watersheds and known watershed issueslakeofthewoodsswcd.org/projects/wtrshd_iss_ppt.pdf · bostic...
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![Page 1: Watersheds and Known Watershed Issueslakeofthewoodsswcd.org/projects/Wtrshd_Iss_ppt.pdf · Bostic Watershed • 31,500 acres • 25% agricultural land • 50-60% wooded wetlands •](https://reader034.vdocuments.net/reader034/viewer/2022051810/601942768f58d0005864d67e/html5/thumbnails/1.jpg)
Watersheds and Known Watershed Issues
Josh Stromlund – Land and Planning Office
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Watersheds
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Bostic Watershed
• 31,500 acres• 25% agricultural land• 50-60% wooded
wetlands• 134 miles of drainage
ditches• Approx. fall within
watershed = 128’
Zippel Watershed
• 62,000 acres• 30% agricultural land• 50-60% wooded
wetlands• 192 miles of drainage
ditches• Approx. fall within
watershed = 164’
Watershed Facts
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Resource concerns
• Excessive sediment in Bostic and Zippel Bays– Zippel core samples show sedimentation is occurring
at 7 times the presettlement rate– Decreased access to lake/increased dredging costs– Degraded spawning habitat– Lake of the Woods listed by MPCA as an impaired
water for nutrients
• Water level fluctuationsHigh flow events and flooding in watersheds seems to be increasing
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Evidence of excessive sediment
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Bostic Bay
1940-41 aerial photo
1999 aerial photo
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Zippel Bay1941 aerial photo
2006 aerial photo
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Core sample data
From Zippel Bay Multi-core Study, Reavie, 2007
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Water sampling site in Bostic Watershed
June 19th, 2006 photo
Over 1/2” rain 2 days prior
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Same site in 2008, two weeks earlier in the season
June 4th, 2008 photo
Over 1/2” rain 6days prior
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Known sources of excess sediment
• Within ditch segments– Ditch side slopes too steep– Subsurface water seepage through ditch
banks causing slumping– Natural soil instability– Ditch bank and ditch bottom scouring
occurring with high velocity flows– Maintenance activities
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Ditch bank slumping
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Another source of excess sediment
• Agriculture– sediment from field drainage– Sheet and rill erosion
Sediment plume
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Other possible contributing factors
• High lake levels creating backwater flow into bays
• Additional (new) drainage
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Evidence of peaking or flooding
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Spring 2004 Summer 04
Evidence is mostly subjective and needs to be quantified
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High velocity flows and peaking events
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Spring 2009
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Possible sources of excess water
• Increasing drainage on the landscape• Changing weather patterns• High lake levels creating backwater flow in
the bays
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In summary...