21 Dec 2016
As April left the US city of Houston, Texas with many neighborhoods under more than a foot of water, the matter of flood control has remained firmly at the forefront in state discussions on environmental management plans.
With major flooding events becoming more common worldwide, government authorities are under intense pressure to find and allocate multimillion dollar funding for proactive flood prevention measures amidst the reactive costs of repairing the physical toll of events barely elapsed. Likewise, water supply and drainage infrastructure must respond to thousand-fold increases in consumption and output since the heart of that infrastructure was originally installed.
The low-lying city of Houston has endured more than 35 significant floods – 26 of these since the 1970s and since the inner city population passed 1 million. RPS Klotz Associates President Wayne Klotz, PE, D.WRE has presided over the Coastal Water Authority Board since 2011 and has run a professional civil engineering business in Houston for over 30 years. In this capacity and as a former president of the American Society of Civil Engineers, he is often approached to discuss the issues from a professional viewpoint.
Wayne notes that the efforts to maintain a built environment on a flat topography, little above sea level and subject to the Gulf Coast’s humid climate, have not kept pace with development. ‘The Barker and Addicks reservoirs [were built] in the 1940s after major floods in 1929 and 1935 [and they were way out in the countryside, but the city continued to grow as cities will, and [they] are now in the middle of a huge municipal center.’
Certainly the two detention reservoirs have reduced flood levels downstream Buffalo Bayou, but they have not grown at the population’s pace. As America’s fourth-largest city and a world-leading business center for energy, biomedical and aeronautics, Houston has a 2 million inner city population, extending to some 6 million counting outlying areas. Its incoming population grew by 90,000 last year alone. Construction on new outlets for the reservoirs began in late 2015 and is expected to complete during 2019. A full operational review of the reservoirs is tabled for 2018.
Over $1 billion has been invested in Houston’s flood-risk protection since 2012, but this has not been able to contend with recent events, notably the Memorial Day storm and April’s ‘tax day’ storm .
Various improvements have been made to the bayous with the current program including creation of new detention basins, channel improvements and state voluntary buyouts of the most flood-susceptible houses. The Sims Bayou improvements off the Houston Ship Channel, completed in 2015, provided three new detention basins, 19.3 miles of channel improvements and 22 new bridges. It should save 35,000 homes and 2,000 commercial structures in the 1:100 flood risk bracket from structural flood damage. Current works on White Oak Bayou include four detention basins, 15.3 grass-lined miles of channel improvements and 12 miles of greenspace.
RPS is engaged on several county projects to deliver an overall improved flood management infrastructure for the city and region. RPS Associate Engineer Francisco Carrillo is engaged on the Bayou Greenways 2020 project. It delivers a plan for the transformation of underused land into protected greenspaces. Appropriate wetland landscaping will increase ground absorbency surface area. It gives the opportunity for residents to better use and take pride in their local landscape as the completed continuous parks system will create a long network of hike and bike trails within easy pedestrian access of most residents – 60% of Houston’s population will be less than a mile and a half from a Bayou Greenway space. With the land used effectively, it is removed from immediate risk of heavy urban development and potential renewed issues of inadequate drainage and increased surface water runoff. The proposal is solid, simple and fairly inexpensive, says Francisco, and what’s more, for the bodies partnering to deliver it, the creation of desirable green areas will attract newcomers, including families, and also outside investment.
One of the largest detention projects that RPS is engaged on is the Willow Waterhole Bayou – a 19-mile-long earth- and concrete-lined channel surrounded by the dense urban sprawl of southwest Houston. RPS Associate Project Manager Morena Arredondo, PE, is leading RPS’ team on the project. It is a section of the Brays Bayou watershed that has suffered significant flooding on several occasions .
Approximately 280 acres of the site is to be transformed into a unique greenspace with a new Willow Waterhole Channel, inflow concrete weirs and six wet-bottom detention basins with a 600m gallon total capacity. The greenspace aspect is led by the Texas Parks and Wildlife Department and will provide a range of community recreational spaces, wildlife conservation plans and prairie restoration .
RPS has helped devise an effective stormwater improvements plan, identifying need to prepare for worst events as a first action and prioritize the health, safety and welfare of its inhabitants. The latest highly accurate reporting and monitoring software tools have been brought on board, says RPS Manager William Conlan, PE, CFM, combined with more hours devoted to gathering reliable data and now able to cover all 130,000 drainage areas effectively .
‘Before there was Houston, the land was swamp,’ Wayne explains. ‘When it rains, it rains a lot and it rains hard. It is a priority to respond efficiently to the drastic flood events the region experiences, but more so to plan way ahead to be certain that we can greatly reduce the impacts of such events before they are felt.’
The Harris County Flood Control District has formal reports on regional flooding events and flood control available to download in PDF format from its website: https://www.hcfcd.org/
i Houston was founded in August 1836 in the south-east of Texas, near the Gulf of Mexico. It was incorporated as a city in 1837. Its population was over 2,000 by 1850, almost doubling each decade until growth slowed in the 1930s. By 1970 the inner city population was 1.2million. Demographics from Wikipedia.
ii The project, worth around $105m, is led by the US Army Corps of Engineers, which originally constructed the two reservoirs.
iiiMemorial Day Storm (24th – 26th May 2015). Houston suffered 23” rainfall in 72 hours, parts of Harris County suffered up to 10” of rainfall within a six hour period. In excess of 6,000 homes were flooded, some press reports noting up to 4,000 of these properties suffering significant damages. Less than a year later, several days of heavy rainfall began on April 17th 2016 with Houston experiencing what the Harris County local flood control district estimated to be a 1 in 10,000 year rainfall event. Over 15” of rain fell on Houston and Harris County within the first 24 hours. Excepting the July 2012 storm, meteorologists are viewing the Tax Day and Memorial Day storm events as the most unprecedented rainfall to affect Houston since the 1960s. Over $3bn has been incurred in insured flood damage for Houston between 1999 and 2009.
iv1983 (Hurricane Alicia), 2001 (Tropical Storm Allison), 2008 (Hurricane Ike), 2015 (Memorial Day Flood).
vThe conservation plans focus on the site’s 36 bird species and the conservation of the endangered Texas Prairie-dawn flower (Hymenoxys Texana) that is unique to Houston’s Gulf Coastal Plain, growing almost solely in the Fort Bend, Harris and Trinity counties of Texas.
viThe former CDP produced in the 1990s only covered 65% of the regions storm-sewers. These 130,000 drainage areas include 33 million linear feet of infrastructure and 12 million linear feet of ditches. Person hours include not only desk-based technical analysis but also physical drive and walkovers with gyroscopes, scanners and sensors.
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