The prognosis of the renewal rates of raw water resources for drinking water supply is still largely based on statistically justified design parameters that have been or are derived from observations of past decades. However, the prerequisite for time-invariant climate conditions is no longer met in Germany today.
The overall objective of the project was to provide a basis for knowledge and decision-making to determine the future water supply and to derive an action strategy for its sustainable safeguarding under the conditions of emerging climate change. This concerned both computational (software) and metrological methods (monitoring).
Methodologically, a deficit analysis of existing investigative procedures was carried out, a process-oriented determination procedure based on the Richards equation and the subdivision into hydrotopes, as well as an innovative monitoring concept was developed, which allows to monitor the individual processes that contribute proportionately to the renewal rates of the raw water resources for certain land uses. Measures to compensate for the decline were compiled and the effects of these measures on groundwater recharge processes were analysed using exemplary examples. These tools were combined in the process-based management tool "PMT Wasser".
Monitoring objective and study area
The monitoring concept is designed to monitor the individual processes that contribute proportionately to the renewal rates of raw water resources in the educational areas. In particular, it is important to measure those proportions that are subject to climate-related changes and changes in land use.
Site A: Well of the Western capture
This site is located in the immediate vicinity of a well of the western capture of the WW Colbitz. It is located in slightly undulating, unforested heathland. The vadose zone of interest for the investigation is dominated by fine sands and reaches up to about 11m below ground level.
Site B: Lysimeter station
This site is located on the site of the Colbitz Lysimeter station operated by the State Agency for Flood Protection and Water Management (LHW). The measuring area is located on a forest clearing. The vadose zone here is characterized by middle Sands and extends to approx. 8m below ground level. The GWN at this site is around 35% lower than at site A. The location offers the possibility to use the data of the lysimeter station including the connected weather station.
Installation of soil water measuring stations
The monitoring concept includes long-term measurements at two innovative soil water measuring stations. By combining various physically based measurement methods, the climate-influenced water balance components are to be recorded directly. It is measured selectively with the frequency range reflectometry (FDR), tensiometers and temperature sensors.
With the geoelectrics on the surface, integral results are obtained for different depths along a profile. Based on differences in electrical conductivity, geoelectrics allow the localization of water in the soil and thus the determination of water saturation and flow movements. Numerous electrodes along a profile line at a distance of 0.5 m can be controlled in such a way that near-surface areas up to the groundwater level can be detected and dissolved.
Frequency range reflectometry (FDR) determines the volumetric water content of the soil in the area of each probe by the influence of soil moisture on signal propagation in uninsulated electrical conductors. The installation depth of the three probes is 0.3 m, 0.9 m and 1.5 m.
Tensiometers determine the suction voltage of the soil. Water in a ceramic is sucked out at high suction voltages. This suction is measured. In this way, currents can also be recognized. The installation depth is analogous to the FDR probes.
The autonomously operating soil water measuring point, controlled via remote data transmission, regularly transmits its data for evaluation.
The management tool was tested exemplarily in the catchment area of the Colbitz waterworks. As a result of the project, the "PMT Wasser" is a decision-oriented management tool available, with the help of which
- determine the future water supply in the catchment areas of raw water, which are changing naturally and socio-economically and are characterised by a wide range of exploitation interests, and appropriate compensatory measures for climate-related and
- changes in available raw water resources due to their use can be derived on the basis of their predicted effect.
This work equipment enables the operators of waterworks to conserve their raw water resources, to manage them sustainably and to optimize the monitoring and control systems.
The following figure shows a screenshot of the software "PMT-Wasser", in which the project results are implemented.
The underlying R&D work was funded by the Federal Ministry of Education and Research under fkz. 02WQ1103. The responsibility for the content of this publication lies with the author.