The Platte River Program — A USGS Priority Ecosystems Program
The Platte River Program—Project Elements
There are eight project elements:
Element 1 — Database Development
Element 2 — Factors Influencing Sandhill Crane Health and Distribution
Element 3 — Surficial Geology and Geochronology
Element 4 — Channel Characteristics and Morphology
Element 5 — Sediment Transport Modeling
Element 6 — Wet Meadow Hydrology, Biotic Resources, and Environmental Factors
Element 8 — Evaluation of Anthropogenic Manipulations of Hydrology, Channel, and Habitat for Ecosystem Improvements
Element 1. — Database Development
Development of a database containing integrated information on the geology, hydrology, ecology, geography, and socioeconomic factors of the project area is a continuing effort of this study element. The intent is to make integrated spatial database products available to the Department of the Interior and other clients who are concerned with natural resource management of the central Platte River. The database will use a logical design based on the spatial, temporal, and thematic characteristics of the data. There will be a continued focus on identifying and cataloging specific data sets for inclusion in the project database. It is important to provide access to the database through the Internet to satisfy cooperator needs. This element also involves continuing to catalog and display of aerial photographs and videographs that have been obtained at least yearly by the U.S. Fish and Wildlife Service and the Bureau of Reclamation over the last several decades. Project-specific data collection within the other study elements will need to be incorporated into the data base, which will incorporate study data for surficial geology, channel morphology, groundwater, river stages, soils, plant community composition, and migratory bird populations.
Element 2. — Factors Influencing Sandhill Crane Health and Distribution
The Platte River Valley of Nebraska is the principal spring staging area for sandhill cranes in North America and has the largest gathering of cranes in the world. Information collected in recent years suggests a marked decline in the capacity of both adult and juvenile sandhill cranes to acquire nutrient reserves needed for migration and reproduction. The area of the river used by cranes has also declined over time. These changespotentially have major implications regarding the status of the midcontinent population and the whooping crane, which occupies similar habitats. Included in this element are studying the magnitude of change in the rate and total amount of nutrient storage among juvenile and adult sandhill cranes, investigating proximate factors responsible for the change in condition, and determining whether condition the status is correlated with status of local wet meadows, cropland, or channel. This element will document the current distribution of sandhill cranes in the Platte Valley, identify changes in distribution over the past two decades, and, with the aid of GIS techniques and in concert with Element 1, assess how the distribution of sandhill cranes currently relates to channel morphology, the distribution and condition of wet meadows, and the characteristics of cropland. Work evaluating how changes in wet meadows and the channel affect crane condition and distribution will be linked with the work being conducted in Elements 3, 4, and 6 to help identify streamflows necessary to maintain wet meadow and channel habitats in a status suitable for crane needs.
Element 3. — Surficial Geology and Geochronology
The goal in this element is to characterize the geologic setting of the Platte River. Specific scale studies will examine the geomorphology of the river channel and the stratigraphy of floodplain deposits to determine past river positions, interchannel terraces, and wet meadows and will place these depositional features in a temporal context. The Platte River from Lexington, Nebr., to Chapman, Nebr., is being examined at an intermediate or subregional scale, to characterize the fluvial architecture of the Pliocene and Pleistocene sediments in the valley floor. Also, valley stratigraphy is being determined at this scale from test wells. At the regional scale, the whole Platte River is being considered in order to place the shorter reaches into context. Such factors as regional tectonics, local structure, and climate change are important aspects of the evolution of the Platte River.
Element 4. — Channel Characteristics and Morphology
Investigations in channel morphology help to define and group characteristic reaches, provide a framework for examining the interaction of flowhydraulics and vegetation on banks and island bars, and identify critical reaches for more intensive study. This study element focuses on grouping reaches on the basis of flow and sediment characteristics, stability of the bed and banks of the channel, and biotic considerations. The physical characteristics of these reaches are identified by examining river profile, observing planform changes, and cross-section changes, analyzing stage-trends, and comparing hydraulic and sediment characteristics along the reach. This investigation relies on previously collected data.
The interaction of vegetation and geomorphology near the channel banks is an important aspect of understanding the stability of the channel form. The resistance to erosion from vegetation is difficult to quantify, and measures to alter this resistance are complicated by interactions with streamflow magnitude and duration, local hydraulic conditions, and biotic factors. This interaction is examined by comparing detailed streamflow duration and hydraulic data to the vegetation communities in these sensitive areas near the channel boundary. Surveys of a limited number of bank segments, islands, and bars will define the role of vegetation in stabilizing these landforms. This work will be augmented by prediction of local velocities and stress fields from the sediment-transport modeling (Element 5).
Element 5. — Sediment-Transport Modeling
The use of multidimensional flow and sediment-transport models will assist in the understanding of potential channel changes that result from streamflow and manipulation of vegetation on islands and banks. Surveys of topography and grain-size distributions will be done to predict local sediment rating curves and critical flows for initiation of motion for grain sizes in both main and secondary flow channels. These surveys resolve topographic variability in the channel itself at 10-cm vertical resolution or better, and horizontal variability is characterized with meter-scale accuracy. At the same location, detailed grain-size surveys will be carried out to characterize spatial and vertical (at-a-point) variability in sediment grain sizes. For a variety of real and hypothetical flow-discharge scenarios, model results will be used to make preliminary assessments of the role of hydrographs in maintaining or modifying channel and bank morphology. In addition, velocity and bottom stress maps of the critical reach will be compared to vegetation patterns to assess the roles of various flows in promoting or discouraging certain types of riparian vegetation.
Element 6. — Wet Meadow Hydrology, Biotic Resources, and Environmental Factors
A series of interrelated scientific tasks seek to answer ecological questions about habitat changes that put important biological communities at risk. This element is designed to develop a better understanding of wet meadow ecology, including the relationship between geomorphology, hydrology, vegetation, and aquatic invertebrates. This understanding will help formulate models on which to base maintenance and rehabilitation strategies for the habitat. The decreased size of wet meadow landscape by corn monoculture has significantly decreased the availability of nutrients for migrating water birds. Increased pumpage for irrigation and public water supply has potentially altered river flows have changed the water table in wet meadow areas. Native wet meadows rely on shallow groundwater for survival. Data collection in the established study sites of wet meadow habitats focuses on surficial geology, elevation, connection with the river channel, basic vegetation and groundwater configurations, and invertebrate sampling. A monitoring program must include methods that do not disturb whooping cranes and other species of interest so that sampling can proceed efficiently through the entire staging season for birds and the whole growing season for vegetation.
Element 7. — Habitat Use and Requirements of Spring-Staging Migrant Waterfowl
The Platte River Valley of Nebraska is a vitally important staging area for midcontinent waterfowl during spring migration. Wetland and cropland resources in this region are important to waterfowl for obtaining sufficient energy to complete migration and for storing nutrient reserves (primarily fat and protein) for reproduction. Water conditions in the basin and in the Rainwater Basin to the south influence waterfowl habitat-use patterns and movements between the two regions, but our understanding of these dynamics, and how they affect the acquisition of nutrient reserves and outbreaks of disease is very poor. This element evaluates the movements of snow geese and northern pintails and the significance of various habitats to these and other migrant species, relative to water conditions. This study element will monitor female northern pintails and snow geese using radiotelemetry to determine habitat use, movement patterns, and survival rates. Additional data on turnover rates (migrational movements out of the region) and habitat-use patterns will be collected. These tasks use GIS-related data (Element 1) for analyses of habitat-use patterns and provide georeferenced data to the database.
Element 8. — Evaluation of Anthropogenic Manipulations of Hydrology, Channel, and Habitat for Ecosystem Improvements
Water will never again flow naturally in the Platte River because water used for irrigation and power generation support the important socioeconomic aspects of agricultural production. However, under current or renegotiated river management, some ecosystem rehabilitation efforts can and are being used to improve habitat quality and quantity for the thousands of water birds that migrate through or nest in the Platte Valley Habitat, and wildlife managers in the basin, including the U.S. Fish and Wildlife Service, the Whooping Crane Maintenance Trust, and others, are currently implementing interventions that are aimed at improving ecosystem functions. Anthropogenic manipulations of the water and habitats of the Platte River floodplain need to be evaluated to determine their effects on the ecosystem and to determine their success. This element is scheduled to begin in 1999 and will become one of the most important elements of the program. Two areas will be investigated: (1) managed rehabilitation of wet meadows, which includes groundwater/ surface water interactions and groundwater pumpage, and (2) modifications to the channel by removing woody vegetation and altering channel banks. Investigations include physical and biological assessment before alteration, monitoring of the system during alteration, and assessment after alteration, which includes the cumulative effects from a series of anthropogenic manipulations.