Quantifying the Impacts of Road Construction on Wetlands Loss: Preliminary Analysis 1. INTRODUCTION

Over the past decades, the role of federal programs in the generation of wetlands losses has received much attention. Nationwide, by far the greatest impacts of federal programs on wetlands have been generated by levee projects, flood control and drainage projects, and agriculture and water management programs. Other federal programs, however, have also contributed significantly to wetland losses nationally. One such program i[s] the Federal Aid Highway Program.¹

The Federal Aid road system has led to wetland loss and degradation both directly and indirectly.² Road construction has led to losses of wetlands through the effects of filling, fragmentation, and alteration of hydrology. Road construction has also led to wetland losses by providing easy drainage outlets for agricultural wetlands conversions in the Upper Midwest and the Southeast. Constructed highways may also have indirectly led to wetland loss by enabling or inducing secondary development, although this effect is debatable.³

While the available literature provides much anecdotal and qualitative evidence of the impacts of the Federal-Aid Highway Program (FAHP) on wetlands loss and degradation, it appears to provide very little in the way of empirical data on these impacts. Review of the literature and consultations with wetlands experts conducted as a part of this analysis did identify a few studies which relied on aerial photography to identify wetland losses linked to road construction in specific regions. However, no quantification of the extent of national wetland loss linked to the FAHP has been undertaken. This is not surprising given that a rigorous empirical analysis would likely require extensive analysis of historical Federal Aid road construction and wetland stock and loss trends at the state or regional level. Such an effort would require extensive data gathering and intensive analytical methods.

This paper makes a more modest and preliminary attempt to quantify the impacts of the FAHP on wetlands loss. The analysis combines readily available data on the extent of Federal Aid road construction and wetland loss over the life of the program with certain assumptions to derive a rough national estimate of the potential magnitude of wetland loss resulting from the FAHP. It also uses the results of the few empirical studies identified in the literature to calculate rough estimates of FAHP related wetland losses for specific regions which are used to augment and provide perspective for the evaluation of the national estimates.

This paper concludes that between about 310,000 and 570,000 acres of wetlands could potentially have been lost due to the construction of FAHP roads between 1955 and 1980, at a cost to replace of between $153 million and $6 billion. The wetland acreages represent rough estimates and the cost figures represent orders-of- magnitude estimates. The magnitudes of these numbers depend on the assumptions used in this analysis. Our assumptions are discussed explicitly throughout this report.

It should be noted again that this analysis addresses FAHP impacts on wetlands during the 1955-1980 time period only. This timeframe was selected to reflect the period in which the FAHP was active and the many environmental controls currently regulating road construction had not been established. As a result, the conclusions of this report should under no circumstance be construed to apply to highway construction since 1980.

The paper is organized as follows. The quantitative analysis of the direct and indirect effects of Federal Aid roads on wetlands is described in Section 2. The results of this analysis are then summarized and evaluated in Section 3. Section 4 combines the results of the impact analysis with various estimates of per acre wetland restoration costs to illustrate the potential costs of a program to replace wetlands impacted by the FAHP. Two appendices and several attached exhibits provide more detail on the roadway and wetland data used in the analysis.

¹U.S. Department of Interior. 1988 and 1994. The Impact of Federal Programs on Wetlands. Volumes I and II. Areas studied in the report include the Mississippi Delta region, the Prairie Pothole Region, southeastern Alaska, California’s Central Valley, Florida’s Everglades, Coastal Louisiana, Maryland’s Eastern Shore, Coastal Michigan, Northern Michigan, the Pocosins in North Carolina, New Jersey, Puerto Rican Mangroves, the Texas Coast, and riparian areas in Idaho, Nevada, and New Mexico.

²As used in this report, the term “direct impacts” refers to impacts caused by the construction of roads themselves within a narrowly defined area around the road. This area can include either the roadway right-of-way or, more narrowly, the area that includes breakdown lanes, travel lanes, and medians only. The term “indirect impacts” refers to impacts of any other kind.