11th International Drainage Symposium August 30-September 2, 2022 Des Moines, Iowa

1. Modeling Drained Pothole Ponding Durations with SPAW
Software to Document Presence or Absense of Farmed
Wetland Hydrology.
Why is Modeling Necessary for Hydrologically Altered
Wetland?
Eleventh International Drainage Symposium
Marriot Downtown, Des Moines, Iowa, USA
August 30 – September 2, 2022
Oral Presentation
Donald D. Etler, P.E. Senior Project Manager, Retired
Jon Rosengren, P.E. Project Manager
Collin Klingbeil, P.E., Project Engineer, Jacobsen Westergard & Associates

2. Farmed Wetland is the Problem

3. Iowa Drainage Districts – The Hot
Spots
BECAUSE, Minnesota and Iowa “experts” met in Ames
120 years ago and decided that a 1/8” D.C. was
sufficient. 70 years ago the standard was raised to ½”.
The installed mains had a 50-year design life…but most
of them have not been replaced after 100+ years.
Despite the obvious vested right to drain, farmed wetland
owners can lose the use of farmed wetland when their
drainage district is improved.
Because farm program participation is considered
voluntary, owners can end up footing the whole bill for
the improved drainage and for the loss of the land.

4. THE Government’s Wetland Bible

5. Wetlands Characteristics &
Boundaries
Committee on Characterization of Wetlands
National Research Council
It is instructive that the National Research Council did
not endorse use of the 1987 Manual or the photograph-
based methods of the NRCS. No agency method was
endorsed by the NRC for hydrologically altered
wetland.

6. Wetlands Characteristics &
Boundaries
Committee on Characterization of Wetlands
National Research Council
RECOMMENDATIO
NS
In Summary the NRC Committee Instructed:
In hydrologically altered sites, the presence of wetland
hydrology CAN ONLY BE DETERMINED by monitoring (direct
measurement) or by mathematical modeling.

7. Hydrology Tools for Wetland
Determinations
Reviewers

8. Hydrology Tools for Wetland
Determinations
The SPAW software has been recommended for
pothole water budgeting to determine the 7-day
ponding duration for USDA wetland hydrology
determinations in every version of the Hydrology
Tools since 1997.

9. Hydrology Tools for Wetland
Determinations

10. Hydrology Tools for Wetland
Determinations

11. 35 YEARS OF WETLAND MAPPING
CONFUSION
Finally in 2015 the state offsite mapping conventions of the Iowa NRCS
acknowledged that if drainage mains were not maintained aerial photographs
were compromised and should not be used. Hydrologic modeling became
necessary. SPAW WAS RECOMMENDED.
In October 2017 the 5 prairie pothole states adopted a shared consistent
SOSM for jurisdictional wetland mapping. SPAW WAS RECOMMENDED.
In December 2018 the Iowa NRCS declared that SPAW should not be used.
Between 1987 and 2015 the NRCS stopped and started the wetland
delineation process on several occasions. However, they were consistent
in that only historic aerial photographs taken after c.1981 were used to find
the wetland signatures used to make the determinations.
In 1998, in Barthel v USDA, the 8th Circuit Court found that the NRCS was
not correctly enforcing the law and that Barthel was entitled to the best
historic drainage, and not what existed in 1985. It took more than 15 years
for the NRCS to respond! Iowa is in the 8th Circuit Court’s jurisdiction.

12. State Offsite Methods Manipulations
Iowa SOSM 2018
A MISREPRESENTATION OF SPAW CAPABILITY

13. Field Hydrology: Precipitation, Runoff, Infiltration, Evapotranspiration,
Redistribution, Percolation, Deep Drainage, Etc.
Pond Hydrology: Watershed Inflow, Subsurface Inflow, Pond Inflow,
Sideslope Runoff, External Input, Rainfall, Evapotranspiration, Infiltration,
Seepage, Outlet Pipe, Spillway Outflow, Supply Pump, Drawdown Pump,
Irrigation Demand, Water Table, Permanent Pool, Active Pool, Flood Pool
USDA-ARS Research Agricultural Engineer, and USDA-NRCS Drainage & Wetland Engineer

14. SPAW Hydrologic Processes

15. Assumptions Made For Practical Application of SPAW
1. Include roads in fields.
2. Use each soil type area as a separate field.
3. Assume all fields were in straight row crops in good condition.
4. Assume all fields were under conservation tillage.
5. Start with the current RCN for the field. Although recent changes in
hydrologic classifications increase P2 runoff by 44%.
6. Assume that the drainage district had done its statutory obligation to
replace the old tile with a brand new one of the same size and grade.
7. Assume adequate intakes existed.
8. Assume that there was only one foot of soil for infiltration in the pond
bottom.
9. Assume that the sides of the pond had 100% runoff.
10. Assume only gravity flow in the outlet tile and proportionally reduce the
available tile capacity for downstream watershed of the tile.
11. Assume that the existing drainage in the adjoining fields would eliminate
the potential for a normal two-year storm to cause material seepage to the
ground surface.

16. A Case Study: Skow FW Pothole Appeal
6.85 Ac FW
• DD Tile installed 1913
• Cropped through war years.
Pastured after 1950.
• Tile performance declined.
Cause not found. DD removed
tile shown in 2017.
• NRCS Agency Expert stood by
open trench and noted tile in
good repair!
• Agency determined the 1953
aerial photograph, after 40 years
and 1.5 feet peat subsidence
and before 32 more years of
legal tiling was historic best
drained condition.
• Agency Expert found FW.

17. A Case Study: Skow FW Pothole Appeal
Proof of peat subsidence in FW pothole.

18. A Case Study: Skow FW Pothole Appeal
SPAW Model of Ponding for 30-Years Daily Weather
Seven days ponding occurs in only 10 years out of
30, wetland ponding hydrology criteria is not met
under best historic drained condition.
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19. A Case Study: Skow FW Pothole Appeal
Van Shilfgaarde
Lateral Effect
Analysis:
The existing tile removes
saturation in the
remaining time before 14
days establishing that
the 14-day wetland
criteria for saturation is
also not met.
Under best historic drained
conditions a scientific
analysis proves there would
be no wetland hydrology
present in the pothole under
the farm program or the
Clean Water Act.

20. A Case Study: Skow FW Pothole Appeal
Skow lost the appeal before a local National Appeals
Division hearing officer. The NRCS claimed that the
tile was in good repair, that the 1953 aerial
photograph was the best historic drainage and that it
showed wetland indicators.
Skow lost an appealed to the National Appeals
Division Director. [His decision: The agency followed
its policies therefore it is right.] Skow chose not to
appeal to federal court. Auer deference was too
powerful.
Skow paid a drainage assessment of about $15,000
on the 6.85 acres and abandoned its further use.

21. A Case Study: Skow FW Pothole Appeal
Computation of 30-year avg RCN for P2 Storms

22. A Case Study: Skow FW Pothole Appeal
Single P2 Storm Ponding Duration, Varying RCN and n.
7 Days Duration