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June 19, 2001, 6:11PM

Here’s what we can control: Damage from floods

By JOHN S. JACOB

AFTER Tropical Storm Allison, we ask: what can we do? Will we be ready for the next one? We’ve been asked if we can afford the $1 billion it would take to engineer our way out of the next flood. I ask: Can we afford to continue to develop as we have?

Was the flooding from Allison preventable? I suggest that it was, at least in part. Yes, this was a rainfall event of incredible proportions. But what sense does it make to call it the “flood of a lifetime” or a “500-year flood”? We have had several such events just in the past 25 years. Granted, these unusual rainfall events do not occur evenly across the area. But one thing we can be sure of — we will see more rain like this. So how do we prepare? Some suggest more large-scale stormwater projects. Costly, yes, but we have to do it, and “we know how,” they say. There might be some who would say that suggestion is just a little bit self-serving, but I believe the proposal is sincere.

There is no doubt that we need structural stormwater engineering to be able to live on this flat coastal plain. If we had no stormwater system, we would certainly flood much more often and in more places than we do now. But there is a question as to whether or not engineered stormwater controls, such as drainage ditches and detention ponds, should be the sum total or even the largest part of our drainage program.

Flooding occurs in flood plains. That is a fundamental fact that should not be forgotten. Let’s not build in flood plains! I said above that the flooding from Allison was preventable. In reality, the flooding was not at all preventable. What is preventable is the damage from the flooding. We don’t have to build in flood plains. A problem, of course, is that development upstream often enlarges flood plains downstream because there is much more runoff associated with the impervious surfaces of streets and shopping malls. But we still know enough to stay out of the flood plains.

One problem is that our flood plain maps don’t serve us very well. We have maps of 100-year and 500-year flood plains. What we really need are maps of relatively flood-prone and relatively flood-free areas. I had the privilege of assisting some flood victims recently in damaged homes near Mesa Road and Halls Bayou. I checked the Federal Emergency Management Agency flood maps (available online for Harris County at www.efloodmap.com, or other counties at http://www.esri.com/hazards/) and found that this particular area was not mapped with any flood risk at all, and yet the subdivision was adjacent to Hall’s Bayou. Five feet of water in those houses suggests more than the average flood risk. However, there was not five feet of water in houses everywhere it rained 30 inches. Water flows downhill, and it accumulates in flood plains. There was a pattern to this flood.

Let’s use our flood plains for what they were intended — to convey flood water. Could the damage I witnessed in the Mesa Road area have been prevented? Certainly. But it would have required some foresight on the part of planners and developers, and that was sadly lacking 50 years ago when that area was built out. A much larger green belt should have been preserved along the bayou.

We are told our population in the metro area will double in the next 20 to 50 years. More people with the same kind of development pattern we have had means more impervious surfaces and even more flooding in the future. Perhaps it is time to do some strategic planning to avoid preventable heartache in the future.

We have to develop our “green” infrastructure in parallel to our “gray” infrastructure, and we have to rethink how we design our gray infrastructure.

Green infrastructure includes our bays, bayous, forests and wetlands. These areas provide us with important ecological services, not the least of which is flood control. Let’s preserve wide swaths of land along our bayous and let them flood when they will. We may have to buy out some developed areas and restore natural hydrology.

Let’s preserve and restore as many of our wetlands as we can. These depressions act as natural flood detention basins, and they clean the water that runs through them. And they do it much cheaper and better than any system we can build. In addition to these very tangible services, these natural areas also provide us with much beauty. How can we be against that? Yes, it will be very expensive, but if we start now, we can make a real difference for the next generation. Development of our green infrastructure will be much cheaper in areas of new development, but we had better act quickly — it’s going fast.

“Gray” infrastructure is our built system. Our gray infrastructure of “big-ticket” projects needs to be rethought. “Moving the flood” (from upstream residents to downstream locales) has been called the fundamental issue. I agree this is an issue but would argue that “detaining” the flood might be the more fundamental issue. We need to do all we can to mimic nature. Natural areas have pervious soils and surfaces that allow water to percolate into the soil. Our natural areas also have an abundance of small depressions that detain water before it runs off.

“Micro-detention” is the new watchword in the cutting edge of stormwater technologies. We have to find ways to engineer swales, “rain gardens” and other such features into our landscapes and built areas that temporarily retain stormwater right at the site, rather than in large, usually ugly, detention basins. And these features can be engineered into our landscapes in such a way that the detention is not long enough to permit mosquito swarms to build after every rainfall.

The most important issue in terms of our gray infrastructure, or built environment, is sprawl. The preservation of our increasingly important (and increasingly scarce) green infrastructure is inconsistent with our free-for-all development pattern that is largely based on the automobile. We must explore some of the pedestrian-friendly developments that are being experimented with around the country that permit a somewhat denser development, but that are actually much more livable than our disconnected suburbs. It seems incredible, but, yes, we could actually have more livable neighborhoods and preserve significant natural areas that would serve us as floodways and areas of natural beauty.

Yes, we are going to have to open up our pocket books. But if we are really going to be successful, we are going to have to open up our imaginations as well. We can imagine a better future. Let’s get started.

John Jacob is an environmental quality specialist for the Texas Agricultural Extension Service and Texas Sea Grant Program.