What are the benefits to the City if the dam remains (not in order):
- Enhance attractiveness of Island Park & maintain Windom town heritage -- need to preserve every benefit it has going for it
- Preserve pond environment – slow down flow of water, minimize water level fluctuations and minimize erosion in reservoir
- Restore a premier migratory bird habitat – attraction to the city
- Restore fish friendly body of water that includes fish passage provisions (DNR concern)
- Preserves the potential for an enhanced bird habitat by creating a linear island with 4 shorelines
- Preserves the potential for a unique trail system using the island which could connect with the land using pedestrian bridges and interconnect with a trail system building from Jackson to Kilen Wood State Park
- Eliminate confrontational property-taking issues should such a trail system be built later along the river through a nasty condemnation process
- Slowed down water flow helps protect ballfield investment – minimize damage of faster flowing water
- Minimizing water level fluctuations helps reduce associated water table fluctuations in the Rolling Green and Remick Ridge hillside areas – promotes long term stability in areas with shallow groundwater
- Slower, evened out water flow promotes thicker ice for safer winter sports and kids
- Reduces erosive risks of faster flowing floodwaters to public and private property
- Reduced liability risks to city, if city actions would otherwise cause damage to property
- Eliminate potential risks to sanitary sewer and water lines adjacent to Highway 62 bridge
- Eliminates new risks to bridges – discuss with MnDOT
- Eliminates fire risks associated with dry vegetation adjacent to landowners
- Eliminates pockets of stagnant boggy ground – mosquito habitat
- Attractive feature to draw people to Windom and reconnect with the river and nature
Phase 1: Dam Restoration
- Verify soil conditions in abutment area as needed.
- Riprap retrofit downstream face of dam, sufficient height to breakup hydraulic roller effect unless aesthetic concerns indicate a full height retrofit was appropriate.
- Rehab / modify wingwalls as needed – sawing, shotcrete, etc.
- Utilize existing concrete “riprap” as base of additional riprap; suggest Sioux Red Quartzite as source of riprap (durable, attractive, local quarry is north of Windom).
- Widen dam using riprap will also establish fish connectivity and maintain pool height at existing dam crest elevation, use this new flow area for fishing pools.
- Above would serve as basis to revitalize the Island Park area and help turn this specific area into a key attraction for the City.
- Also map sediment in basin, using historic aerial photos to help reliably establish what is actually there
(Cottonwood SWCS has previously indicated watershed erosion control efforts are paying off;
farmfield deep drain tiling also significantly reduces erosion from tilled fields).
- Work with above information, develop conceptual plans for linear island concept,also consider stilling basin or submerged check dam concepts as a control to deposit future sedimentation at a convenient location.
- Some material may be removed; some or all may actually be reshaped in the river itself and left in the reservoir.
- This Phase 1 scope of work is a “standalone” project to restore river to an enhanced version of the status quo with public and environmental benefits.
Phase 2: Reservoir Island Earthwork
- Develop and implement the above conceptual plan for a linear island concept, considering the following factors:
- acceptability of sedimentation for on land farmland disposal (sediment sampling needed);
- location and haul to farmland for a dewatering basin (as was done at Sleepy Eye by Mathiowetz Construction);
- if appropriate, temporarily remove a portion of the “fish passage” riprap dam to lower the water levels sufficient to allow scraper hauling of any removed dredging (most economical); or just use a small dredge as per Sleepy Eye’s project (ideal water depth for migratory birds = 4 feet?);
- assess feasibility of check dam/stilling basin concepts to manage future sedimentation;
- optimally design channels and island to maximize low flow volume water velocities to best resemble “natural” river channels – improves downstream water quality;
- above efforts would appear ideal for state wetlands restoration statewide tax funding if it passes;
- should discuss with US Army Corps of Engineers since they are faced with these same issues on a larger scale in the Missouri River Basin and may be interested in this as a pilot scale project;
- particularly study the Pierre, SD area, where LaFramboise Island could be considered a larger-scale prototype of this linear island concept, in the Missouri River adjacent to Pierre);
- or obtain state bonding funds as was done for Lake Redwood;
Phase 3: Trail Development (utilize the investment)
- Use the Island as a basis to develop a minimalist nature/walking trail (Windom Riverwalk);
- would connect to mainland downstream at the Rolling Green sanitary sewer force main station property, adjacent to the Highway 62 bridge;
- upstream connection has various possibilities;
- could eventually interconnect with trail system building from Jackson;
- would eliminate contentious issues with forced property acquisition for a trail along the river;
- This would be the key selling point for landowners if further permission is needed beyond existing flowage easement;
- would help people reconnect with the river and environemtn in a unique healthy manner;
- trail could be closed during high water/spring nesting season;
- environmental education tool for schools;
- great attraction for city, something to be proud of, and may be a deciding factor for some to decide to move to Windom;
- DNR Trails program and/or Transportation Enhancement funds could easily fund this phase.