HURRICANE KATRINA'S EFFECTS ON WATER WITHDRAWALS FOR PUBLIC SUPPLY IN SOUTHEASTERN LOUISIANA

About 440,000 people relocated from Orleans, Plaquemines, and St. Bernard Parishes to other places, including other parishes in southeastern Louisiana, after Hurricane Katrina in August 2005. In 2007, the La. Geological Survey and the U.S. Geological Survey began a study to determine whether the migration affected water withdrawals for public supply. Monthly water-use data collected from the 36 of the largest public suppliers in the 22-parish area for 5 years prior to Katrina and 16 months after Katrina were analyzed for temporal and areal variations.

The 16-months of post-Katrina withdrawal data for 36 utilities provided a 576 (36x16) value dataset. Using a random distribution of withdrawals for the 16 month period, withdrawals during 1 month are expected to be 2 or less standard deviations (SD) below or above the 5-year monthly means (FYMM). The actual distribution of monthly withdrawals showed withdrawals for 169 months were greater than 2 SD or more above the FYMM, and withdrawals for 56 months were less than 2 SD or more below the FYMM, which is 8.7 times more than the outcome expected from a random distribution (26 months).

Areally, withdrawals from 5 public suppliers located between Slidell and Baton Rouge, La., were 2 SD or more above the FYMM 12 or more months during the study period. Withdrawals at 2 public suppliers in St. Bernard and Plaquemines Parishes decreased by 2 SD or more below the FYMM during 12 or more months.

Withdrawals during the fourth quarter (selected to minimize the effects of seasonal water use, such as lawn watering) of 2005 (FQ2005) and 2006 (FQ2006) were compared to the FYMM. Monthly withdrawals during FQ2005 for 14 of the 36 public suppliers were more than 2 SD above the FYMM. Withdrawals during the FQ2006 were more than 2 SD above the FYMM for 9 public suppliers.

Changes in withdrawals in response to possible post-Katrina secondary population migration from Baton Rouge to surrounding towns were investigated. Average monthly withdrawals at the 2 largest public suppliers in Baton Rouge increased by 3.2 SD above the FYMM during the FQ2005, but increased by 1.5 SD above the FYMM during FQ2006. Average monthly withdrawals at 6 public suppliers in nearby towns increased by 1.5 SD above the FYMM during FQ2005, and increased by 2.2 SD above the FYMM during FQ2006.