Thursday, September 7, 2017

Wetlands in Huston Areas

Blog 4 

Houston’s development boom destroyed wetlands that naturally absorbed flood water.

The historic rainfall in Houston in September 2017 has left the Space City underwater with thousands of its citizens displaced.
As the city continues to struggle with the devastation of Harvey, questions have already bubbled up about why the flood has been so devastating.
A big factor could be the lack of rules that helped develop Houston into the country's fourth-largest city — and the biggest without a formal zoning code.
Experts believe the lack of regulation, building in the federally designated flood area, and paving over wetlands might've contributed to the storm's severity.
The stormwater system has never been designed for anything much stronger than a heavy afternoon thunderstorm."
Houston has lost a significant portion of its prairie and wetlands in the last 25 years — and with it a natural absorbent for rain water.
Harris County, which is primarily made up of Houston, lost almost 30% of its wetlands between 1992 and 2010, according to a Texas A&M study.
"Loss of wetlands on this scale means a substantial loss in the ability of the landscape to detain and remove pollutants from stormwater," the report warned. "The results are increased flooding and degraded fishing grounds in downstream bayous and marshes."
Much of that was lost to development, causing water to gush down streets instead of flow into the wetlands.
And for Harris County, that meant $350 million in lost stormwater detention, the report found. The entire Houston area — made up of several counties — lost wetlands that could detain 4 billion gallons of stormwater worth $600 million.
Instead of water being absorbed by these wetlands, it flows into the pair of bayous Houston relies on for drainage, along with two reservoirs, But those, too, get overflowed and spill into area homes.
Uncle Sam has tried to preserve more wetlands through the Clean Water Act, which requires affected developers to replace destroyed areas with new ones. The Trump administration has indicated it wants to undo the requirements, which had been emboldened by the Obama administration.
Development in Houston has also had trouble abiding by this rule. A 2015 joint study by Texas A&M and Houston Advanced Research Center examined permits between 1990 and 2012 in the Houston area. What they found was less than half actually had documentation to show the lands were replaced.
Many of the new homes built have been in the 100-year floodplain, a federally designated area that is at a higher risk of being hit by a bad storm.
Some 4,000 new structures have been built within that 100-year floodplain in Harris County since 2010.
Over development in flood zones has incised some after Harvey dumped several feet of rain on Houston. 
But the impact of flooding, particularly in densely developed areas like cities, is far more constant than a massive, natural disaster like Harvey exposes. The reason cities flood isn’t because the water comes in, not exactly. It’s because the pavement of civilization forces the water to get back out again.
Under normal circumstances, rain or snowfall soaks back into the earth after falling. It gets absorbed by grasslands, by parks, by residential lawns, by anywhere the soil is exposed. Two factors can impede that absorption. One is large quantities of rain in a short period of time. The ground becomes inundated, and the water spreads out in accordance with the topography. The second is covering over the ground so it cannot soak up water in the first place. And that’s exactly what cities do—they transform the land into developed civilization.

Roads, parking lots, sidewalks, and other pavements, along with asphalt, concrete, brick, stone, and other building materials, combine to create impervious surfaces that resist the natural absorption of water. In most of the United States, about 75 percent of its land area, less than 1 percent of the land is hardscape. In cities, up to 40 percent is impervious.

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