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Here’s the Corps’ Draft Report
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Oct. 22, 2020
Seems that nobody likes the Corps of Engineers’ draft proposal for killing Buffalo Bayou. Not even the coalition of developers, car dealers, concrete makers, contractors, homebuilders, realtors and others that was pushing hard for it.
But then the vague draft report has many parts. It’s an initial stage in a $6 million attempt to figure out a solution to the disastrous flooding in and around Buffalo Bayou and its tributaries connected to the federal flood control dams during Harvey in 2017. The report looks at a future of increased heavy storms and increased development surrounding the sinking, cracking dams built by the Corps in the bayou’s upper watershed more than seventy years ago. (p. 13)
Besides deepening and widening Buffalo Bayou to an apparently uniform width of three-quarters of a football field, the proposals include building a dam on Cypress Creek and a 22,000-acre reservoir behind it. (p. 18) During heavy rains the creek overflows south across the prairie into one of the federal dams that, during Harvey, could not contain all the stormwater running into it.
Building the dam on Cypress Creek would probably encourage development on land that now floods, leading to more flood problems, the Corps admits. Another major drawback acknowledged by the Corps: the project would significantly degrade more than two-thirds of the remaining Katy Prairie, which serves to hold and slow stormwater. (p. 176)
Nevertheless, the Corps’ draft report is leaning towards building the dam and deepening and widening Buffalo Bayou, laying back the ancient high banks for some 22 miles from the dams to downtown. This would be done to accommodate a flow of some 15,000 cubic feet per second (cfs).
The idea also is to buyout property downstream on Buffalo Bayou that was inundated by the opening of the floodgates on the federal dams during Harvey in 2017, as well as possibly property upstream that flooded because they didn’t open the floodgates.
Flood stage in Buffalo Bayou differs upstream and downstream as the bayou channel naturally widens as it winds downstream. From the dams for some six miles downstream to West Beltway 8, the Corps in the 1950s straightened and narrowed the bayou, effectively reducing its capacity. According to the National Weather Service, flooding begins in this area when the US Geological Service gauge goes over 8,000 cfs. For the USGS gauge downstream at Piney Point, flooding begins around 7,500 cfs. At the Shepherd gauge closer to downtown Houston, flood stage is around 18,000 cfs.
However, the Corps, which needs to keep the reservoirs empty in order to be able to capture runoff from the next storm, operates the dams on the basis that property downstream will begin to flood when the Piney Point gauge goes over 4,000 cfs.
Total estimated cost for the dam and bayou “improvement” is upwards of $4 billion. (Correction Oct. 24: upwards of $7 billion. p. 144)
According to Brian Harper, chief of the Galveston District’s planning branch, the Corps in its cost benefit analysis did not put a financial value on the loss of environmental benefits and functions of the bayou or the prairie, which include cleansing polluted urban and agricultural runoff, not to mention the growing local (p. 105) and worldwide problem of biodiversity loss.
Misunderestimating Buffalo Bayou
The Corps would also line the bayou channel bottom and banks with articulated concrete block in areas of “high erosion,” whatever that means. Never mind that concrete block does not actually work in Buffalo Bayou. The Corps’ Project Delivery Team (PDT), most of whom are from Corps offices in other parts of the country, does not seem to be aware that bank instability in our bayou is mostly from slumping, sliding down vertically. This happens no matter the steepness of the slope. Adding the weight of concrete block, which is designed for erosion caused by horizontal flow, only increases the likelihood of collapse, according to our experts and common sense.
And would it be piling on too much to point out that the report is so sloppy that its cover photo of a flooded Buffalo Bayou in Buffalo Bayou Park between Allen Parkway and Memorial Drive is misidentified as a flooded Interstate 10?