Recent news on the earthen embankment: January 2010

The City of Ann Arbor recently released a study of the condition of Argo Dam’s embankment that has good news but also suggests an erroneous conclusion. While it shows there is no immediate danger of the dam collapsing, it leads you to assume the embankment is solid and in no need of repair. The toe drain repair is still necessary and will cost about $300,000.

Great news and a reality check.

In 2004, the Michigan DEQ’s Dam Safety Office inspected Argo Dam and found a potentially hazardous condition. They wrote, “Seepage water was discharging around and above these [toe] drains, indicating that the toe drain system is failing, and thus weakening the embankment.” The DEQ was concerned that because of drain problems, the embankment was becoming saturated with water, which can lead to the sudden disintegration of a dam. (In fact, saturation is the second-most common cause of embankment dam failure.) The DEQ’s findings were alarming, which is why the Dam Safety Office ordered the city to fix the problem or remove the dam.

The new study used piezometers to measure just how saturated the embankment has become. It found that there is some saturation, which is cause for concern, but that it is not at dangerous levels. SME recommends monitoring the embankment, because saturation can still occur, but says that the dam is safe at this time.

The piezometer data shows us that we don’t need to be as concerned for the near-term safety of the dam as the DEQ study indicated.

The Huron River Watershed Council welcomes this new information. We have relied until now on the DEQ’s 2004 study, but this data alleviates our immediate public safety concerns.

We continue to call for the removal of Argo Dam. This study might persuade the DEQ to give Ann Arbor more time to make a decision about the dam, but beyond that, every rationale for removing Argo Dam remains exactly the same.

First, the environmental benefits of removing Argo Dam are many and clear. Dams are inherently bad for rivers; they prevent rivers from doing what they are meant to do, which is to move water and sediment. And Argo is particularly bad: it is the second-worst dam in the state for changing river flow—which is the DNR’s number one measure of a river’s health. To cite just one critical benefit of removing Argo Dam: it will create some 20 acres of floodplain that will filter pollutants, reduce flooding and erratic flows, and create habitat for native species.

Second, the toe drain problem still exists and it is not a trivial one. Toe drains are vital to the integrity of the dam; if the dam remains, the City needs to repair them. Cost: $300,000. The DEQ may now allow the City to postpone these repairs, but that does not mean that the City is permanently off the hook.

More to the point, the toe drain costs are just the most current of many. It is very expensive—both in money and environmental costs—to maintain a dam. You can’t just fix it and forget it: the longer the dam stays in, the more it costs.

Many problems remain to be solved whether the Argo Dam stays in or comes out. The piezometer study is good news for everyone, and we hope that it will create space for the city to answer these lingering questions.

Will the river return to it’s original channel on to the DTE property?

Recently, some people have expressed concern about the possibility that if Argo Dam is removed, the Huron River will begin flowing over land downstream of the dam which is contaminated with pollutants. This land, owned by DTE, is some of the most contaminated in the watershed, and the possibility that the river could be polluted by running over it is a concern. But there is reason to believe that in fact the dam removal will not affect the site at all.

The Huron River Watershed Council has been aware of the problems with the DTE site for years, and we do not want to see the river’s course changed to flow over contaminated land. That is why, long before HRWC suggested removing Argo Dam, we asked several outside scientists and engineering firms to assess the likelihood of that happening.  Their initial assessments were that removing Argo Dam would probably not redirect the river over the contaminated land.

Their explanations are a bit technical, but here are the basics:

Water coming through the dam gates plunges 15 feet down. These concentrated flows have blasted a “scour pool” in the river bed below the dam. If we remove Argo Dam, that sudden 11-foot elevation drop will be “regraded” and dispersed over a longer stretch of river.  Rock veins (rock structures) can be placed above and below the dam site to even out the elevation drop where the dam used to be and to catch and store sediment.  When you distribute the drop over a larger section of the river, the flow or force of the water will be reduced substantially.  In addition, dam removal will add an additional 20 acres of floodplain upstream of the present dam site, which means there will be  more storage  to absorb large stormwater flows.  Barton Dam, sitting about two miles upstream, also greatly mitigates extreme flows in this section of the river.

Finally, the banks of the DTE site are already protected by a retaining wall. If more complete studies suggest that flow  may spill over on to the DTE property, another option is to add additional armoring to the existing seawall.

These are initial reviews, not exhaustive studies. No one has data—yet—to show definitively whether the river would or would not be directed over the DTE site.

For that reason, HRWC has always included, in its cost estimates and proposals for dam removal, funding for such a study, to accompany studies of sediments and safe removal practices. Similar studies are part and parcel of all dam removals; they are common-sense safeguards against any hazards involved with removing a dam.

River flow models (HEC-RAS) were completed in earlier studies of Argo Dam, but we need City Council’s direction to conduct further analysis of both options.  In the near-term, the HRWC requested a quote from Barr Engineering to conduct a full-fledged study of the river direction after dam removal.  Barr Engineering has worked on over 200 dam projects across the Midwest and conducted the initial sediment analysis in 2001 for Argo Pond.

Some people have said that the dam is in good condition. Why does HRWC say that the dam is failing?
We’ve said that Argo Dam is failing because the Michigan Department of Environmental Quality says it is failing. In 2004, the DEQ’s chief of water management wrote the City of Ann Arbor a letter that read, in part, “the toe drains along the downstream side of the raceway canal embankment are failing. …The toe drain system should be repaired immediately…”

The DEQ sent this letter almost five years ago—and in it complained that it had been trying to get the city to take action on Argo since 2001. Today, the dam has still not been repaired.

Part of the dam, specifically the concrete section, is indeed in good condition. Unfortunately, most people believe this is the full extent of the dam. One aspect they are not considering is the toe drain, which is also a part of the dam, and which the DEQ said was failing. The toe drain is covered under the dam permit and all technical descriptions, as are the gates, chains, mill race, mechanics, etc.

The toe drains are deteriorating and not draining the water in the earthen embankment adequately. These drains reduce the elevation difference, and therefore the water pressure, between the mill race and the river.

The Michigan Department of Environmental Quality is concerned that parts of the earthen embankment will liquefy and fall into the river. The water in the mill race would then rush into the river, carrying loads of sediment with it and creating a “new” channel. This may cause flooding downstream, obstructions and back-ups in the river, and could kill plants and animals.

Moreover, the MDEQ and MDNR staff have been dogging the City of Ann Arbor to come up with a plan for the dam since 2001. Over that same time period, staff and budget cuts have led the MDEQ to publicly announce that it would not be able to respond to minor pollution concerns, review wetland permits, or review minor applications for new permit discharges. In short, MDEQ has been forced to take action only on significant environmental dangers. MDEQ cannot afford to fret about minor problems. The fact that they have expressed this raised level of urgency about Argo dam and the risks associated with an embankment collapse causes the Huron River Watershed Council great concern.

Can we fill in the mill race in order to solve the toe-drain problem?
It’s possible to do, but the City of Ann Arbor staff explored and dismissed this idea for two reasons. First, the upstream portions of earthen embankment add stability to the Argo impoundment. Water from the impoundment also puts pressure on the upstream portions of the embankment therefore requiring some toe drain repair. Additionally, and more costly, is moving the Argo canoe livery operations or adding a long portage. City of Ann Arbor staff’s preliminary cost analysis suggests that moving the paddling put-in spot will cost just as much as or more than fixing the toe drains.

Is HRWC against rowing?
Absolutely not. HRWC wants rowing to survive and thrive in Ann Arbor. If Argo Dam is removed, the four rowing teams that use Argo Pond would have to move. Some rowers have argued that it’s impossible for their teams to move, but there’s reason to believe that the teams could do well elsewhere.

More important, Argo Dam will not be removed unless the rowing teams can be accommodated. Every key document in the Argo Dam discussion—from the HRIMP report to the resolutions of the city’s Parks and Recreation and Environmental Commissions—has included a crucial provision: Argo Dam will only come out once the rowers have found other homes. HRWC not only endorses that provision, as a member of the HRIMP committee, we participated in writing it. HRWC is committed to helping the rowing community find alternate venues in Ann Arbor if Argo is removed.

Could rowing work on another pond?
Moving rowing is a complicated issue. Argo pond was not the rowing community’s first choice of venue, but they are now settled and happy there. 1983 Michigan Rowing Association matrix. Many rowers contend they simply cannot move. We believe, however, that it is possible and for some teams at least, desirable. For more than a decade, HRWC has been working with members of the rowing community to deal with problems at Argo Pond. The pond, like most dam impoundments, has a problem with weed growth, which interferes with the boats and requires continual mowing and not enough depth to row, from the sediment build-up

The rowing course on Argo is not long enough to hold regattas. It is also overcrowded with rowers who have to jockey for time on the water. Four teams use Argo: Pioneer and Huron high schools, the U-M men’s club team, and the Ann Arbor Rowing Club. The U-M women’s team practices at Belleville Lake; EMU at Ford Lake. With the new high school, Skyline, another team needs to find space on the water. In short, Argo is far from perfect.

Other ponds—Barton, Gallup, and Superior—have limitations too. Like Argo, none of these ponds is long enough for a rowing course; rowing would have to move to Ford or Belleville Lakes to meet the straight and long distance requirements. Argo provides a rowing distance of 3,200 feet. Barton is wider but a bit shorter (3,000 feet of water and a longer race course) due to a low railroad bridge, and there are questions about accessing the pond through the private property of Barton Hills. Gallup has a shorter rowing length due to pedestrian bridges that form a “pinch point” where two rowing sculls could not pass at the same time. Superior pond has shorter rowable water and some impassable or difficult bridges.

These problems would need to be overcome and have not been thoroughly explored with the City and rowers. Other objections do not hold water. For instance, because the U-M and high school teams row in April-May and September-October, they would not interfere with users from the Gallup or Argo liveries, which are closed at those times. And in some cases, moving a team could be an opportunity. Gallup Park, for example, is across the street from Huron High, and if the venue problems can be solved, Gallup would be a natural spot for the team.

Will removing a dam increase flooding?
Argo Dam does not provide flood control (very few dams in Michigan do). The City of Ann Arbor is legally required to keep the pond level at a set level. The City cannot hold water back to prevent downstream flooding or empty the pond in advance of a heavy rain.  Argo Dam removal will actually create approximately 20 new acres of  flood control. The removal itself will be done gradually over several weeks to prevent downstream flooding and stabilize sediments. Once the dam is removed, the river will be reconnected with its floodplain, allowing the river to expand in heavy rain events. The new floodplain will absorb the water, reduce the flow, and settle out sediments and nutrients.

Will the dam removal matter if other dams in the system are not removed?

Argo Dam is ranked as one of the top three dams best suited for removal by the Michigan Department of Natural Resources. Their Huron River Assessment Report lists the the top three strategic dams to remove on the Huron (the others are Mill Creek, which was removed last year, and Peninsular Paper in Ypsilanti).

Removing Argo Dam will restore 6 miles of free flowing river to the Huron in an urban setting. The MDNR studies suggest that this stretch could be restored to a higher quality fishery. Recreational opportunities will be expanded to faster-moving water for paddling and tubing. Ecological diversity will also improve, such as mussels and more sensitive macro invertebrate species.

Some rivers are so heavily developed and dammed that removal of one dam on that river will only return flows to a small portion of the river. Generally, dams that have been targeted for removal are strategically located. Removal will open up a section of the river critical to fish and wildlife and/or recreation. In some cases, this additional section of river is enough to sustain crucial populations of endangered or threatened species of fish, mollusks, and other wildlife.

Moreover, we should not NOT take action just because that action won’t solve every problem. The Huron River’s health is damaged by thousands of minor cuts, wetlands fills, pipe discharges, pollutant spills, etc. Taking out the Huron’s three high-priority dams will have a positive impact. In addition, if we take out some dams, when the large federally regulated dams (such as Barton) are up for permit renewal, we have more leverage to get them to moderate flows to more “natural” levels and add fish passage.

How does dam removal affect fish?

Dam removal benefits riverine fish in many ways, including: (1) removing obstructions to upstream and downstream migration; (2) restoring natural riverine habitat; (3) restoring natural seasonal flow variations; (4) eliminating siltation of spawning and feeding habitat above the dam; (5) allowing debris, small rocks and nutrients to pass below the dam, creating healthy habitat; (6) eliminating unnatural temperature variations below the dam; and (7) removing turbines that kill fish.

In this case, a free-flowing Huron river will replace a poor quality fishery with a higher quality smallmouth bass fishery and a more biodiverse fishery. In addition to the ecological benefits are the recreational and economic benefits from an improved fishery.

What are the potential environmental downsides to dam removal?

Dam removal does result in fundamental changes to the local environment. The reservoir will be eliminated, and with it the flat-water habitat that had been created. Wetlands surrounding the reservoir will also be drained, although new wetlands are created both in the newly restored river reach above the former dam site and in the river below. Sediment that collects behind a dam, may contain toxics such as PCBs, dioxide, and heavy metals. An initial sediment analysis conducted by Barr engineering shows that Argo Pond’s sediments are not contaminated, but further tests will have to be performed before the dam is removed.

Through proper removal techniques sediment release downstream can be prevented, water turbidity diminished, and water quality protected.

Why history isn’t a good reason to preserve Argo Dam?

In a city that supports efforts to preserve historic houses and public buildings and even whole neighborhoods, Argo Dam might seem a logical candidate for historic preservation.  Argo Pond has existed in some form since 1832 and the current dam since 1914, and both have played a significant role in the history of the community. But the argument for historic preservation quickly breaks down when applied to natural systems as opposed to features of the built environment.  The impoundments that dams create, like Argo Pond, may give the impression of permanence but are in fact continually changing.  Algae blooms spread and sedimentation gradually increases, eventually necessitating remedial actions if the qualities that make the impoundment attractive are to be preserved.  A dam disrupts the natural flow of a river, at the expense of its aquatic diversity and overall health.  Argo Dam causes extreme fluctuations downriver, with damaging environmental effects and occasional hazard to those using the river, as in a case this past summer when a log jammed the gate and caused a surge that suddenly raised the level of water below the dam.  Communities may decide that the benefits of a dam outweigh the considerable environmental and financial costs of maintaining it, particularly if the dam generates significant hydroelectric power, but preserving a dam and the impoundment it creates has nothing in common with restoring historic buildings or maintaining the integrity of historic neighborhoods.  The analogy is a misleading one and should not be allowed to muddy the argument about the future of Argo Dam, which is ultimately an argument about the future of a dynamic natural system, the Huron River.

Will it cost a lot to restore the land that dam removal uncovers?
An estimated 30 acres will be reclaimed by the City as parkland with dam removal. This parkland will be natural areas with paths and benches and fishing access docks, An estimated additional 21 acres will be floodplain. This stretch of the river will have a great canoeing or kayaking stretch, and be a nice place to walk, bike, bird-watch or sit.

One concern about this new land is the potential appearance of invasive plant species. The concern is legitimate but addressing it will not be particularly expensive. According to the MDNR,
“Reclamation of the former impoundment area should not be a significant expense unless the city is anxious to restore a wooded environment more rapidly than the 20+ years that may take naturally. The impoundments generally have a store of healthy, viable, native plants that colonize quickly as the drawdown takes place. A seed mix of native flowers and grasses (that will establish slowly) along with an annual cover crop of rye for example will help to prevent soil erosion during rain events while the soil is drying out and vegetation is reestablished. Cottonwoods and willows will colonize immediately too and can grow to several feet in their first couple of years. Some seed bearing shrubs or small trees would be a nice addition but entirely optional. These are the kinds of things that are easily funded with grants and done by volunteers.” Sharon Hanshue, MDNR

How quickly do rivers recover after dam removal?
Rivers are very dynamic and resilient systems, and natural river systems can be restored relatively rapidly after dam removal. Locally, fish in Mill Creek passed through the former dam site within days of the dam’s removal. As an impoundment is a seedbank and nutrient source, the vegetation of the old impoundment returns within weeks. An invasive species management plan is required for the dam removal permit, and adequate invasives management and streambank stabilization techniques help reestablish a stable river channel quickly

What will it look like with the dam removed?
Argo Dam was placed at a high gradient reach and without it, the river will go back to drops, pool, riffles. It will probably look much as it does upstream of Delhi Metropark.

Many people fear a stinky, muddy flat where the pond used to be. In fact, riverbeds respond quickly and fill with plants, wetlands, and floodplains along a free-flowing, fast, and cool river.

Click here for a picture of what restoration could look like at Argo Pond

Who supports removing Argo Dam?

• The Michigan Department of Natural Resources
• Washtenaw County Water Resources Commissioner
• The Ecology Center
• American Rivers
• Huron River Fly Fishing Club
• Huron River Paddlers
• Washtenaw Audubon
• Ann Arbor Area Trout Unlimited
• Michigan Trout Unlimited
• Kayaking Club of U-M
• Michigan League of Conservation Voters

Is it cost effective to remove a dam?
In most cases where dams have been removed or are being considered for removal, money is actually saved over the long term compared to rehabilitating and maintaining a dam. Removal eliminates the expenses associated with maintenance and safety as well as direct and indirect expenses associated with fish and wildlife protection (e.g. fish ladders and mitigation for fish mortality). In addition, removal often generates income from newly available recreation opportunities—including fishing, kayaking, tubing, and rafting?which may actually result in a net economic benefit.

If river water quality has improved so much over the past 30 years, why do we need to do more?

Water quality has improved over the past 30 years due to the passage of the Clean Water Act. That law regulated “point source” pollution and required that polluting entities (manufacturers, sewage treatment plants, etc.) get permits and adhere to certain clean water standards. But now, the primary sources of pollution to the river are “nonpoint source,” meaning they do not come from one point. It is stormwater runoff from parking lots and streets, phosphorus rich runoff from fertilized lawns, and agricultural runoff. This is much more difficult to control and will increase as development increases in the Huron River watershed. City of Ann Arbor residents rely on the Huron River for drinking water and discharge of their treated wastewater to the Huron River. We need a Huron River that can function as a healthy ecosystem AND better assimilate the affects of this additional development.

Isn’t the real water quality problem the sewage discharge to the river, not dams?

The water quality problems posed by dams are at least as serious than those caused by wastewater plant discharge. Some communities, including Ann Arbor, send treated wastewater into the Huron River. This discharge is regulated by the MDEQ through a federal permit program. Over the past 35 years, this program has been largely responsible for significant improvements in water quality in the Huron River.

What are the effects of a dam on a river?
Dams prevent rivers from doing what they’re supposed to do: move water and sediment. They put a chokehold on the life within the river: preventing the flow of plants and nutrients, impeding the migration of fish and other wildlife, and blocking recreational use.
Dams slow rivers: Many fish species depend on steady flows to flush them downriver early in their life and guide them upstream years later to spawn. Stagnant reservoir pools disorient migrating fish and block or significantly increase the duration of their migration.
Dams alter water temperatures: By slowing water flow, dams increase water temperatures. Fish and other species are sensitive to these temperature irregularities, which often destroy native populations.
Dams alter timing of current flows: The Huron River at Argo Dam has one of the top two most erratic flow regimes in Michigan, according to the USGS. These irregular releases destroy natural seasonal flow variations that trigger natural growth and reproduction cycles in many species.

Dams decrease oxygen levels in reservoir waters: When oxygen-deprived water is released from behind the dam, it kills fish downstream.
Dams hold back silt and nutrients: By slowing flows, dams allow silt to collect on river bottoms and bury fish spawning habitat. Gravel, logs and other debris are also trapped by dams, eliminating their use downstream as food and habitat.