VERNON COUNTY - Although the USDA-NRCS is not ready to provide results of an engineering study of the dams that failed or were damaged in the late August 2018 floods yet, the county is considering a modeling project with the U.S. Army Corps of Engineers (USACE), according to Vernon County Conservationist Ben Wojahn.
If approved, results of the study to model impacts of land use practices on water runoff are projected to be available nine months from the time the study starts.
The study would, according to Senior Civil Works Program Manager Nathan Campbell with USACE-St. Paul, “be a model that would help to inform decisions that are made down the road about what to do about Vernon County’s flood control dams.” The proposed project could be described as a “pilot,” which if found to yield results of practical use, could be employed in other parts of the Kickapoo River Watershed.
Vernon County Conservationist Ben Wojahn shared a preliminary first draft of a Corps proposal for a ‘Vernon County Flood Damage Reduction Study’ with the Vernon County Land and Water Conservation Committee on Thursday, Dec. 13. The work to develop the study had started, prior to the recent flooding, and is viewed by the Corps as a high priority project, according to Wojahn.
The study will build off previous, less detailed, modeling for the Kickapoo River watershed, and the focus of the more detailed pilot project will be on Vernon County and a selection of the county’s flood control dams – Jersey Valley/Klinkner/Ostrem in the West Fork of the Kickapoo River, and Sidie Hollow and Runge Hollow in the Bad Axe River Watershed.
The financial details of the preliminary plan are yet-to-be-determined, but the general framework for the study is fairly well developed and would represent a somewhere in the neighborhood of $145,000 value to the county.
“The priority in this study is to get the information we need to determine where to focus our time and resources to best effect,” Wojahn said. “We also need to be interacting with farmers to get their input about what practices really work. Overall, our goal will be to focus on practices that are more permanent or ‘hard,’ which are less likely to change over time.”
“As far as the matching funding for this study, it’s looking like the financing will be there for only one of the two $75,000 positions you’ve asked to have funded with Ho-Chunk funds – mapping and a technician. If you have to choose, which one is more important?” Supervisor Rod Ofte asked.
“Both positions are of crucial importance, but if I had to choose for the short term, I would choose the mapping position,” Wojahn responded. “And both the Ho-Chunk funds and Valley Stewardship funds can be used toward the Corps’ match.”
“We have to get this right this time,” Committee Chair Supervisor Will Beitlich said. “This is going to take years, not months, but I don’t think we can wait too long. Fixing the structures this time is a bigger issue. If we fix them, then we need to understand how to protect the dams, and if we don’t fix them, then we really need to understand how to slow down the runoff.”
“Just to clarify, the Corps will provide information about how to relieve the dams from runoff,” Wojahn explained. “NRCS will provide us information about what it would take to repair the dams.”
Both the proposed modeling position and the proposed study would make use of LIDAR technology.
LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the earth. These light pulses—combined with other data recorded by the airborne system— generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.
“Your department has also requested $50,000 for LIDAR data,” Supervisor Rod Ofte stated. “Currently the funding for that is zero in the Finance Committee – is there ‘LIDAR Light?’ If you could reduce the dollar amount you’re asking for, it would be more likely to be funded.”
The primary purpose of the proposed study is to assist the VCLWCD in providing recommendations that may reduce or delay flow [of water] to the structures [dams] of concern, reducing the maximum loading on the dams during flood events.
Suggested actions include applying the Agricultural Conservation Planning Framework (ACPF) to the basins of concern with the option of constructing a calibrated hydrologic model of the Kickapoo and Bad Axe River watersheds that can be used to assess the impacts of landscape changes on flood flows.
The ACPF is a tool that leverages high-resolution GIS data (elevation, land use, soil data, etc.) to identify site-specific opportunities to install conservation practices across small watersheds to reduce, trap and treat hydrologic flows. The tool requires modification of the base model present in raw LIDAR to incorporate elements of “hydrologic connectivity” such as culverts, small streams, etc…
Ultimately, the goal is to provide location and structure recommendations to reduce or delay (water) flow upstream of the dams chosen for the study. Applying the tool is intended to yield best management practice (BMP) placement and locations that may reduce (water) flow volume or timing upstream of the dams.
The study will consist of two components: development of an HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model, and generation of flow-frequency relationships at critical locations throughout the study. HEC-HMS model output for various precipitation events will be tied to the flow-frequency relationships for critical locations and exceedance probabilities.
The HEC-HMS is designed to simulate the complete hydrologic processes of dendritic (having a branched form resembling a tree) watershed systems. The software includes many traditional hydrologic analysis procedures such as event infiltration, unit hydrographs, and hydrologic routing.
Providing information for the study, there are currently four active and one inactive U.S. Geological Survey (USGS) stream flow data sites within the Kickapoo River Basin: Ontario (2001-present); LaFarge (1986 to present); Steuben (1986 to present); and West Fork/Peaceful Valley Road/Cashton (2010 to present). Inactive since September 1977 is the one in Gays Mills.
There are no known stream gauges on the Bad Axe River. Therefore the Kickapoo River calibration will provide guidance for an approximate calibration of the Bad Axe River basins. Only the Side Hollow Lake-South Fork Bad Axe River, and Pumpkin River-North Fork Bad Axe River will be modeled.
The U.S. Army Corps of Engineers-St. Paul District has recently developed an HEC-HMS hydrologic model for the Upper Mississippi River Basin between Anoka, Minnesota and Guttenberg, Iowa as part of a water management system regulation-forecasting project.
The model previously developed includes the Kickapoo River Watershed, but was constructed to a much coarser scale than what would be required for the Vernon County project. In the model, the Kickapoo River is split into only four sub-basins and does not explicitly model any dams or hydraulic structures.
Initially, the more detailed model to be developed in the study would be calibrated to rainfall events, with the option to eventually calibrate the model to snowmelt events.
Flow frequency analysis will be developed for the Kickapoo River at the LaFarge stream gauge station and the Steuben stream gauge station. To aid in the derivation of these relationships, at minimum, frequency analysis will also be generated for the inactive stream gauge at Gays Mills.
To meet the requirements laid out in U.S. Army Corps of Engineers Engineering Construction Bulletin 2016-25, Guidance for Incorporating Climate Change Impacts to Inland Hydrology in Civil Works Studies, Designs and Projects, a climate change assessment will be conducted for the Kickapoo River Basin. This assessment will consist of a qualitative evaluation of the “stationarity assumption” or the “constancy over time assumption,” a literature review, a first order statistical analysis of trends in both observed and projected hydro meteorological variables, as well as a screening level vulnerability assessment.