What River Runs Backwards? Unraveling the Mystery of Reverse Flow
The river that often runs “backwards” is the Chicago River. This doesn’t mean the river defies gravity, but rather that its flow was historically engineered and sometimes naturally influenced to flow away from Lake Michigan.
The Chicago River’s Unique History and Engineering Marvel
The Chicago River is a remarkable testament to human ingenuity and the ongoing battle against the forces of nature. For millennia, the river naturally flowed into Lake Michigan, carrying with it the city’s sewage and waste – a scenario that posed a significant threat to the city’s drinking water supply. In a bold and unprecedented engineering feat completed in 1900, the river’s flow was reversed, diverting it away from the lake and into the Chicago Sanitary and Ship Canal, ultimately connecting to the Mississippi River system. This monumental project transformed the river from a source of pollution to a crucial component of the region’s navigation and wastewater management. However, during periods of intense rainfall, the river can revert to its natural flow, temporarily reversing back towards Lake Michigan, a concerning phenomenon managed through careful control of the river’s lock and dam system.
Understanding the Reverse Flow: Engineering vs. Nature
The artificial reversal of the Chicago River hinges on a complex interplay of engineering and natural forces. The Chicago Sanitary and Ship Canal (CSSC) acts as the primary driver, providing a lower elevation outlet that encourages the river to flow away from Lake Michigan. However, heavy rainfall overwhelms the canal’s capacity, causing the river to rise and potentially flow back into the lake. To prevent this, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) operates a network of locks and dams along the river, carefully managing the flow and preventing backflow events. They also employ reservoirs and deep tunnel systems, called the Tunnel and Reservoir Plan (TARP), to store excess stormwater, further reducing the risk of reverse flow during storms.
The Role of the Sanitary and Ship Canal
The CSSC is arguably the most crucial element in the Chicago River’s reverse flow. This massive canal connects the Chicago River to the Des Plaines River, which eventually flows into the Mississippi River. By deepening the canal and creating a gentle downward slope away from Lake Michigan, engineers effectively “tricked” the river into flowing in the opposite direction.
The Impact of Rainfall and Lake Michigan Levels
While the CSSC provides the mechanism for reverse flow, natural factors like rainfall and Lake Michigan levels significantly influence the river’s behavior. Prolonged periods of heavy rainfall can overwhelm the CSSC’s capacity, causing the river to rise and potentially reverse direction. High lake levels exacerbate the problem, as they reduce the gradient between the river and the canal, making it more difficult to maintain the reverse flow.
Environmental Implications of Reverse Flow
The reversal of the Chicago River has had profound environmental consequences, both positive and negative. On the positive side, it significantly reduced pollution in Lake Michigan, safeguarding the city’s drinking water. However, it also introduced Chicago’s wastewater into the Illinois River and ultimately the Mississippi River system, raising concerns about water quality and the spread of invasive species.
Impact on Lake Michigan
Before the reversal, raw sewage and industrial waste routinely flowed into Lake Michigan, contaminating drinking water sources and posing a public health hazard. The river reversal dramatically improved water quality in the lake, making it safer for recreation and consumption.
Impact on the Mississippi River System
While benefiting Lake Michigan, the river reversal introduced Chicago’s wastewater into the Mississippi River system. This has raised concerns about the potential spread of invasive species, such as the Asian Carp, and the overall impact on water quality in the Illinois and Mississippi Rivers. The increased nutrient load has also contributed to the “dead zone” in the Gulf of Mexico.
Frequently Asked Questions About the Chicago River
Here are some commonly asked questions about the Chicago River and its unique characteristics:
1. Why was the Chicago River reversed?
The primary reason for reversing the Chicago River was to protect Lake Michigan, the city’s primary source of drinking water, from pollution. Before the reversal, sewage and waste were routinely discharged into the lake, posing a significant public health risk.
2. How was the Chicago River reversed?
The reversal was achieved through the construction of the Chicago Sanitary and Ship Canal (CSSC), a deep canal that connected the Chicago River to the Des Plaines River, which flows into the Mississippi River system. By deepening the canal and creating a downward slope away from Lake Michigan, engineers redirected the river’s flow.
3. Is the Chicago River always flowing backwards?
No. While the river is designed to flow away from Lake Michigan, heavy rainfall can overwhelm the canal’s capacity and cause the river to temporarily reverse direction, flowing back into the lake. The MWRD operates locks and dams to mitigate this risk.
4. What are locks and dams and how do they help prevent backflow?
Locks and dams are structures built along the river to control water levels and regulate flow. During periods of heavy rainfall, the MWRD uses the locks and dams to prevent the river from flowing back into Lake Michigan. They essentially act as barriers to contain the rising water.
5. What is the Tunnel and Reservoir Plan (TARP)?
TARP, also known as the Deep Tunnel Project, is a massive underground system of tunnels and reservoirs designed to store excess stormwater and sewage during heavy rainfall. This helps to prevent the river from overflowing and reversing direction, while also reducing pollution in waterways.
6. What is the environmental impact of the river reversal on Lake Michigan?
The river reversal has had a positive impact on Lake Michigan, significantly reducing pollution and improving water quality. This has made the lake safer for recreation and consumption.
7. What is the environmental impact of the river reversal on the Mississippi River system?
The river reversal has had a mixed impact on the Mississippi River system. While it has provided some benefits to navigation, it has also introduced Chicago’s wastewater into the system, raising concerns about pollution and the spread of invasive species.
8. What are Asian Carp and how are they related to the Chicago River?
Asian Carp are a highly invasive species of fish that pose a threat to the Great Lakes ecosystem. The Chicago Sanitary and Ship Canal provides a potential pathway for Asian Carp to migrate from the Mississippi River system into Lake Michigan. Preventing their passage is a major concern.
9. How is Chicago preventing Asian Carp from entering Lake Michigan through the Chicago River?
Chicago employs several strategies to prevent Asian Carp from entering Lake Michigan, including electric barriers, physical barriers, and intensive monitoring programs. These measures are designed to deter the fish from migrating through the CSSC.
10. Is it safe to swim in the Chicago River?
While the Chicago River has become significantly cleaner in recent years, it is generally not recommended to swim in the river. Although there are regulated swimming events from time to time, bacteria levels can fluctuate, especially after heavy rainfall.
11. How has the Chicago River been cleaned up in recent years?
The Chicago River has been cleaned up through a combination of factors, including the river reversal, the construction of TARP, improved wastewater treatment, and increased public awareness. These efforts have significantly improved the river’s water quality and overall health.
12. What are the current challenges facing the Chicago River?
Despite the progress made, the Chicago River still faces several challenges, including managing stormwater runoff, preventing pollution from combined sewer overflows, controlling invasive species, and ensuring the river remains a valuable resource for recreation and navigation. Continuous monitoring and management are essential to maintaining the river’s health.