Water Resources Research Act Program

Principal Investigators: Elena Evans

Abstract: Sediment routing is important to riverine ecosystems, river morphology, and understanding how anthropogenic activities will alter natural river systems. Anastomosing, multi-thread channels may have historically been more prevalent in unconfined valleys of the Rocky Mountains before changes in land use and channelization. Sediment flux and budget predictions through these multi-thread reaches are difficult to quantify. This study investigates how fine sediment alters flow dynamics and impacts sediment routing and flux through these complex reaches. Sediment pulses resulting from dam removals and changes in land use are altering fish habitat, river dynamics, and morphology. Fine sediment infiltration is a key component in this change, yet is poorly constrained in gravel bedded streams. Infiltration occurs when finer-grained sediments fill the pore space in larger grain matrices. The removal of the Milltown Dam on the Clark Fork River has created a unique opportunity to examine fine sediment infiltration and sediment routing in a multi-thread channel. Fines deposition from the dam removal sediment pulse is visible throughout the Kelly Island reach, four kilometers downstream of Missoula, Montana and 14 kilometers downstream from the site of the Milltown dam. Better understanding of sediment flux is important to policy decisions and river restoration efforts.