Sandtraps
Most aquatic conservationists agree that sand is the major “pollutant” in Michigan’s rivers and streams. In the early 1970’s a study was done at Hunt Creek to determine exactly the impact of sand on trout reproduction. The conclusions verified their concerns as it was shown that sand destroys what trout like: deep pools, gravel riffles, cold water; it sandblasts large woody debris smooth (destroying insect habitat); it scours and buries the substrate and fills the pools and channels.
As a result the Michigan Department of Natural Resources (MDNR) and United States Forest Service (USFS) installed numerous of these sediment basins throughout the state. At one time over 160 sandtraps were being maintained on an annual basis. The Pere Marquette Watershed Council became 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. Following removal of the sand, the pad was prepared and then seeded by PMWC volunteers.
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.
In 2010 both state and federal agencies announced that all statewide sandtrap maintenance would be abandoned. The PMWC and the Pine River Watershed Restoration Committee co-hosted a symposium September 21, 2010 in Traverse City to determine what is known now about sand, what will be the impact of abandonment and what alternatives will be available to protect our waters.
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 capturing coarse sand or “fines” (clay, silt), and if located properly.
- Traps are most effective in their early year and lose efficiency over time (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.
A 2011 update from Eric Lewis, member of the board of directors, PMWC.
SAND TRAPS GOOD . . . OR BAD
Since the early 90s the PMWC has been involved with the operation of two sand-traps (sediment basins) in the Pere Marquette watershed. The Bell trap was installed in the Little South Branch in 1993 upstream from James St. near Merrilville Road by the MDNR. It was 385 feet long, 85 feet wide, and 6 feet deep. The Turk trap was installed by the PMWC on the Middle Branch of the PM just below Queens Highway in 1996. It was 122 feet long, 27 feet wide and 6 feet deep.
The Turk trap was installed above several long runs of gravel and cobble on the Middle Branch and was deliberately designed as a study area by the PMWC. It was named after the well-known and legendary conservation officer (retired) Chuck Turk, who is also on the board of directors of the PMWC. The trap was emptied once a year and often twice a year after installation, yielding 200-300 cubic yards of sand on average per year – twenty to thirty 10-cubic yard dump trucks.
The Bell trap on the Little South Branch was much larger and yielded prolific amounts of sand, averaging around 1,000 cubic yards a year. The PMWC website contains a history of this trap and description of the enormous mountain of sand removed from the Bell trap over the years.
Several years ago the PMWC board began to ask if the continued maintenance and expense of these two sand-traps were scientifically justified. Serious erosion sites and poor road-crossings upstream on both rivers had been largely addressed over the years, and there were no known major agricultural or industrial inputs of sediment pollution. We asked the district MDNR fish biologist to review both traps and advise us on the wisdom of continuing the maintenance. As a result of that investigation and on-going evolution of knowledge about sand-traps on Michigan trout streams, the PMWC decided to decommission both traps in 2009. Simultaneously, both the U.S.F.S. and the MDNR announced that they would end sand trap construction and maintenance at all of their sites, with few exceptions. A USFS officer here in Baldwin summarized it like this – paraphrasing: “a lot of money and effort have been invested over decades now by both government and non-government organizations to fix road crossings, drains, erosion sites and deforested areas to remedy man-made sand pollution of our rivers. The time has now come to stop (the expensive) maintenance of these artificial sand-traps in the rivers here because we’ve accomplished what we set out to do.”
The popularity of sand-trap techniques in midwest trout streams started in the early 70s with the famous experiments on Hunt Creek in northern Michigan. The MDNR deliberately dumped large amounts of sand into a high-quality trout stream to study the effects on trout. Prior to then it was widely assumed that sand pollution damaged trout reproduction and survival, but there was little empirical data. The results were as expected, both for fish and smaller organisms. After those studies, sand-traps became widespread in Michigan.
Since then, on-going long-term studies in both Michigan and Wisconsin began to show that sand-trap techniques were a lot more complicated than earlier understood. In some cases, the traps do no good. In others there is some benefit. In others, they can damage a stream. In nearly every case, they do not remove the finest, lightest particles, which can be very damaging to the biologically active gravel interstitial spaces of the substrate, the hyperheos. And, they are expensive to maintain.
At the Bell trap, in particular, the PMWC directors kept asking: what is the source of all these football fields full of sand removed from this trap? Someone said: “if you build it they will come.” In the great movie-”Temple Grandin”- the girl character insistently asks her mother at an open-casket funeral: “But where do they go?” We kept asking: Where does it come from? There were no longer any known major man-made inputs of sand upstream in the Little South Branch, or the Middle Branch. Is it “natural” bed-load or something else? (Sediments are moved two ways in a stream, lighter particles may travel in suspension for long distances – heavier particles move constantly along the surface of the river bed, mostly in high-water events, and are called “bed-load.”)
All rivers have a “natural” bed-load of sand/sediment. Figuring out what is natural and what is not turns out to be a hugely complex question in many of our trout streams. Everyone has an opinion, but only those trained in hydrology, geology, sedimentology and other specialized fields are really qualified to render them. Detailed, scientifically defensible studies are very expensive and must be tailored to each stream. To complicate matters more, these rivers, like a living organism, need some level of continuing input of sand and sediment in order to maintain their physical and biological integrity. If too much natural bed-load of sediment is removed from a river, it will become “sediment-starved” and seek ways to replace it, causing in-stream bank erosion, widening and shallowing of the stream, and other damaging morphological changes which negatively impact fish.
This growing scientific knowledge is even forcing us to question how, when, and why to actively pursue bank stabilization and other erosion control projects along the PM River system. The recurring question always remains: is a particular erosion site part of a “natural” process or somehow man-made? We know the impacts of the logging era (and some would also include the extirpation of the beaver which are now allowed to thrive only in some areas) are still affecting some streams, but it is difficult to impossible to know what the “natural” regime would be without those impacts. Some man-made impacts are obvious – washed out road crossings, poorly designed bridges, livestock in the stream, dams, etc. Emerging scientific consensus is that deforestation and agricultural activity in a watershed causes pulses of rain water to enter the streams without the natural buffering and storage of the water by heavy tree or vegetative growth. This in turn causes a river to become “flashier” and results in channel erosion, widening, and shallowing of the river. In the report by DNR fish biologists Rich O’Neal and Todd Wills (2010), which was issued at the request of the PMWC, they commented:
“Another consideration with removing natural sand bedload from Michigan streams is the potential for increasing bed and bank erosion. These types of effects may not be visible for many years after sediment removal begins. *** “The issue of increased bank erosion becomes even more of a concern considering the extensive artificial bank stabilization that has occurred in the [P.M] over the past 25 years. Bank stabilization using rip-rap or similar hard materials is not recommended because it changes natural shoreline characteristics. Bank erosion is a natural process and should be viewed from that perspective.” Fish Population and Sediment Control Summaries for the Pere Marquette River, 3/17/10, p.6.
In their closing comments O’Neal and Wills offered their own recommendations on what our focus should be for the PM watershed: “Habitat management activities should consider a broad range of landscape issues including protecting and increasing forest cover, controlling urban sprawl, increasing riparian setbacks, and reducing artificial drainage. Channel work should be focused on preservation of natural river characteristics, restoring wood structure, removal of dams and evaluation of other artificial alterations.”
The PMWC has been actively involved in most of these management recommendations for a long time now. (Restoration of more woody structure in the PM watershed is important to a healthy fishery for a lot of reasons. In the tributaries this can be done as much as resources allow, but in the main branch it is more difficult where restoration of “natural” conditions conflicts with navigation and commercial interests.)
Although we are still keeping an open mind about some of the conclusions and recommendations of O’Neal and Wills, we have learned a lot from their report, and are grateful for their willingness to evaluate these two sand traps for us. When you stop asking questions, you stop learning. It is pretty clear that our maintenance of sand-traps on the PM system has, at least for now, come to a close. We are also grateful to retired DNR biologist Andy Nuhfur, who has agreed to independently monitor the Turk trap for us for several years into the future so we can objectively measure if the high-quality spawning habitat there changes following the decommissioning of the Turk trap.