FLOOD08146

• County: Statewide
• Community: Otoe CountyNebraska
• Stream Name: Missouri River Miles 551.7-555.8
• Basin: Statewide
• Title: Hamburg Bend Habitat Restoration / Preservation Project Volume 1
• Date: 8/1/1994
• Prepared For: US Army Corps of Engineers
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Project

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the Central Lowlands Physiographic Province of the Interior Plains. The area is relatively flat
with an approximate average elevation of 910 feet above mean sea level. Historical maps of this
area indicate that the river channel had changed course several times prior to channelization.
Depressional areas and drainage patterns remnant from the previous overbank channels and
backwater system are evident. These areas presently hold water seasonally and during high-
water events due to flow blockage caused by riprap closure dikes which traverse the site.

The soils in the project site are part of the Haynie-Onawa-Albaton association (USDA
1982), This association consists of deep, nearly level, moderately well drained to poorly drained
silty and clayey soils that formed in alluvium on bottomlands and are subject to flooding. These
soils formed in stratified calcareous alluvium and have small snail shells and disseminated lime.
The Haynie and Onawa soils are at slightly higher elevations than the Albaton soils (Exhibit 2),

Approximately 4.1 miles of the main Missouri River channel (river miles 551.7 to 558.8)
border the eastern side of the project site. The navigation channel is maintained by
approximately 15 revetments constructed along the east bank of the river and approximately 16
spur dikes along the west bank, Sedimentation is occurring behind many of the spur dikes.

b. Water Quality: The U. S. Geological Survey maintains a Survey Station a short
distance upstream of the project site at Nebraska City, Nebraska. The chemical content of the
Missouri River in this area is highly variable throughout the year, but exhibits no obvious
limiting factors for the indigenous aquatic fauna of the area (OPPD 1975).

The principal water quality concerns at the Hamburg Bend site result from high summer
water temperatures and the related low dissolved oxygen concentrations, While these conditions
may occur in many chute situations, they are of particular concern at this site because of the
proximity of the Omaha Public Power District's (OPPD) Nebraska City Station which is located
approximately 0,8 mile upstream of the project site.

The OPPD Nebraska City Station is a coal-fired steam-electric generating facility with
a net capacity of 250 megawatts. The plant is designed for once-through cooling and discharges
a maximum of 2.76 x 109 British Thermal Units (BTUs) of heat per hour to the Missouri River.
According to a report prepared by OPPD in 1975, at maximum load during the warmer months
of spring, summer, and fall, the Nebraska City Station may discharge water as much as 18"
Fahrenheit (F) above the ambient Missouri River temperatures.

The annual water temperature ranges from a low of 320 F to as high as the mid-80" F.
The Missouri River water temperature can also fluctuate as much as 2.40 F within a 24-hour
period (OPPD 1975). The OPPD report attributed some of this extensive diurnal temperature
fluctuation to the effect of feeder streams such as the Platte River which can be as much as 150
F warmer or 70 F cooler than the Missouri River for a given day. The Missouri River has an
average pH of 8 and a hardness of 228 parts per million (ppm) for calcium carbonate.

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