Establishing a healthy riparian zone and vegetative buffer helps keep sediment and nutrients like phosphorus from entering the stream, and eventually, Green Lake.
by Alison Thiel
Brian Olmen knows exactly where he was on June 13, 2008. He wa standing on the western banks of a typically small stream that meanders nearly a mile through his and his wife’s property.
On that particular day, however, he saw a raging river carving new channels and redepositing trees and debris north.
Fueled by the infamous storm of 2008, 4 inches of rain were delivered on ground that already was saturated from 6.5 inches of rain the week prior.
For most, the temporary images of untethered docks and muddy storm water runoff are left in the past. For others, like Brian and Jodi Olmen, the negative impact of this single flood event is long-lasting, as evident from the scars of an eroded landscape.
“Since the flood,” Brian Olmen recalled, “an increasing amount of vertical banks, in some cases 6-feet high, developed. This was causing the loss of well-established trees, particularly in the section located south of County Highway K.”
The flood managed to transport an old, abandoned culvert, 6-feet wide and more than 20-feet long, several hundred yards downstream.
The culvert now rests wedged among large trees 30 yards off and 10 feet above the stream.
When large volumes of storm water runoff enter streams at rapid speeds, banks become increasingly unstable and are more likely to erode — delivering tons of phosphorus-loaded sediment downstream.
In lakes, one pound of phosphorus can fuel the growth of 500 pounds of algae. Since the average drop of water is in Green Lake for 21 years, water-quality consequences can persist for decades.
Fortunately, stream-restoration projects are in place, led by forward-thinking landowners interested in restoring Green Lake’s vulnerable areas.
The Olmens recently partnered with the Green Lake Sanitary District and the Green Lake County Land Conservation Department (LCD) to collectively fund and implement a stream-restoration project for 1,700 continuous feet of this extension of Hill Creek, the same section damaged from the 2008 flood.
This particular project was identified from a multi-year inventory of Green Lake’s major tributaries, sponsored by the LCD, Green Lake Association and Ripon College. The inventory allows for systematic identification and prioritization of stream sections in need of restoration because of severe erosion or other issues.
Referencing the stream inventory, LCD Soil Conservationists Derek Kavanaugh and Jordan Dornfeld guided the Olmens through the stream-restoration project.
Sections of the stream were regraded to replace incised stream banks with gentle slopes that mimic natural systems.
During future larger rain events, stream flow will be able to expand into the floodplain and return to the channel during normal flow conditions.
The modified stream will be more resilient to larger rain events and resistant to erosion, which also provides water-quality benefits downstream for Green Lake.
“By creating a more accessible floodplain, this reduces the stream’s velocity during high-flow conditions,” Kavanaugh explained. “When vertical banks prevent water from expanding to the floodplain, the rushing water places a tremendous amount of stress on a stream bank,” increasing the likelihood of erosion.
The Olmens’ restored stream section also includes a vegetated buffer to slow storm water runoff from adjacent farm fields. The buffer allows sediment to be captured, preventing it from entering Twin Lakes, Hill Creek and, eventually, Green Lake.
Eight years later, the Olmens stand on the banks of the same section of Hill Creek and see a much different picture. Their hope is that this project will encourage other landowners to initiate similar projects and contribute to a cleaner Green Lake Watershed.
Alison Thiel is the project manager for the Green Lake Association, a local not-for-profit that works to improve water quality for Green Lake. She writes this on behalf of the Lake Management Planning team.