Component Number 2:
Channelization
The proposed One Lake Project consists of three infrastructure components. The second component is the further channelization of the river.
Channelization is an effective and well-tested but ecologically destructive flood risk mitigation practice. The massive scale of channelization in the proposed lake project may introduce potential health and economic hazards to the Jackson metro.
The channelization component will create space for the proposed lake. However, the component does not require a lake in order to reduce flood risks.
What is channelization?
Channelization refers to “a group of engineering practices” that may be used to reduce flooding. Channelization in Pearl River Project includes widening, deepening, and straightening the river.
These modifications will be achieved through the large-scale excavation of 24.5 million cubic yards of material, enough to fill up the New Orleans Superdome five and a half times.
The following image shows a simplified cross section of a river after it has been dredged and excavated.
Image description
The image is a simplified cross section of the river. The water would flow into or out of the page. The dashed line shows were the ground before excavation. The yellow shows how the excavated material would raise the area surrounding the river.
Image source -
How does channelization reduce flood risks?
Deepening and widening a river can give flood peaks more space to spread out. Straightening the river reduces its length, which increases its slope. The higher the slope, the faster the river. Channelization also reduces the roughness of the river, which further increases the river's speed. A faster river can move flood peaks through Jackson and give them less time to accumulate.
The term for increased space and faster flows is increased conveyance. Channelization increases conveyance "to reduce flood stage and flood duration."
Use the excavated material
The material excavated will be used as fill to elevate certain properties surrounding the river. Elevating a property may reduce its risk of flooding and promote real estate development.
Channelization is well-tested but destructive.
Channelization has been used for flood control since prehistory, but its heyday started in the 1800s and lasted through the mid 1900s. Major rivers such as the Ohio, Missouri, and Mississippi were extensively channelized during this period of time.
River channelization is ecologically destructive. The immediate and long term changes caused by the modifications can make the river and its surrounding ecosystems inhospitable to native wildlife. In one case, it was found that channelization reduced biomass by 87 percent.
Notes on history -
Notes on ecology -
The Pearl River at Jackson is already channelized
The Pearl River at Jackson was channelized in the 1960s as part of a flood control project sponsored by the United States Army Corp of Engineers. The ecological damages caused by the previous channelization have been used to justify additional damages anticipated from the proposed Pearl River Project.
The following images are aerial photographs of the river before and after channelization.
Justification note -
Image description
The images are aerial photographs of the Pearl River at Jackson before and after the channelization in the 1960s. The coliseum has been highlighted in both images as a reference.
Image source -
Localized problems with channelization
Aside from ecological impacts, the proposed channelization will have other undesirable local impacts.
Release of hazardous toxic waste
The excavation and fill will affect hazardous toxic waste sites. The disturbance of these sites may introduce “large amounts” of “hazardous substances” into the Pearl River and other ground and surface water sources.
One substance is creosote, which is used as wood preservative and pesticide. Another substance is leachate, which is the tea that forms when landfill waste is steeped in water.
Stresses to the drinking water infrastructure
Excavation "could potentially increase the turbidity of the surface waters to levels unacceptable for human consumption." The affected area includes the J.H. Fewell Water plant; therefore, the channelization modifications "could include a temporary loss of the secondary water supply" and force the City of Jackson to "evaluate temporary water supply alternatives during the duration of dredging and construction activities."
Stresses to bridge infrastructure
The massive excavation operation will likely cause the "catastrophic failure" of seven bridges owned by MDOT and "severely" reduce the capacity of another two. The cost of repairing or replacing these bridges was not included in the cost estimates of the project, at least not in the 2018 One Lake feasibility study. There are at least two additional bridges, not owned by MDOT, which may be affected.
The following map shows the area that will be dredged, excavated, and filled. It also shows the bridges negatively affected by the project.
Quoted -
Image description
The map shows the area modified under the proposed One Lake Project. Darkened area will be dredged or excavated. The hashed area will be filled. The project might damage the nine bridges highlighted.
Map source -
Bridge list -
Channelization and the One Lake Project
River channelization does not by itself create a lake. It's the new dam that will create the lake. However, the massive scale of channelization in the proposed One Lake Project may be designed to create depth for the lake.
Images created by the Rankin-Hinds Pearl River Flood & Drainage District show the channelized area as the river.
Channelization is costly. The massive scale of channelization in the One Lake Project makes it the most expensive of the three infrastructure components.
Table source -
The table shows the approximate costs of the three components that make up the Pearl River Project. The data was taken from Appendix C, PDF page 222, Table 4.1.
This page and the linked articles were written by Juan David Fernández and edited by Lucy Kaplan, a teacher and Jackson resident.