Re: Hydraulic pressure through gravel

30 meters is easy, I've seen it on a number of sites that are adjacent to
the San Francisco.

I work one remediation site with more than a dozen wells that typically
shows a gradient away from the bay (0 to 30 meters from the edge of the
site) into the hill. That is because my tech goes early to get across the
bridges and is usually gauging the wells on an incoming tide. We've given
up trying to map or calculate gradient direction. Differences in the
underlying sand and gravel result in a really rough water surface in the
wells. The wells range from almost fresh to almost salt water. The
ground is dump truck formation -- Bay Fill. My impression is that some of
the wells close to the bay will show significant response within 15 to 20
minutes,.

Bob



"N Cook" <diverse8@xxxxxxxxx> wrote in message
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N Cook <diverse8@xxxxxxxxx> wrote in message
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Assuming the soil is gravel and the rainwater table is some distance
down.
Can seawater drive up the water table ,almost immediately, over a
horizontal
distance of about 30 metres.
Background
For a low lying road near me if you monitor the water level under the
grill
of drains in that road this last week of high tides it goes up and down
at
the high tides. No blockage as such the natural water trap level being
about
0.7 m down which it duly drops to when the tide has gone below that
level..
In fact for similar weeks but low atmospheric pressure , so the sea water
level can rise much further, then local flooding starts from water
flowing
up out of these drains. So defeating the 0.5 metre or so of elevated
ground
beteween this road and the tidal river.
Assuming its not due to the drain system going to a river outlet with
malfunctioning flap valves, none seen locally, but assuming the drain
piping
is not sealed so groundwater can get in.





I should have said sand and gravel




.

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