Spillways are used to control the flow of water downstream. Spillways do not relieve pressure from upstream areas, but rather divert the flow of water to take pressure off of the downstream systems.

The Morganza Floodway diverts the excess floodwater from the Mississippi into the Atchafalaya Basin. The control structure and Floodway is designed to pass 600,000 cfs of excess water to the Gulf, which takes pressure away from mainline levees downstream from the Mississippi. Operation of the Floodway occurs when the flow of the Red River Landing is predicted to reach above 1.5 million cfs.

The Bonnet Carre Spillway was designed to divert floodwaters away from the New Orleans metropolitan area as well as other downstream communities. The floodwaters are redirected to flow into Lake Pontchartrain to relieve stress on downstream levees.

The National Weather Service

Rainfall in the upper Midwest.

Atchafalaya River

Gulf of Mexico

Lake Pontchartrain

The Mississippi River

Red River

Sand Boils occur when the pressure of a high river on the soil layer of the levee exceeds the accepted conditions causing the water to ooze to the surface of the levee. The sand/soil of the levee will bubble or “boil” hence the name. Seepage occurs when the water of the river flows away from the channel and below/through the levee.

River levees are used to protect against overflow of river waters and run parallel to the river. Hurricane levees' primary objective is to divert waters from specific areas/cities during a storm surge. The hurricane levees and river levees often work collectively; however, a hurricane levee is used to protect cities from flooding during a storm surge.

When water breaks through the structure or levee

Located outside the USACE New Orleans District, the trigger point for Phase I and Phase II flood fight events. Measures the height of the river based off of sea level, not river depth.

A single structure with multiple responsibilities. Example, a gated structure with pumps.

Phase I:

                                When the river is above 11ft at the Carrollton Gage.  Preliminary responses activate. Patrols of levees occur twice weekly. Construction within 1500ft of the levees must cease. However, waivers for construction are granted on a case by case basis.

Phase II:

                                When the river is above 15ft at the Carrollton Gage. Daily inspections of the levees are mandatory and all construction within 1500ft of the levees must cease, no exceptions.

A gate that can be opened or closed to take in or discard water during a flood event.

An artificial barrier used to restrain water that could rise to extreme/unusual levels. Serves the same function as a levee but with a reduced footprint.

Steel wired baskets filled with sediment and sand used to help divert and prevent flooding during an event. Similar to a floodwall, only temporary.

Infrastructure systems that provide the New Orleans area with a 100 year risk reduction from a storm surge with a 1% chance of occurring.

 The use of Turf-reinforced mats and concrete slabs to strengthen the levee system for future flood events. Armoring increases the resilience of levees.

Risk communication tool to identify risks associated with the levee systems. Levee safety program developed to balance and inform assessment of levees within the program. Goal is to evaluate and prioritize levee safety decisions.             

A ridge of sediment and materials built to prevent overflow of a river or body of water

Designed for flood control and features tributary basin improvements, levee/floodwall installments/upkeep, floodways, and channel improvements/enhancements.

Serve as a drainage conduit for much of New Orleans, usually from surge in Lake Pontchartrain and other major bodies of water.

The breaching of water over a levee or structure passing onto to low-lying areas.

This station closes off the outfall canals.

Flooding caused by rainfall.

Trace amounts of water pushed under the levee via the pressure of the water. 

Reduces the risk of flood damages due to rainfall in Orleans, Jefferson, and St. Tammany parishes.

Large sandbags often dropped from helicopters.

Specific type of floodgate that helps prevent a storm surge from flooding the area behind the barrier.

For example: The Inner Harbor Navigation Canal Surge Barrier in New Orleans East defends against surge from Lake Borgne entering into the IHNC.

The largest pump station in the world. Used to protect West Bank homes from flooding events based on the HSDRRS standards. The structure gates can close off the Harvey and Algiers Canals from storm surge while pumping rainfall drainage from the canals to the other side of the structure.