RECRUITMENT OF IN-CHANNEL WOOD ON A DAMMED RIVER IN COASTAL MAINE

In-channel wood is an important factor in river dynamics, altering three aspects: sediment transport, channel morphology, and channel dynamics. Despite the importance of in-channel wood to increasing geomorphic and biological heterogeneity in streams, there are minimal studies in systems fragmented by dams. We examine the current sources of wood recruitment on the Mousam River in coastal Maine, as well as the impact of hydrologic and land use changes over time on wood inputs in a dammed watershed. Recruitment is connected to planform adjustments over time which are related to the local geology, streamflow, and reservoir management. Additionally, land use and vegetation alter the presence and quantity of wood that can be recruited and retained in the river. Possible sources of wood include tributaries, downstream transport, landslides, and undercut banks. By understanding the presence, recruitment, and movement of wood in a dammed river such as the Mousam, we may be better able to predict how these dynamics will change if and when the dams are removed.

The dams along the Mousam serve to break the natural flow and alter recruitment of wood, so that recruitment and retention is more localized. We hypothesize that wood recruitment is mainly from local landslides, which is a function of geology, land use and reservoir management. Field observations and measurements provide insight into the volume of wood present in a particular reach of the river and the current sources of input. Measurements of aerial photos from the 1940s to the present in ArcGIS are used to investigate periods of planform alterations and determine how changes in land use and vegetation can result in fluctuations in wood recruitment. Climatic changes between 1940 and the present are assessed using the USGS gage at Mousam River in West Kennebunk. Results indicate that although there are other sources of wood, the current principal inputs are landslides and undercut banks. Furthermore, river planform has remained stable since the 1940s because of the presence of dams regulating channel flow, reducing the likelihood of wood recruitment from overbank flows.