The Missouri River long has been an integral tributary in North America’s largest conveyance system—the Mississippi River system—for transporting sediment from interior uplands to the coastal ocean. During the twentieth century, the volumes of sediment transported downstream and to the Gulf of Mexico by these rivers were reduced markedly by numerous changes to river hydrology and sedimentary processes. During this period, several large mainstem dams were constructed across the Missouri River, along with numerous dams on the river’s tributaries. In addition to the dams, hundreds of miles of river channel engineering structures were built to facilitate commercial navigation. These channelization and bank stabilization projects fixed the river channel in place and supported a serviceable navigation channel from Sioux City, Iowa, downstream to the Mississippi River confluence near St. Louis. In doing so, the projects immobilized vast amounts of sediment, as portions of the former river channel and banks were converted into floodplain lands behind revetments and other structures.
The cumulative goals of the dam and the bank stabilization projects—flood control, hydropower generation, water supply, recreation, and a commercial navigation channel—have been realized. At the same time, these structures have sharply changed the river’s sediment transport and deposition regime. These changes include large reductions in the volumes of sediment transported through the system, lowering of the river channel bed downstream of dams and along some channel reaches, reductions in turbidity, and changes in landforms and riverine habitat important to native biota.
These changes in Missouri River sediment processes have greatly affected near-shore and riparian habitats important to some native species. As a result, three of these species—two birds (the least tern and piping plover) and one fish (the pallid sturgeon)—are today listed under the federal Endangered Species Act. Changes to the river’s sediment regime also are having impacts on important physical infrastructure. Channel bed lowering, for example, is eroding foundations of flood protection structures in and near Kansas City, and of bridge foundations at many sites along the river and its tributaries. Lower river levels also cause problems at intakes for municipal and industrial water supply systems along the river.
The U.S. Army Corps of Engineers oversees operations of the Missouri River mainstem reservoir system. The U.S. Fish and Wildlife Service issued Biological Opinions in 2000 and 2003 regarding Corps of Engineers projects and operations along the lower Missouri River (USFWS, 2000, 2003). In response to those Biological Opinions, the Corps has been constructing projects along the Missouri River designed to improve habitat conditions for the endangered bird and fish species. Project construction has been accompanied by sediment discharges into the lower Missouri River. Given the location of these Corps of Engineers habitat mitigation projects on lower Missouri River, much of this report focuses on the river’s channelized portion from Sioux City, Iowa, downstream to the confluence with the Mississippi River.
Discharges of sediment from these projects have prompted concerns regarding not only local water quality impacts, but also questions regarding delivery of sediments and nutrients to the Mississippi River delta and the northern Gulf of Mexico. One section of this report thus considers possible downstream effects on water quality into the northern Gulf of Mexico.
Sedimentary processes and sediment management issues are important along the entire length of the Missouri River. For example, large volumes of sediment are trapped in the Missouri River’s upstream reservoirs and represent a substantial portion of sediment no longer available for transport to the Gulf of Mexico. Other sections of the report thus consider sediment processes, and data collection and evaluation systems, for the entire length of the river.
This report is from the National Research Council Committee on Missouri River Recovery and Associated Sediment Management Issues. The study and report were sponsored by the U.S. Army Corps of Engineers. The committee was appointed in 2008 and held five meetings over the course of its project. Public meetings were convened in four Missouri River cities: Kansas City; Omaha; St. Louis; and Vermillion, South Dakota. A final, closed meeting was held in Washington, D.C., in early 2010 at which the committee worked on its draft report.
This report addresses the topics of Missouri River sediment, its physical and biological importance, how its dynamics and roles in the river system
have changed over time, and its roles in contemporary river management decisions. The committee was asked to address
the roles of Missouri River sediment in river ecology and restoration, and its implications for water quality and coastal restoration downstream in the northern Gulf of Mexico;
environmental and economic considerations regarding nutrient and contaminant loadings;
alternatives for reintroducing sediment into the system; and
current Corps of Engineers restoration actions as they relate to sediment and nutrients, and how they might be improved.
The committee’s full statement of task appears in Chapter 1.
This Summary is organized in parallel with the chapters of this report and contains the following sections: Changes in Missouri River Sediment and Related Processes; Missouri River Governance and Programs for Sediment Management; Missouri River Sediment Management and Ecological Resources; Missouri River Sediment Management Alternatives and Opportunities; Missouri River Water Quality; and Future River Management Decisions.
This report’s findings and recommendations are presented in bold-faced text.
CHANGES IN MISSOURI RIVER SEDIMENT AND RELATED PROCESSES AND SUPPORTING DATA MANAGEMENT SYSTEMS
Roles of Sediment in the Missouri River
Question 1 of this report’s statement of task asked, “How and why is sediment a significant variable in the environmental restoration of a river system like the Missouri River?”
The processes of sediment erosion, transport, and deposition play important geomorphologic and ecological roles in large river systems. Sediments are important, for example, as foundational material for islands and sandbars that, in turn, provide animal and plant habitat. For some native fish species that evolved in highly turbid rivers like the Missouri, these conditions are important in inhibiting predation. In the Missouri and Mississippi river systems, sediment from the Missouri River basin is eventually transported farther downstream by the lower Mississippi River and historically has been of great importance in sustaining wetlands in coastal Louisiana.
Sediment is a significant variable in environmental restoration of a river system like the Missouri River for the following reasons:
Most of the historical, preregulation Missouri River was a sediment-rich system. However, not all tributaries of the Missouri River were sediment rich.
For many river processes and services, sediment concentrations and transport are as important as the quantity and flow of water. For example, sediment is the basic building material for river landforms that, among other things, support habitats for native riverine flora and fauna.
High concentrations of sediment and high turbidity in the preregulation river were important to the evolution and adaptation of native species such as the pallid sturgeon.
Sediment delivered from the Missouri River to the Mississippi River was historically significant in building and sustaining coastal wetlands in the actively accumulating lobes of the Louisiana delta.
The reduced volumes of sediment transported by the postregulation Missouri River relate to Question 5 in this report’s statement of task, which asked, “Are there long-term consequences to the lack of sediment in the system to the human environment, either economically or environmentally?” (Questions 1 and 5 are addressed in Chapter 2.)
The Missouri River underwent a fundamental transformation during the mid-twentieth century. The mainstem and tributary dams, and the revetments and other river control structures built as part of the federal Bank Stabilization and Navigation Project, helped control floods, generate hydroelectric power, provide reliable water supplies, and support commercial navigation. These projects resulted in major changes not only in river hydrology, but also in related sedimentary processes and volumes transported. The reduction of peak flood discharges, for example, reduced the river’s ability to transport sediment downstream. The mainstem dams and reservoirs trapped large amounts of sediment that previously moved downstream. These changes have had many implications for river ecology, local infrastructure, and downstream sedimentary processes in coastal Louisiana.
The primary long-term consequences of a lack of sediment in the system are
loss of habitat for some native species;
bed degradation downstream of dams and extensively along the main channel and the lower reaches of tributaries. This causes problems for infrastructure by undermining levees and bridge foundations and lowering water levels at municipal water intakes; and
reduced volumes of sediments transported downstream to the Mississippi River and delivered to the Mississippi River delta region.
Sediment Data Collection, Organization, and Analysis
The Missouri River basin was once the site of extensive scientific programs for sediment data collection and analysis. Over time, however, these programs received less emphasis and lower priority. Today, data on Missouri River sediment are diffuse and scattered across different agencies, in a variety of locations, and in different formats. There is no single system or center to ensure that data have been updated to be consistent with modern mapping, archiving, and other technologies and applications. Ongoing sediment data studies are being conducted by Corps of Engineers and U.S. Geological Survey scientists, and these are improving knowledge of sedimentary processes along the river. These efforts, however, are not being conducted as part of systematic sedimentary studies for the length of the river.
Thus, despite useful ongoing efforts, sediment data collection and management programs are fragmented and do not provide a reliable, accessible knowledge base for river managers, scientists, and interested members of the public. Along the river today, there are several relatively new river ecosystem management initiatives. For example, the Missouri River Recovery Program (MRRP), initiated in the mid-2000s, is being led by the Corps of Engineers and the U.S. Fish and Wildlife Service, in partnership with tribes, states, and other agencies, to develop and implement Missouri River ecosystem recovery actions. The MRRP, along with other new initiatives—including the Missouri River Ecosystem Restoration Plan (MRERP) and the Missouri River Recovery Implementation Committee (MRRIC)—are likely to be central in the coming decades of Missouri River ecosystem management decisions. As such, they will benefit from a coherent, detailed, and accessible database of sediment processes. Compared to databases and related science programs in other large river and aquatic systems that are sites of major ecosystem management activities—such as the Colorado River in the Grand Canyon and the Florida Everglades—data systems for the Missouri River and its ecosystem are less developed.
The systems and processes for evaluating, archiving, and retrieving Missouri River sediment data are fragmented and not well organized. 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. More informed future Missouri River resource management decisions will benefit from a comprehensive and accessible Missouri River sediment database and sediment budget.
Corps of Engineers and U.S. Geological Survey (USGS) scientists have been conducting valuable collaborative investigations of Missouri River sedimentary processes that should be used as the foundations for a more detailed and extensive sediment budget. Over time, continued collaboration may lead to a more formal program for data collection and evaluation. The Corps and the USGS should extend their collaborative efforts and develop a detailed Missouri River sediment budget from the headwaters to the river’s mouth, with provisions for continuing revisions and updates as new data become available.
MISSOURI RIVER GOVERNANCE AND PROGRAMS FOR SEDIMENT MANAGEMENT
This section provides background for understanding Missouri River governance, especially as it relates to management of sediment and related resources. It also addresses Question 7 in this report’s statement of task regarding improved management strategies and actions (these topics are addressed in Chapter 3).
An important piece of legislation in the history of Missouri River operations is the Flood Control Act of 1944. That act authorized the Corps of Engineers to construct Missouri River mainstem dams as part of the “Pick-Sloan Plan,” which represented a merger of plans between the Corps of Engineers and the U.S. Bureau of Reclamation. Under Pick-Sloan, the Corps constructed six mainstem dams in the 1950s and 1960s and for many years had preeminent authority regarding their operations. The U.S. Congress today continues to create authorities and responsibilities that support the Corps of Engineers in this role as Missouri River “water master”—and hence sediment manager—as well. At the same time, a flurry of new institutions and programs created in the past five years has broadened the decision-making context of Missouri River operations.
In 2007, the Congress authorized the Corps to execute the MRERP, and in 2009 authorized the Corps to conduct the Missouri River Authorized Purposes Study. These two major programs are studying and guiding ecosystem recovery and reviewing the authorized purposes of the Missouri River dam and reservoir system, respectively.
In addition to these programs, in 2007 the Assistant Secretary of the Army for Civil Works created the MRRIC. The MRRIC was established with broad representation of numerous basin stakeholders to promote shared Missouri River decision making. Although the MRRIC’s roles have yet to be fully clarified, they will need to be defined with regard to Corps of Engineers authorities. The Missouri River states, tribes, commercial interests, and nongovernmental organizations all seek a more active voice and role in river management decisions. At the same time, the Corps retains
authority to operate the Missouri River dam and reservoir system. Furthermore, several recent, major river management initiatives and studies—such as the 2000/03 U.S. Fish and Wildlife Service Biological Opinion and the mitigation program—have added greatly to compliance requirements for the Corps. These changes have complicated the Missouri River governance structure for the Corps and others as they try to reach agreement on programs such as Biological Opinion program implementation, broader ecosystem recovery, and sediment management planning.
The Missouri River Recovery and Implementation Committee has the potential to play a central role in building consensus among a broad group of federal agencies and stakeholders in matters related to water and sediment management. To help realize that potential, the Assistant Secretary of the Army for Civil Works should periodically review the MRRIC mission statement, operational rules, and accomplishments; implement modifications to the mission, rules, and operations as deemed appropriate; and report its results to the Congress.
MISSOURI RIVER SEDIMENT MANAGEMENT AND ECOLOGICAL RESOURCES
Question 7 in this report’s statement of task asked, “Are current Corps management strategies, restoration tools (e.g., channel widening, creation of chutes, shallow water habitat, etc.) and other activities adequate and comprehensive enough to address issues associated with sediment and nutrients in the system? If not, how might such strategies and activities be improved?” (This question is addressed in Chapter 4.)
The Corps of Engineers has been constructing numerous Emergent Sandbar Habitat (ESH) and Shallow Water Habitat (SWH) projects along the Missouri River in compliance with the 2000/03 Fish and Wildlife Service Biological Opinion. The Biological Opinion directs the Corps to implement and operate those projects according to adaptive management principles. In addition to project construction, the Corps has been monitoring these projects and has been developing adaptive management guidance documents. The ESH and SWH projects are being implemented as part of and within the larger MRRP and they have important ecological and institutional linkages with other MRRP programs for ecosystem recovery.
To date, the Corps of Engineers ESH and SWH projects have been implemented and monitored with only limited strategic guidance and have not been part of a systematic, long-term adaptive management program. The reversal or slowing of declines of endangered and threatened bird and fish species cannot be accomplished immediately. Similarly, management of sediments and nutrients associated with these projects will be an ongoing, long-term process that will be affected and guided by new scientific infor-
mation, possible changes in laws and water quality standards, and shifting social preferences regarding Missouri River management and resources.
If a more systematic form of adaptive management is to be developed and applied to Missouri River ecosystem, sediment, and related resources management, it will entail more than development of appropriate guidance documents. At a minimum, it will require a sustained commitment of resources for monitoring and science programs, stakeholder participation and discussions, expert input and advice, and patience in working with large ecological systems and species that do not respond quickly or predictably to management actions.
If federal agencies and others are to implement a more structured adaptive approach to habitat and broader ecosystem restoration, those efforts will be more effective to the extent they are founded on the following:
Develop performance objectives that are tied to ecological and biological variables and designed to determine if compliance actions are reducing jeopardy to listed species.
There is a need to expand on the “acres created” metric used by the Corps of Engineers for mitigation projects along the river. Development of indicators more closely linked to life cycles of the endangered species should better determine the degree of project success.
Conceptual ecological models for the three endangered species, which will consider and evaluate all variables that affect reproduction and survival, should be developed. Development and refinement of these types of models will allow for testing of multiple hypotheses regarding environmental variables and their influences on life cycles, recruitment, and regeneration.
Ensure that ecosystem monitoring is targeted to testing of hypotheses derived from the conceptual models, and that findings are used to further refine the models and gauge progress toward attaining management goals.
Monitoring that has been conducted to date has been extensive and can form a good platform for future evaluation. There will, however, have to be a stronger link between monitoring and subsequent evaluation in order to help determine if management objectives are being met. It also will be important to ensure that ecosystem monitoring is clearly and strongly tied to the central components of a clearly defined management agenda.
Explicitly assess progress of relevant MRRP programs towards achieving the 2000/03 Biological Opinion goal of reducing jeopardy to the three listed species.
Corps management strategies to address sediment and nutrient issues in the Missouri River are undertaken through multiple interdependent programs within the MRRP under their Biological Opinion compliance responsibilities as directed by the U.S. Fish and Wildlife Service’s reasonable and prudent alternatives. An essential element of adaptive management is
to review management actions in light of new information from monitoring and assessment programs, and to revise management alternatives as needed. An adaptive management process requires confirming that existing management actions are necessary and adequate for contributing to species recovery, or if MRRP program elements or Biological Opinion reasonable and prudent alternatives need to be adjusted based on evaluation of results and what has been learned.
The ultimate outcomes of these site-level projects, and whether they will result in jeopardy status being removed for endangered bird and fish species, are not known—nor will they be known for years. Adaptive management principles would dictate that, in addition to these ongoing projects, consideration be given to alternatives that might be implemented if ESH and SWH project objectives are not achieved.
Given the uncertainties associated with outcomes from Corps of Engineers Emergent Sandbar Habitat and Shallow Water Habitat programs, it is possible that they may not meet requirements of the Biological Opinion to avoid jeopardizing the continued existence of the tern, plover, and sturgeon. The ESH and SWH programs, and the suite of new Missouri River system initiatives and studies, thus should formulate alternative actions that eventually may need to be implemented to increase the likelihood of endangered species recovery.
MISSOURI RIVER SEDIMENT MANAGEMENT ALTERNATIVES AND OPPORTUNITIES
Question 6 from this report’s statement of task asked, “Are there alternatives for reintroducing sediment into the system? What are they and what are the key constraints surrounding these alternatives?”
Question 3 in the statement of task asked, “What is the significance of the Missouri River sediments to the restoration of Louisiana coastal wetlands?”
(Both questions are addressed in Chapter 5.)
The Corps is implementing its ESH and SWH projects consistent with reasonable and prudent alternatives as specified in the 2000/03 Biological Opinion. These projects aim to restore a portion of some features of the preregulation Missouri River to help protect endangered bird and fish species. High turbidity was a prominent feature of the predevelopment Missouri River. Along with local sediment implications of these projects, parties downstream in Louisiana are interested in the prospects for increasing the volumes of sediment delivered from the Missouri River to Louisiana in hopes of slowing or reversing losses of coastal wetlands.
Sediment Reintroduction Alternatives and Constraints
Primary alternatives that might be employed to reintroduce additional sediment into the Missouri River are removing bank stabilization and control structures; limiting commercial dredging; bypassing sediment around mainstem dams; dam removal; and increasing sediment from tributaries.
Implementation of any of these alternatives would be constrained by financial, technical, and other factors. A major constraint on any alternative is the degree to which current economic activities, transportation infrastructure, water quality, and public safety depend on the existing system of dams and river bank control structures. It is not likely that major reconfiguration of the river channel, or removal of a large dam, would be desirable or acceptable to a large majority of Missouri River valley residents in the near future.
Bypassing of large amounts of sediment around Gavins Point Dam may be technically feasible. This option, however, would be expensive and have little potential to significantly reestablish preregulation supplies of sediment that were delivered to Louisiana. Substantially increased contributions of sediment from large tributaries to the Missouri River downstream from Gavins Point Dam, such as the Kansas River, are unlikely under present sediment management rules because these rivers have their own large storage reservoirs.
Implications for Coastal Louisiana
Before 1900, the Missouri and lower Mississippi river system transported an estimated annual average of 400 million metric tons of sediment from the interior United States to coastal Louisiana. From 1987 to 2006, this volume averaged 145 million metric tons per year. This annual sediment “deficit” thus is on the order of roughly 250 million metric tons per year. Some of the sediments previously delivered downstream are trapped in Missouri River reservoirs, while some of the sediments have been immobilized by river engineering activities and structures such as meander cutoffs and riverbank revetments.
If all the sediment excavated for the Corps of Engineers’ shallow water habitat projects were to be delivered to the channel, the added sediment would equal about 34 million tons/year. This would represent roughly a 10 to 20 percent increase in sediment delivered to Louisiana for at least the next 15 years, depending on the trapping efficiency of the Mississippi floodplain. This figure is less than the annual 250 million ton “deficit.” The bypassing of sediment from Lewis and Clark Lake around Gavins Point Dam would at best increase the supply of wetland constructing sediment to the Mississippi delta by only a few percent. Other prospects for mobilizing sediment in the Missouri and its tributaries are more likely to have
local effects on bar building and local channel mobility than to contribute significantly to wetland construction in the Mississippi delta.
The amounts of sediment likely to be available for transport from the Missouri River to the Mississippi River delta are smaller than the quantities that made the journey before the construction of mainstem dams and implementation of the major bank-stabilization structures.
WATER QUALITY AND MISSOURI RIVER SEDIMENT MANAGEMENT
Question 2 in this report’s statement of task asked, “What is the significance of the Missouri River sediments to the Gulf of Mexico hypoxia problem?”
Question 5 in this report’s statement of task asked, “What are the key environmental and economic considerations regarding nutrient loads and/or contaminants in Missouri River sediment? To what extent can such issues be addressed with management strategies?”
(Both questions are addressed in Chapter 6.)
Corps of Engineers ESH and SWH projects are directly depositing sediment into the mainstem Missouri River. Concerns have been expressed regarding the potential water quality impacts of those projects downstream into the northern Gulf of Mexico.
An upper-bound estimate of the increase in phosphorus loadings to the Gulf as a result of the Corps SWH projects is a 6 to 12 percent increase. Similarly, an upper-bound estimate of the downstream deliveries of bypassing sediment around Gavins Point Dam is that the additional sediment would increase total phosphorus load by roughly 1 to 2 percent. Both these estimates represent upper bounds. In reality, sediment deposition processes in the Missouri and lower Mississippi river channels would reduce loads delivered to the Gulf, and actual downstream deliveries would be less than these values.
A comparison of potential phosphorus loads from Corps SWH projects, with load increments required to produce measureable changes in the areal extent of Gulf hypoxia, shows that these projects will not significantly change the extent of the hypoxic area in the Gulf of Mexico. Additional comparisons of other alternatives for reintroducing sediment to the river—namely, bypassing sediment around Gavins Point Dam—yield a similar conclusion that they will not significantly change the areal extent of the hypoxic zone.
There also have been questions regarding annual areal changes in the hypoxic zone in the northern Gulf of Mexico and the relations of these changes with sediment loadings from the Corps ESH and SWH projects along the Missouri River.
In addition to nutrient loadings, multiple factors—including meteorologic, hydrodynamic, and timing factors—affect the size of the hypoxic zone
each year. Given the relatively small volumes of sediment loadings from the Corps’ Missouri River ESH and SWH projects, it is not appropriate to relate changes in the areal extent of the hypoxic zone to sediment and nutrient loadings from Missouri River ESH and SWH projects in any given year.
The sediment that was essential to preregulation river morphology and landforms, and to the turbidity that supported the ecosystem of native species, had certain characteristics. Development of narrative or numeric water quality criteria that are sensitive to these historic conditions will consider such factors in setting limits on sediment, as well as phosphorus, discharges to the mainstem river, and as a basis for regulating such discharges. Native species recovery objectives can be reconciled with the requirements of the Clean Water Act by basing waterbody use designation and associated criteria on aquatic life use that recognize the needs of native species.
The mainstem Missouri River historically carried a large sediment and nutrient load that was important to the evolution and survival of native flora and fauna. These preregulation characteristics should be considered in the process of developing water quality standards for the Missouri River.
The federal agencies that are partners in the MRRP, and other major Missouri River ecosystem program and initiatives, should collaborate with ongoing Environmental Protection Agency (EPA) nutrient criteria guidance development process to achieve agreement among themselves and with the states on designated uses for the river, by river segment, to reflect requirements for native species. As a result of this effort, EPA should support states that revise their existing narrative criteria for the mainstem Missouri River in order to reflect requirements for native species, even if such separate narrative sediment and nutrient criteria are later replaced by numeric criteria. As appropriate, downstream considerations (such as Gulf hypoxia) may be considered in the setting of phosphorus criteria.
There has been a good deal of discussion regarding Corps of Engineers habitat restoration actions along the Missouri River that introduce sediment to the main channel. Specifically, some parties have asserted that private entities are held to a higher standard of permitting and monitoring than a federal agency such as the Corps of Engineers. In order to obtain better, more systematic information on sediment dynamics along the river and specific activities that introduce sediment, it is important that all major activities that discharge sediment—whether private sector or governmental—be similarly monitored and evaluated.
All actions by the Corps of Engineers that discharge sediment to the Missouri River, either during project construction or through erosion following construction, should be subjected to monitoring requirements for sediment physical and chemical characteristics. This monitoring should be conducted to ensure that sediment or other pollutants discharged into the river comply with applicable water quality criteria.