Why did they raise the streets in Chicago?

Related questions

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2. Does Chicago have an underground city?
3. Was Chicago founded by a black man?
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5. Is Chicago cleaner than New York?
6. Which side of Chicago is the safest?
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8. Is Uptown Chicago Safe?
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Tags

1. #elevation
2. #planking
3. #tried
4. #raised
5. #streets
6. #would
7. #chicago
8. #underground
9. #sewers
10. #since
11. #entire
12. #michigan
13. #water
14. #unless
15. #failed
16. #properly
17. #above
18. #grading
19. #drain
20. #river
21. #level