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environment, pollution & animal rights
Flooding is not a new problem in Houston and Harris County. Houston has had flood problems since it was founded in the 1830s.Even though the Harris County Flood Control District spends millions of tax dollars every year, the flooding problem just never seems to get better.
To begin to understand the flooding problem, you must first understand the flood control system. Harris County is made up of bayous and ditches designed to carry rainwater to the Gulf of Mexico. These waterways have a maximum amount of water that they can handle at any one time. Over the years, they’ve been expanded to have larger capacities. For most of the flood control system’s history, that has been the plan of action -- to get the water down stream as fast as possible.
The problem with a system to speed-up the water flow is that as urban development takes place, the natural run-off into the bayous is increased. In other words, where there used to be grass and dirt, there is now concrete. Concrete moves water into the drainage systems much faster than the same piece of land before it was developed. According to Water Resources and Environmental Engineer Larry Dunbar, Houston’s flooding problems are largely based on the way the Harris County area developed.
“It basically started around Houston and grew outward, said Dunbar. “Well, all the bayous tend to run from west to east almost through Houston on their way to Galveston Bay. Development started to build around the downstream end of these bayous, then as development grew outward, it basically went upstream along the bayous, so you had more development upstream sending more of that water downstream into an area that couldn’t handle it.”
Fred Garcia of the Harris County Flood Control District says knowledge of flood control methods has improved since the district was created.
“In those days when these massive bayou type conveyances were being designed and constructed, that was the accepted method to build this large conduit or large conveyance and over time as methods and means have evolved, we’ve found that detention basins are a big part and should be a big part of the tools in the tool box,” said Garcia. “And so we do rely on large regional detention basins real heavily these days.”
Detention basins are designed to hold water created by increased run-off from developed land and release it at a rate that matches the pre-project development flow rate. In other words, if a piece of undeveloped land discharges water at a rate of 0.125 cubic feet per second, then a detention basin for a development on that same piece of land must discharge water at the same rate of 0.125 cubic feet per second, otherwise the development will have an adverse impact on flood control.
Harris County has criteria to regulate the flow rate from detention ponds built by new developers, but some say their math is to blame for the flooding problems around the county. The district uses what’s called a “Site Runoff Curve” to determine that amount of outflow a developer’s detention pond can produce. According to Dunbar, the curve misrepresents the natural runoff rate of land in Harris County.
“It gives you a flow rate of around 1.5 cubic feet per second per acre. The real question is: does an undeveloped piece of land in Harris County produce 1.5 cubic feet per second per acre of runoff? If it does, then you’re restricting it to the true undeveloped condition,” said Dunbar. “But what if that undeveloped piece of property only produces a half cubic feet per second per acre? You then can use the curve as a developer and say, ‘OK, what I’m allowed to release is 1.5 cubic feet per second per acre,’ so what have you just allowed a developer to do? You allow them to increase the flow off their site, while at the same time being able to stand up in public and say, ‘See we’re making developers mitigate their impact.’”
Houston Voters Against Flooding has asked Houston and Harris County to fix loopholes in their detention basin criteria and to restrict the maximum allowable release rate from detention ponds to .125 cubic feet per second per acre, which is the standard used by surrounding counties, including Fort Bend and Clear Creek.
The Flood Control District and Houston officials have begun an Urban Storm Water Management Study to examine flood control policy. Garcia says development criteria will be looked at.
“Those certain criteria are gong to be looked at and evaluated, and if we find through the review that there should be modifications to the criteria, then appropriate recommendations will be made,” said Garcia.
According to the Houston Voters Against Flooding and Dunbar, changes in the criteria must be made. Otherwise the district will continue to fight a losing battle by spending money on projects that won’t solve the problem.
“It doesn’t do you any good to go spend millions or billions of dollars to try to fix existing flooding problems while on the other hand you’re allowing new development to come in and worsen it,” said Dunbar. “That’s what’s happening and that’s what needs to be corrected.”
© Copyright World Internet News 2006-07
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