Many municipal airports are surrounded by beautiful (but sometimes encroaching) natural resources. Fitchburg Municipal Airport is no exception. The Nashua River snakes around three sides of Fitchburg Municipal Airport. It is closest to Runway 14-32 at its southern Runway 32 end where it takes a sharp 45o turn to the east and then a sharper 90o turn to the south some several hundred feet later. These sharp turns have historically created riverbank erosion. However, between the time of bidding the runway reconstruction project and the beginning of construction, the river swelled and eroded the riverbank to bring it 13 feet closer to the planned Runway 32 end.
What Should Airports Do if River or Streambank Erosion Threatens Their Runway?
Mitigation of riverbank erosion is straightforward through stabilization and construction using riprap. For Fitchburg, when the river suddenly swelled due to snow melt and heavy, localized rain, the immediacy of the erosion issue required accelerated stabilization of the riverbank to protect the planned Runway 32 end and to holistically address the ongoing erosion. The riverbank was stabilized by encompassing the entire runway end with marine grade ½” thick steel sheet piles, which extended approximately 20’ below grade. The riprap consisted of 42” blasted stone extending from the top of the riverbank, to 4’ below the mean water level.