Hofmann Dam Removal

Hofmann Dam Removal. . , The Dam and Fish , In a study conducted in 1998, it was concluded that the Hofmann dam decreased the overall health of species above the dam. Fish were collected and counted both above and below the dam. Four times the number of fish passed by below the dam than above the dam. In addition, only two species of sportfish were found above the dam while seven species of sportfish were found below the dam. This disparity in abundance was caused by the slow-moving, lake like water above the dame which resulted in less habitat diversity than down river in addition to wide swings in oxygen levels and temperature. The wide swings in oxygen are an effect of the stagnant water found above the dam. This slow moving water resulted in less aeration as well as an increase of algae population. The large algae population, while creating oxygen during the day, used up much of the surplus oxygen during the night, resulting in lower oxygen levels for fish above the dam. In addition the water above the dam was particularly susceptible to increases in temperature. The slow moving water presented a large surface area to the sun for an increased amount of time compared to the fast moving water below the dam. The increased temperatures were one of the contributors to the lower number of fish found above the dam. in addition, the Hofmann dam limited the recovery of upstream areas from factors such as water quality or other degraded conditions. This is due to the restriction of migration from re-colonization sources by the Hofmann dam. For example, many mussels perished because mussels rely on fish for dispersion. The removal of the dam resulted increased the number of fish found above the dam after removal, twenty-nine species of fish were found above the dam This demonstrates that the removal of the dam resulted in a healthier environment. , , [Captions accompanying the photos of fish:] , Largemouth bass- Largemouth bass are freshwater game fish that become more available in the restored above dam ecosystem. , , Northern Pike- The Northern Pike is an intolerant species that became one of the many sport fishes that were available after the dam was removed. , , Benefits of Restoring the Natural Flow of the River , Hofmann Dam blocked the flow of the Des Plaines River, creating large silt deposits that built up over time behind the dam. This build up also robbed the downstream portion of the river of minerals and silt that provide nutrients in order for nearby plants to grow because silt was not able to pass the Hofmann Dam. The removal of the dam naturalized nutrient and sediment flow which, in turn, restored a more stream-like habitat. The presence of the dam caused average flow rates of the river to spike. For example, in the last fifty years the average flow rate has doubled. The removal of the dam has slowed average flow rates and created a calmer river in which more species can thrive. The Hofmann dam also presented problems related to the depth of the Des Plaines River. Because of the height of the dam, the water level of the Des Plaines River became higher above the dam, preventing shallow water areas that provided much more natural habitats. The dam also caused native floating vegetation to be submerged by overflow flooding caused by the dam. Not only did the depth of the river affect floating vegetation, it also decreased the quality of riverbeds and the quality of the water. The decrease in the quality of riverbeds and the river water itself resulted in a large lack of diversity concerning aquatic organisms, and a significant loss of migratory fish and fish recolonization. , , [Caption beneath photo:] , The Dam before the removal. , , History of the Dam , The first dam at the Hofmann site was constructed in 1827, by the Laughton brothers. It was placed on a natural waterfall to create the first sawmill in northeastern Illinois, stimulating urban growth. This was short lived, and the dam was removed in 1839. In 1866, the Fox brothers reconstructed the dam in a horseshoe shape and founded the Riverside Milling Company. This dam sustained the Company for 31 years. In 1886, the Riverside Improvement Company suggested that the dam be increased in size to allow room for public water for boating and skating, though it took 40 years for this to be accomplished. In 1907, George W. Hofmann Jr. presented plans for a grand recreation center called Niagara Park which would include boat rides, family picnicking, and and outdoor entertainment. In 1908, Hofmann improved the dam adding a concrete base connecting it with the Hofmann Tower. The park had massive success, but it diminished as an exploding population in the watershed increased pollution in the river. In the 1920's, this forced the park out of business, Hofmann continued to improve the dam between 1930 to 1933. The in 1936, the federal Works Progress Administration made additional improvements to the dam, including adding a retaining wall. In 1950, the dam was replaced by the State of Illinois, and the remains of this dam can still be seen today. In 1984, the original remnants of the Hofmann design were removed, and the only remaining are the wall and boat docks on the south bank, and the Hofmann Tower itself. The United States Army Corps of Engineers removed portions of the dam in 2012 in order to improve the ecology of the river and public safety by restoring the natural flow of the DesPlaines River. , , [Caption beneath photo:] , The horseshoe dam at Niagara Park. ,