Natural Channel Design
The Memorial Park Demonstration Project will address the severe erosion of Buffalo Bayou in the Project area by means of the design and construction principles of Natural Channel Design. Natural Channel Design is based on the re-configuration of banks of streams adversely affected by human activity to emulate the characteristics of stable, non-eroding rivers and streams as observed in nature, using the science of fluvial geomorphology.
Integrating multiple solutions to ensure success
Erosion control for this project requires a multitude of solutions to be fully successful. A part of this is achieved by use of trees with root wads attached and buried below the waterline on the outside of meanders (turns in a stream) at the toe of the adjacent bank to buffer the flow velocity. Known as “toe wood”, this method mimics natural stream conditions and helps to push the main current toward the center of the channel, away from the banks, reducing channel velocities that erode the banks and further protecting the toe of the slope that supports the face of the entire bank. The scouring forces of the current then work mainly to deepen the central channel while depositing the new sediment along the banks, building up a “bench” (i.e., floodplains and point bars on the inside of meanders). This is how Natural Channel Design seeks to regenerate proper channel and floodplain connections of the type exhibited by stable natural streams.
Correcting and restoring using methods that follow nature
The heavy construction aspect of the project will involve digging in the banks to put the toe wood (trunks with attached root wads) in place, restoring flood benches and correcting bend geometry. This method will follow the channel shapes that occur naturally in a stream or bayou whose delivery of watershed drainages were not heavily altered by human intervention and will be sized to accommodate the higher peak flows caused by the urbanization of the watershed. Toe wood will be embedded in outer meander banks, nearly perpendicular to the direction of the current, with the root balls projecting into the stream to dissipate velocity. These locations comprise approximately 32% of the total project reach. There will be selective removal of trees in these zones only in order to correctly place the toe wood and shape the bank. The topsoil removed in these areas will be stored, and after the toe wood is put in place, the topsoil and streambed soil will be put back in place.
Replanting native trees and vegetation
The project plan includes a robust plan for replanting of banks and riparian area with native trees, especially large canopy trees, and vegetation. Flood Control will monitor the revegetation and add more waves of vegetation as needed to restore a vegetated riparian corridor that will eventually provide a mostly closed canopy over the bayou much as it once was before the urbanization of the watershed and the resulting channel downcutting and bank erosion.
BPA recognizes that the success of this project requires all components perform as designed and that the vegetation selection, its survival and vitality are critical to both the bank toe stabilization and the restoring of habitat. Due to the fact that the delivery of water through this reach is in large part controlled by the release of water from the Barker and Addicks reservoirs, the selection of plant species requires not just native plants with strong bank-stabilizing ability, but also plants that can survive and flourish in modified flow conditions.
The proposed project is estimated to cost $6 million. The project’s funding partners – the City of Houston, River Oaks Country Club and Harris County Flood Control District – will share in the cost of the project.
Project Approach & Project Timeline
To meet its objectives, the proposed Memorial Park Demonstration Project is using a methodical, step-wise approach. At each step in the process, information is refined and consensus measured to determine if there is enough support to move to the next step. For example, the initial steps in the process involved determining if there was agreement that Buffalo Bayou’s erosion problem warranted a demonstration project. Further review and support led to the concept of a demonstration project. The next step was to determine where that project might take place and what it might be. Public input has been sought through public meetings and through the HCFCD website.
The proposed project also requires a Corps of Engineers individual permit, as well as a public hearing under Texas Parks and Wildlife Code, Chapter 26, to determine if protected park land (Memorial Park) can be used for other purposes. Both of these processes include the opportunity for public input. If these steps are successful, the final design could be completed by fall 2014, and construction could begin by the end of 2014. The project would take approximately 12 months to construct with a currently unspecified extended time period for vegetation establishment and possible replantings through an iterative process conducted by Flood Control.Results of Proposed Project