Identifying Drained and Filled Wetlands

In the side-by-side aerial photos above, streams are highlighted in yellow. The site on the left features a linear creek which is actually a water-filled ditch, while the site on the right contains a natural, sinuous stream. The presence of the linear ditch like the one pictured on the left is a likely indicator that wetlands were previously present at the site, and were drained and filled.

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Article adapted and shared with permission from Tom Biebighauser. Learn more about the author and his How to Build a Wetland series below.

Drained Wetlands Are Restoration Opportunities

Previously drained wetland sites, i.e. ones that no longer meet wetland hydrology, are prime opportunities for restoration, and offer significant advantages in the context of wetland mitigation. If you’re a mitigation provider, it’s helpful to familiarize yourself with signs that indicate a drained wetland to identify these opportunities. 

Restored wetlands are given preferential regulatory treatment in the mitigation hierarchy. The U.S. Army Corps of Engineers and EPA’s 2008 Final Compensatory Mitigation Rule emphasizes a preference for restoration over creation, particularly when it can return a previously drained wetland to its natural state. The rule states that in-kind, on-site, and in-watershed mitigation projects are generally preferred, and among types of mitigation, restoration is preferred over establishment, enhancement, and preservation (33 CFR Part 332.3).

In order to represent a good restoration opportunity, the site must have been drained in the somewhat distant past and not simply missing hydrology.* It’s necessary to describe how hydrology has been manipulated in order to show how it would be restored. 

*The passage of time since drainage matters, because it demonstrates that the wetland wasn’t drained for the purpose of creating the restoration opportunity. Similar considerations exist for tree clearing to prevent bad faith environmental alterations. 

In this video, Tom Biebighauser demonstrates how to identify signs of a drained wetland. We’ve also listed signs that indicate a drained wetland below.

54 Signs of a Drained Wetland

1. A shallow or deep ditch is present within or near the area. 
2. A deep ditch or channeled stream is observed within 1-mile of the area.
3. Moved, straightened, or channeled streams are present.
4. Ditches or streams meet at a 90-degree angle.
5. Ditches are present along the edge or between old fields.
6. Streams in the area are basically straight when flowing over level ground where slopes are less than 6-percent.
7. The streams in the area contain vertical banks that are eroding. 
8. Streams are flowing along the base of a hill or mountain. 
9. Tributary streams turn at right-angles when entering larger valleys and then flow along the base of a hill. 
10. Streams are flowing in straight lines along the edge farm fields, or between farm fields. 
11. Streams entering existing wetlands contain head-cuts. 
12. Streams contain head-cuts. 
13. The flow from a spring basically follows the base of a hill or mountain. 
14. The flow from a spring enters a ditch or buried drainage structure. 
15. The land downhill from a spring is dry, indicating the presence of buried pipes and drainage structures. 
16. Irrigation ditches are present that are bordered by sedges or rushes. 
17. The lands pattern is present with dead furrows, or can be seen on historic aerial photos. 
18. Adjoining land of different ownership contains wetlands, with ditches separating the properties. 
19. Buried drains made from logs, poles, boards, rock, clay, or plastic are present 
20. Pieces of clay tile or plastic slotted plastic drain pipes are found on the surface of the ground, or in nearby ditches and streams.
21. The open end of a pipe (outlet) is observed along a stream or ditch. 
22. Surface blowouts (vertical holes) are present. 
23. Crayfish burrows and chimneys are observed in a field. 
24. A vertical pipe (surface inlet) is present. 
25. A patch of rock, representing a surface inlet, is present in a field.
26. Pump station is present. 
27. Historic aerial photos show the presence of a wetland, while recent photos do not.
28. Lidar images shows a basin with straight line or ditch on one or more edges. 
29. Basins have smoothened surfaces where natural pits and mounds were filled and leveled. 
30. Area contains a mixture of topsoil, soil, rock, or trash, showing it was filled. 
31. Hydric soils are found buried beneath construction fill. 
32. The site contains a thick layer of topsoil, showing it was filled by pushing in topsoil surrounding the wetland. 
33. Test holes reveal that topsoil is buried on the site. 
34. Test holes uncover trees and branches cut by beaver.
35. Ruts formed by rubber-tired vehicles are present, some containing water.
    
36. A motor vehicle has become stuck in the mud while driving over the location. 
37. Crayfish burrows are present, either in a farm field, old field, or lawn. 
38. Puddles of water are present in fields. 
39. Very small wetlands are present. 
40. The ghosts or shadows of drained wetlands are visible on aerial photos. 
    

    

41. Scattered wetland trees, shrubs, sedges, or bulrushes are present.
     

    

42. Constructed farm or ranch ponds are present (many were made from natural wetlands). 
43. A landowner or neighbor remembers a wetland on the site. 
44. Hydric soil is present that is being farmed. 
45. Unplanted depressions growing trees or shrubs are present within larger fields. 
46. Area contains a shallow depression growing trees that are surrounded by farmland. 
47. Depressions containing clay texture soils only contain water following a heavy rain, indicating that buried drainage structures have been installed to drain the wetland. 
48. Shallow depressions in fields contain crops killed by standing water 
49. Shallow drainages contain upland plants instead of sedges and rushes, indicating the presence of buried drainage structures. 
50. An area is dominated by reed canary grass or phragmites. 
51. Water flows from the wetland in a narrow stream with high banks. 
52. Natural vernal pools are present that have a very short hydro-period. 
53. The overflow from a natural wetland flows into a ditch. 
54. Shells from crustaceans are present in the soil.

Download this list as a PDF from the Wetland Restoration and Training website.

About the Author

Tom Biebighauser has been enthusiastically restoring wetlands, lakes, streams, and rivers since 1979. A former wildlife biologist for the U.S. Forest and Wildlife Service, he has designed over 10,000 wetland projects and has successfully supervised the construction of over 3,000 wetlands and streams. Biebighauser founded Wetland Restoration and Training LLC in 2014 with the mission of encouraging and helping people build naturally appearing and functioning wetlands.