It’s been about two years since the last flood in Iroquois County, and Thursday evening information was presented on what’s been learned about flooding and the iroquois River to someday lessen the impact of flooding.
It was presented by Siavash Beik, vice president and principal engineer of Christopher B. Burke Engineering, and Robert Barr, research scientist from the Center of Earth and Environmental Science Department of Earth Sciences at Indiana University Purdue University Indianapolis.
Iroquois County Board Chairman John Shure welcomed residents to learn what’s been going on behind the scenes.
The Indiana conservancy agency decided to start a study — the Kankakee River Flood and Sediment Management Work Plan, and it was decided to include Iroquois County in the study.
As Barr pointed out, not much was known about Iroquois County’s portion of the river before beginning the study. “It became clear the extent the river goes into Illinois, as to do it right we needed to do it all.”
He said, “The Iroquois River in Iroquois County has a whole different set of issues, a whole different landscape becomes a factor.”
The goal is to diagnose the root cause of erosion, sedimentation and flooding through detailed field and desktop assessment, he said, and to communicate the extent of existing risks and expected trends, identifying strategies for addressing the issues in a system-wide approach. Then, a work plan can be developed to implementing various strategies specific to each area within the watershed. All this can be done in a joint Indiana-Illinois effort to address a legacy problem facing both state.
In Illinois, he said, the sand load is increasing, as Indiana has an abundance of sand it sends downstream to Illinois. More sand bars are developing. The channel in the Momence area is shifting, and flooding is increasing in Momence, Aroma Park and Watseka. Dredging and tree removal in Indiana are concerns because of their potential of increasing flows and sediment.
The Iroquois River begins near Rensselaer, where it has its own history of being flooded, and goes to Brook, Indiana, where it was straightened. Below Brook it gets its natural meandering river slowing the waters again. From there it has its forested corridor with a fairly natural river. It becomes a larger, faster river. “There’s a lot of energy, a lot of power.”
He said the findings became a surprise in how long the river is and how much it meanders. There’s a variability in the river system. He said it’s basically two different rivers in the differences between the Indiana and Illinois portions of the river.
The discharge of the Iroquois River at Chebanse is three times more than that at Momence and the Kankakee River. That means more sentiment. “Iroquois has more water and more sentiment than the main stem of the Kankakee ever thought about.”
This started them thinking about the problem differently.
Barr said sediment is different in the Iroquois than it is in the Kankakee. The Iroquois has twice as much tonnage but what’s coming out of the Iroquois is clay and silt, not the sand that’s in the Kankakee. Sand is really visible and piles up. Silt and clay will go on down river.
They wanted to know where it was coming from, because there was some erosion but mostly it was in good shape, he said.
What was found were rills, a deep valley with a flat plain. “This is a problem we can fix fairly easily.”
What can’t be fixed is the amount of rain. This was explained by Beik.
One of the big problems is that the infrastructure was built in the early 1900s. Rain fall has increased 42 percent in the last 50 years.
That lends to vulnerabilities to floods. “If you’re in the flood plain, flooding is expected.” The flood plain is getting larger in size. According to studies done, today’s 500 year flood plain, within 30 years will be a 100 year flood plain, he said.
Controlling the flooding isn’t as feasible as it was thought because the target is changing. “The types of projects we have should be to manage the system versus eliminating the hazards. We should be looking at solutions that are more absorbent of those fluctuations.” He said nature-based solutions are the way to go.
Another big problem is the building within the flood plain, and Watseka has a lot of structures built in the flood plain.
Recommendations include a two-prong approach in addressing the systemic flooding and sedimentation in the face of a changing climate
The area needs to adapt and recognize that flooding is going to occur and taking steps to reduce existing and future vulnerabilities to reduce pain and suffering. Also, mitigation to reduce the stressors to the system and flooding and sedimentation sources to the extent possible through common sense and feasible actions without adverse impact to others.
Adaption strategies include:
— Develop flood response plans, since flooding can’t be prevented. This will help emergency responders with forecasting, detecting, classifying severity, and waring and evacuation priorities associated with an event.
— Develop flood resilience plant, as strategies are needed to curb increase in flooding vulnerability. The most effective resilience plans offer geographical-specific resilience strategies.
— Conduct a detailed system assessment and develop a work plan for the entirety of the Iroquois River and Sugar Creek. The Iroquois River contributes more water and sediment to the Kankakee River downstream from the confluence than the Kankakee but has been studied much less. A detailed system assessment on the Iroquois River, both in Indiana and Illinois, as well as along the Sugar Creek is needed to address increased peak discharges and sediment contributions that impact Watseka, Aroma Park, and downstream areas.
Beik recommended mitigation strategies for the Iroquois River watershed like sediment supply reduction, to address rill/gully erosion, and to reduce sediment supply from severely eroded banks; mitigate increase in flows caused by tiling and surface ditching like constructing new storage areas and implementing soil health practices such as cover crops; and selective flood proofing to strategically protect critical facilities, infrastructures, and roads from flooding.
He said there could be offline retention or detention storage areas along laterals. This is needed to offset the increase in runoff due to past and ongoing land drainage activities in the watershed and/or increased rainfall. Plus, he said future drainage improvements by farmers or drainage board/districts should incorporate detention storage as part of improvement.
What’s not recommended are levees, bypass channels around Watseka, large flood control reservoirs upstream of Watseka, clearing trees from banks, increased tile drainage to reduce farm flooding, and construction/improvements of rivers and ditches to increase flood conveyance, he said. These are not recommended due to the potential adverse impacts they could create.
The duo gave what residents should take away from the study.
Most of the problems along the streams in Indiana and Illinois are flooding, erosion and stream instability, and sediment aggradation.
The root causes of these problems are stressors within the watershed like increases in the flows due to climate change, unwise urban development, and farmers and drainage boards’ response to increased rainfall and runoff. Another cause are the missteps in attempts to fix problems in one location like dredging, tilling, berming, armoring banks without an understanding of the entire stream system.
Given a changing climate the only way out is embracing a systemwide watershed-based approach of adaption and mitigation that includes no adverse impact development decisions, smart growth resilience strategies and nature-based solutions.
Sustainable funding is needed to successfully implement the work plan recommendations.