Changing climate and land use methods are bringing prolonged periods that high water come the reduced Mississippi River. New management practices are required to defend people, industry, and also the land.

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A dredge works through the night to clean shoaling follow me the Mississippi flow at new Orleans in solution to the prolonged high flow discharges of 2019. Dredging that the shortest Mississippi River proceeds 24 hours a day, 7 work a week, except during perilous weather. Credit: Brendan Yuill

By June in most years, the water elevation of the Mississippi flow in new Orleans, La., has peaked and also is falling. But 2019 was not like most years. Winter and also spring 2019 brought many stories of flooding in the Midwest, significantly on the Missouri River and its tributaries, which eventually flow into the Mississippi. Even before the 2019 Midwest floods made the news, though, Mississippi river water level were greater than normal in the brand-new Orleans area.

The U.S. Military Corps of designers (the corps) monitors the dams regularly when river phase (water height) access time 4.6 meter (15 feet) in new Orleans, about 0.6 meter below flood stage. Water height on the Mississippi River remained high transparent water year 2019 (which ran from 1 October 2018 v 30 September 2019), exceeding the 4.6-meter level in brand-new Orleans top top 164 days (Figure 1). In contrast, there were just 49 together days in 1991, the previous record holder amongst data going ago to 1990.


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Fig. 1. Choose years and daily average (computed using water year 1990–2018) the Mississippi River height in brand-new Orleans as videotaped by the U.S. Military Corps the Engineers’ Carrollton gauge (01300). The river was greater than typical every day in water year 2019. The Bonnet Carré Spillway was open up from 27 February to 11 April 2019 and also from 10 might to 27 July 2019. In water year 1993, there was significant flooding in the Midwest, and also gauge elevation in new Orleans was over average for most of the year, yet the Bonnet Carré Spillway was never ever opened. Data native water year 2005 display the storm surge from Hurricane Katrina. Over there was considerable flooding on the Mississippi river in water year 2011, and the Bonnet Carré was open up from 9 might to 19 June 2011.

The vulnerabilities of current water administration practices ~ above the Mississippi river were readily apparent in water year 2019, when the extraordinary amount that water had actually a selection of effects, including stressing ecosystems and contributing come shipping mishaps and disruptions. The water level was still elevated in July 2019 as soon as Hurricane Barry moved right into the Gulf and threatened to link the case with storm surge, which could have to be catastrophic. The high water has ongoing into this year. In fact, together of 28 February, the Mississippi river had currently exceeded the an essential 4.6-meter surveillance threshold on 21 days in water year 2020, compared with 16 work by the same date in water year 2019. Since 1990, there have actually been only five water years (1991, 2005, 2016, 2019, and 2020) with an ext than 1 day over the 4.6-meter stage by 28 February. And also with incredibly high antecedent soil moisture and also abnormally high snowpack transparent the Missouri River basin this year, in addition to record precipitation regionally, the expectation is because that yet more flooding along the lower Mississippi.

To safeguard people and also industry, the corps has actually engineered the flow to a big extent. The deltaic Mississippi River, or the critical 540 kilometers the the Mississippi before it beginning the Gulf that Mexico, is inside wall with much more than 483 kilometers of concrete and also rock revetments that avoid channel migration and also the development of new distributary networks <Smith and Winkley, 1996>. The Mississippi River and also Tributaries job includes substantial system of levees that aid keep the river and also its tributaries in place and prevent flooding. There are levees on the deltaic Mississippi flow all the means to Venice, La. (about 16 kilometers from whereby the flow flows into the Gulf the Mexico), and also to date, no levee constructed to the Mississippi flow Commission’s current standards, enforced in 1978, has ever before failed <U.S. Army Corps the Engineers, 2014>.

Despite every the design of the river—including manage structures, spillways, and also a stabilized channel—there space now brand-new challenges for regulating the deltaic Mississippi River. Historically, river monitoring practices have been design assuming stationarity, or the concept that the average and home window of variability in river flow are not changing <Milly et al., 2008>. However, since of the effects of climate change, consisting of increasing yearly precipitation and land use transforms in the watershed the deliver an ext water downstream faster, the past is no longer a great indicator the the future when it comes to river flow. In other words, creating flood control practices utilizing historical circulation information, such as a static, 100-year overwhelming estimate, is no longer reasonable.

When a river overtops or division its levees, water inundates the neighboring floodplain, which decreases the flow, and the overwhelming hazard, downstream. In fact, purposefully breaking levees—long one illicit method of flood control, together in the an excellent Mississippi flood of 1927 when world blew up levees around new Orleans to conserve themselves—can be part of an effective water administration plan. However the deltaic Mississippi flow needs more than damaged levees to do it sustainable.

Controlling Nature

Upstream of where the Mississippi river enters the Gulf of Mexico, the river becomes part of a distributary delta system. In its natural state, the river separation into multiple branches, or distributaries, and the key distributaries periodically switched locations. There have actually been five main distributary systems of the Mississippi Delta in the past 5,000 years <Coleman, 1988>. Today, the Mississippi flow distributary device splits into two main branches. The larger branch is the 540-kilometer stretch the we describe as the deltaic Mississippi River; the second branch is the Atchafalaya River, which flows around 230 kilometers come the Gulf (Figure 2). Although these two branches started naturally, castle are currently in a extremely engineered state.


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Fig. 2. Setup of the Deltaic Mississippi River and also locations discussed in this article. Only rivers and surface waters in the state that Louisiana space shown. The inset illustrates the U.S. Army Corps the Engineers’ style flood, which shows the approximate maximum operation that various structures and rivers space engineered to withstand.

McPhee <1989> poetically recorded the story of how the deltaic Mississippi River became one the the many engineered rivers in the human being in his publication The manage of Nature. Vital to the story—which, like the river, has numerous twists and turns—is the the corps figured out that the circulation of flow between the two distributaries together it remained in 1950 should remain permanently: 70% down the Mississippi and also 30% under the Atchafalaya <Mossa, 1996>.

In 1954, congress acted top top the corps’ recommendation and also authorized the Old River control Project. Today, the corps continues to regulate the Old River control Structure, i beg your pardon controls this flow circulation on a minute come minute communication (Figure 2). The current system that structures, which to be upgraded and added to ~ the catastrophic Mississippi flood of 1973, deserve to handle discharge increase to about 20,000 cubic meters (700,000 cubic feet) per 2nd into the Atchafalaya River. For comparison, the average circulation in the Niagara flow in Buffalo, N.Y., upstream that Niagara Falls, is around 5,700 cubic meters (200,000 cubic feet) every second. Had the Old River manage Project not been in place during the overwhelming of 1973, many of the flow would have likely switched to the Atchafalaya River.

Diverting High operation on the Mississippi

There are many reasons why maintaining flow within a range that sustains valuable uses while limiting flooding in the deltaic Mississippi flow is critical. Both new Orleans and, aside from that upstream, Baton Rouge, Louisiana’s capital, have ports with considerable shipping and train yards and also are surrounding by billions of dollars that industry, including oil refineries and also chemical plants that rely on the deltaic Mississippi River.


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The Bonnet Carré Spillway top top 31 march 2018, after recently being opened, is presented in this aerial photo. In its an initial 77 year of operation, from 1931 come 2008, the spillway, which drains into Lake Pontchartrain, was opened eight times. In between 2008 and 2018 it to be opened 4 times. The was opened twice in 2019. The spillway (foreground) is directly across the flow from a chemistry plant and also just upstream from an oil refinery in Norco, La. Credit: Nicole Gasparini

To protect these areas, the corps additionally controls two significant spillways to relax water away from the deltaic Mississippi River during floods (Figure 2). Upstream of brand-new Orleans but downstream that Baton Rouge is the Bonnet Carré Spillway, i m sorry was developed in response to the an excellent Mississippi flood of 1927 and became operational in 1931. This spillway is design to relax up to about 7,000 cubic meter (250,000 cubic feet) per second of water right into Lake Pontchartrain, a brackish lake connected to the Gulf of Mexico, providing relief mostly for the Greater brand-new Orleans area and also downstream.

Between 1931 and also 2008, the Bonnet Carré was opened up eight times. In between 2008 and also 2018, it to be opened four times. Last year ended up being the very first year in which the Bonnet Carré was opened up twice. Also with the Bonnet Carré open, flow in the deltaic Mississippi River remained high in 2019 (Figure 1). Opened the spillway comes through costs. For example, the oyster season has historically to be less productive when the Bonnet Carré Spillway is opened because the brackish waters that Lake Pontchartrain might freshen significantly. Further, the river water entering Lake Pontchartrain regularly has really high nutrient loads—enriched by farm yard runoff indigenous 32 states—that encourage toxic algae blooms, which are particularly deadly come benthic marine animals like oysters.

The larger of the 2 spillways is the Morganza, situated downstream the the Old River control Structure and also upstream that Baton Rouge. Morganza is designed come take as much as 17,000 cubic meter (600,000 cubic feet) per second of circulation from the deltaic Mississippi River and also drain it into the Atchafalaya Basin. Because there room homes and farms in the Atchafalaya floodplain that deserve to be affected by together drainage, opened the Morganza is more controversial 보다 opening the Bonnet Carré, and also it has actually been opened only twice in its history: during the 1973 and 2011 floods. Over there was speak of opening it again in June 2019, yet that did not happen.


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False-color photos of the Morganza Spillway and also surroundings created with data indigenous NASA’s Terra satellite. The left image was handled 21 April 2007, throughout an mean flood season top top the Mississippi River. The right picture was tackled 18 may 2011, 5 days after the spillway was opened, whereby time floodwater had actually spread around 30 kilometers south of the spillway. In these images, clean water is blue, sediment-laden water is dull blue gray, and vegetation is red. Irradiate gray rectangular patches are likely cleared farm fields. Credit: NASA earth Observatory pictures by Robert Simmon, utilizing data indigenous the NASA/GSFC/METI/ERSDAC/JAROS, and also U.S./Japan ASTER science Team

Conservation that mass way we cannot do water disappear. So sustained high water way greater potential because that flooding—whether that is deliberately induced by people via spillways or not—and more water ~ above the floodplains the both the deltaic Mississippi River and the Atchafalaya River, which endangers people, crops, and wildlife favor the indigenous Louisiana black bear.

High phase Raises Concerns

High phase on the deltaic Mississippi flow throughout the summer has implications because that water management. Hurricane season officially begins on 1 June, as soon as the median river phase in new Orleans is around 3.4 meter (11 feet) and dropping top top the communication of data indigenous 1990 come 2018 (Figure 1). ~ above 1 June 2019, river phase was at 5 meters (16.5 feet). Hurricane-induced storm surge indigenous the Gulf the Mexico can increase the stage in the deltaic Mississippi river in brand-new Orleans and even Baton Rouge. For example, Hurricane Katrina journey the river phase up by around 3.4 meters in just 1 day (28–29 august 2005; number 1).

The dams all follow me the deltaic Mississippi have been improved since Hurricane Katrina. Since peak overwhelming season in the deltaic Mississippi River and peak hurricane season perform not generally coincide, however, the river levees are not designed come accommodate storm surge on a submarine river. Once Hurricane Barry threatened to hit brand-new Orleans in mid-July 2019, the river phase was about 4.9 meters (Figure 1). Levee heights vary, yet the lowest levees are at around 6.1 meters. Luckily, the storm results were not as great as originally forecasted, levees on the deltaic Mississippi flow did not overtop, and also a Katrina-scale catastrophe was averted.

In 2019, the total load of products shipped top top the Mississippi river was 25% reduced than the 10-year average.

High stage also method that the dams are at greater risk the failing. As river water piles increase on levees, the added weight increases the susceptibility the the underlying soil to seepage and also formation that sand boils that might undermine the integrity of levees over time.

Even when dams do not overtop or fail, an extensive flooding has impacts on industry. Navigating on the winding deltaic Mississippi river is always facility and requires different ship captains through localized expertise in different stretches of the river even in the best circumstances. However, higher stage way swifter flow, do the river much harder for ships come navigate. There are more shipping accidents, sometimes causing deaths, once the river is high.

Stronger currents also mean that ships in ~ anchorage deserve to be unmoored and drag anchors. More space is required in between anchored vessels, resulting in fewer spots for anchorage, and some ports become entirely unusable in high water. Tugboats likewise push smaller tons at greater discharge, additional resulting in decreased shipping. In 2019, the total load of commodities shipped top top the Mississippi river was 25% reduced than the 10-year average. Downstream trips space faster, however upstream trips are slower and also require much more fuel. And dredging efforts cannot save pace with siltation at the mouth of the river, limiting the dimension of delivery that can come increase the river.


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A ship towers end the dams of the Mississippi flow in brand-new Orleans on 23 in march 2019 near a renowned public area known as The Fly, i beg your pardon hosts activities such together fishing, crawfish boils, and soccer games. This photo was taken from atop the levee in this location, i m sorry is a grass-topped earthen hill. Through the water this high, visitors have the right to lean down and touch the river, i m sorry is not normally the case. Also, the trees seen right here are not commonly submerged. Credit: Nicole Gasparini

A silver Lining

Amid the obstacles of prolonged flooding is the silver- lining that higher flows on the deltaic Mississippi river could contribute to soil building. Coastal wetlands protect new Orleans and all of southern Louisiana from the results of hurricanes. One often-cited statistic is that Louisiana loses the equivalent of a football ar of wetland every hour, or 42.9 square kilometers per year, since of organic delta deterioration processes exacerbated through subsurface fluid withdrawal and also construction that canals <Couvillion et al., 2011>. The $50 billion Louisiana seaside Master Plan intends to mitigate this land loss, and also one of its proposed strategies requires harnessing organic delta-building procedures to create land with sediment diversions native the deltaic Mississippi River right into selected areas of shallow deteriorating marshes.

Optimized sediment diversions would happen only throughout high-stage, sediment-laden discharges come maximize the amount of flow sediment beginning receiving containers in the coastal marshes when minimizing the advent of fresh water right into saltwater ecosystems. The state the Louisiana is at this time designing two big sediment diversions, each through a circulation conveyance capacity of around 2,100 cubic meters (74,000 cubic feet) every second, to be located about 50 kilometers downstream of new Orleans (Figure 2). Ultimately, the land-building potential of these tasks will depend on sea level rise; however, numerical modeling argues they might produce 20–60 square kilometers of brand-new marshland, or the identical area that the contemporary Wax Lake Delta, end 5 years of operation.

There space caveats come this approach, however: together we have learned from spillway operations, changing salinity in the estuaries bordering the delta may negatively affect habitat for species such as oysters, brown shrimp, blue crab, and also bottlenose dolphins. In addition, a wide selection of stakeholders managing or do a living from seaside resources would most likely be impacted by sediment diversions, creating numerous legal and economic constraints that might require selective use of diversions and also limit potential floor building.

An uncertain Future

The future that the deltaic Mississippi River remains uncertain, in part because that is surrounded by many transforming systems. Over the previous century, the upstream network the delivers water and also sediment to the deltaic Mississippi River has been extremely engineered. Dams manage flooding and also reduce sediment supply, whereas increased channelization of the network alters flow patterns and also travel times. The watershed has also seen extensive urban and agricultural development, which result in faster and also greater-volume deliveries the water come the Mississippi network.

Climate change will also continue to have actually multiple impacts. Compare the duration from 1986 come 2015 with that from 1901 to 1960, lot of the upper Mississippi flow watershed has experienced increases in precipitation varying from 5% to an ext than 15% <Easterling et al., 2017>. ~ above the downstream end, the number of hurricanes overall and the number of very intense hurricanes space predicted to rise <Kossin et al., 2017>. Further, loved one sea level rise will drive the terminus that the flow upstream.

The only real certainty is that past recipes for controlling the river through hard-structure design will no be adequate offered all the stressors top top the system.

The architecture of flood management framework has typically relied on historic precedent, such together flood frequency records. Walking forward, these designs have to account because that the potential the future problems looking significantly different native those that the past. Efforts to modernize to plan are helped by the fact that researchers have made an excellent strides in improving abilities to predict future problems through the advance of high-quality ar hydrologic and climate number models Kauffeldt et al., 2016>. Ambitious physical activities models are additionally providing methods to test the results of proposed speculative river management projects such together those pertained to sediment diversions.

Ultimately, the only real certainty is that past recipes for managing the river v hard-structure design will no be adequate given all the stressors ~ above the system. After big floods, there are frequently discussions around relocating world away from floodplains and also about an altering zoning laws, yet as the lot of time since a disaster increases, the feeling of urgency for such alters dwindles. The urgency is now right here to stay.

Creative, although possibly unpopular, solutions past infrastructure are additionally required to manage the deltaic Mississippi River. The many effective choices for the long term room nature-based solutions that leverage ecosystem functions, together as fostering vegetation development to dissipate storm surging <Barbier et al., 2013>, and that are an ext adaptable to transforming environmental problems than concrete and also steel structures. Hard decisions, consisting of abandoning some locations where civilization live, might be part of the answer as well, and these discussions are currently occurring. Solutions have to not put the entire burden of adjust on marginalized socioeconomic communities, however, as has arisen with other advance projects in the region, such as the siting of brand-new industrial plants. One equitable equipment that counts on sound science need to be the priority.

Many groups have duties to play in addressing the future that the deltaic Mississippi River, from scientists, engineers, and river managers to stakeholders, politicians, and the public. The question now is whether these groups will be brave sufficient to embrace innovative and perhaps yet to it is in designed solutions.

Acknowledgments

We thank R. Waid, A. Ferchmin, and R. Perez for info on shipping conditions and boating mishaps during Mississippi river floods and also J. Corbino for info on dredging practices.

References

Barbier, E. B., et al. (2013), The worth of wetlands in protecting south-east Louisiana indigenous hurricane storm surges, PLoS One, 8, e58715, https://doi.org/10.1371/journal.pone.0058715.

Coleman, J. M. (1988), Dynamic changes and also processes in the Mississippi flow delta, Geol. Soc. Am. Bull.100, 999–1,015, https://doi.org/10.1130/0016-7606(1988)1002.3.CO;2.

Couvillion, B. R., et al. (2011), land area change in coastal Louisiana native 1932 to 2010, U.S. Geol. Surv. Sci. Invest. Map, 3164, scale 1:265,000, https://doi.org/10.3133/sim3164.

Easterling, D. R., et al. (2017), Precipitation change in the unified States, in Climate science Special Report: fourth National Climate Assessment, vol. 1, edited by D. J. Wuebbles et al., pp. 207–230, U.S. Global Change Res. Program, Washington, D.C.

Kauffeldt, A., et al. (2016), Technical evaluation of large-scale hydrological models because that implementation in operational overwhelming forecasting schemes on continent level, Environ. Modell. Software, 75, 68–76, https://doi.org/10.1016/j.envsoft.2015.09.009.

Kossin, J. P., et al. (2017), extreme storms, in Climate science Special Report: 4th National Climate Assessment, vol. 1, edited through D. J. Wuebbles et al., pp. 257–276, U.S. Worldwide Change Res. Program, Washington, D.C.

McPhee, J. (1989), The regulate of Nature, Farrar, Straus, and Giroux, new York.

Milly, P. C., et al. (2008), Stationarity is dead: Whither water management?, Science319, 573–574, https://doi.org/10.1126/science.1151915.

Mossa, J. (1996), Sediment dynamics in the lowermost Mississippi River, Eng. Geol.45, 457–479, https://doi.org/10.1016/S0013-7952(96)00026-9.

Smith, L. M., and B. R. Winkley (1996), The solution of the lower Mississippi flow to river engineering, Eng. Geol.45, 433–455, https://doi.org/10.1016/S0013-7952(96)00025-7.

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U.S. Military Corps of engineers (2014), Mississippi River and also Tributaries Project: Levee system evaluation report for the nationwide Flood insurance money Program, Miss. Sink Div., Vicksburg.