Earth tides; Fw: Pump drawdowns: [NatureNS] Freshwater Shortages and

From: David & Alison Webster <>
Date: Mon, 16 Jul 2012 21:09:18 -0300
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Hi Steve & All,
    Sounds like an earth tides effect---
----- Original Message ----- 
From: "David & Alison Webster" <>
To: <>
Sent: Monday, July 16, 2012 4:56 PM
Subject: Pump drawdowns: [NatureNS] Freshwater Shortages and Bay of Fundy 

> Hi Steve & All,
>    I tried Google Chrome and was able to read where Internet Explorer 
> failed namely--
> This is not light reading but examples 6.3 a&b & 6.4 provide samples of 
> effects at a distance from the well. In 6.4 e.g. water table was lowered 
> 1m at a distance of 500 m from the well after continuous pumping at 3888 
> M^3/day for 4.3 days. This reach is greater than I had remembered but this 
> rate is rather large.
> Yt, DW
> ----- Original Message ----- 
> From: "David & Alison Webster" <>
> To: <>
> Sent: Sunday, July 15, 2012 10:09 PM
> Subject: Re: [NatureNS] Freshwater Shortages and Bay of Fundy Tides
>> Hi Steve & All,                July 15, 2012
>>    I wouldn't care to suggest that I have the physics correct; just a 
>> very crude first approximation of the effect of head gradients over 
>> distance. But way more correct than the one you advance.
>>    Except for very simple artificial situations (assumptions that seldom 
>> apply in practice) problems of liquid flow in porous media can not be 
>> solved analytically and require computer modelling or field measurements. 
>> But flow to any sink such as a well, tile drain or Gloosecap's buried 
>> garden hose, from a phretic surface, will be at right angles to 
>> isopotential lines. I recall this only in vague terms now but as distance 
>> from the sink increases there is a dramatic increase in the length of 
>> flow paths and transit times.
>>    I tried to find a sample representation of pumped well steady-states 
>> but keep getting run time errors (started about a week ago with Internet 
>> Explorer.
>> Yt, DW, Kentville
>> ----- Original Message ----- 
>> From: "Stephen R. Shaw" <srshaw@Dal.Ca>
>> To: <>
>> Sent: Sunday, July 15, 2012 1:24 AM
>> Subject: Re: [NatureNS] Freshwater Shortages and Bay of Fundy Tides
>>> Quoting David & Alison Webster <>:
>>>> Hi Patricia & All,                    July 13, 2012
>>>>    I don't know Greg Gerrits but I do know Elmridge Farm produce;  top 
>>>> quality and this implies unusually good management. So I would  be 
>>>> inclined to accept his observation of well replenishment rates as  a 
>>>> function of something to do with tides but it can not caused  directly 
>>>> by height of saltwater in the 'nearby' shore.
>>>>    Flow of any liquid in a porous medium is directly proportional to 
>>>> hydraulic gradient (head z/lateral displacement y) and inversely 
>>>> proportional to resistance. A head difference of 10m over lateral 
>>>> displacement of 10 km (hydraulic gradient = 0.001) would induce 
>>>> essentially zero flow  Or approaching this from the other direction, 
>>>> when water is pumped exhaustively from a well the water table  (drawing 
>>>> on memory) is seldom lowered beyond a radius of 50 metres.
>>> Dave, Patricia:
>>> I don't know if you have the physics of the above idea correct, Dave, 
>>> but if you have, here is a possible suggestion/way out of your 
>>> pessimistic assessment.
>>> Suppose that the water table out there is in part a continuous sheet  or 
>>> lake of (almost) incompressible water that extends all the way from  the 
>>> farm out to within, say, 1 meter of the Bay of Fundy.  Your  hydraulic 
>>> gradient now rises to 10 instead of your 0.001, and the  resulting 
>>> forced flow, now feasible, would impress some seawater into  the 
>>> supposed continuous aquifer under pressure. The resulting pressure 
>>> change would be felt very quickly even 10 km inland, explaining the 
>>> increase in pressure in the well (as in water coming out of a long, 
>>> full hose immediately after the tap (pressure source) is turned on --  
>>> no delay). This amounts to saying that there is zero resistance to  flow 
>>> over 10 km, which is not possible physically because of  frictional wall 
>>> effects (Poiseuille's law for tubes -- lower flow near  the edges), but 
>>> you can speculate that this might be a relatively  small effect if the 
>>> depth of water table is significantly large.  A  bit of the sea water 
>>> would mix in at the edges but most would be  removed again at the next 
>>> low tide.
>>> I don't know if this is a physically reasonable model of what's down 
>>> there, but if it is, it might make the farmer's observation feasible. 
>>> Obviously it goes against your belief that the water table is  extremely 
>>> local.  Do geophysicists conceptualize the water table  around there as 
>>> in part a continuous, shallow underground lake?  Someone must have 
>>> investigated this if you knew where to look or whom  to ask.
>>> Steve (Halifax)
>>>>    I would suspect that a tidal effect leads to a local artificial 
>>>> hydraulic gradient. In effect, water running uphill to the well (and 
>>>> well vicinity) during this peak inflow period.
>>>>    I ran into NatureNS by accident some years ago while trying to  find 
>>>> some understandable explanation of tidal effects on the  internet. The 
>>>> nearest I have come to an explanation was some  oracular comment to the 
>>>> effect that it is explained by math that  almost no one understands. 
>>>> But meanwhile the tides come in and go  even though I don't understand 
>>>> how it works.
>>>> YT, Dave Webster, Kentville
>>>> ----- Original Message ----- From: "P.L. Chalmers" 
>>>> <>
>>>> To: "NatureNS" <>
>>>> Sent: Friday, July 13, 2012 2:28 PM
>>>> Subject: [NatureNS] Freshwater Shortages and Bay of Fundy Tides
>>>>> For most of my life, my family home in Bedford was dependant on a 
>>>>> drilled artesian well, as there was no municipal water supply in  our 
>>>>> neighbourhood.  This is no longer the