Don’t Repair the Estabrook Dam

Does sedimentation impact the sustainability and uses of the Estabrook impoundment?

Management of sediment quality and quantity is the most important issue affecting the near-term (years) and long-term (decades) outcome following a decision to repair and operate a dam or to remove a dam. Sediment functions as the major storage and recycling compartment for virtually all material that flows into and out from aquatic ecosystems. The quality and quantity of sediment directly or indirectly affects all of the other management issues. Managing sediment quality and quantity is the most technically challenging and costly part of maintaining or removing a dam, especially in developed watersheds and in particular those with a large contributing urban land use.

Mr. Holmes stated that “In terms of sediment accumulation, based on the storage capacity of the impoundment relative to the mean average annual flow volume of the Milwaukee River, the sediment trap efficiency of the impoundment should be nearly zero”.

There are a number of time consuming analytical and empirical methods to conclude that the Estabrook impoundment was and will continue to be an effective sediment trap. However, recent planning and construction documents for the Estabrook Impoundment dredging and sediment remediation project should be adequate. Over the course of the Estabrook Impoundment’s Blatz Pavilion, and Phase I and Phase II sediment remediation projects, hundreds of samples were obtained to document the thickness, volume and mass of accumulated contaminated sediment. The survey boundaries included the lower reach of Lincoln Creek, and the impoundment extending from the Estabrook Dam upstream to just beyond the confluence of the river’s “east” and “west” oxbows in Lincoln Park.

While the thickness of accumulated sediment was variable, large amounts of sediment had accumulated in all areas of the impoundment up to 10-feet. The total volume of accumulated sediment in the Estabrook Impoundment is not readily available. However, the current estimate of just the volume of contaminated sediment removed from the impoundment is 176,200 cubic yards, equivalent to over 12,580 dump trucks. In relative terms, if estimates included the volume of uncontaminated sediment, the total volume of all accumulated sediment in the impoundment would be much larger.

The original Public Service Commission approval for constructing the dam in the 1930s was for a full pool and run-of-the-river dam, meaning that the gates would be closed year round, except under extreme flood events. Over the last several decades and for reasons not entirely understood, the County has departed from this operating protocol by opening the gates every fall and closing the gates in spring.

These extended drawdowns negatively impact habitat upstream and downstream of the dam by eroding accumulated sediment and debris. During just a single drawdown event sampled on October 12, 1994, an estimated 103 tons of sediment and 1.1 pounds of PCBs were initially scoured from the impoundment when the gates were opened. The amount of sediments and pollutants flushed from the impoundment during the remainder of the 7-month drawdown and higher spring flows was not sampled or quantified by the study. If the County had not been conducting these annual drawdowns, the amount of accumulated sediment in the Estabrook Impoundment would have been much larger.

Additional impacts associated with partial or complete seasonal impoundment drawdowns include scouring of polluted sediment and debris downstream; high flows and freeze/thaw cycles that contribute to erosion of river bed and banks; desiccation (drying out of parts of the river), freeze-out and increased predation of mussel beds; desiccation, freeze-out and erosion of aquatic plants, invertebrates, and herptiles; de-watering of floodplain wetlands; loss of fish spawning substrate and juvenile fish refuges; fish stranding and fish kills by asphyxiation, and poor fish year class recruitment; and degraded  aesthetics to describe a few.

Should the dam be repaired, the DNR’s Operational Order may not, and should not, allow the County to practice a partial or complete annual opening of the dam gates which would allow flushing of accumulated sediment downstream, and other negative environmental impacts. All impoundments accumulate sediment. Depending on the quality and quantity of accumulated sediment, the desired function and uses of the impoundment may not be sustainable. With respect to the Estabrook Impoundment, the County and dam repair proponents must recognize that the negative environmental impacts of annual drawdowns greatly exceed any perceived benefits of flushing accumulated sediment from the impoundment. If owners of the dam and a limited number of power boat users of the impoundment are unwilling to accept the consequences of sediment accumulation, they should consider other dam management alternatives and uses of the river that are sustainable, benefit the environment, provide more diverse uses for a larger segment of the population, and all at a lower cost.

The Estabrook Impoundment will continue to accumulate sediment high in nutrients and organic matter. With sufficient sunlight penetrating all water depths throughout the impoundment, conditions will be ideal habitat for producing nuisance amounts of benthic algae and rooted aquatic plants. These conditions were present in the former North Avenue impoundment and other impoundments in the Milwaukee River watershed prior to dam removal and were responsible for nuisance amounts of algae and rooted aquatic plants, in particular non-native Eurasian watermilfoil and Curly-leaf pondweed, which unlike many native plant species, are tolerant of degraded habitat. Native fish diversity and abundance were greatly reduced and the destructive non-native carp populations were abundant. The Estabrook Impoundment will not be immune to developing similar nuisance conditions.

When the final accounting is completed, the cost to taxpayers to remove just the accumulated contaminated sediment will approach $49 million dollars, dwarfing the $6.2 million cost of repairing, operating and maintaining the dam and proposed fishway over the 20-year lifetime left for the structure. According to structural engineers, the entire gated section of the dam will have to be replaced 20-years down the road. Repairing the Estabrook Dam will lead to more sedimentation over time and negatively impact the environment and recreational uses.  Following the sediment remediation projects and the extended 7-year drawdown since 2008, the Estabrook Impoundment is as good as it will be. As sediment continues to accumulate, the functions and uses will decline, and assuming the County will not be able to flush sediments as in the past, the rate of degradation will be at a faster rate than previously experienced. If the dam is repaired, will the next generation of residents along the impoundment and their County Supervisor ask the rest of the County taxpaying residents to repeat this financially burdensome dam replacement and dredging process?

What are the impacts of the Estabrook Impoundment on Fish and Aquatic Life and Habitat?

The addition of fish passage will have no bearing on fish habitat in the Estabrook Impoundment. It will not affect habitat aside from the footprint it is constructed on. A fishway will not affect the most important issue impacting fish habitat and the fishery in the impoundment, that being the quality and quantity of sediment and the rate by which it accumulates.

The quality and quantity of sediment has a direct and indirect effect on fish and aquatic life habitat. Nutrients and organically rich sediment can produce nuisance growth of plant material that decrease dissolved oxygen levels (through plant respiration and decomposition) that contributes to sediment oxygen demand or lower oxygen levels). Eutrophic and turbid water quality conditions benefit pollution tolerant, non-native aquatic plant species such as Eurasian watermilfoil at the expense of native species that are better utilized for food and cover by fish, other aquatic life and wildlife. The accumulation of impounded sediment enriched by substances such as heavy metals and PAHs from urban runoff can have acute and chronic impacts on fish and aquatic life at all life stages and the impacts can extend over generations. The accumulation of silty-clay sediment, potentially toxic compounds, nutrients and organic matter from benthic algae and decomposing plant material create very inhospitable habitat for fish and other aquatic life. This condition will not be changed with dam repair.

The value of flowing rivers and streams with clean and coarse substrates and connected floodplain wetlands as critical fish habitat cannot be over stated. Most of the approximately 60 native fish species present in the Milwaukee River and its tributaries evolved and are specialized for all or a portion of their life cycles (spawning/reproduction, development, feeding and growth) in flowing rivers or streams, and floodplain wetland habitats. Fish require clean and coarse substrate for spawning and successful embryonic development;  their diets are primarily aquatic insects that also require clean and coarse substrate;  they spend most of their lives in direct contact with the substrate; many are intolerant of degraded water quality and sediment; and some require wetlands and aquatic plant vegetation for spawning and nursery habitats. These critical features are generally absent from the Estabrook Impoundment. As the impoundment continues to accumulate silty sediment, habitat suitable for preferred native species will be poor, which means less native fish will successfully reproduce and recruitment to local populations will be low.

Habitat quality affects the diversity and abundance of the fish community. Inversely, the presence and abundance of a single species can change the dynamics of a river ecosystem, including its habitat. There may be no better demonstration of a fish species’ negative impact on aquatic ecosystems than the non-native common carp. Carp will do very well in the Estabrook Impoundment. No other species, native or non-native, is so well adapted to degraded habitat, and modifying habitat to their benefit and at the expense of native species as the carp. Carp spawning success is reduced in flowing water with coarse substrates. Optimum spawning habitat is slack backwater areas with vegetation. Carp tolerate high water temperatures and turbidity, and low dissolved oxygen levels, and incubating carp eggs can tolerate silty sediment.  As omnivores, carp consume a wide range of food types and can adapt to changing food supplies caused by environmental degradation. As bottom feeders, they have adapted to feeding on small invertebrates also tolerant of fine silty substrate and poor water quality. As carp feed, they re-suspend nutrient-rich silty sediment and uproot aquatic vegetation and by doing so increase turbidity. Turbid water is not tolerated by native aquatic plants, and as a result, native plants populations decrease and non-native plants tolerant of turbidity such as Eurasian watermilfoil and benthic algae flourish. Turbid water limits site feeding by top predators such as northern pike and bass that might otherwise feed on younger carp before they reach spawning age. The accumulation of silty substrate and turbid water quality also negatively impacts the bottom of the food chain—the aquatic macroinvertebrates that live in the streambed—as well as aquatic mussels. Absent natural controls, carp populations can proliferate in just a few years. Successful spawning and recruitment of carp will infect more than just the Estabrook Impoundment as offspring will migrate to other reaches of the Milwaukee River and its tributaries, the Milwaukee Estuary and Lake Michigan. Prior to removal of the Milwaukee River’s North Avenue Impoundment, the feasibility study correctly predicted a decline in carp populations and an increase in smallmouth bass populations. These predictions were consistent with those observed following the removal of the Milwaukee River Woolen Mill Dam at West Bend.

Following removal of the North Avenue Dam, improvements in the riverine habitat increased native fish species diversity several fold in the formerly impounded area from six native species in 1990 to 35 native species in 2012. Smallmouth bass became and remain the most abundant game species. Additional native game fish include walleye, northern pike, channel catfish, largemouth bass and rock bass. Concurrent with the improved diversity and relative abundance of native fishes, there has been a dramatic decrease in common carp populations that once comprised over 90% of the numbers of fish and total biomass. Overall environmental quality as measured by the fish-based  Index of Biotic Integrity (IBI) bioassessment model increased from “poor” prior to removal of the North Avenue Dam in 1996 to “good” to “excellent” following dam removal in 1997 and through 2012. Similar improvements in fish habitat and fish communities have been observed at dam removal projects elsewhere in the Milwaukee River watershed. There are no reasons not to expect comparable improvements in the Milwaukee River habitat and the fish community should the Estabrook Dam be removed. Inversely, as the Estabrook Impoundment continues to accumulate polluted silty substrate, there is no reason not to expect degraded fish habitat and a fish community dominated by a few tolerant species and an abundant carp population. Removing the Estabrook Dam will have the greatest positive impact on fish and aquatic life habitat, preferred native  fish stocks, and both recreational and subsistence fishers.

Will Wawrzyn is a former employee of the Wisconsin Department of Natural Resources. Prior to retiring in 2015, he was a water resources biologist (1977-1996) and fisheries biologist (1997-2015) working out of the UW-Milwaukee School of Freshwater Science. 

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