Tensions on Buffalo Bayou
August 19, 2018
The Harris County Flood Control District presented to Harris County Commissioners Court Tuesday, Aug. 14, its final list of flood risk reduction projects that could be funded with the proceeds of $2.5 billion in bonds over a period of 10-15 years.
Early voting on the bonds started Aug. 8 and continues through Tuesday, Aug. 21. The election is Saturday, Aug. 25. The $2.5 billion target is widely considered a small down payment on a $20-30 billion county-wide flood resiliency program that should emphasize buyouts, land acquisition and preservation, floodplain restoration and other non-structural approaches.
The list of 237 projects includes 38 projects that were added as a result of community meetings held across Harris County in June, July and August, according to the district website. Note that the list of potential projects is not fixed or obligatory, and citizens should still have opportunities to influence future plans and priorities.
These include $30 million for design and construction of replacement bridges along Buffalo Bayou, apparently targeting bridges that went under water during Harvey or are thought to be obstructing the flow.
The new list includes $500,000 for studies to investigate “bridges over Buffalo Bayou, the channel conveyance capacity around Beltway 8, Rummel Creek Road bridge and potential high flow bypasses at various locations along the bayou for the purpose of reducing the risk of flooding along the channel.”
Also newly included is $200,000 for investigation of the “effectiveness of small detention sites in the Buffalo Bayou watershed for the purpose of reducing the risk of flooding.”
Tensions Upstream and Downstream
The reference to “channel conveyance capacity around Beltway 8” and “potential high flow bypasses” reflects a simmering tension between residents on the straightened upstream of Beltway 8 and those on the meandering downstream. Neighborhood activists upstream of the beltway blame the “kinks” and “bottlenecks” downstream for causing flooding of their homes. Michael Huffmaster, president of the Briar Forest Super Neighborhood and chair of the Super Neighborhood Alliance, has been advocating a plan to cut through meanders downstream and install large underground concrete culverts to speed the flow.
Rivers and streams are dynamic systems, evolving through the landscape to find equilibrium, balancing energy, flow, and sediment transport. While meandering streams carry more water because they are longer (p. 9), artificially straightening streams shortens the channel and increases the speed of the flow, which can cause more erosion and flooding. (See below.) Meandering streams are more stable, healthier, cleaner, and more biologically diverse. (p. 2)
Some six miles of Buffalo Bayou below Barker Dam was rerouted, stripped, and straightened in the late Forties and Fifties by the Corps of Engineers through what is now Terry Hershey Park to several hundred feet below Beltway 8. Environmentalists, including Terry Hershey, Frank Smith, George Mitchell, and others, many of whom also lived on the bayou, led a popular movement in the Sixties and Seventies to stop the Corps from stripping, straightening, and concreting the bayou all the way to the Shepherd Bridge.
As a result, much of Buffalo Bayou remains in a relatively natural, meandering state.
Straightening and concreting streams has since been discredited and largely abandoned as a flood management tool because it causes more flooding (p. 24) as well as polluted waters and ecological destruction, and more. (pp. 154-55) Dredging and artificially deepening and widening streams has also been shown to be ineffective, causing more flooding, bank collapse, and continuing maintenance problems. (See also here.)
In the interim, however, subdivisions were built along and on top of the former channel and remaining oxbows of the straightened section of Buffalo Bayou in what is now Terry Hershey Park, now owned by the flood control district. A great many homes flooded in these subdivisions, along with other residences up and down the bayou.
Altogether 25,010 houses flooded in the entire Buffalo Bayou watershed including Addicks and Barker reservoirs, followed by the 24,730 homes that flooded in the Greens Bayou watershed, including Halls Bayou, and the 23,810 houses that flooded in the Brays Bayou watershed, according to a June 4, 2018, report from the flood control district. (p. 14) (See this map and this map of the regional watersheds. The boundaries or definitions of the various watersheds that make up the entire San Jacinto River watershed vary.)
These figures do not include apartments, condominiums, commercial or other structures that flooded.
Buffalo Bayou flows through Barker Reservoir. Other streams flowing through and around Barker and Addicks reservoirs also empty into Buffalo Bayou, as well as numerous major and minor tributaries downstream of the dams.
Major Flooding Up and Down Buffalo Bayou
Though Huffmaster, whose house flooded on a remnant oxbow of the bayou adjacent to Terry Hershey Park, claims in his proposal that “east of Piney Point, few structures flooded even at 16000 cfs [cubic feet per second],” (p. 15) anecdotal reports from residents downstream are that entire neighborhoods had anywhere from a foot to as much as eight feet of water in their homes all the way to Shepherd Bridge. Residents upstream and downstream describe the peak of the Harvey flooding beginning the morning of Sunday, Aug. 27, and passing that evening downstream. However, in response to the unprecedented amount of rain runoff flowing into the reservoirs, the Corps of Engineers was forced to begin controlled releases from the dams around 1 a.m. Monday, Aug. 28. This precipitated a second wave of flooding primarily hitting those upstream neighborhoods closer to the dams, including some that hadn’t flooded earlier. Many of those devastated neighborhoods, as well as neighborhoods all over the county, are still attempting to recover even as voters go to the polls.
The district report describes the four-day total rainfall from Harvey, Aug. 25-29, 2017, in the larger Buffalo Bayou watershed, as well as in the majority of Harris County, as an event so large it should only occur once every 5,000-20,000 years. Southeastern Harris County’s four-day rainfall is described as a 20,000-year-plus event. (p. 30)
More Water Flowing Faster
The list of projects, while including some new detention proposals, emphasizes “improving” channels for stormwater conveyance, which means more and faster water flowing through channels and into the overburdened reservoirs, for example. Still included is $10 million for a controversial plan to remove forest and dig a series of small linear detention basins on the south side of Buffalo Bayou in Terry Hershey Park. These basins would temporarily capture overflow from the bayou in order to balance increased flow into the bayou from future City of Houston drainage projects. Trees and vegetation, however, have important detention functions of their own, not to mention other important environmental and health benefits.
Flooding begins on the land, and modern flood management focuses on stopping and slowing stormwater before it floods a stream. “Lag time” is the amount of time it takes for peak rainfall to hit the ground and run over the land (and through drainage pipes) into a stream. The shorter the lag time, the higher the peak flow in the stream.
Not included is addressing the problem of massive stormwater outfalls pointing directly across the bayou, of which there are several in Terry Hershey Park including at Beltway 8. Stormwater drainage pipes perpendicular to the stream block the flow and are in violation of the flood control district’s design manual. (p. 111)
The list also includes funds proposed to be used in collaboration with Army Corps of Engineers, which owns and operates Addicks and Barker, to evaluate the effectiveness and operation of those 70-year-old dams.
Potential projects supported by bond funding include:
- Channel modifications to improve stormwater conveyance
- Regional stormwater detention basins
- Major repairs to flood-damaged drainage infrastructure
- Removing large amounts of sediment and silt from drainage channels
- Voluntary buyouts of flood-prone properties
- Wetland mitigation banks
- Property acquisition for preserving the natural floodplains
- Drainage improvements made in partnership with other cities, utility districts, or other local government agencies
- Upgrading the Harris County Flood Warning System