Watonwan Judicial Ditch 18 Improvement
Watonwan County/Brown County, MN | Water
ISG performed a feasibility study on Judicial Ditch 18 (JD18), a large watershed that lies within Madelia, Riverdale, and Lake Hanska Townships, after televising revealed severe deterioration on the mainline tile. ISG water resource experts made recommendations for infrastructure and drainage improvements for a more functional and sustainable system.
Originally constructed in 1916, JD18, which consists of approximately 70,460 linear feet of tile that outfalls into 500 linear feet of ditch, was experiencing severe flooding due to aging infrastructure. The Watonwan County and Brown County Joint Board were petitioned by landowners to improve a majority of the system’s tile to prevent future flooding.
As a consistent partner in JD18 improvements, ISG completed a topographic survey, and a Preliminary and Final Engineering Report (FER) prepared from original JD18 profile drawings and alignment maps provided by Watonwan County. Utilizing XPSWMM Model, LiDAR contours, and aerial drone footage, ISG analyzed the approximate 4,700 acre watershed that differed in elevations of 95 feet, and created a detailed 2D model to analyze the data and determine practical and feasible recommendations to improve the system.
The FER outlined two options to improve drainage throughout the watershed with detailed cost estimates applied to each. Recommendations provided a minimum of five feet of cover in low spots along public tile alignments, increased tile grades to improve capacity, and provided deeper outlets for private tile. To improve the drainage coefficient, the water resource team recommended that the ditch portion of the system be cleaned throughout its length, trees be removed, and new tile be installed for the mainline, branches, and laterals.
To decrease peak flows from the improvement system to existing flows, a 5.81 acre storage pond with a sediment trap was recommended to reduce sediment transport and provide a source for nutrient rich sediment that can be reapplied to the fields. A Multi-Purpose Drainage Management (MDM) Plan was included in the FER that incorporated Best Management Practices (BMPs) designed to reduce sediment and nutrient loading and improve water quality. This plan was shared with landowners within the watershed to help implement some of these practices.
ISG grant writing experts worked with the County to explore potential external funding sources that the County could use to keep the project moving forward. ISG is currently working on construction drawings and construction is anticipated to begin on the project in 2021 and be finalized in 2022.