350
300
250
200
150
100
50
0
30
20
10
0
10
20
Average Air Temp (C)
Figure 6. Distribution of average daily air temperatures at Fremont, Nebraska,
during selected ice-affected periods at Platte River at North Bend, Nebraska, gage
from 1965 through 1994.
Platte River at North Bend, Nebraska, gage
This gage is located in eastcentral Nebraska, about 45 miles northwest of Omaha. It (USGS
gaging station 06796000) is situated on the north (left) bank of the river, about 80 ft west (upstream)
of State Highway 79 (Fig. 4) and about 0.7 miles south of North Bend, Nebraska. The drainage area
of the gage is 70,400 mi2. Daily streamflow data have been compiled at the gaging station since
April 1949. Station records through WY 1995 show a maximum instantaneous flow of 112,000 ft3/s
on 29 March 1960, a minimum daily mean flow of 36 ft3/s on 29 July 1974, and an average of 4569
ft3/s. Air temperature data were obtained from a weather station at Fremont, Nebraska,* which is
located about 15 miles east of the gaging station (Fig. 4).
Streamflow at the gaging station is subject to a complete ice cover during the winter. Ice effects
are common in November through March; there are severe ice jams at the gage in most years. In this
report, 27 years of daily streamflow and climatological data were analyzed: WY 196567, 196970,
197290, and 199294. Intervening periods were omitted owing to missing stage or climatological
data.
Within the period analyzed, 28.9% (2179 days) of daily streamflow values were affected by ice, as
indicated by a streamflow ratio of less than 1. The distribution of streamflow ratios during periods
of ice effects is skewed to the right, with a mode class of 0.30 (Fig. 5). For the periods of analysis, the
minimum streamflow ratio was 0.045 and the mean of ice-affected streamflow ratios was 0.43. The
corresponding distribution of daily mean air temperatures on days of ice effects has a mode class of
0C and a mean of 4.1C (Fig. 6).
APPLICATION OF EXTENDED KALMAN FILTERING
Grewal and Andrews (1993), Bar-Shalom and Li (1993), Bozic (1994), Mendel (1995), and Brown
and Hwang (1997) all provide detailed information on the mathematical development and general
application of Kalman filtering. A Kalman filter estimates the state of a dynamic system, given
measurements that are related to the state. The extended form of the Kalman filter was selected
* Personal communication with Mat Werner, Climate Resources Specialist, High Plains Climate Center, University of
Nebraska-Lincoln, 1996.
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