Low water increase
An increase in the low water level is intended to provide navigable rivers with sufficient water even in times of little rain, especially in the summer months, so that shipping traffic does not have to be stopped.
For this purpose, dams or reservoirs were usually built at the tributaries , which catch the water from the winter and spring months with high levels of precipitation and pass it on to the rivers in the event of prolonged drought. It is almost comparable to flood protection , although here the reservoirs were primarily built to initially hold back the water in the rainy months to protect the villages on the rivers from flooding and only release it later in doses.
In the case of smaller rivers, increasing the low water level can also have the purpose of reducing the pollutant concentrations increased by wastewater discharges through dilution.