from different epochs of the earth’s history.
The "torte central europe was ripped open in the middle by the rhine rift valley and the strata became slanting with the edges. The rheingraben is the best known part of the rough european rift zone between marseille and lake mjosa in norway.
Exactly at the fub of such a stratification stage lies hetzles. At the "open" seepage water escapes from the edges of the separating layers; in geology, this is referred to as stratum springs.
Well known in our region are the hunger wells. These are periodic, often quite strong springs on high of the boundary layer under the white limestone and dolomite rock. They bubble up especially in spring after the snow melts, because limestone is a particularly water-permeable rock, just think of the fissures and hollows in french switzerland.
Water permeability was also the reason why, until a few decades ago, rainwater had to be collected in open cisterns called hullen in the villages on the alb plateau. Drinking water had to be carried up from springs in the valley or pumped up with simple mechanisms.
These springs at the fub of the dogger layer are on average considerably weaker, but flow more continuously. This is due to the soft, rather fine-pored sandstone. It takes much longer for the surface water to penetrate it. That is why schmidtlein spoke of the three to four weeks needed for the debris to recover, based on local experience.
On a hike from the village of hetzles to the mountain of the same name, one can easily follow the sequence of strata through the different vegetation. Starting point is the coal plate. The name comes from the dark rock, the liasschiefer, which emerges in a hollow way towards the mountain.
It is said to contain oil. Today, oil extraction is implemented in the USA by means of the so-called fracking.
The hiker recognizes the sandstone layer of the dogger especially in spring through the dense stand of barlauch in the sparse deciduous forest. One tracks, here the land is wet due to the stratified springs.
On this layer of rock, the people of hetzles planted oak trees, whose shoots they cut back every year to produce tanbark. The head oaks along the path are now a natural monument and the home of rare oats that live in the wood.
Shortly before you reach the edge of the hetzle, you have the feeling of walking through a pile of gravel. It does not carry; here loose limestone lies in flat plates. The plant world has changed noticeably. Hairy leaves, a protection against desiccation, stand out. And at its bleeding time, various lime-loving orchid species.
Help from the neighbor
To protect against water shortages, hetzles has joined the neighboring leithenberg group. However, hetzles can only help out to a limited extent with coarser quantities of water, because it has also reached the limits of its extraction quantities. But for completely different reasons.
The leithenberg group obtains its water from deep wells in the second groundwater level, in contrast to the city of forchheim, which obtains its drinking water from shallow wells in the zweng. It taps in the first groundwater level to some extent the subterranean wiesent. Only a few meters below the earth’s surface, the water that has penetrated the highly permeable limestone layer in the center of the french-speaking part of switzerland flows in abundance.
Deep wells offer more security against water contamination because the surface water takes much longer to pass through the subsurface and is thus filtered for a longer time. The wells are located in the area around kersbach and effeltrich, in the hills before the actual alpine stage, the core of which belongs to the same rock strata as the area west of the regnitz river.
Arsenic causes problems
The stone there is called castle sandstone. Its natural components include arsenic inclusions. And it is precisely this toxic mineral that keeps causing problems in water extraction, because the more water is pumped, the more it is washed out. As a result, fountains had to be shut down again and again or the withdrawal rate curtailed because the concentration exceeded limits.