Sand Trap Symposium
In May 2009 PMWC was informed that the Michigan Department of Natural Resources & Environment (MDNRE) would not have funding available to clean the Bell Sandtrap on the Little South Branch of the Pere Marquette River that year. The Pere Marquette Watershed Council had become involved in 1993 assisting the MDNR in maintaining the Bell Sandtrap on PM’s Little South Branch. Through 2010, the partners have removed 17,826 cubic yards of sand, the equivalent of a football field covered with 13.41 feet of sand. PMWC has also been active in the cleaning of the Turk Trap on the PM Middle Branch as well as monitoring the maintenance of the sandtrap on the Baldwin River’s.
We asked the MDNRE to do a study on how and why the traps continue to accumulate such volume (no obvious point-source exists upstream) and what would be the impact on habitat if the traps were to be abandoned. MDNRE’s Rich O’Neal and Todd Wills surveyed the Bell Trap in October of 2009. Their formal report in March of 2010 listed a number of conclusions. In general, the report noted that sand reduces trout populations by reducing macro invertebrates (food) and reducing survival of eggs and fry due to degraded micro habitats. Also that removal of the sand bedload has the potential for increasing bed and bank erosion. In the Pere Marquette, 80% or more of sediment collected is natural bedload. The report stated that there is no relationship between brown trout biomass and sediment removal in the PM River. Although the brown trout population did gradually increase following sediment removal (1993), it had already been high. Juvenile steelhead did not show and strong increasing trend since 1993. The MDNRE recommended that the cleaning of the Bell Sandtrap be discontinued and rather that the habitat management going forward should address protecting and increasing forest cover, controlling urban sprawl, increasing riparian setbacks and reducing artificial drainage.
Within weeks of learning of the MDNRE’s proposal to abandon sandtrap maintenance throughout the State, the United States Forest Service (USFS) also announced that they too would discontinue cleaning their 18 sandtraps throughout the state in favor of treating the sources on the sand. Seven traps, including the one on the Baldwin River, would continue to be maintained for research purposes.
PMWC contacted the Pine River Watershed Restoration Committee, who had similar concerns and together we hosted a symposium to review the role of sediment basins in stream restoration. The all-day conclave was held in Traverse City, September 21, 2010, with over 40 environmentalists participating. Representatives from ten watershed councils along with those from Conservation Resource Alliance (CRA), Central Michigan University (CMU), Trout Unlimited (TU), USFS and MDNRE attended.
The symposium surprised many attendees, revealing the decision was not just economical, but also ecological. Presenters were Jim Segelman – PhD Army Corps of Engineers, hydrology and limnology; Todd Wills – MDNRE Hunt Creek fish biologist; Troy Zorn, PhD MDNRE; and Chuck Bassett – USFS.
The findings were that:
- Traps can be made to be very effective, designed for capturingcoarse sand or “fines” (clay, silt), and if located properly.
- Traps are most effective in their early year and lose efficiency overtime (despite cleanings).
- Traps affect stream morphology (depth and width) both upstream and down. Streams deepen more upstream than down, widths also change, not as much but more upstream.
- Without question, effective traps benefit trout, when maintained.
- When new types are installed, habitat downstream improves first. Increased fish population follows two to three years later.
- Consensus is developing that placement of large woody debris (LWD) is now more effective than sandtraps, producing a more lasting effect.
In summary, sandtraps may not make sense financially or ecologically anymore. It appears that the current focus should be on preserving the river’s natural characteristics, placing Large Woody Debris (LWD) strategically, repairing old fish cover structures, and using our dollars more wisely to improve riverine habitat.