Impacts of Tile Drains on Flood Mitigation Ecosystem Services ...

<strong>Impacts</strong> <strong>of</strong> <strong>Tile</strong> <strong>Drains</strong> on Flood
Mitigation Ecosystem Services Provided
by Prairie Pothole Wetlands
Brett Werner, University <strong>of</strong> Illinois at Springfield,
John C. Tracy, University <strong>of</strong> Idaho
Carter Johnson, South Dakota State University
Presented at the 2013 AWRA Specialty
Conference
St. Louis, MO March 26 th , 2013

Purpose:
To understand how the placement <strong>of</strong>
tile drains within the Prairie Pothole
region <strong>of</strong> North America will impact the
flow-frequency relationships for
drainages that contain pothole wetland
systems.

Outline:
‣ Factors driving tile drain installation
‣ Analysis approach
‣ Potential <strong>Impacts</strong> to flow-frequency
‣ Summary

Tiling <strong>of</strong> the Prairie Pothole Wetlands
From US Fish and Wildlife Service
Orchid Meadows Field Site
(Johnson, WC – SDSU)

Tiling <strong>of</strong> the Prairie Pothole Wetlands
‣Significant conversion <strong>of</strong> agricultural land from
grain to corn has been occurring within the
northern plains region over the last decade, driven
by:
‣ Increase in the average length <strong>of</strong> the growing season;
and
‣ Historically high prices for feed corn
‣To help increase corn crop yields, extensive
installation <strong>of</strong> drainage tiles is occurring in order to
lower localized groundwater tables

Tiling <strong>of</strong> the Prairie Pothole Region
Projected North and Westward Expansion <strong>of</strong> Corn belt and Tiling

Tiling <strong>of</strong> the Prairie Pothole Wetlands
‣ Bois de Sioux Water District has kept statistics on tile
installation:
• 1999 – 2.9 miles <strong>of</strong> drain tile permitted
• 2009 – 779 miles <strong>of</strong> drain tile permitted
• 2011 – 1558 miles <strong>of</strong> drain tile permitted
• 2012 – Amount permitted exceeded 2011
‣ Spacing <strong>of</strong> the tiles is dependent on the soil types,
climate and topography, but approximately 32 miles
<strong>of</strong> drain tile will cover a square mile <strong>of</strong> land.
‣ This means that at the current pace <strong>of</strong> installation,
tile drained lands are increasing at a rate <strong>of</strong> ~ 3% per
year in the Bois de Sioux Water District.

Analysis Approach
A model that was developed to predict impact <strong>of</strong> tile
drains on a single wetlands hydrology (WETSIM) was
modified for use in this study
Flux <strong>of</strong> water into the
nearest tile drain to the
wetland boundary is
simulated using the van
Schilfgaarde equation,
modified to account for
radial flow
No field data yet
exists to compare
with the modeled
results.

Analysis Approach
Modifications to Single Wetland Model
‣ Assume placement <strong>of</strong> tile drains follows the USDA-NRCS
rules regarding allowable lateral effect <strong>of</strong> drain at
wetlands edge (< 1 foot drawdown) and provided soil
dewatering for optimal corn production (drains placed at
4 foot depth) (Lateral distance = 50 meters and depth
below wetland bottom = 0.75 m)
‣ Model was modified to calculate the total flux <strong>of</strong> water
exiting the wetland complex via surface, subsurface and
tile drain pathways
‣ A drainage basin with a single semi-permanent wetland
type in the Prairie Coteau region is used as a surrogate for
the analysis.

Analysis Approach
Simulation Procedure
‣ Daily meteorological data is used as model input from
1983 to 2010 for Orchid Meadows site.
‣ The daily flux <strong>of</strong> water exiting the wetland basin is then
calculated using the single wetland basin model.
‣ The daily flux is then used to calculate the flowfrequency-exceedance
relationship.
‣ The flow-frequency-exceedance relationships for the
single basin wetland without, and with, tile drains are
then compared for a range <strong>of</strong> wetland to drainage area
ratios and spillway depths.

Potential <strong>Impacts</strong>
100.00
Frequency <strong>of</strong> Exceeding Flow Rates - SP Type Wetland
Drainage Area = 150,000 m 3 ; Wetland Area = 15,000 m 3
Spillway depth = 0.5 m; <strong>Tile</strong> Drain Depth = 0.75 m; Lateral Distance = 50 m
10.00
Frequency <strong>of</strong> Exceeding Flow
1.00
0.10
1 10 100 1,000 10,000
With <strong>Tile</strong> Drain
Without <strong>Tile</strong> Drain
0.01
Flow Rate (cubic meters per day)

Potential <strong>Impacts</strong>
Frequency <strong>of</strong> Exceeding Flow Rates - SP Type Wetland
Drainage Area = 150,000 m 3 ; Wetland Area = 15,000 m 3
Spillway depth = 1.0 m; <strong>Tile</strong> Drain Depth = 0.75 m; Lateral Distance = 50 m
100.00
10.00
Frequency <strong>of</strong> Exceeding Flow
1.00
0.10
1 10 100 1,000 10,000
With <strong>Tile</strong> Drain
Without <strong>Tile</strong> Drain
0.01
Flow Rate (cubic meters per day)

Potential <strong>Impacts</strong>
Frequency <strong>of</strong> Exceeding Flow Rates - SP Type Wetland
Drainage Area = 150,000 m 3 ; Wetland Area = 37,500 m 3
Spillway depth = 0.5 m; <strong>Tile</strong> Drain Depth = 0.75 m; Lateral Distance = 50 m
100.00
10.00
Frequency <strong>of</strong> Exceeding Flow
1.00
0.10
1 10 100 1,000 10,000
With <strong>Tile</strong> Drain
Without <strong>Tile</strong> Drain
0.01
Flow Rate (cubic meters per day)

Potential <strong>Impacts</strong>
Frequency <strong>of</strong> Exceeding Flow Rates - SP Type Wetland
Drainage Area = 150,000 m 3 ; Wetland Area = 37,500 m 3
Spillway depth = 1.0 m; <strong>Tile</strong> Drain Depth = 0.75 m; Lateral Distance = 50 m
100.00
10.00
Frequency <strong>of</strong> Exceeding Flow
1.00
0.10
1 10 100 1,000 10,000
With <strong>Tile</strong> Drain
Without <strong>Tile</strong> Drain
0.01
Flow Rate (cubic meters per day)

Summary and Conclusions
‣ Drain tiles reduce the antecedent moisture conditions
in the wetland drainage
‣ Drain tiles also increase the mobility <strong>of</strong> water within
the wetland drainage
‣ Result is that the flow-exceedence-frequency
relationship is rotated, not shifted
‣ This preliminary analysis suggests that with extensive
tile drain installation that:
• Lower occurrence frequencies will have higher flows
• Higher occurrence frequencies will have lower flows