To document the effects of the dam removal project, the USGS study is using a multi-discipline approach that includes the collection of water-quality and sediment samples, monitoring of streamflow and physical properties, measurements of river profiles, and habitat assessments of selected river reaches. The study began in December 1999 with the establishment of a streamflow gaging station and will continue through September 2002.

The study reach extends from Whites Bridge in White Pine Trail State Park downstream to where the Muskegon River intersects the dividing line between sections 23 and 24 of Big Rapids Township (T15N R10W). This section dividing line coincides with the upstream limit of Rogers Dam Pond as designated by the Federal Energy Regulatory Commission. The streamflow gaging station is located at the Big Rapids sewage treatment plant. Data from this station is used to calculate sediment loads. Also located at the station are a continuous water-quality monitor and two automatic suspended-sediment samplers. The continuous water-quality monitor records hourly readings of water temperature, specific conductance, and dissolved oxygen concentrations. One automatic suspended-sediment sampler collects a daily sample, whereas the other sampler is set to trigger during storm events to collect additional samples.

Water-quality, suspended-sediment, and bed-load samples are collected from Whites Bridge and the M-20 Bridge above the sewage treatment plant. The Whites Bridge samples are used to establish a water-quality base line and to estimate the sediment load entering the study reach. The M-20 bridge samples are used to assess changes in water-quality and sediment load within the reach containing the dam remnant. The M-20 sediment samples are also used to calibrate the continuous suspended-sediment monitors.

Thirty-nine river transect stations have been established within the study reach to track changes in stream bottom and gradient. Data from these stations will also be used to calibrate and verify the model, which is a one-dimensional mixed-size sediment transport model (Bennett, 2001). Seventeen of the transect stations are located within the five habitat assessment reaches. Habitat assessments consist of both the habitat assessment portion of the MDNR Great Lakes and Environmental Assessment Section (GLEAS 51) (Michigan Department of Natural Resources, 1991) and the USGS National Water Quality Assessment (NAWQA) transect procedure (modified) (Meador, 1993).

From an analysis of the water-quality samples collected at White's Bridge and the M-20 Bridge prior to the dam remnant removal, the dam remnant appeared to have no discernable effect upon water-quality in the river. The reservoir behind the dam remnant was run-of-the-river with a small storage capacity and short residence time.

Preliminary examination of the habitat assessments finds that Reach B upstream of the dam remnant has had a dramatic improvement in habitat quality since the dam remnant removal, whereas downstream Reaches C, D, and E have shown slight habitat degradation. Reach B habitat score improved from a fair rating of 69 to an excellent rating of 112. The score for Reach C remained in the good range but dropped from 88 to 79; the score for Reach D dropped from an excellent rating of 108 to a good rating of 102; and the score for Reach E dropped from a fair rating of 68 to a fair rating of 54.

River bottom transects were made prior to the dam remnant removal (prior), a few months after the removal (short-term), and one year later (one-year). This last set was made after the removal of the rock cofferdam. Two areas upstream of the dam remnant show erosion of sediments. The upstream area near transect 8 shows the annual deposition and erosion of sediments near the upstream end of the backwater from the dam remnant and that some erosion has occurred in this area since the dam remnant was removed. Immediately downstream at transect 9, no erosional effects have been observed. The area upstream of the dam remnant has undergone significant removal of sediment. Some of this sediment was dredged during the dam remnant removal, the remainder was remobilized to be captured by the sediment traps or to be transported down river. Transect 14 demonstrates this removal of sediment.

Downstream of the dam remnant, aggradation or sediment deposition varies with the reach. Transect 19 is the first transect downstream of the cofferdam. When the prior and short-term profiles are compared, there is little difference in river bottom levels. The one-year profile, however, shows substantial aggradation in the deep channel. Downstream at transect 28, there is little evidence of deposition from the profiles. This transect is the downstream end of habitat assessment reach D and, as noted in the habitat assessment, it is a high gradient reach with increased velocities. Transect 36 is the middle transect of habitat assessment reach E. The one-year profile show aggradation over the entire channel with the deeper sections completely filled in.