Os EUA acabaram de enfrentar uma das mais severas temporadas de chuvas, com enchentes durante a última primavera do Hemisfério Norte, afetando e causando calamidades e muitos prejuízos em cidades, plantações, estradas, indústrias, áreas portuárias etc.
A situação provoca uma reflexão sobre a ocupação de áreas de várzeas, os seus riscos e consequências.
O artigo abaixo, faz referência a uma expressão utilizada por Gilbert White, um dos precursores do movimento de gestão de planícies inundáveis nos EUA, que alertou:
"Enchentes são atos de Deus; prejuízos causados por enchentes são atos dos Homens". Sempre haverá chuvas, mas as decisões que nós tomamos sobre como cuidamos dos nossos rios e usamos as nossas várzeas é que determinam a extensão dos danos durante uma enchente.
(“Floods are an act of God; flood damages result from the acts of man.” The rain will always fall, but the decisions we make about how we manage our rivers and use our floodplains determines how extensive the damages are during a flood).
Veja, a seguir, a extensão da calamidade das chuvas enfrentadas nos EUA nos últimos meses.
MAKING ROOM FOR FLOODS IN THE MIDWEST
In the coming weeks and months, the communities and landowners across the Midwest will want to act as quickly as possible to get back on their feet. A key step will be deciding whether to rebuild back the way things were, or to choose new options that could make us more prepared for the next flood.
There’s a famous quote by Gilbert White, the founder of the floodplain management movement: “Floods are an act of God; flood damages result from the acts of man.” The rain will always fall, but the decisions we make about how we manage our rivers and use our floodplains determines how extensive the damages are during a flood.
The rivers across the Midwest, and much of the country have been dramatically altered from their natural states over the last century. Before Europeans settled in the Midwest, big rivers like the Missouri and Mississippi would spread their flood waters out across wide floodplains, slowing the flows, and rejuvenating robust floodplain habitats. As farmers sought to make their land tillable, they straightened streams and created extensive levee systems to keep flood water off their land and in the streams. About a century ago, the Army Corps became the official flood control agency of the United States building monster levee systems along our big rivers. At last count, they oversee almost 30,000 miles of levees across the United States.
|Levees in the United States, National Levee Database|
As shown in this excellent piece by Propublica, relying on levees can have unfortunate consequences. Levees create the illusion of safety, and the “protected” floodplain can be attractive places for people to build communities and businesses. But trapping flood waters in a narrow channel forces water to move downstream more quickly, which puts stress on levees. When floodwaters overtop or breach a levee, the results can be catastrophic to the communities and fields behind it. To make matters worse, when levees fail, it tends to happen at the same spots meaning we see a damage and repair cycle play out flood after flood.
In many areas across the country where a historic reliance on levees has led to increased flood risk, communities and landowners are choosing to reduce the risk of future levee failures by creating more room for flood waters to spread out across the floodplain. These natural flood management approaches to alter levee systems and make room for rivers to flood can come in many forms.
- After the 2011 Missouri River floods, a flooded landowner was tired of having his levee fail during floods, and asked the Army Corps to do a levee setback rather than rebuild it back along the river.
- In 2010, the Army Corps worked with Iowa Department of Natural Resources to acquire the 300 acres of floodplain land and transfer it to the Green Island Wildlife Management after a repetitively damaged levee breached on the Maquoketa River in Iowa.
- In Yakima County, Washington, after repetitive damage to their levee system, the flood control district is proactively reconnecting the Yakima River to the floodplain to reduce future flood damage.
|NOAA’s 2019 Spring Outlook flood risk map|
After the 2011 Missouri River flood, the Omaha district of the Army Corps explored levee setbacks, and potential to implement projects after a flood. River managers across the Midwest should build upon their past success and planning to implement projects that give the river additional room to flood whenever they are repairing damaged levees. We need to work as quickly as possible with landowners and other stakeholders to identify opportunities to create more room for rivers to flood within the existing flood control system.
Fonte: American Rivers