Endangered and Threatened Species of the Platte River (2005) / Chapter Skim
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4 Scientific Data for the Platte River Ecosystem
4 Scientific Data for the Platte River Ecosystem
Pages 108-154
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From page 108... ...
Department of the Interior (DOI) have evaluated research into the habitat requirements of the whooping crane, piping plover, interior least tern, and pallid sturgeon for survival and recovery and have based their recommendations for instream flows and river management on the relevant studies.
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From page 109... ...
It then describes the basic connections that sustain the Platte River ecosystem (including its hydrology and geomorphology) and the habitats important for its threatened and endangered species.
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From page 110... ...
Restoration of the central and lower Platte River ecosystems to their presettlement conditions is not possible, even if the prehistoric target conditions could be specified. The central river and lower river are at the downstream end of a far-flung drainage basin and river system, and they exhibit characteristics that are determined by processes throughout the watershed.
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From page 111... ...
Therefore, even if adjustments could be made for some "natural" target in the central and lower Platte River, those adjust ments are not likely to be easily coupled with changed runoff and storage conditions upstream of those reaches. Finally, the water-control infrastructure of the river is in place as a result of public decision processes that sought to create the present hydrology, characterized by suppressed flood peaks and a dependable water sup ply even in dry months.
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From page 112... ...
Sediment, in turn, influences the morphologic characteristics of the channel. As outlined in Chapter 2, the central and lower Platte River have a braided channel, but the variety of forms is shaped by interactions between the volume of sediment to be transported and the water, with its accompanying energy, that is available for the work of transport.
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From page 113... ...
Groundwater, which is influenced by pumping and seepage from fields and unlined canals, also contributes to stream flow. Human-induced changes in the controlling flows of water in the Platte River Basin are larger and more important than climate-induced changes in controlling the Platte River ecosystem and habitats for endangered species.
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From page 114... ...
may be necessary to complement restoration activities. In general, because habitat requirements of individual endangered species that use the central Platte are linked to more natural functions of the entire ecosystem, it is possible to pursue ecosystem restoration goals even when the presettlement conditions cannot be fully attained.
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From page 115... ...
Available Data on the Platte River Ecosystem One purpose of this report is to evaluate the scientific validity of DOI's conclusions about what the instream flows should be and how they influence other aspects of the Platte River ecosystem. Part of that evaluation entails a review of the available data that DOI used to reach its conclusions.
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From page 117... ...
The additional complications of variations in exchanges between surface water and groundwater are also difficult to discern in the stream-flow record. The long-term gaging data from the North Platte, South Platte, and Platte Rivers show that river discharge has changed (Murphy and Randle FIGURE 4-1 Periods of stream-flow record from gaging stations in Platte River Basin.
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From page 118... ...
, probably because of transmountain diversions into the river from outside the basin and return flows from high groundwater. The increased annual discharges through the Platte River in the later parts of the record have not TABLE 4-1 Annual Mean Platte River Flows, cubic feet per second Gaging Station 1895-1909 1910-1935 1936-1969 1970-1999 North Platte River 3,190 2,750 646 862 at North Platte, NE South Platte River 582 492 322 619 at North Platte, NE Platte River 3,780 3,240 968 1,480 at North Platte, NE Platte River 3,550 3,020 461 981 near Cozad, NE Platte River 3,660 3,160 1,140 2,100 near Overton, NE Platte River 3,580 2,950 1,080 2,110 near Grand Island, NE Source: Randle and Samad 2003.
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From page 119... ...
To investigate the flow movement and distribution in the entire basin, a central Platte OPSTUDY hydrological model has been developed as a management tool to incorporate all hydraulic structures, water-rights demands, and so on. The basic function of this mass-balanced hydrological model is to simulate all the flow inputs and outputs at various locations from the inflows of the North and South Platte River down to the flow at the lower Platte River.
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From page 120... ...
The first complete coverage of the geomorphology of the river resulted from the USGS topographic mapping program, which produced maps for Nebraska and the river based on conditions in 18961902. Private maps followed, showing parts of the river at various dates FIGURE 4-3 Photograph of central Platte River near 100th Meridian in vicinity of Cozad, Nebraska, in 1866.
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From page 121... ...
Further calculations use the sediment rating curves and gaged water discharges to produce the estimates of total sediment transport. The best understanding of sediment discharge through the central Platte River derives from DOI work summarized by Randle and Samad (2003)
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From page 122... ...
The increase was probably the result of erosion in upstream reaches. The central Platte River has two distinct segments from the perspective of sediment: the segment upstream of Cozad and the Johnson-2 return, which is accumulating sediment (aggrading)
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From page 123... ...
123 l (1) to m hed fro Centra report.
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From page 124... ...
This section addresses river ecosystem and habitat interconnections, the next section reviews instream flow issues, and a third section addresses the habitat suitability issue. Data outlined earlier in this chapter paint a general picture of environmental change in the corridor of the central and lower Platte River.
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From page 125... ...
. The changes FIGURE 4-5 Johnson-2 diversion on central Platte River, a feature that influences local distribution of flows in river and provides valuable irrigation water for agriculture.
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From page 126... ...
Most time-series graphs start with channel widths measured on GLO plat maps, which are followed by estimates made from aerial photographs, first available in the late 1930s. Standard methods have not been used or developed to measure width or area, so comparisons among studies are difficult; studies vary widely in reaches sampled, dates of photography, sample sizes (number of transects or sample points)
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From page 127... ...
Source: USBR 1998. FIGURE 4-8 Aerial photographs from 1938 (left)
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From page 128... ...
Rather, they began in 1938 when aerial photographs first became available; that is, any woodland expansion before 1938 was not estimated. Several quantitative patterns since 1938 are evident (Figure 4-10)
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From page 129... ...
SCIENTIFIC DATA FOR THE PLATTE RIVER ECOSYSTEM 129 AREA CHANNEL 1938 OF GE A PERCENT FIGURE 4-10 Changes in channel width at various cross sections of the central Platte River as interpreted by C Johnson on basis of aerial photography.
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From page 130... ...
support the following multifactor explanation. Reduced stream flow in late spring (the period when reservoirs are filled)
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From page 131... ...
About half the floodplain of the central Platte River reverted to woodland that became relatively stable in area and in location; however, bank erosion along active channels in these wooded areas creates new areas of open channel incrementally (Figure 4-12)
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From page 132... ...
In 1938, both parts were open and mostly without vegetation except for small islands that were wooded. In 1998, active channels are more narrow, but southern channel remains braided.
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From page 133... ...
Currier (1997) speculated that the cause of the narrowing at Grand Island was alteration of stream flow by upstream water development.
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From page 134... ...
Despite varied interpretations, studies of woodland processes in the central Platte River generally agree on the following. First, woodland was an important and permanent part of the presettlement Platte, but its aerial coverage has increased substantially in the modern, regulated river.
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From page 135... ...
135 to 1. Eleva Further 200 agencies Surface DOI Waddle programs.
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From page 136... ...
. There may be many such curves for each species of interest, with each curve representing the amount of suitable habitat available during different life stages of the species.
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From page 137... ...
Uncertainty also enters the analysis because it is unclear that if habitat is reconstructed, it will serve the needs of the threatened and endangered species. However, as discussed in Chapter 3, science does not offer perfect certainty.
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From page 138... ...
The software is in the public domain, and it is used by university researchers and private consulting firms for contract work. During the period when USFWS was determining its instream-flow recommendations for the central and lower Platte River, the agency used IFIM and applied it to the three threatened or endangered avian species along the river.
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From page 139... ...
139 flow e recommended ,Population Dynamics ies nativ Habitat e Ser Alter unity of Regimes ectiv define Time w Species Eff to Comm Flo Analysis le ies ies agencies Ser Usab Ser Macrohabitat Habitat DOI le Time Total Time ies by Usab Ser Microhabitat used le le Time Usab Usab (IFIM) Habitat Negotiation Total le le Method 2001.
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From page 140... ...
Instreamflow targets for general purposes or specific species represent discharge conditions that are intended to result in favorable habitat for the threatened and endangered avian species along the central Platte River and for pallid sturgeon in the lower Platte River (Table 4-3)
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From page 141... ...
. TABLE 4-5 Peak-Flow Recommendations of USFWS for Central Platte River, Nebraska Recurrence Interval Recommended Flow, cfs Notes 1 of every 5 years (20%)
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From page 142... ...
The proposed instream flows that resulted from the DOI agencies' analysis and that are summarized in Tables 4-3, 4-4, and 4-5 appear to the committee to be in the correct magnitude and timing to achieve the desired results of using river processes to foster habitat for the threatened and endangered species. The flows represent reasonable calculated estimates of the magnitude needed to readjust the channel geomorphology, channel deposits, and channel-side landforms to suit the needs of the species better
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From page 143... ...
PHABSIM is especially beneficial in the process of sorting out habitat suitability because it uses the same ecosystem elements as do the habitat characteristics. Over the last 2 decades, USFWS developed habitat suitability guidelines for the four listed species in the central Platte River.
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From page 144... ...
The guidelines can be broadly defined or sensitive, depending on how much is known about the selected species and the degree to which the physical environment can be codified or quantified. Habitat suitability guidelines for the listed species on the central and lower Platte River emerge from processes outlined by USFWS (unpublished material, June 16, 2000)
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From page 145... ...
For example, 58 species of fish live in the central Platte River (Chadwick et al.
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From page 146... ...
In addition to the different outcomes of applying the PHABSIM-IFIM and normative models, the two approaches are underlain by fundamentally different philosophies. IFIM deals with the issue of connecting river flows to physical characteristics of the river one species at a time.
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From page 147... ...
The Platte River presents a management conundrum. Riparian woodland established in the central Platte River between the 1930s and 1960s is now in its most productive and diverse stage and supports the majority of species on the floodplain.
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From page 148... ...
The adverse consequences of clearing include loss of wooded nesting and migratory habitat for many species of songbirds; proliferation of invasive purple loosestrife due to soil disturbance and chopping of mature plants; possible oversupplying of sediment to downstream reaches, a cause
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From page 149... ...
Restoration sometimes focuses on benefits to the threatened and endangered species, but unintended detrimental consequences for other species ought to be minimized. In the case of the central Platte River, clearing of woodland to improve habitat for whooping cranes, for example, entails removal of forest environments for some songbirds.
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From page 150... ...
Approaches to restoration in the central Platte have been under way for over 2 decades. Thus far, crane populations have increased during this period, and there is strong evidence that they followed cleared areas for roosting purposes (Faanes and LeValley 1993)
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From page 151... ...
, "these flow recommendations are intended to achieve the flow-dependent goal of rehabilitating and maintaining the structure and function, patterns and processes, and habitat of the central Platte River Valley ecosystem." Four types of flow recommendations were made: for species flows, annual pulse flows, peak flows, and program target flows. The values of the species flows for dry, normal, and wet years were based on a consultation process initiated in the 1980s and concluded with the discussions in the March 8-10, 1994, workshop, summarized by David Bowman (1994)
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From page 152... ...
Because the return flows from diversions (except Kearney Canal return) occur upstream near Overton, Nebraska, the relative flow effect of water-resources development is considerably greater on the upper Platte River than on the central Platte River.
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From page 153... ...
Two-dimensional models have limited application because two-dimensional flow data are often unavailable to calibrate them. The committee recognizes six approaches for potential improvement of DOI investigations into ecosystem dynamics on the central and lower Platte River: · Field data collection and methods for the monitoring of the effects of various flow recommendations and mechanical removal of vegetation must be carefully designed long before the occurrence of the targeted flow events or vegetation manipulations.
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From page 154... ...
· Restoration of the central Platte River should include water processes and forms, control of invasive species, and some grazing and fire if research shows these phenomena to be important aspects of the pre-European river. · More emphasis should be placed on the management of the Platte River as an ecosystem, rather than keeping the focus exclusively on listed species.
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