Submitted by kingintheyunk t3_10l9f7u in philadelphia
Kamarmarli t1_j5vzaft wrote
There are underground mill streams in Philadelphia. Here is one map. https://i0.wp.com/www.hiddenhydrology.org/wp-content/uploads/2018/10/wplp_maps.png?ssl=1
lizacovey t1_j5w9e8i wrote
I saw a hydrologist give a talk about this when I was in college. Blew my mind.
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