ASSESSING CORRELATION OF MID-CHANNEL ISLAND GEOMETRY WITH PRESENCE OF IN CHANNEL DAMS USING REMOTELY SENSED DATA

The goal of this project was to find the correlation between damming of rivers and island geometry. We were interested in how island geometry changed based on where the mid-channel islands were located with respect to location down river (i.e., more islands should be located downstream due to sediment transport, and downstream islands should be larger than upstream islands) and with proximity to dams (i.e., more islands upstream of dams and less islands downstream of dams). We focused on the Grasse River in Northern NY, which is currently the least dammed of the rivers draining into the St. Lawrence River. Most of the dams have been removed to date and therefore it is the river most likely to be rebounding to an undammed river state. In Northern NY, the occurrence of these mid-channel islands is of interest because roughly 12,000 years ago the entire area was under glaciers. With these streams being relatively young, they are still developing but had an extensive history of damming.

We measured the geometry of the islands using remotely sensed data from a combination of Google Earth Pro and ArcGIS Pro. Preliminary results of island measurements show that in areas currently dammed, the islands are narrower (ranging from 17m long x 6m wide to 78m long x 9m wide) or the islands form grouped together (places like Madrid, NY with a collection of 6 islands ranging from 92m long x 32m wide to 446m long x 186m wide). As you move to areas not dammed, the river starts to meander and create oxbow lakes. The bigger islands that are not coincident with dams (the biggest being 197m long x 79m wide) are created when the stream cuts itself off. In the dammed parts of the river this does not occur because the stream lacks the meandering pattern.