Teen falls into sewer; finds and survives with old man and eats white lobsters

All I remember is this teen (i don't know if boy or girl) moves into a new home and explores behind the new home. There is a big river of fast moving water that they fall into and are sucked into the sewer where an old man pulls them out of the water in the sewer. The old man uses a water clock to tell the time and eats white crawfish/lobster to survive. The family eventually finds them and I think the old man dies or jumps into the sewer to find help.

Leepike Ridge?

Yes! Thank you :D