Ice Impacts on Flow Along the Missouri River
JAMES L. WUEBBEN, STEVEN F. DALY, KATHLEEN D. WHITE,
JOHN J. GAGNON, JEAN-CLAUDE TATINCLAUX AND JON E. ZUFELT
plex interactions between weather, water discharge,
INTRODUCTION
hydraulic geometry, and ice processes, the results are
This project was undertaken as part of the Mis-
probabilistic rather than deterministic in nature. That
souri River Master Water Control Manual Update
is, the user must decide upon an acceptable level of
Project. One of the major factors prompting a review
risk prior to determining a future, ice-affected release
of the operation of the main stem reservoirs is the
schedule.
effects of extended low flow periods, such as the
moderate to severe drought experienced in the Mis-
souri River basin during the last 5 years, on water
APPROACH
needs in the basin. This recent period of low flows has
resulted in severe impacts on navigation, hydro-
The overall plan for the project is to develop a
power, water supply, and recreation. Specifically,
graphicaltabular decision aid for dealing with ice-
this study has examined the impacts of winter ice
related low-flow events. The effort comprised three
formation on flow regulation and water supply re-
basic components: a statistical analysis of weather
quirements from Gavins Point Dam to the confluence
records, a review of existing ice records and ice-
of the Missouri and the Mississippi rivers.
related low-flow events, and a synthesis of the first
During the winter months, periods of cold weath-
two components to allow an empirical estimate of ice
er can cause ice covers or ice jams to form at numerous
effects based on predicted weather conditions and
points along the river. Since such formations retard
planned water discharges. This graphicaltabular
the flow of water, they can result in significant quan-
approach allows a user to estimate required releases
tities of water accumulating (going into storage) be-
from Gavins Point Dam for either annual planning
hind them. As the water collects, upstream water
using long-term statistical information or a near-term
levels rise until there is sufficient depth to pass all
response to an anticipated cold snap based on current
approaching water through the ice-covered reach.
weather, levels, and flows.
During this time when water is being placed in
For the case of long-term planning, the user
storage, flow depths increase upstream of the ice-
must select an acceptable level of risk. Then, based
covered reach, and there is a corresponding decrease
on weather statistics and long-term average dis-
in water discharge and depths downstream. This
charge patterns and corresponding to the selected
flow deficit takes the form of a negative wave of
risk, anticipated minimum release requirements
reduced water flow that travels downstream, reduc-
from Gavins Point Dam can be defined to ensure
ing water levels and perhaps impairing or prevent-
adequate water depths for water intakes. Using
ing the operation of water intakes far downriver from
this approach, the recommended minimum re-
the location of the ice formation. This report reviews
leases are defined for each 2-week time period
the interrelation of water discharge and weather in
throughout the winter ice season. This release plan
forming these discharge deficit events and suggests
is based solely on long-term weather and dis-
means of regulating discharge in the river below
charge patterns and does not consider current year
Gavins Point Dam to minimize disruptions to the
weather or tributary inflows.
operation of municipal and industrial water intakes.
The second approach is targeted at near-term
Since discharge deficit events are the result of com-
operation. It allows the user to estimate the magni-
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