Study Questions Use of Dams and Urges Focus on Causes, Not Symptoms, of Flooding
County Commissioners to Discuss Flood Strategy, Funding, Tuesday, March 27, 10 a.m.
March 26, 2018
An “incredible” 70 percent of stream gauges in Harris County show significant increases in peak flow – as much as 6,400 percent in one case — since the beginning of record keeping by the US Geological Survey.
More streams in Harris County are increasingly flowing higher than in any other part of the state, according to a study recently published in the March 2018 issue of the Texas Water Journal, a publication of the Texas Water Resources Institute.
Three stream gauges on Buffalo Bayou have shown the greatest increase in peak flows since the federal dams were built in the 1940s to reduce flooding on the bayou, according to the report.
Significantly, two major streams, Langham and Bear creeks, feeding into one of these dams — the overburdened Addicks Reservoir — showed some of the largest upward trends in peak flow. The record amount of runoff flowing into Addicks during Hurricane Harvey was a major factor in the unprecedented decision to open the floodgates on both dams during the storm in order to prevent the dams from overtopping. Thousands of homes both below and behind the dams were flooded, and three people died.
The area in western Harris County above and behind Addicks Reservoir is experiencing some of the greatest development pressure in the region, particularly since the construction of the Grand Parkway (Highway 99). Buildings, paved surface, and other hard structures, including pipes, associated with development cause more and faster and more polluted rain runoff into streams, leading to flooding.
“An Overreliance on Flood Storage Reservoirs”
The report noted “the difficulty of maintaining lower peak flows below a reservoir when the inflows to the reservoir exhibit extraordinary increases year over year.”
“It is much easier for impoundments to store flood flows when these flows are not rapidly increasing on an annual basis. Thus, relying on large impoundment projects alone likely will not achieve success and again points back to our central emphasis of identifying causes, not just symptoms [of flooding].”
The study, titled “Peak Flow Trends Highlight Emerging Urban Flooding Hotspots in Texas,” was authored by Matthew D. Berg, CEO and Principal Scientist, Simfero Consultants, in Houston.
The USGS gauge on Greens Bayou at Cutten Road in northwest Harris County experienced the greatest increase in peak flow – 6,400 percent over a period of several decades.
Other rapidly increasing stream flows are occurring in Keegans Bayou at Roark Road in southwest Houston (nearly 5,000 percent), Greens Bayou near Highway 45 in north Houston (1,200 percent), Langham Creek near Addicks Reservoir in west Houston (750 percent), and White Oak Bayou near Heights Boulevard (600 percent).
Harris County Commissioners Court will meet Tuesday, March 27, to discuss flood management strategies and a possible bond referendum to pay for them. Also on the agenda is a proposal to study the feasibility of digging massive tunnels to drain stormwater from western Harris County into Galveston Bay. The contract to be negotiated is with Fugro USA Land, Inc.
The commissioners’ meeting begins at 10 a.m. on the ninth floor of 1001 Preston in downtown Houston. Those who wish to speak can sign up before the meeting here.
Image courtesy of Matthew D. Berg, Simfero Consultants, Texas Water Journal, Texas Water Resources Institute
The observed trends in NWIS historic stream gauge data are perhaps unsurprising, given the rate of growth in the Houston metropolitan area. It would be interesting to determine whether a correlation exists between peak flow trends and impermeable surface area growth trends, by watershed. This would require examination of historic Landsat land use/land cover classification data, a task easily within reach of current Geographic Information System (GIS) technology. This might make for an interesting thesis topic for an enterprising geosciences grad student at UH or Rice.
Setting aside the subject of major impoundments like Barker and Addicks, one suspects that existing local-level impoundment capacity (i.e. the “amenity” lakes found in more recent subdivisions) is insufficient to the task at hand, particularly for intense, prolonged rain events like Harvey. It also begs the issue of what to do with Houston’s older neighborhoods, which generally lack runoff mitigation of any sort (beyond bar ditches and the like). Regardless, if Harvey taught us anything, it’s that we’re going to have to get a lot smarter about stormwater management. For extra credit, it would be really nice if we could do so while at the same time preserving/expanding our remaining metropolitan riparian habitats, and making such habitats more accessible to, and livable for, all Houstonians.
Excellent comment. Thank you.