Flood Regimes

Historic flooding events have dominated the news this week as heavy rain and snowmelt pummel the Midwest.  While we may feel powerless during flooding events, we have the power, with help from CWPPRA, to restore our wetlands that protect us from this surplus of water. Because wetlands act as sponges, they store floodwaters that can otherwise damage our communities.

Flooding events played a key role in forming the wetlands of coastal Louisiana. During times of high water, the Mississippi River would flood, resupplying our wetlands with much needed sediment and freshwater. As sediment collected along the banks, the river would change course to travel to the Gulf of Mexico along the path of least resistance.

By building our communities on the banks of the Mississippi and installing levees along the river to protect us from these natural flooding events, we have starved our wetlands. In addition to starving our wetlands, we have hardened and paved our communities. Concrete and asphalt parking lots, driveways, and sidewalks cannot absorb excess rainwater like wetlands can, increasing the likelihood of flooding events and greatly impacting our communities.

Flood regimes are determined by a set of characteristic flooding conditions in a watershed including climatic and geologic influences as well as human modification. [1] In Louisiana, the Mississippi River’s flood regime responds to snowmelt and heavy rains upriver as well as any rain in the lower basin. Periods of high water in the southern half of the river usually occur during spring and early summer. [2] The three largest floods the river has seen in the last 100 years (1927, 1993, and 2011) occurred in April and May. Hydrology, the study of water flow, is crucial to planning for flood events. Through extensive study, the flood regime of the Mississippi River and many of its tributaries (and its primary distributary, the Atchafalaya River) are understood well enough to predict where flooding will occur after heavy rain throughout the watershed. The Army Corps of Engineers manages floodgates and spillways by diverting excess water to flood control areas to keep property damage to a minimum. Consequently, those flood control areas can accrete sediment and build land.

Natural events, like flooding, turn into natural disasters as we further impact the natural processes within our ecosystems. Wetlands are vital natural flood protection strategies in Louisiana as well as throughout the world. CWPPRA works to restore coastal wetlands to protect communities from inundation.

[1] https://pdfs.semanticscholar.org/c6c5/f7a18ebb57f4bb247a98618df850794101f5.pdf

[2] https://www.britannica.com/place/Mississippi-River#ref39994

[3] https://www.usgs.gov/faqs/what-a-1000-year-flood?qt-news_science_products=0#qt-news_science_products


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