In this lecture, we'll talk about about the different types of aquifers in Switzerland, as well as the changes in groundwater levels over time. Water and aquifers, aquifers can be stored in pores between particles, in fractures and in large cavities such as in caustic rocks. Alluvial aquifers, aquifers are one of the most important aquifers. They are mainly found in the valleys. Many valleys in Switzerland were shaped by glaciers, glaciers. As the glaciers retreated, they deposited fine sediment. sediment, then the rivers build up the alluvial floodplains of course coarse sand and gravel. Floodplain, alluvial sediments are important aquifers because of the high productivity. However, they are also very vulnerable because the water table lies close to the surface, and it's not protected by any layer of low permeability. Therefore, the water quality is strongly influenced by anthropogenic activities such as agriculture. The water level in a [inaudible] aquifers is influenced by the river. During low flow conditions, when the water level in the river is low, usually the water flows from the groundwater to the river. However, during high stream flow streamflow conditions, for example during snow melt events, the water level in the river may be higher than in the aquifer, so that the water flows from the river into the aquifer. This allows for very fast recharge of the groundwater reserves. Molasse rocks form the Swiss plateau, the heterogeneous sedimentary rocks and consist of clays clays, morals minerals, sandstones and conglomerates. Only the sandstone and conglomerate layers are aquifers. Springs appear at the contact between these layers and the low permeability layers below. In molasse rocks, ground water flows through fractures and joints but dissolution of the carrier cement has increased increased the pore space as well. Crystalline bedrock aquifers can be found in areas with granites. Silicate rocks can also be aquafers aquifers. They are generally not porous nor soluble. However, discontinuities such as false, faults and unjoined, joint can provide permeability and this water can flow through these. Carbonate aquifers are also very important. Groundwater flows in limestones through both small fractures and pores, as well as through large conduits and cavities. These conduits and cavities are the result of the dissolution of carbonate, by dissolved carbon dioxide that comes from the atmosphere and the soil. Water flows very quickly through these large conduits. But but the amount of water stored in them can be very small. Sometimes, water can flow so quickly through these large conduits that creeks can disappear completely. However, these small fractures and the small pores are also very important because they store a lot of water. Groundwater levels in these aquifers change in response to precipitation and drainage. At the moment, groundwater levels are monitored at more than 900 locations in Switzerland by the Federal Office of the Environment, control cantonal agencies and private parties. The water level changes in an aquifer also depends on the geometry and the type of aquifer. Here Here, we see the time series of water levels in three different aquifers over a period of four years. We see very large changes in the groundwater level, in the granite aquifer, and very small changes in the groundwater level in the gravel aquifer. A lot of water can be stored in a gravel aquifer. When the they add a certain amount of water to it, the water level rises only very little. However, if we add the same amount of water to a granite aquifer, the water level will rise a lot because of the smaller amount of water that can be stored in a granite aquifer. The amount of water that we can drain from an aquifer, or add to an aquifer for one meter of water level change, is called the specific field. yield. This is a very important property of an aquifer. In addition to change shifting groundwater levels due to rainfall difference and slow drainage, there are also often very persistent parenting groundwater levels. Here, we see the ground water levels in [FOREIGN LANGUAGE]. And what What we see is that in the early 1990s, groundwater levels were low for many years in a row, and then in the mid-1990s, grum groundwater levels were high for several years in a row. This is what we often see in groundwater levels. The effects of a drought can lead to low groundwater levels for many years. In this lecture lecture, we've discussed the different types of aquifers in Switzerland, as well as changes in groundwater levels. We also have a video that explains how you mesh in groundwater levels.
