The heavy rains and subsequent floods last year in Chennai had one positive impact on the city: it raised the shallow ground water levels while also improving its quality.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/why-rains-will-not-solve-countrys-growing-ground-water-problems
[2] http://admin.indiaenvironmentportal.org.in/category/author/hari-pulakkat
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/economic-times-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/groundwater
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rainfall
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/groundwater-recharge
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/gujarat
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/western-ghats
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources