Groundwater level indicator phreatic groundwater for the time of year (monthly update)

Description

What is the groundwater level indicator? The groundwater level indicator shows the current state of phreatic groundwater compared to normal (in a 30-year reference period). This analysis of groundwater levels is based on monthly level measurements by the VMM, SCK and De Watergroep. These monthly level measurements are supplemented by daily model calculations for the period 1991 - present. Only the phreatic levels are discussed. These are the levels in the upper groundwater layers that are not closed by a sealing layer at the top, and are therefore in contact with the atmosphere. For the analysis, a selection of phreatic level filters with continuous measurement series of at least 5 years, and usually with relatively shallower groundwater levels, is used. The groundwater levels of these level filters best reflect the influence of recent climatic variations, while they can also be tested against a relatively longer meethistory. Per level filter, the current groundwater level is compared with the levels in recent years. At the same time, it is determined whether there has been a relative increase or decrease in the past month. The data is processed in a map and a number of graphs. This gives an idea of how high or how low the groundwater level is compared to the levels in the reference period and which direction it goes with the groundwater level. The groundwater level indicator is drawn up on a monthly basis. Construction of the groundwater level indicator Monthly level measurements are carried out at the selected measuring sites. In addition, a Pastas time series model [https://pastas.readthedocs.io/stable/] has been drawn up for each measurement site to model the groundwater level based on observed daily precipitation and evaporation, and calibrated to the measurements. The daily modelling is then combined with the monthly level measurements. The resulting time series of daily simulated groundwater levels is processed into the indicator. How is the ground wattage indicator map layer set up? The map layer shows the state of the phreatic groundwater for the time of year per measuring location via a colour code and via a symbol whether the groundwater level has decreased / risen / remained stable compared to a month earlier. For each measuring site, the simulated groundwater level (combination of monthly level measurements and daily modelling with the Pastas model) per day is compared with the simulated groundwater level of the same day in the year in the 30-year reference period. It is estimated how many percent of those years the day under consideration has a groundwater level that is lower than the simulated groundwater level for this year. For example, in 15% of the years, the groundwater level on a given day in the year is lower than the groundwater level considered on the same day, corresponding to the 15th percentile (P15). The percentiles are divided into 5 classes: • Very low (P90): the groundwater level is among the 10% highest on the same day of the year in the reference period The increase or decrease is determined between the groundwater level of the previous month and the groundwater level at the reference date of this report. If the change in the groundwater level at a measuring point is more than 5 % of the difference between the 10th and 90th percentiles of the groundwater level at that measuring point, this shall be regarded as an increase or decrease. Otherwise, the situation is considered stable.

Resources

Name Format Description Link
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Tags

  • grondwaterstand
  • vmm
  • vlaanderen
  • freatisch
  • hydrogeologie
  • watervoerende-laag
  • freatisch-water
  • ondergrond
  • dov
  • grondwaterpeil
  • stijghoogte
  • databank-ondergrond-vlaanderen

Topics

  • REGI
  • TECH

Categories