TWO APPROACHES FOR A HEALTHIER FOX
The primary focus of the Fox River Implementation Plan is to recommend projects and stormwater/wastewater discharge goals to communities which, if accomplished, would result in numerical improvements to key water quality criteria (dissolved oxygen, phosphorus, and chlorophyll-A).
The Fox River Study Group (FRSG) is also evaluating river restoration practices that river communities can undertake to restore natural processes and habitat to the river channel and its banks. FRSG recognizes the relationship between the quality of the water discharged into the river and the manmade physical changes to the river itself (dams, bridges, filled in river banks). Both are interconnected and combine to determine the overall health and quality of the river as a natural resource.
The Fox River, a valuable natural resource in Northeastern Illinois, is nevertheless heavily impacted by our current and past activities within and along its banks. These activities include discharge of our treated wastewater into the river, and discharge of our urban and agricultural stormwater runoff (in most cases untreated) into the river during periods of precipitation.
The Fox River also provides drinking water in cities such as Elgin and Aurora. In addition to these current activities, the river is also heavily impacted by historic activities which once occurred along the Fox River. Through Kane County, for example, much of the river’s shoreline (stream banks) has been filled in or re-graded to allow past users to utilize the land immediately adjacent to the river, usually for industrial/manufacturing purposes but also for residential development.
DAMS ON THE FOX
The single largest physical change that has been made to the river has been the construction of 15 low head dams across the river, which occurred during our region’s early industrial period when early settlers required mechanical water power to power the first mills and industries in the Fox River Valley. Those industries have long since moved away from the riverfront, in large part due to the advent of electricity. However, the dams built to serve those industries have remained.
The dams on the Fox River between Carpentersville and Yorkville (10 total) are classified as “run of the river” dams, which means that they are simply a weir structure built across the width of the river for the purpose of raising the water level upstream. In the early history of the region, this allowed industry to harness the river’s flow to drive mechanical equipment in mills.
Today, the impoundments created by these dams are used primarily for recreational boating by adjacent landowners or visitors seeking flat water recreational opportunities, such as power boating, paddling, rowing clubs, etc. None of the dams provide any type of flood control function, unlike the Stratton Dam and Algonquin Dam, which have moveable flood gates to vary the flow of water past the dam. The Dayton Dam at the downstream end of the Fox River was built for and still serves as a small hydroelectric dam.
Detailed Views of Fox River Dams:
HOW DAMS IMPACT THE FOX
Dams on the Fox River have the largest impact over any other physical feature on the river. This is because of the number of the dams on the Fox River (13 remaining in Illinois) and the area of the river channel that is impounded by the 15 dams (about 50%). Restoration of the river is therefore inextricably tied to mitigating the impacts of the dams and the impoundments they create.
Most of the dams on the Fox River were originally constructed by the early settlers prior to 1870 using timber and stone crib construction. During the 1900’s these dams were reconstructed using stronger, more permanent materials – namely concrete. These new concrete dams were usually designed with a special geometric configuration at the downstream base of the dam to reduce scouring of the dam’s foundation created by the water falling over the dam. The resulting hydraulic phenomenon is what is often referred to as a “roller” or “keeper”. In engineering terms, it is known as a submerged hydraulic jump and it is what makes the dams on the Fox River so very dangerous to anyone who goes over the dam or gets too close to the downstream face of the dam. The graphic below illustrates the safety hazard that exists below most of the dams on the Fox River.
The dams are a very real SAFETY HAZARD to persons near them. Many people have drowned on the Fox River where the dams were constructed and left in place after their builders moved on. Drownings across the country have been INCREASING over the years as more and more people choose to recreate in our nation’s rivers and get too close to these structures.
Brigham Young University maintains a web page which includes information on submerged hydraulic jumps at dams and an inventory the fatalities that have occurred across the US from these dangerous flow features. This information can be found HERE.
Dams also impact the Fox River’s fishery. The dams fragment the river into a series river segments. Fish utilize the “segment” of the river they are in (between the dams), but they cannot move upstream of the dam. This has an substantial impact on the overall fishery in the river, as fish cannot access tributaries to spawn. This becomes very important following extreme river conditions (such as a drought) when the ecology (fish or their food source) in a particular segment of the river is stressed or severely diminished. In a river without dams, the ecology either moves out of the stressed environment to a healthier one or specimens from adjacent reaches of the river “recolonize” the segment that was impacted. Dams prevent this movement and/or recolonization from taking place.
Water quality problems have contributed to the disappearance of many fish and mussel species and the dams on the Fox River prevent migration back into historically degraded sections, despite recent improvements in water quality. As a result, dams present a major impediment to aquatic ecosystem restoration efforts in the watershed.
Dams modify the hydrologic regime of the Fox River, resulting in a degradation of the river’s water quality. As water flows from upstream into the impoundment created by the dam, a variety of biological and physical changes takes place. The dam artificially raises the water level, which decreases the slope of the water and increases the cross sectional area of the river channel. This results in a dramatic decrease in water velocity. As the velocity decreases, fine grain particles being carried by the river’s flow begin to settle out in the impoundment, which is observed by the often thick, sandy/organic sediment seen upstream of the dams (compared to the rocky/gravelly river bed below the dams). As the water slows and widens in the impoundments above the dams, phosphorus in the water (from our wastewater plants, streets, yards, and farm fields) feeds the algae in the river, which is ideally suited to rapidly growing in the slow moving warm waters above the dams during the summer. While algae adds oxygen to the water during the daytime via photosynthesis, it respires at night and consumes oxygen from the river, which causes dissolved oxygen levels in the river to drop so low that many fish and other river organisms have a hard time surviving.
As discussed in the water quality section above, a major physical impact dams have on the Fox River is the interruption of the flow of sediment downstream. The result is that the river bottom in the impoundments above the dams are covered in fine-grained sediments and organic debris, similar to what you would see in the bottom of a detention pond. This sediment covers over the sands, gravels, and cobbles that make up the natural river channel to create a vast underwater “desert” of sediment. The loss of bottom diversity (in the sands, gravels, and cobbles buried by sediments in the impoundments) results in a loss of ecological diversity as all the fish and macroinvertabrates that thrive in the diverse natural river channel below the dam are forced to find refuge outside of the sediment-filled impoundment.
THE MOST EFFECTIVE RESTORATION ACTIVITY
Over the last 20 years, much study and analysis has been conducted on determining the impact of dams on rivers. The resulting knowledge base from these studies indicate that the old low head dams on the Fox River are having a profound impact on the safety, ecology and water quality. These scientific studies show that the river could be substantially improved if the antiquated dams and their impoundments were eliminated.
As of 2014, there have been 23 dams removed in Illinois. The State of Illinois has engaged in a state-wide removal initiative to remove the safety hazards caused by low head dams and restore the state’s natural riverine resources. The IL Dept. of Natural Resources, working with the US Army Corps of Engineers, Cook County Forest Preserve District, and Lake County Forest Preserve District, has removed 5 of the 8 dams on the Des Plaines River and will eventually remove all the dams, which will effectively reconnect the entire Des Plaines River to the Illinois River. Stakeholders in DuPage and Will Counties are planning to remove the dams on the DuPage River in order to address water quality and ecological impairments reported by the IEPA (which mandated watershed improvements to bring the DuPage River into compliance with state water quality standards).
On the Fox River, the North Avenue Dam (in Aurora) and the South Batavia Dam were removed in 2005 and 2006, respectively. The Kane County Forest Preserve District and Village of North Aurora are currently working with the Illinois Department of Natural Resources to explore removing the dams in Carpentersville and North Aurora.
WHAT HAPPENS WHEN A DAM IS REMOVED?
WATER LEVELS, RIVER FLOW
When a dam is removed, the upstream water level drops to about the level of the river below the dam under normal flow conditions. There is no change in the amount of flow entering the river reach with the dam or leaving the river reach with the dam (flow in = flow out), so the river will not “dry up”. What does occur is that the river channel under normal flow conditions narrows to closely match the river channel one observes below where the dam is located, which means the portion of the channel covered by water under normal flow conditions will become much smaller in width compared to the river width when the channel was impounded (generally a 25%-50% reduction in width, depending on the dam height and impoundment width). There is relatively little change in the floodplain width or flood levels in the river after a dam removal because the low head dams on the Fox River are relatively small compared to volume of water in the river during a flood (10,000-25,000 cubic feet PER SECOND). The largest impact (reduction) in flood levels, if any, would be experienced in the immediate vicinity of the removed dam crest and would quickly diminish as one moves upstream and away from the dam. As a result, the presence of the low head dams on the Fox River (Carpentersville to Yorkville) has virtually no impact on flooding, positively or negatively, on the adjacent communities.
SEDIMENT BEHIND DAMS
In most cases, the low-head dams on the Fox River have very little sediment stored up directly behind the dam in the middle of the river channel. Most of the sediment is located along the edges of the impoundment along the shoreline just below the water line. This is due to the way in which large floods sweep a majority of the sediment they carry downstream, leaving only a small fraction of the total sediment to settle out along the edges where stream velocities are small. When a dam on the Fox River is removed, these sediments will be exposed, dry out, and become covered by new vegetation - grasses, flowers and some shrubs. The sediment is composed of soil and sand particles that have washed off of the landscape. Studies conducted on the Fox River indicate that the sediments behind most of the dams is from recent floods and is not contaminated (Reference: Santucci/Gephard Fox River Fish Passage Feasibility Study, 2003) and likely can be left in place following a dam removal. While the sediment on the exposed river bottom will naturally revegetate over time, most dam removal projects include an active replanting/reseeding component to ensure that the exposed sediment is completely covered with native vegetation to enhance the restored river corridor.
RECREATIONAL USES CHANGE
Because the depth of flow in the river will more closely match the depth observed downstream of the dam to be removed, flatwater recreational activities such as powerboating, jet skiing, and rowing may not be feasible in the former impoundment reaches. The Fox River in its natural, free-flowing state is typically too shallow (1-3 ft) to support such activities. Instead, the river through the former impoundment areas will provide improved canoeing, kayaking, and fishing opportunities, as it will be shallower, swifter, more diverse, and connected to the downstream reaches of the Fox.
Will recreational opportunities on the Fox River change when a dam is removed? Most likely yes.
Will it be better or worse than before? That answer depends on an individual’s recreational desires. One thing is for sure, the river, when it is restored to a more natural condition without dam impoundments will serve more functions more effectively for more people and more plants and animals than it can serve under the highly modified, impounded condition which now dominates the Fox River.