Integration between river and groundwater level

Hi Users of FEFLOW,

In my 3D model, the 3rd kind BC is assigned for the River with time varying values (river water level is influenced by Tidal). Regarding to problem setting, the model is running with saturated, 3D phreatic aquifer, transient flow. Observation points closed to the river showed that the trend of observed groundwater level are similar to those of the river. This means that there are integration between river water level and groundwater level. However, the simulated results of these observation points show a single line (no fluctuation compared to observed values), although the parameters such as In-transfer rate and out-transfer rate have been adjusted). The similar results are also occurred for the observation points located near the coastline which is the 1st kind BC of the Domain.

What are the reasons for that? Do you know some other parameters (factors) need to be further changed?

Thanks in advance,
Lamm

There are different options that may lead to the model showing no significant reaction to a variation of the BC values. For the river, the main factor besides the transfer rates is the drain-/fillable porosity. If this is large, the aquifer has more ability to buffer water level changes in the river. Are you sure that the system is perfectly phreatic? If there is one (or several) low-permeable layers (e.g., thin clay layers) on top or within the otherwise phreatic aquifer, the system may in reality be (at least partly) confined, leading to the fast reaction on river levels.