Why SGD (submarine groundwater discharge) generally decreases with water depth? Which are all the possible reasons?
Although SGD submarine groundwater discharge data vary widely, discharge estimates tend to decrease fairly systematically with increasing water depth over about three orders of magnitude.
From Makoto Taniguchi 2002
Investigation of submarine groundwater discharge
Well,
Increasing the depth of the groundwater, means a decrease in the groundwater column(a decrease in the Head of water (h) relative to the sea level) and thus leads to a decrease in the values of hydraulic gradient , and depending on the Darcy equation (Q= KA dh/dl) the discharge values will decrease.
Regards
Submarine groundwater discharge ( SGD ) into the ocean is of general interest because it acts as vehicle for the transport of dissolved contaminants and/or nutrients into the coastal sea and because it may be accompanied by the loss of significant volumes of water. There is report of observation made which that SGD rates obtained by seepage meters at some sites of mid-latitude generally decrease with increasing water depth ( D ) . These lower SGD rates for greater water depths ( lager D ) were interpreted from the potential difference between land and sea., which decreases with increasing waterpressure. For more information consult https://agupubs.onlinelibrary.wiley.com
Geophysical Research Letters/Volume 38, issue 8
Not quite my area of experience, but you may need to consider basic hydrostatics.
Sea water has a density of about of 1,030 kg/m3 compared to fresh water at 1,000 kg/m3. The deeper you go, the higher the source for the freshwater will need to be to discharge into the sea. That is, at 100 m depth, a freshwater aquifer column will need to have a static head greater than 103 m before discharging into the sea. Of course this is complicated by the usual mixing of water near shore.
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