Complex sentence: With much fanfare the US ACOE completed their last dredging of the canal in 1955 and soon afterwards abandonded the regular dredging of the Gowanus Canal, deeming it to be no longer cost effective.
Split into simpler sentences: With much fanfare the US ACOE completed their last dredging of the canal in 1955. But soon after the US ACOE gave up on the regular dredging of the Gowanus Canal, deeming it to be no longer cost effective.