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I am a newbie for hydrology. If the question seems to have "well known answer", I appreciate if you point me to the resources. I will add details to the question based on comments.

Consider a town of 30km x 30km, nearby a hill, in a place where rain averages 40cm per year. The town is at an average elevation of 30m compared to the surroundings. It gets water mainly from rain. The water table seems to drop off as we walk away from the hill (30m near the hill, 90m once we walk 30km away from the hill).

If we concertize the town (fill every road, every open place with concrete 1m thick), what effect would that have on water table (water availability in earth)? Would the water flow away and sink into outer places (away from the town)?

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    $\begingroup$ Well, that seems an obvious yes. Where else would it go; it's too much to evaporate. BTW You don't need 1m thick concrete, plastic cling film will do as long as it isn't punctured ;-) $\endgroup$ – Jan Doggen Apr 2 at 11:53
  • $\begingroup$ @JanDoggen, Is there a case where the water may seep back under the town slowly (from outskirts, even in spite of elevation of the town)? The general discussion is, "Are we losing water tables because of concretization?". If so, "roughly by how much?". I know, I probably need more parameters about the land. Right? $\endgroup$ – blackpen Apr 2 at 18:20
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    $\begingroup$ I'm not yet sure how to extrapolate this a larger scale, but one thing I've noticed about lawns which are bounded by expanses of concrete (paths & driveways, etc.) is that during summer when the lawns are dry due to lack of rain or watering, a green edge, along the concrete remains for most, if not all of summer. Presumably, the soil beneath the concrete has retained moisture & the grass can survive within a certain distance of the concrete, whereas the grass in the center of the lawn dies because of no moisture. On a larger scale, the effect of concretization would depend on the proportion .. $\endgroup$ – Fred Apr 3 at 0:47
  • $\begingroup$ ... of the land area that has been covered with concrete & the extent of seep holes within concreted region. $\endgroup$ – Fred Apr 3 at 0:47
  • $\begingroup$ @Fred, Yes. That reminds me of similar observation at my previous place of my living. $\endgroup$ – blackpen Apr 3 at 21:02
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I found this on the USGS website. It states the effect of increased pavement coverage due to urbanization is to reduce the recharge rate of ground water, because the water is diverted elsewhere.

Also, with urbanization comes the use of storm water drains. The rain water that would have soaked into the ground and recharged the ground water is diverted to streams via the storm water systems (pipes and channels) which can result in flooding elsewhere.

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