Missouri River Planning Recognizing and Incorporating Sediment Management (2011) / Chapter Skim
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2 Changes in Missouri River Sediment and Related Processes
2 Changes in Missouri River Sediment and Related Processes
Pages 19-50
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From page 19... ...
Before construction of mainstem dams and extensive river-training structures in the twentieth century, the Missouri River was a major contributor of sediments to the Mississippi River, which transported portions of these sediments downstream and to the Gulf of Mexico. Before 1900, the Missouri and lower Mississippi river system transported an estimated 400 million metric tons per year of sediment from the interior United States to coastal Louisiana (Meade and Moody, 2009)
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From page 20... ...
Current volumes of sediment transported into Louisiana by the Missouri and Mississippi rivers average roughly 145 million metric tons per year, of which only 55 million tons now pass Hermann, Missouri (Meade and Moody, 2009)
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From page 21... ...
1950, large quantities of sediment were transported into the Mississippi River and eventually to the Mississippi delta at the Gulf of Mexico. The transport processes were episodic, carrying some sediment particles only short distances each runoff season, storing the particles on the channel bed or in the floodplain during falling-water stages, and resuspending stored particles as the river waters rose again during subsequent seasons.
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From page 22... ...
Sediment yields from land encompassed by the Missouri River drainage basin have undergone dramatic and complex changes through settlement and subsequent development. Cropland agriculture was the first of the large human-caused alterations to this millennial-scale pattern of sediment delivery from the Missouri River basin to the Mississippi River and the Gulf of Mexico.
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From page 23... ...
and it settles from suspension onto the channel bed FIGURE 2-1 Grain-size-dependent transport mechanisms and their relationships to Figure 2-1.eps measured sediment loads. bitmap
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From page 24... ...
As river systems are dammed, channelized, and otherwise affected by human activities, there typically are changes to the stream's chemical load. Two nutrients of concern in the Missouri and Mississippi river basins today are phosphorus (P)
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From page 25... ...
From a broader historical perspective, since the Missouri River always has carried a tremendous sediment load, and since natural suspended sediments carry a certain amount of phosphorus, the preanthropogenic river thus likely carried significant phosphorus loads into the Mississippi River. However, it is not known what portion of these phosphorus loads reached the Gulf, were trapped in coastal wetlands, or were captured further upstream in the system.
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From page 26... ...
Dams, levees, dikes, and revetments have been constructed and now are operated to facilitate services such as transportation of bulk commodities through commercial navigation, flood protection for farms and cities, reliable water supply, hydropower generation, and water-related recreation. This section describes key historical changes to the Missouri River, with an emphasis on changes to or relevance of sedimentary processes for the preregulation Missouri River, the postregulation Missouri River, and changes to Missouri River ecology.
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From page 27... ...
. The processes of river bank erosion and lateral migration of the river channel were prominent in the preregulation Missouri River.
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From page 28... ...
Channel migration also contributed to floodplain species biodiversity by creating a mix of landforms such as oxbow lakes, sloughs, and backwater swamps with differing soil textures, chemistry, and inundation regimes. Distribution of riparian vegetation was also heterogeneous because tree species differ in their tolerances to flooding, sedimentation, and physical damage from floodwaters and debris (Hupp, 1988)
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From page 29... ...
Riparian vegetation stabilized riverbanks and sandbars and slowed bank erosion and channel migration rates (Gran and Paola, 2001; McKenny et al., 1995)
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From page 30... ...
Bank and Channel Stabilization The federal Missouri River Bank Stabilization and Navigation Project (BSNP) created an inland waterway transportation system, as well as providing protection for utilities, transportation networks, bridges, and adjacent landowners and farms by preventing river channel migration and reducing the potential for overbank flooding.
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From page 31... ...
Beginning in the late nineteenth century, the navigable portion of the Missouri River channel was narrowed to as little as one-half to one-third of its original width (Funk and Robinson, 1974; Hallberg et al., 1981; Pinter and Heine, 2005) primarily through the emplacement of "wing dikes," structures built perpendicular to the bankline to trap sediment, stabilize river banks, and produce a single channel (Figure 2-5)
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From page 32... ...
. These photos illustrate substantial alteration of riparian and in-channel habitats.
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From page 33... ...
Farther downstream, delivery of sediment from the Missouri into the Mississippi River system was reduced greatly following the closure of the Missouri River mainstem dams. The closure of the two farthest downstream dams on the Missouri River -- first Fort Randall Dam (South Dakota)
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From page 34... ...
Following dam construction (data available for 1964-1973) , however, annual sediment loads of the Kansas River averaged just 10-12 million metric tons (USACE, 1970, 1972, 1976)
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From page 35... ...
bitmap SOURCES: Sediment data through 1974 from Corps of Engineers (USACE, 1951, 1957, 1965, 1970, 1972, 1976)
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From page 36... ...
. A recent publication on Mississippi and Missouri river sediment transport volumes, and how they have changed over time, stated: Before 1900, the Missouri–Mississippi River system transported an es timated 400 million metric tons per year of sediment from the interior of the United States to coastal Louisiana.
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From page 37... ...
Meander cutoffs and the construction of river-training FIGURE 2-7 Schematic diagrams of average annual suspended-sediment discharges in Missouri–Mississippi River basin. Figure 2-7.eps SOURCE: Reprinted, with permission from Meade and Moody, 2009.
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From page 38... ...
38 MiSSOuRi RivER PlANNiNg Figure 2-8.eps bitmap
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From page 39... ...
structures on the Missouri and lower Mississippi rivers also have immobilized large amounts of sediment throughout the basin and along the Missouri and Mississippi mainstem (Meade and Moody, 2009)
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From page 40... ...
Since this period also witnessed continuing engineering projects to sequester sediment within the floodplain and stabilize the channel, tributary streams must have been supplying more than 175 million tons per year, but a more precise figure is unknown without further analysis of volumetric changes in floodplain storage. However, by 1980, when the main period of sediment sequestration was declining, the total amount of sediment stored within the floodplain behind groynes and levees as a result of engineering projects dating back to the early part of the twentieth century was approximately 3.2 gigatons.
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From page 41... ...
. Decreases in specialized native big river fishes have been attributed to reductions in suspended sediment and turbidity in the lower Missouri River, including the now federally listed as endangered pallid sturgeon, and imperiled paddlefish, blue sucker, and flathead chub (Pflieger and Grace, 1987)
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From page 42... ...
Fish and Wildlife Service today are implementing actions along the Missouri River, downstream of Gavins Point Dam in South Dakota, Nebraska, Iowa, and Missouri, designed to improve habitat conditions for the pallid sturgeon (Chapter 4 provides details on the Corps' ongoing Missouri River emergent sandbar habitat and shallow water habitat projects)
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From page 43... ...
Effects on Riparian Floodplain Vegetation The preregulation Missouri River ecosystem was a storehouse of biological diversity maintained by a highly dynamic flow and sediment regime. The active river channel moving across its broad floodplain created enormous environmental heterogeneity and a complex mosaic of aquatic, riparian, and terrestrial ecosystems, including in-channel islands and sandbars, oxbow lakes, marshes, sand dunes, and riparian forests (see also Figure 2-4)
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From page 44... ...
In-channel nesting birds face similar prospects because of the absence of floods that historically created sandbar islands in the river that are required for their successful nesting. DATA FOR EVALUATING MISSOURI RIVER SEDIMENT DYNAMICS A systemwide understanding of the sources, traps, and modes of transport of sediment through the Missouri River system is important for well-informed sediment-related decisions, including but not limited to endangered species protection.
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From page 45... ...
The lack of a centralized, accessible sediment database may be inhibiting better understanding of sediment dynamics of the Missouri River system. Moreover, given plans for future system-wide ecosystem management (see the discussion of the Missouri River Ecosystem Restoration Plan in Chapter 3)
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From page 46... ...
river systems have faced similar data collection challenges that are encountered today in the Missouri River basin. Experiences from other U.S.
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From page 47... ...
FIGURE 2-9 A generalized framework for a Missouri River sediment budget. 47 SOURCE: Data from Boyd et al., 2009; Hotchkiss and Huang, 1994; Jacobson et al., 2009; Stark and Pridal, 2009, USACE, 1996.
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From page 48... ...
The preregulation Missouri River's large sediment load and high turbidity were important to the survival and propagation of native plants, fish, and bird species. Sediment delivered to the Mississippi River was significant in building and sustaining coastal wetlands.
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From page 49... ...
The dams and reservoirs reduced peak flood discharges, thus reducing the river's ability to erode and transport sediment downstream. The mainstem dams and reservoirs trapped large amounts of sediments that previously moved through the system and into the Mississippi River and its delta.
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From page 50... ...
These gaps are of special concern given plans for future investments in Missouri River ecosystem management and reevaluation of authorized purposes for the Missouri River mainstem dams and the Bank Stabilization and Navigation Project. Effective project implementation, operations, and management requires useable knowledge of sediment dynamics; this includes quantities and fluxes of suspended and coarse bedloads, and changes in sediment storage and resultant changes in channel morphology.
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