Sedimentation
The Mississippi River has experienced excessive sediment buildup in New Orleans; this has been caused by land clearance, erosion, dredging activity and large eroding river banks. Sediment buildup is an important factor that holds back the river from flowing freely and can lead to flooding. Although sedimentation is natural, activities such as dredging and land clearance can increase the sedimentation rate and spur further accumulation. As sediment piles up behind the Mississippi River’s embankments and other landforms, normally dry land becomes inundated and susceptible to flooding.
Another issue likely to have impacted Mississippi’s ability to flow freely in New Orleans is the poor engineering decisions made in the past. In 1921, a levy system was implemented that was focused on controlling the river by disconnecting it from the lake and replacing it with a lake-filled drainage channel. This engineering decision resulted in the creation of a lake that filled with sediment, making draining more difficult. Furthermore, the levy system caused the water level of the lake to become much higher than the water level of the river, which hampered the natural flow of the river.
Hydrologic Modifications
Hydrologic modifications, such as modifying the size and shape of wetlands around the Mississippi River, have had an impact on New Orleans’ ability to retain water during flooding. As wetlands are reduced, the water holding capacity of the landscape is diminished, leading to more frequent and intense floods. This is because wetlands act as natural buffers and traps, slowing the flow of water and capturing sediment, allowing the water to slowly seep into the surrounding environment.
The Army Corps of Engineers is currently building an embankment, known as the West Closure Complex, around the Mississippi River to act as a barrier between the river and the swamp area, in order to address the flooding issue. The West Closure Complex will provide an additional layer of protection from floods, allowing engineers to control the height and width of the canal which will result in better water management, leading to better flood control.
Coastal Erosion
Coastal erosion is another factor that has an impact on the ability of the Mississippi River to flow freely in New Orleans. Coastal erosion occurs when wave action and strong currents gradually erode sediment away from the coast, leading to land loss. This reduces the Mississippi River’s ability to travel upriver, since coastal erosion makes it difficult for the river to access the larger coastal ecosystems. This can be seen in the Southeast Louisiana area, where more than 1,880 square miles of land have been lost since the 1930s due to coastal erosion.
As a result of coastal erosion, coastal marshes are being replaced with open water. This open water increases the potential for floods and for salt water intrusion into the freshwater ecosystem, impacting on fish populations and their habitats.
Dam Building
The construction of dams has had an impact on the ability of the Mississippi River to flow freely in New Orleans. Dams are either constructed for hydropower, electricity generation, or for water storage purposes. While these dams could theoretically provide a source of water for a city, actually, the world’s largest dams, including the Mississippi River, reduce the flow of water downstream and create an artificial reservoir that can increase the risk of flooding in certain areas.
Additionally, dams have an impact on the sediment load of the Mississippi River. As the water passes through the dams, the sediment load is diminished, leading to areas downstream being hit by higher sediment concentrations than what would have been natural. This leads to the deposition of sediment and the narrowing of the channel, which can reduce the flow of water.
Nutrient Inputs
Nutrient inputs also have an impact on Mississippi River’s ability to freely flow in New Orleans. Nutrients such as nitrogen and phosphorous are often present in runoff from agricultural lands, which can lead to areas of high nutrient concentrations in the river downstream, resulting in the growth of algae and aquatic weeds. This, in turn, can cause oxygen depletion in the river, making it difficult for aquatic life to survive.
Nutrients can also interact with other pollutants in the water, resulting in an increased likelihood for toxic chemicals to bind to sediment particles in the river and accumulate in the sediment that accumulates in the bottom of the river. This can cause further damage to the river’s health, as the sediment accumulates and builds a barrier between the river and the bottom of its source.
Urban Development
Urban development along the length of the Mississippi River has also had an impact on the ability of the river to flow freely in New Orleans. The development of urban areas increases the amount of surface runoff and the amount of solid waste and chemicals that are disposed of in the river. This leads to an increase in the amount of pollutants entering the river, which can result in the river becoming unhealthy and less able to cope with abnormalities such as floods.
Furthermore, the construction of dwellings and infrastructure in the area also impact on the ability of the river to flow freely. This is because urban areas provide less area for rainfall to be absorbed, leading to increased levels of runoff and higher concentrations of pollutants in the water.
Levee System
Finally, the presence of a levee system along the banks of the Mississippi River in New Orleans can reduce the river’s ability to flow freely. Levees are typically constructed to protect areas from floods, but they can also restrict the flow of water, inhibiting the natural flow of the river. As the levee system is designed to contain the water, it becomes increasingly difficult for the river to access the floodplain, which is needed for the river to move naturally and effectively.
Eutrophication
Eutrophication is another factor that can inhibit the Mississippi River’s ability to flow freely in New Orleans. Eutrophication is when nutrients used as fertilizer in agriculture and urban areas become dissolved in waterways and cause an increase in the growth of aquatic plants. This can lead to a decrease in water quality in the river, reducing its ability to cope with floods and other disturbances.
Additionally, eutrophication can lead to an increase in the amount of pollutants in the water due to increased levels of bacteria and the release of toxic compounds during eutrophication processes. These pollutants can have harmful effects on the health of the river, reduce the biodiversity of the river ecosystem, and lead to the death of aquatic species.
Overfishing
Overfishing of fish species native to the Mississippi River can also have an impact on the river’s health. Overfishing can lead to a decrease in fish populations, which can lead to an increase in the number of nutrients in the water, leading to eutrophication and decreased water quality. Additionally, overfishing can cause damage to fish habitats by reducing the number of prey species present and reducing the abundance of habitats species need for shelter and spawning.
Furthermore, overfishing can cause an imbalance in the food chain, resulting in an increase in predators that can feed on other fish species. This can negatively impact the health of the river and reduce the number of native species in the river.
Sediment Control
Sediment control is an important factor when it comes to improving the health of the Mississippi River in New Orleans. Various methods, such as dredging, can be employed to improve sediment control, allowing the river to flow more freely. Sediment control can also reduce the risk of flooding by decreasing the accumulation of sediment in the river. Additionally, sediment control can be used to restore the natural flow of the river and to help improve water quality.
Various methods can also be implemented to reduce the amount of sediment entering the river. These include methods such as land clearance, prevention of erosion, and reducing the amount of fertilizer used in agriculture. Additionally, controlling the amount of nutrients entering the river can help reduce eutrophication and improve the health of the river ecosystem.
Flood Reduction
In order to reduce the risk of flooding in New Orleans, interventions such as the West Closure Complex, as well as implementing more sustainable land management practices, can be used. These interventions can help to reduce the amount of sediment and pollutants entering the river, as well as reduce the amount of runoff entering the river. Additionally, implementing floodplain zoning and building flood protection systems can help to reduce the risk of flooding in the area.
Furthermore, researchers are working on developing strategies such as trap and treat systems to reduce major pollutants such as nitrogen, phosphorous and suspended sediment from entering the river. These strategies involve trapping the pollutants as they enter the river, thus preventing them from entering the environment.
Water Quality
In order to improve the water quality of the Mississippi River, multiple strategies need to be employed. Controlling nutrients, reducing sedimentation and other pollutants, improving stewardship and controlling runoff are all important strategies that can be implemented. Additionally, increasing the number of native fish species in the river can help to improve water quality and reduce the risk of flooding.
Additionally, the development of green infrastructure, such as wetlands, can be used to reduce the amount of runoff entering the river, helping to reduce levels of sediment and reduce the risk of flooding. Wetlands can also act as a natural filter for the river, trapping sediment and other pollutants and helping to improve water quality.
