by Scott Saenger
Vice President, H&H Deputy Practice Leader
In a recent article published by Michael Bloom and Steve Stagner, “Boomtown, Flood Town Reconsidered: An Engineer’s View”, got me thinking about flood planning and drainage solutions in the Greater Houston Metropolitan area. My thanks to Michael and Steve for initiating this discussion and providing factual, objective information on flooding without the emotional aspects of the issue. The following are some general thoughts on the issue of flooding.
As engineers, we need to recognize (as done in the article) that flooding is a terrible thing, and it raises emotional levels that can’t simply be dismissed with logical, engineering explanations. How many times have we as engineers heard, “It’s never flooded before” or “I‘ve lived here 20 years and it’s never flooded before.”
I generally concur that most of the flooding we’ve seen is not directly man-made and the current design standards are working well. In my opinion, the biggest design standard that has minimized flood damage to structures is the minimum slab elevation recommendations, where homes are now built one to two feet above adjacent ground verses inches as commonly seen with older homes.
Drainage solutions are not one-size-fits-all, especially in the Greater Houston area. Flooding is a terrible thing. In more than 30 years working as a drainage engineer, I’ve seen the devastation and how flooding can impact lives. I’ve helped friends haul out moldy carpet and sheet rock, waded through flooded streets to help neighbors, stood at the edge of levees and watched the water rise (knowing there was little else that could be done at that time). I’ve delivered notices to residents door-to-door informing them that they may be without access for days if the Brazos River rises as predicted and attended numerous public meetings where I can empathize with those who talk about a helpless feeling with flood waters rising around them and how much they’ve lost. I’ve lived that throughout my career.
As pointed out in the article, the area’s understanding of how to evaluate and address drainage issues has grown and developed. Today, we don’t handle drainage and development the way we did in the 70’s and 80’s. In the 80’s we gained technology that gave the engineering community the ability to use computer models to estimate runoff and flood depths in systems more quickly and with precision. That technology grew stronger in the 90’s, with more desktop application tools to evaluate drainage. In the 2000’s, satellite imagery, GPS topography and LiDAR technology became available as a tool to use in the flood evaluation arena. Today’s tools are almost too sophisticated, and the issues can be analyzed ad infinitum.
With all these technological tools in the toolbox, we still design most of our drainage systems (storm sewers, channels and detention basins) as passive systems. That is, they fill up and drain as water reaches certain elevations without regard to what’s happening upstream or downstream. They are designed to function based on specific statistical storm events and while they have been proven effective; they are certainly not utilized in the most efficient manner. With current technology, why shouldn’t we start looking at more active systems, where we use radar rainfall to project rainfall runoff through the system of pipes, channels and detention basins and use remotely activated gates and valves to make better use of our existing drainage systems? Worst case is they fall back to a passive system, but how much more efficient could they be if operated based on real time storm events? Addicks and Barker Reservoirs vary release rates based on rainfall conditions, why not other systems? Yes, I know this would take a considerable effort, but we should at least look at how the community can benefit from an active flood control system.
This brings me back to my initial statement, “Drainage Solutions are Not One-Size-Fits-All.” We need to understand which problem we’re trying to solve and use the proper tools to address them. While flooding in the Greater Houston area has typically been from excessive rainfall, flooding happens in many different forms.
House flooding – The way homeowners landscape their yards and place gardens and fencing can create flooding of the home. Heavy rains that can’t flow easily around the home to the street find the path of least resistance, which may be through or at least into the home. Homeowners need to be educated about the steps they can take to reduce their risks of flooding.
Street flooding – As you pointed out, streets are an important part of the design of our local drainage systems and are expected to hold and convey water in heavy rain events. Street flooding can directly impact mobility, emergency services and can lead to structural flooding. The use of streets as part of the drainage system should not impair emergency vehicles and should be limited to a level that avoids any structural flooding of homes or businesses. It would also seem prudent to identify specific streets for hurricane evacuation and emergency access that should have limited use if any part of the drainage system becomes impacted. The public needs to be informed of streets that are prone to flooding, areas to avoid during certain rainfall events, and where evacuation corridors exist.
Riverine Flooding – Rivers, bayous, creeks and streams are where most people perceive flooding. While this is not always the primary source of our flooding it is the one area that, if improved, can reduce house flooding and street flooding. It is the backbone of our drainage system. Harris County Flood Control has done an outstanding job in identifying and implementing projects to help reduce riverine flooding and continues to progress with many of the identified projects as funding allows. The City of Houston’s recent commitment to speed up funding for flood control projects will aid in this flood reduction, thus improving the overall level of flood protection for the area. Natural riverine floodplains are areas that development should try to avoid, but they can offer an ideal location for amenities such as parks and trails. More and more developers are seeing the benefit of enhancing these areas as amenity areas, thus avoiding the placement of homes in flood prone riverine areas.
Overland sheet flow – When rain falls on a tract of land, where does it go? The simple answer is that it flows to the lowest point traveling the path of least resistance. Over the eons, Mother Nature has dictated these conditions with the vegetation growing in an area, the types of soil or rock, and the overall topography or fall of the land. With the relatively flat land around the Greater Houston area, water is not always channelized but will flow with relatively shallow flow over larger areas. If homes or other structures are placed in this path, they can either block flow from the upstream area potentially causing flooding, flood themselves as water flows across/around the structure or cause water to be funneled to a concentrated location and flood areas downstream.
Back to the initial statement, “Drainage Solutions are Not One-Size-Fits-All.” Before effective drainage solutions can be evaluated, the cause of the flooding needs to be understood. The public needs better education for a deeper understanding of the issues involved with flooding and to go beyond the mantra that flooding is all caused by new development.
Scott Saenger, PE, Vice President, Jones|Carter