Natural Flood Mngt Projects
ASHLAND COUNTY FLOODING
Flooding is Wisconsin’s most frequent and costly disaster. Like many areas of the state, Ashland County has recently been affected by severe rain events, including multiple 100- and 500-year storms. These events have endangered public safety resulting in the loss of human life, caused many millions in damage to transportation infrastructure and private property, impacted water quality, and caused degradation of wildlife habitat. For these reasons, flooding is a significant concern for Ashland County departments tasked with emergency management, public safety, conservation, transportation, and economic development. In northern Ashland County, road-stream crossings have been particularly vulnerable because this area is naturally challenged by steep terrain and erodible clay and sandy soils. Many forms of current and historic land use alterations have taken place such as clearcut logging, ditching, beaver removal, and road infrastructure. These complex landscape conditions, combined with more frequent and extreme rain events, have caused or accelerated the development of erosion hazards that increase flood damages. This area has abundant headwater storage and low energy ephemeral streams, but there is evidence on the landscape that erosion hazards are multiplying and intensifying the loss of headwater storage and floodplain connectivity. As a result, flashy flood flows and excess sediment and debris are causing repetitive and severe flood damages.
2019 ACT 157 OVERVIEW
In response to these concerns, 2019 Act 157 allocated $150,000 to Ashland County from the urban nonpoint source water pollution abatement and storm water management fund. This funding was designated for up to three innovative natural flood risk reduction demonstration projects. According to Act 157, Ashland County is required to submit a report to the Department of Natural Resources (DNR) summarizing the results of these demonstration projects. Additionally, the DNR must report to the Legislature and Wisconsin Division of Emergency Management with a summary of results and recommendations for state policy or funding adjustments to create incentives to protect and restore natural infrastructure and reduce floods.
ASHLAND COUNTY FLOOD RESILIENCE WORK
Ashland County has proactively engaged in a variety of watershed-scale vulnerability assessment and planning projects, resulting in the adoption of strategies to restore the hydrologic functions of wetlands, streams, and floodplains. Examples include:
- Land and Water Resource Management Plan: Developed in collaboration with the Northern Institute of Applied Climate Science (NIACS) to address increased precipitation and flooding.
- Hazard Mitigation Plan Addendum: Adopted to recognize the benefits of restoring hydrology to reduce flood risks and damages. This addendum, titled "A Strategy for Natural Flood Management and Climate Resilient Infrastructure," emerged from a FEMA-funded project that assessed erosion hazards and prioritized restoration opportunities.
PROJECTS
1. Tody Ravine (purple area) to reconnect an eroding and incising channel to its floodplain.
2. Anderson Farm/Berweger Road Culvert (red area) to reconnect floodplains and construct a road crossing that accommodates future flows and excess sediment and debris. This project did not advance due to issues related to FEMA Zone AE and other waterway regulations.
3. Fischbach Wetland (orange area) to restore degraded habitat and allow wetlands to capture and slow the flow of runoff that enters the property from the north.
4. Berweger Farm (green area) to mitigate severe gullying, improve soil health, and reduce flashy runoff and sediment loads from a large, eroding ravine encroaching on cropland.
5. Mackey Wetlands (yellow area) to preserve and improve hydrologic conditions upstream of structural risks near Marengo River Road. This project did not advance due to issues related to FEMA Zone AE and other waterway regulations.
TODY RAVINE - HEADWATERS REPAIR
THE PROBLEM:
• The Tody Ravine is experiencing severe gully erosion exacerbated by recent extreme storms interacting with a landscape containing the effects of upstream hydrologic alteration.
• Upstream gully erosion has caused sediment deposition across the valley bottom.
• As the unstable channel carves deeper into the valley bottom during high runoff events, floodplain disconnection increases and flood storage decreases.
• The result is flashy flows swiftly moving water and sediment downstream and ultimately into the Marengo River.
HISTORIC CONTEXT:
Reliable information regarding historic conditions and hydrologic functions at the Tody site is not widely available. The Act 157 Project Team relied on information related to landscape setting, landowner knowledge, and other tools such as the General Land Office (GLO) surveys and historic aerial photos.
PROJECT GOALS:
• Reduce flood flashiness and sediment loads moving downstream.
• Rebuild floodplain connectivity to allow for more water and sediment to be captured, stored, and slowly released on the landscape.
• Test and explore the cost-effectiveness of low-tech approaches that mimic, promote, and sustain natural processes such as wood accumulation and floodplain formation.
PROJECT ACTIVITIES:
he installation of channel-spanning post-assisted log structures (PALS) was selected as a low-tech approach to establish wetland, stream, and floodplain conditions that achieve project goals along the 850-foot project site. These structures were designed to capture sediment in the incised channel, lifting the grade of the channel to reestablish more frequent floodplain connectivity during small and large floods.
• Nine PALS were originally planned to be installed approximately 100ft apart in straight sections of the project corridor. Eleven PALS were ultimately authorized and installed as extra material was available.
• Two rock riffle structures were placed at the upper and lower portions of the channel to stabilize the project site. Angular rock was used to minimize the potential for failure of the constructed riffles.
PRELIMINARY OBSERVATIONS:
1. Cost-effectiveness
2. Minimal engineering needed
3. Redundancy is key
4. Beaver recolonization is likely
5. KEY LESSON! Think beyond the single-channel system
6. KEY LESSON! Height matters
7. Overbuild the keyed zone
8. Prioritize energy dispersal
9. Expect and plan for adjustments
10. Start from the top
POST-RESTORATION INITIAL OBSERVATIONS:
Wood, debris, and sediment appear to be accumulating behind the flow-through PALS as intended. Assessments will be completed in the Fall 2024 by USGS to measure short-term changes in bank erosion, floodplain connectivity, and water table elevations.
USGS deployed a Hydrologic Imagery Visualization and Information System (HIVIS) to help monitor the Tody project. HIVIS cameras will allow USGS and the Act 157 Project Team to observe the site and structural performance during varying flow conditions.
To view the camera images, go to:
• Camera #1 – Mid Reach:
(https://apps.usgs.gov/hivis/camera/WI_Tody_Ravine_Mid_Reach_Upstream_of_HWY_112_near_ Marengo)
• Camera #2 – Hwy 112 Bridge:
https://apps.usgs.gov/hivis/camera/WI_Tody_Ravine_at_HWY_112_near_Marengo
FISCHBACH - WETLAND RESTORATION
PROJECT GOALS:
- Slow the flow of sediment-laden runoff and spread flows through restored wetlands (smooth the hydrograph).
- Erase the effects of ditching and channelization along the ephemeral stream.
- Improve wildlife habitat.
PROJECT ACTIVITIES:
- Construct five in-line wetland scrapes along an ephemeral stream to provide wildlife habitat and capture runoff.
- Construct a berm to help distribute flows throughout the reconnected wetlands and to prevent headcutting.
- Replace an undersized (18-inch) culvert with a rock spillway along the access road to improve hydrologic connections to adjoining wetlands.
PRELIMINARY OBSERVATIONS:
- Accommodate landowner goals.
- Hydrologic restoration can be accomplished in a variety of ways.
- The need for monitoring.
- The need for periodic adjustments.
BERWEGER FARM - GULLY STABILIZATION
THE PROBLEM:
A large gully on the west portion of the site is actively headcutting northward into a cropped field. Gully expansion occurs several times per year following floods. As a result, flashy runoff flows passing through the gully deliver increased amounts of sediment-laden water downstream each year.
PROJECT GOALS:
- Reduce flood flashiness and sediment loads moving downstream.
- Intercept flood flows from road and agricultural drainage ditches, to reduce gully expansion and reduce flood peaks and soil loss during small and severe storms.
- Accommodate landowner preferences for the pastured and cropped fields, including the use of structural practices to maintain farm access and control water levels to support agricultural needs.
PROJECT ACTIVITIES:
- Construct a wetland scrape at the upper edge of the field to manage ditch flows entering the site. A water control structure is incorporated to support on-farm water management.
- Create a grassed waterway to stabilize an eroding agricultural ditch and manage flows from the wetland scrape to the downstream stream corridor.
- Stabilize the outlet of the grassed waterway that enters the severe gully in a manner that dissipates energy and creates steps within the eroded channel.
- Construct a Zuni Bowl at the outlet of the grassed waterway and head of the severe gully to dissipate energy and create steps within the eroded ravine channel. A Zuni Bowl is a low-profile "Zeedyk" or grade control structure made of rock to capture sediment and restore headwater wetlands impacted by headcutting, gully erosion, and channel incision.
- Install a rock-lined waterway and apron to stabilize the grade of the eroding ravine.
PRELIMINARY OBSERVATIONS:
- Accommodate landowner goals.
- Expand the toolbox.
- Apply an outcomes-based approach.
POST-RESTORATION OBSERVATIONS:
The Berweger Gully Stabilization was completed in September 2024. Therefore, there have been limited opportunities to monitor the project's success.
