A Complex Wetland Delineation Case Study in Minnesota, USA

Home , Sapric

Steve Eggers U.S. Army Corps of Engineers Regulatory Branch St. Paul District

June 5, 2012

US Army Corps of Engineers

BUILDING STRONG® Anoka Sand Plain

BUILDING STRONG 6/21/2012 2 ® Sandy, Glacial Lake Plain

PEAT 5m PEAT

SAND 21m

BUILDING STRONG 6/21/2012 3 ® 1902 “Wiregrass Marsh” >9,000 ha

Site

BUILDING STRONG® Pre-Disturbance Condition

Carex lasiocarpa

BUILDING STRONG 6/21/2012 5 ® Wire-Grass Marsh • Original land survey (mid-1800s) described delineation site as a “floating marsh” • Ditching began in late 1800s • Ditches effective in removing ponding – no more “floating marsh”

BUILDING STRONG 6/21/2012 6 ®

1960s

Approx. 125 ha Public Ditch Public

BUILDING STRONG® 1980s

BUILDING STRONG® 2005

Non-Hydric Non-Hydric Soils Soils

Non-Hydric Soils Hydric Soils (82 ha)

Fill

BUILDING STRONG 6/21/2012 9 ® Network of Drainage Ditches

BUILDING STRONG 6/21/2012 10 ® Phalaris arundinacea (FACW) Phragmites australis (FACW) Typha spp. (OBL)

Site Conditions 2005

BUILDING STRONG 6/21/2012 11 ® Regulatory Purposes

• Delineation involved Federal, state and local regulators as well as several private consulting firms representing landowners • Determine which areas of the site, if any, meet wetland criteria • Consensus was that site had hydric soils and was dominated by hydrophytes • Question was hydrology

BUILDING STRONG 6/21/2012 12 ® Evaluating Disturbed Hydrology

• Drainage equations • Monitoring well study • Modeling (e.g., MODFLOW, DRAINMOD)

See USDA Natural Resources Conservation Service. 1997. Hydrology Tools for Wetland Determination. Chapter 19, Engineering Field Handbook.

BUILDING STRONG 6/21/2012 13 ® Partially vs. Effectively Drained

30 cm

Ditch

Lateral Effect Effectively drained means that the wetland hydrology criterion is no longer met: inundation or a water table 30 cm or less below the soil surface for at least 14 consecutive days during the growing season in most years

BUILDING STRONG 6/21/2012 14 ® van Schilfgaarde Equation

d = depth K = permeability

QUESTIONS? Ditch

BUILDING STRONG 6/21/2012 15 ® SOILS

Ditch Depth

BUILDING STRONG 6/21/2012 16 ® Ditch Cross Sections

Ditch

Peat Sand Ditch

Sand Ditch

Peat

BUILDING STRONG 6/21/2012 17 ® Differential Drainage Effect

PEAT (e.g., 2.5 cm (1 inch)/hour) Ditch

SAND (15 cm (6 inches)/hour)

Lateral Effect

BUILDING STRONG 6/21/2012 18 ® Sedge muck (sapric) 1m Heterogeneity of Organic Soil Woody peat (fibric) Deposits 2m Charcoal layer Woody peat (hemic)

Sedge muck (sapric) 3m

Woody peat (fibric)

4m Sand

BUILDING STRONG 6/21/2012 19 ® Results of Applying van Schilfgaarde Equation

BUILDING STRONG 6/21/2012 20 ® Monitoring Well Designs

Backfill with native organic soils

Driven Well Augered Well

US Army Corps of Engineers. 2005. Technical Standard for Water-Table Monitoring of Potential Wetland Sites.

BUILDING STRONG 6/21/2012 21 ® Monitoring Well Study

BUILDING STRONG 6/21/2012 22 ® Monitoring wells spaced 10m apart

Ditch

Lateral effect

Transects of closely spaced monitoring wells perpendicular to a ditch can measure actual lateral effect. Data can be used to calibrate drainage equations and/or groundwater models.

BUILDING STRONG 6/21/2012 23 ® Monitoring Well Data

21 consecutive days

Soil Surface 30cm

BUILDING STRONG® Monitoring Well Data

Soil Surface

30cm

BUILDING STRONG® 34 ha of 82 ha of hydric soils met wetland criteria

Final Wetland Delineation

BUILDING STRONG 6/21/2012 26 ® Conclusion • In this case of organic soils, the van Schilfgaarde equation did not work well for estimating scope and effect of ditches • The monitoring well study provided the most reliable data although very short- term data was collected (<3 years) • Regulators , consultants and landowners reached concurrence on the delineation

BUILDING STRONG 6/21/2012 27 ®