Indirect wetland drainage in association with Federal highway projects in the Prairie Pothole Region

Abstract

Wetland losses associated with Federal-aid-interstate, primary, and secondary highways were documented in the Prairie Pothole Region of North Dakota, South Dakota, and Minnesota in the Spring of 1986. Data on indirect wetland loss were collected using a fixed-wing aircraft and were stratified by state, physiographic region, and type of highway. We recorded 734 wetland basins totaling 574.3 ha being drained via open ditches or subsurface tiles into rights-of-way along 3,503 km of roadway. Total estimated loss in the tristate area was at least 11,243 ha along 56,737 km of roadway constructed using Federal monies. No differences (P<0.05) in drainage rates (ha per km of roadway) were detected when states, physiographic regions, or roadway types were compared. No differences (P<0.05) were found between newly reconstructed and existing older roadways. Recommendations as a result of this study include the assessment and documentation of potentially illegal drains into the rights-of-way of Federal aid highways to enforce current wetland protection efforts. Another recommendation calls for the establishment of a “highway-impact-area” in which a zone of wetland loss could be delineated and monitored. This information can potentially be used for mitigation efforts and for a more informed approach to the planning process of future Federal-aid highway projects.