Brush Creates New Banks and Needs to Stay
Aug. 28, 2015
Updated Aug. 29, 2015, with a response from the Harris County Flood Control District. See below.
We were afraid of this.
Big floods are powerful. Anyone who has lived on or spent any time on a river in the wild knows that a river can rearrange its banks with an awesome, even frightening force. Yet floods in nature are necessary.
Buffalo Bayou is an 18,000-year-old river, our Mother Bayou. We are privileged to have a forested stretch of the bayou passing through the middle of the city in our great public Memorial Park. But during the Memorial Day flood and the record-high water released by the Army Corps of Engineers from the upstream dams during the days that followed, the rushing bayou took down trees and shrubs in Memorial Park, the Hogg Bird Sanctuary and elsewhere. The bayou was reordering its banks, replenishing and reseeding the floodplain, adjusting to the changing flow, as it has done for a very long time.
Not all of this was erosion exactly. Our geologists explain that some of it was slumping caused by the overflowing of the banks. The overflowing floodwater saturated the high ground and seeped into the internal layers of clay soil that turned to pudding and slid out, creating the concave look that you see on some of the banks. This particular slippery geologic makeup of Buffalo Bayou is one reason why we believe the Harris County Flood Control District’s costly and misguided $6 million “stabilization” project, known as the Memorial Park Demonstration Project, won’t work on the high banks of our untamed Buffalo Bayou, a rare natural asset to have and learn from in the middle of the city.
Our Muddy, Maligned, Mistreated Bayou Knows Better
But trees and brush falling onto the banks (and into the water) is part of a natural process, an important natural rebuilding process. The brush collects sediment from the waters of the bayou, building up new banks that the bayou replants with stabilizing and colonizing native vegetation. Yes, amazingly, our muddy, maligned and mistreated living bayou does that, with its own superior intelligence and life force. The bayou restores itself, replenishing its important ability to filter pollutants, neutralize bad bacteria, cleanse the water, protect against further erosion and provide aquatic habitat, among many other important functions, including trapping our trash and plastic debris before it ends up in the bay and oceans.
Indeed, a part of the so-called Natural Channel Design method proposed by the Harris County Flood Control District for this natural stretch of the bayou passing by Memorial Park and the Hogg Bird Sanctuary is based on this natural cycle. But flood control’s proposed project, currently being considered for a permit by the Army Corps of Engineers, would pointlessly destroy the bayou and rebuild it into an artificial landscape that would have none of this capability and would, in all likelihood, wash out.
We Were Hoping the Authorities Would Know Better
Still, in the meantime we were hoping the authorities and landowners would respect the bayou’s natural restorative process. Downed trees are also the basis of a natural bank stabilization method known as a “brush mattress.”
Alas, just yesterday, August 27, we saw that someone has begun sawing up the fallen trees on the banks of Memorial Park. We don’t know yet who is responsible for this folly or whether they intend to leave the cut pieces in place on the bank. The possible culprits are the city parks department, the Memorial Park Conservancy, or the flood control district.
We will find out, try to explain why this is wrong, and urge them to let nature take its wiser, more efficient course.
A General Lack of Understanding
Sayeth one of our esteemed hydrology and environmental experts:
“Sawing and removing the logs highlights the point that there is a general lack of understanding of how the riverine environment and natural restoration operates. … A comprehensive storm water management plan that truly understands the hydrology, geomorphology, and ecology of riverine systems needs to be developed for Buffalo Bayou.”
Update August 29, 2015
The Harris County Flood Control District has responded that it has been cutting up the trees on the banks of Buffalo Bayou in Memorial Park, and presumably elsewhere, as part of its regular maintenance activities. We are relieved to hear that the cut pieces will be left on the banks to allow the bayou to rebuild its banks naturally. Please note that we are talking about trees and brush lying on the high banks, not trees in the middle of the channel.
District practice is that the trees and woody debris are “cut into manageable pieces and left in place. Root balls are left within the bank of the bayou to aid in sediment entrapment and bank stability,” wrote Jason Krahn in an email August 28. Krahn is the construction division project manager for the district.
Here is Krahn’s full response:
“The Harris County Flood Control District (District) is currently conducting maintenance activities along Buffalo Bayou.
“These maintenance activities are conducted in an effort to ensure Buffalo Bayou is open for stormwater conveyance and public paddling/boating opportunity and safety. The District is contacted throughout the year by citizens concerned about trees and other woody debris which has fallen into Buffalo Bayou due to erosion. Their concerns are usually based on the fear of flooding or public paddling/boating opportunity and safety caused by the blockage of Buffalo Bayou by trees and other woody debris noted by them in the system.
“District maintenance activities on Buffalo Bayou consist of reviewing Buffalo Bayou post substantial stormwater event or during our scheduled bi-annual operations by airboat, identifying areas of downed trees or woody debris which has fallen into the bayou and cutting them up with chainsaws into manageable pieces which will not pose a danger to stormwater conveyance capacity of public paddling/boating opportunity or safety.
“District practices call for trees and woody debris which have fallen into the bayou or are in imminent danger of falling into the bayou to be cut into manageable pieces and left in place. Root balls are left within the bank of the bayou to aid in sediment entrapment and bank stability. Cut pieces are left in the bayou for habitat and other benefits to the Buffalo Bayou system.
“The District recognizes the benefits of woody debris within the Buffalo Bayou system and the Buffalo Bayou Watershed but must also consider the potential for flooding hazards and public paddling/boating opportunities and safety. District maintenance practices on Buffalo Bayou are designed to recognize and address the concerns of the district and the public while still providing for environmental benefits to Buffalo Bayou and the Buffalo Bayou Watershed.”