(Reuters) - The governor of Louisiana and the mayor of New Orleans declared a state of emergency for the city on Thursday due to torrential rains that overwhelmed a municipal drainage system already diminished by power shortages.

At a press conference, Mayor Mitch Landrieu also called for a private, third-party company to assume management of a pumping system meant to lower the risk of floods.

The emergency declarations by Landrieu and Governor John Del Edwards are to remain in effect until Sept. 3.

The drainage system for the city, much of which lies below sea level, was inundated last Saturday by storms that dumped up to 9 inches of rain in three hours in some areas, causing flash flooding, according to the mayor’s press secretary, Erin Burns.

New Orleans officials said its Sewerage & Water Board lost service on Wednesday night to a key turbine providing power to a majority of pumping stations for the East Bank section of town, hindering stormwater drainage in that area.

Local media have reported that Landrieu, disappointed by the handling of the response to the heavy rains and flooding, this week accepted the resignations or retirements of four top officials for the New Orleans Sewerage & Water Board and Public Works Department.

The drainage system, when at full capacity, “can drain 1 inch of rainfall in the first hour, and a half inch of rainfall every hour after that,” New Orleans emergency operations chief Aaron Miller told Reuters.

Miller said the system is running less efficiently than that, but he could not quantify the capacity as of Thursday.

The intensity of Saturday’s rains caught city officials by surprise. But this week’s problems with stormwater drainage paled in comparison to the major floods that devastated parts of New Orleans after Hurricane Katrina in 2005, when levees failed.

Gavin Phillips, a National Weather Service forecaster in New Orleans, said this week’s flooding was due in part to a fluke of nature that saw wide variations in rainfall totals from one part of the city to another.

If the heaviest showers on Saturday had occurred 5 miles farther north, those rains would have fallen into Lake Pontchartrain with little or no consequence, he said.

Daily rainfall of less than an inch to 2 inches is expected for another week in the area, Phillips said, much like the rate of rainfall since Saturday’s deluge.