NEW ORLEANS – With the approach of Tropical Storm Barry, the Sewerage and Water Board of New Orleans has released a digital map of the city’s drainage system to help residents better understand how we manage storm water.

Explore the map to see where the pump stations stand, what neighborhoods they drain, and where the water goes.

The drainage system was designed around the turn of the 20th century, and much of its original equipment is still in use.

It is comprised of more than 68,000 catch basins, 1,400 miles of lateral, underground drainage pipes, 280 miles of open and underground canals and 120 pumps housed in 24 drainage pump stations (DPS).

The system starts on your roof and chiefly runs on gravity.

Runoff goes into the streets, then enters the network through the catch basins.

Storm water must then travel through pipes and canals to reach the pump stations, which send it either into outfall canals or directly into Lake Pontchartrain or nearby waterways.

Of the 120 pumps, 51 run on an older frequency of electricity, 25 Hertz (Hz).

The remaining pumps run on modern, standardized 60 Hz power.

The smallest pumps are called “constant duty” or “dry weather” pumps because they are most often used to regulate groundwater that seeps into canals.

There are 21 of those.

A workhorse drainage pump can be as big as 14 feet across and can move approximately 1,100 cubic feet of water per second (that’s the equivalent pumping power of more than 700 fire trucks).

While all are not that big, there are 99 pumps solely focused on drainage.

Because the pumps are different sizes and serve different purposes, the drainage pumps cannot all be run at the same time.

In some cases, to do so would overflow downstream canals, causing neighborhood flooding.

While impressive, the system has its limitations.

When it was designed more than a hundred years ago and built afterward, it could move about 1 inch of water out of the city in the first hour of a storm and about half an inch of water each hour after that.

Intense rainstorms that drop more than an inch of water in an hour will most likely outpace the system’s capability, leading to street flooding until it can catch up.

When water is flowing swiftly through canals, residents can be assured the pumps downstream are working.