How to measure groundwater recharge? - Saturated GW (or deeper aquifers)
16 important questions on How to measure groundwater recharge? - Saturated GW (or deeper aquifers)
How does the Water Table Fluctuation method estimate recharge to the deeper aquifer?
In a phreatic aquifer the recharge is accommodated
via a rise in the water table.
Hence, the magnitude rise in water table can be
quantitatively interpreted as the volume of recharge,
taking into account the specific yield (Sy) of the aquifer
(setting the volume of water water is taken up/released
by the aquifer for a unit rise/drop in water table).
Give the formula for the WTF method to estimate recahrge to the deeper aquifer.
What are downsides about the WTF method, besides it's widely used application?
Although the WTF method has been widely applied, care should be taken in the interpretation of water table fluctuations for recharge. Many other processes can cause water tables to fluctuate, such air movement in the vadose zone, groundwater abstraction, and ET.
Also, Sy could be uncertain, but in coarse sediments will be close to porosity.
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What are typical residence times of GW in an unconfined aquifer with a well/river (outflow)? Mention this for locations close to the outflow location and further away. Notice that this is thus the saturated zone (below the water table).
Further: years
What is the typical residence time of GW in a confined aquifer below an unconfined aquifer and a confined aquifer even deeper than the first confined aquifer? Note that the water eventually flows towards the river/pumping well in the unconfined aquifer (through the confining beds separating them).
Confined under confined: milennia
Where is GW age/residence time zero and why?
To estimate GW age, decay time of chemical components can be used. Based upon a decaying activity once isolated from the atmosphere, name the GW residence time that Tritium (T) +CFC, 14C, 36Cl, 81Kr, 4He are suitable to estimate.
Name the up/downsides about the various decay chemical components when using these for estimating GW residence time.
14C: needs corrections for carbon chemistry
36Cl: Problematic in saline aquifers. Initial activities are
known to vary over geological time.
81Kr: Can be used in more variable settings than 36Cl. Atmospheric concentration very constant. Needs very large sample volumes.
4He: Quasi age indicator, difficult to accurately calibrate as production rates vary spatially. However, relative age determinations possible along flow paths. Very old (10’s of My) groundwater ages have been interpreted
using 4He (e.g. Paris Basin)
Which relationships does this formula represent? (Name the parameters that include variable aquifer properties).
![]()
d: depth
P: recharge [m/d]
t: GW age
n: porosity
The relation between GW age and depth can be plotted.
Effects of convection on regional scale heat transfer
Analytical vs. Numerical 1D-age distributions. How do these numerical simulations compare to the analytical solution we have
seen earlier?
How can hydraulic conductivity in an aquitard be estimated to help approximate GW recharge rates? Which condition needs to be met? See also the picture. ![]()
Using Darcy’s Law, but only where hydraulic heads above and
below an aquitard are known (e.g., h1>h2), and qz independently
assessed.
Slide title: Impact of one-dimensional vertical fluid flow on the TD-profile + Surface warming.
Give the titles for these graphs:
![]()
Middle: transient stage
Right: new steady state
Inflection point propagation for contrasting groundwater flow conditions in a warming climate. Check lecture for question about this.
Mention differences between GW age-depth and TD profiles for deep GW recharge
How can climate warming be indicated by a time-depth profile?
Climate warming induced TDP inflection point
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