Erosion Analysis Lab Plants Roots in Freese and Nichols’ Raleigh Office
Imagine sharing your office space with hundreds of tree roots gathered from stream banks across multiple states.
The root-cleaning station in Freese and Nichols’ Raleigh office isn’t like a backyard stack of cordwood or a peculiar desktop toy collection. It’s an in-house laboratory. Our specially trained engineers use it to apply the science of erosion analysis and help communities repair waterways, reduce flood risk and build resilience. Call it engineers working with nature to provide better solutions for restoration and infrastructure improvement.
The process involves collecting exposed tree root sections from damaged banks, cleaning them and examining slices under a digital microscope. Changes in the root anatomy can tell a story of erosion’s impacts — without requiring spending years monitoring on-site.
Details such as abnormalities in the growth rings, the size and shape of cells, and the presence of scars explain what’s been happening on the ground and answer key questions:
- When were the droughts and how long were they?
- Were there rainy periods that caused heavy sediment transfer along the waterway?
- How long was a root exposed to the elements instead of being encased in a supporting earthen bank?
This information can be combined with measurements in the field to calculate how fast erosion can be expected to continue and determine how quickly repairs are needed to prevent damage to nearby infrastructure.
Freese and Nichols has developed this method of exposed root analysis, known as dendrogeomorphology, into a valuable tool for helping cities and counties plan infrastructure repairs and capital improvement programs. Projects so far have been completed or are underway in North Carolina, Texas, Georgia and Oklahoma.
A North Texas example
When a North Texas city asked Freese and Nichols for solutions to address creek erosion that potentially threatened a sewer line and recreation trail, the team included a root study to help determine where deterioration might dictate immediate action. The field team collected 12 exposed tree root samples and sent them to Raleigh for examination. The analysis estimated erosion rates at between 1.9 inches per year and 6.1 inches per year, depending on location. The results helped inform the options the team could present the city for reducing erosion and moving the sewer line.
A North Carolina application
A North Carolina project to restore a major creek and multiple tributaries incorporates natural channel design concepts while creating ecological uplift along the project corridor, restoring floodplain connectivity and improving water quality within the creek’s watershed.
For this project, the team has studied more than 100 roots to understand erosion rates along the waterway and used root analysis to show how addressing erosion can improve water quality downstream by reducing the amount of sediment carried along the creek. The water quality improvement aspect helped the project qualify for state funding.
Knowledge from nature
Emily Brown, PhD, PE, a biological engineer specializing in riverbank stability and stream restoration, said that even though dendrogeomorphology involves removing pieces of a tree, the technique is less damaging than other methods, such as installing rebar pins in the bank to measure erosion over time.
“There’s enough root structure (remaining) that you’re not going to kill the tree,” she said.
Typically, anywhere from five to 150 root sections sit in a freezer in the Raleigh office to prevent deterioration while they’re awaiting study.
“Cleaning and preparing the sample takes the longest,” Emily said. About 20 samples can be studied in two hours, then the data are plotted for analysis.
“If you’re looking at a specific location for the erosion rate, you can tell how much soil you’re losing in that location,” she said. The client can determine whether they need an emergency repair or have time to add the restoration to a longer-term plan. It’s also better for overall knowledge of your system.”
