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Scientific Investigations Report 2007-5267


Publications Warehouse SIR 2007-5267

Prepared in cooperation with the LOWER PLATTE SOUTH NATURAL RESOURCES DISTRICT

Temporal Differences in the Hydrologic Regime of the Lower Platte River, Nebraska, 1895–2006

By Daniel Ginting, Ronald B. Zelt, and Joshua I. Linard


SIR 2007-5267 Contents | Citation

Abstract

In cooperation with the Lower Platte South Natural Resources District for a collaborative study of the cumulative effects of water and channel management practices on stream and riparian ecology, the U.S. Geological Survey (USGS) compiled, analyzed, and summarized hydrologic information from long-term gaging stations on the lower Platte River to determine any significant temporal differences among six discrete periods during 1895-2006 and to interpret any significant changes in relation to changes in climatic conditions or other factors. A subset of 171 examined hydrologic indices (HIs) were selected for use as indices that (1) included most of the variance in the larger set of indices, (2) retained utility as indicators of the streamflow regime, and (3) provided information at spatial and temporal scale(s) that were most indicative of streamflow regime(s). The study included the most downstream station within the central Platte River segment that flowed to the confluence with the Loup River and all four active streamflow-gaging stations (2006) on the lower Platte River main stem extending from the confluence of the Loup River and Platte River to the confluence of the Platte River and Missouri River south of Omaha. The drainage areas of the five streamflow-gaging stations covered four (of eight) climate divisions in Nebraska—division 2 (north central), 3 (northeast), 5 (central), and 6 (east central).

Historical climate data and daily streamflow records from 1895 through 2006 at the five streamflow-gaging stations were divided into six 11-water-year periods: 1895–1905, 1934–44, 1951–61, 1966–76, 1985–95, and 1996–2006. Analysis of monthly climate variables—precipitation and Palmer Hydrological Drought Index—was used to determine the degree of hydroclimatic association between streamflow and climate. Except for the 1895–1905 period, data gaps in the streamflow record were filled by data estimation techniques, and 171 hydrologic indices were calculated using the Hydroecological Integrity Assessment Process software developed by the U.S. Geological Survey. A subset of 27 nonredundant indices (of the 171 indices) was selected using principal component analysis. Indices that described monthly streamflow—mean, maximum, minimum, skewness, and coefficients of variation—also were used. Comparison of these selected indices allowed determination of temporal differences among the six 11-water-year periods for each gaging station.

The lower Platte River basin was affected by moderate to severe drought conditions in the 1934–44 period. The widespread drought was preceded by mildly to moderately wet conditions in the 1895–1906 period, followed by incipient drought to incipiently wet conditions in the 1951–61 periods and mildly wet conditions in 1966–76 period, moderately wet conditions in the 1985–1995 period, and incipient drought to mildly wet conditions in the 1996–2006 period. Monthly streamflow of the Platte River from Duncan through Louisville, Nebraska, correlated significantly with the monthly Palmer Hydrological Drought Index. Temporal differences in median values of monthly-mean and monthly-maximum streamflow measured at Duncan, North Bend, and Ashland stations between the two moderately wet periods (1895–1905 and 1985–95) indicated that streamflow storage reservoirs and regulation some time after 1906 significantly reduced monthly streamflow magnitude and amplitude—the difference between the highest and lowest median values of monthly mean streamflow. Effects of storage reservoirs on the median values of monthly-minimum streamflow were less obvious. Temporal differences among the other five periods, from 1934 through 2006 when streamflow was affected by storage and regulation, indicated the predominant effects of contrasting climate conditions on median values of monthly mean, maximum, and minimum streamflow. Significant temporal differences in monthly streamflow values were evident mainly between the two periods of greatly contrasting climate conditions: the monthly flows in the 1934–44 drought period were significantly lower than those in the 1985–96 moderately wet period.

The monthly coefficients of skewness and variation of streamflow, and the counts of nonredundant indices showing temporal differences among the periods, together pointed to difference in streamflow regimes between the central Platte River system and the lower Platte River system. Seven out of 13 indices of the discharge from the central Platte River system at Duncan station that demonstrated potential temporal differences were indices of streamflow variability; five of nine indices for two or more of the lower Platte River stations that showed potential temporal differences were indices of streamflow variability. The nonredundant indices of the streamflow regime from the central Platte River system computed for Duncan station during the 1934–44 and 1951–61 periods had potential differences from the other periods, that is, the largest variability in base flow and monthly minimum streamflow values, highest frequency of low-flow pulses, lowest flood frequency, largest number and least variability of zero-flow days, and largest variability of the daily and monthly flows.

Nonredundant indices for the lower Platte River that demonstrated potential temporal differences at two or more stations were: high-peak streamflow, variability in low-flood pulse count, variability in high-flow pulse count, flood frequency, annual minimum daily streamflow, variability in low-flow pulse duration, variability of annual maximum of 1-day moving average streamflow, variability of annual maximum of 3-day moving average streamflow, and number of streamflow fluctuations. The variability in low-flood pulse count and variability in high-flow pulse count were generally highest in the 1996–2006 period because this period was a mixture of five wet years (1996–2000) and six drought years. The number of streamflow fluctuations was higher in the 1966–76, 1985–95, and 1996–2006 periods than those in the 1934–44 and 1951–61 periods for the North Bend and Leshara stations, which was associated with climate and increasing water regulation and management.

Posted April 2008

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Contents

Abstract

Introduction

Purpose and Scope

Data and Methodology

Streamflow Data

Period 1895–1905

Period 1934–2006

Estimation of Missing Daily Streamflow Data

DAFLOW Simulation

Statistical Approach

Climate Data and Association with Streamflow Gages

Selection of Nonredundant Hydrologic Indices

Statistical Analysis and Tests

Two-sided Nonparametric Prediction Interval for Indices

Comparison of Nonredundant Hydrologic Indices

Nonparametric Statistical Comparison of Monthly Climate and Monthly Streamflow

Association of Monthly Climate and Streamflow

Temporal Differences in Climate and Hydrologic Indices

Temporal Differences in Climate and Association with Monthly Streamflow

Temporal Differences in Monthly Streamflow Indices

Temporal Differences in Nonredundant Hydrologic Indices

Magnitude of Streamflow Events

Frequency of Streamflow Events

Duration of Streamflow Events

Timing of Streamflow Events

Rate of Change of Streamflow Events

Summary and Conclusion

Acknowledgments

References Cited

Citation

Ginting, Daniel, Zelt, R.B., and Linard, J.I., 2008, Temporal Differences in the Hydrologic Regime of the Lower Platte River, Nebraska, 1895-2006: U.S. Geological Survey Scientific Investigations Report 2007–5267, 43 p.

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