Complex Wetland Delineation

ARM’s wetland scientists conducted field investigations for wetlands and streams to facilitate project planning and serve as technical documentation for permitting. ARM’s experience and knowledge associated with complex wetland conditions allowed for the advancement of the project by maintaining site design goals and project schedules and by reducing overall permitting costs.

Aquatic Resource Investigation

The property consists predominantly of active agricultural fields. The area of investigation (AOI) has a land use history of agriculture dating back until at least the 1930s that has influenced the vegetation, soils, and hydrology of the site.

Wetland and stream delineations of the site were challenging due to several factors, including:

  • Site conditions influenced by several decades of agricultural operations (altered vegetation,
    hydrology changes, conservation planting practices that improve soil permeability, and soil loss);
  • Historic above normal rainfall levels;
  • The presence of red parent material soils; and
  • Historic wetland extents that did not reflect present conditions.

Due to the presence of problematic vegetation, soils, and hydrology at the site the wetland delineation rationale was based upon the use of a reference wetland and problematic procedure methods described in the regional supplement and Corps Wetlands Delineation Manual (1987). The reference wetland for the site was located within old field habitat, adjacent to the agricultural fields. Prior to the field investigation, a review of historic aerials and infrared imagery was conducted to identify hydrology signatures on the site. Field investigations were conducted by ARM in 2017 and 2018 that represented differing plant communities and hydrologic conditions.

The wetland boundaries from historic delineations were substantially reduced from the current wetland conditions and supported by reference materials, on-site observations and data recordation, and landowner interviews. The extents of the current wetlands were based upon the presence of all three wetland parameters even if one criterion extended beyond the boundary or was singly present in other areas of the agricultural field.

  • Wetland hydrology indicators observed in the reference wetland were present within the site wetlands during each field investigation, including over multiple seasons.
  • Red parent material had indicators of hydric conditions (oxidized rhizospheres on living roots, concretions) with dominant hydrophytic vegetation. Soils observed in the delineated wetlands and the reference wetland had similar characteristics.
  • A dominance of hydrophytic vegetation based primarily on the prevalence index was dominant within the delineated wetland in areas planted with hay.

Both wetland boundaries were evaluated by the United States Army Corps of Engineers (USACOE) during the agency review process. A preliminary jurisdictional determination (PJD) was conducted to verify the extent of the wetlands. The USACOE concurred with the current wetland delineation approach and delineation. As a result of the USACOE’s determination the wetland area was substantially less allowing the project schedule to advance, redesign and permitting efforts were not required and all wetland and stream impacts were avoided.