DISCONTINUITIES CAUSED BY THE PRESENCE OF RUN-OF-RIVER DAMS ON FLUVIAL SYSTEMS

In addition to the variety of natural features that control river process and form, human modification, such as the installation of run-of-river dams during the industrial era, has created further discontinuities in river processes. Now, over one century later, run-of-river dams are becoming increasingly targeted for removal by river management agencies, which must also ensure that the fluvial response to dam removal does not adversely affect ecosystems, river stability and nearby property and infrastructure. River managers rely on knowledge acquired through studies of existing run-of-river dams to inform scientific and policy requirements during removal planning. To assist in the conversation, this paper presents results of a detailed field study of the effects of four run-of-river dams on the morphology and sedimentology of rivers in low-gradient environments, typical of Illinois. Our study demonstrates that geomorphological effects vary among the four dams, and consequently, each structure has created its own degree of fragmentation and discontinuity. Variation was observed in the quantity of fines stored by these structures, and in the extent of channel widening that has occurred downstream. These results provide guidance to the river management community about key features to identify in the field to inform planning phases for removals. The variability across sites demonstrates that detailed examination of morphology and sediment characteristics is critical to developing appropriate removal strategies for particular dams. Lessons learned from this research project should also provide guidance for practicing geomorphologists to conduct effective assessments for dam removal and river restoration efforts.