Adaptive Stream Restoration Strategies that Add Large Woody Material to Headwater Streams to Improve Aquatic Life, Channel Complexity, Hyporheic Exchange, and Floodplain Connectivity

Elaine Langone Center, Gallery Theater

Sustainable and effective stream restoration strategies should focus on assisting the recovery of ecological integrity in degraded sections of a watershed by (1) reestablishing hydrologic, geomorphic, and ecological processes and (2) replacing lost, damaged, or compromised biological elements. This presentation provides examples of chop-and-drop adaptive restoration techniques used in headwater streams in Pennsylvania and Maine that can be applied to watersheds throughout the Mid-Atlantic and New England. The streams contain coarse channel sediments that are naturally sorted into a complex network of log jam/step/pool and gravel bars. In their equilibrium state, the channels have a braided or multi-threaded pattern, with numerous side channels and depressions present across their floodplains. However, during the 19th and 20th century, many of these watersheds were clearcut and the streams channelized, straightened, bermed, and “cleaned” of logs and large boulders. Their braided patterns were reduced to a single channel to facilitate seasonal log drives or route flood waters quickly downstream. We have been experimenting with new, adaptive restoration strategies such as “chop and drop,” where selected trees in a riparian corridor are strategically felled directly into the channel and the stream self-adjusts over during high water events. Larger “digger” logs promote step-pool formation and finer “sweeper” branches promote bar formation, improve grain size distribution of the channel bed sediments, and spawning habitat for fish. Channel complexity and aquatic habitat is greatly increased. The hyporheic zone is also improved, with increased groundwater-surface exchange and transfer of carbon and nutrients between the forested floodplain and stream. In selected reaches, larger trees are being dropped into the stream at the head of the braid bar to redirect a portion of high-water flow to the abandoned side channels, thereby reconnecting the stream to its floodplain. This results in sediment being filtered out, water quality improved, groundwater recharge increased, and downstream flood peaks reduced. Chop and drop restoration approaches improve carbon sequestration within the local watershed system and the branches and leaves provide a food for macroinvertebrates and shelter for fish, amphibians, and reptiles. Compared to traditional methods, project costs can be reduced by orders of magnitude, because these methods require less materials and human resources to complete.