Evaluation of Policies for Tile Drain Placement in the Prairie Pothole Wetland Landscape

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1 Evaluation of Policies for Tile Drain Placement in the Prairie Pothole Wetland Landscape Brett Werner, University of Illinois at Springfield, John C. Tracy, University of Idaho Carter Johnson, South Dakota State University Richard Voldseth, Concordia College Glenn Guntenspergen, USGS Presented at the 2013 AWRA Specialty Conference St. Louis, MO March 26 th, 2013

2 Purpose: Develop a systems based model to simulate the impact that tile drains will have on hydrologic conditions in prairie pothole wetlands; and Utilizing this model, examine the efficacy of methodologies currently being used to determine the set back distance for tile drains near wetlands in the Prairie Pothole Region.

3 Outline: Prairie Pothole Region Current Approach to Determining Setbacks Simulating Tile Drain Impacts on Wetland Hydrology Potential Impacts on Wetland Hydro-periods Summary

4 Prairie Pothole Region Conservation Programs Wetlands Reserved in USDA Programs ~ 5.4 million acres From US Fish and Wildlife Service Wetlands Reserved in USFWS Programs ~ 1.4 million acres Orchid Meadows Field Site (Johnson, WC SDSU)

5 Prairie Pothole Region

6 Current Setback Calculation The NRCS has developed a methodology based on calculating the lateral effect of drainage tiles The van Schilfgaarde equation is used to calculate lateral effect In 1997, NRCS in SD, ND, MN, IA and NHQ, NTC, WSI all agreed to use this equation for uniformity Key factors that determine lateral effect distance: Soil characteristics Depth of the drain Time period lateral effect ground surface tile zone of influence

7 Current Setback Calculation To meet NRCS-USDA wetland conservation program provisions, the tile drain must be placed a lateral distance from the wetland edge where the drawdown is 1 foot at the wetland s edge. Time period used in the drawdown calculation is the number of days to accumulate 1 inch of rainfall in May and recharge the upper foot of the soil profile (NWCC analysis, days). wetland 1 foot lateral effect ground surface 4 feet hydric soil upland soil tile

8 Current Setback Calculation The Lateral effect distance is then adjusted based on a number of factors: Slope - Depth of tile drain is adjusted relative to wetland elevation Encirclement - If tiling near a groundwater-driven wetland, the lateral effect distance is multiplied by 3 Surface inlets - Surface inlets cannot divert water from downstream wetlands

9 Current Setback Calculation USFWS Approach The US Fish and Wildlife Service has decided to adopt a process similar to NRCS for some level of consistency between federal agencies regarding wetland conservation. Same equation and parameters are utilized Allowable drawdown at the wetlands edge is 1 for purposes of conservation easement

10 Wetland Model Development A Previously developed Single Wetland Model (WETSIM) was modified to account for impacts of Tile Drains Flux of water into the nearest tile drain to the wetland boundary is simulated using the van Schilfgaarde equation, modified for radial flow. No field data yet exists to compare with the modeled results.

11 Wetland Model Development WETSIM was calibrated to wetlands at the Orchid Meadows Site Prairie Coteau Region North S1 SP1 T3 S3 T2 T1 S2 SP4 SP3 SP2

12 Wetland Model Development WLS93to10GW WLS93to10SW Model Calibrations for Semi-Permanent Wetland-4 at the Orchid Meadows site

13 Wetland Model Development Model Calibrations for Seasonal Wetland-3 at the Orchid Meadows site

14 Wetland Model Development Impacts of Tile Drainage are simulated for two wetlands at the Orchids Meadows Site SP 4 S 3 Area of Drainage (m 2 ) 131,901 6,869 Wetland Area (m 2 ) 32,750 2,928 Hydraulic Conductivity (m/day) Drainage slope (%) 3 % 5 %

15 Wetland Model Development Impacts of Tile Drainage are simulated for two wetlands at the Orchids Meadows Site 5 inch drain pipe is simulated Lateral distance of tile drain nearest to the wetland is varied from 30 to 300 meters Depth of the drain tile relative to the bottom of the wetland is varied from 0.5 meters above the bottom to 1.25 meters below the bottom Simulations are performed using meteorological data from 1993 to 2010 For periods of non-frozen ground, the frequency of inundation, average depth of water in the wetland and the volume of water captured by the tile drain closest to the wetland are simulated.

16 Potential Impacts Volume of Water Drained versus Drain Depth and Lateral Distance for SP 4 - Drainage for drain tile encircling wetland - -Cumulative Drainage for 18 year simulation period- Lateral Distance (m) 30 meters 50 meters 100 meters 150 meters 200 meters 300 meters Depth of Drain Tile (m) , , , , , Volume of water drained (cubic meters)

17 Potential Impacts Frequency of Inundation versus Drain Depth and Lateral Distance for SP 4 - Inundation during non-frozen ground conditions- -Frequency with no drain = 91%; 18 year simulation period Lateral Distance (m) 30 meters 50 meters 100 meters 150 meters 200 meters 300 meters Depth of Drain Tile (m) Frequency of Inundation (%)

18 Potential Impacts Volume of Water Drained versus Drain Depth and Lateral Distance for S 3 - Drainage for drain tile encircling wetland - -Cumulative Drainage for 18 year simulation period- Lateral Distance (m) 30 meters 50 meters 100 meters 150 meters 200 meters 300 meters Depth of Drain Tile (m) , , Volume of water drained (cubic meters)

19 Potential Impacts Frequency of Inundation versus Drain Depth and Lateral Distance S 3 - Inundation during non-frozen ground conditions- -Frequency with no drain = 52.8%; 18 year simulation period Lateral Distance (m) 30 meters 50 meters 100 meters 150 meters 200 meters 300 meters Depth of Drain Tile (m) Frequency of Inundation (%)

20 Conclusions Key decision variable for installation of tile drains near permanent and semi-permanent wetlands is the depth of the tile below the bottom of the wetland There is great potential to change characteristics of semi-permanent wetlands to seasonal wetlands if tile drains are installed below the bottom of the wetlands Wetland monitoring should be part of the protocol for installation of tile drains near wetlands that are part of the USFWS conservation program.