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Lake Level Overview
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The Commission oversees the lake’s water
level by tracking the lake’s surface
elevation and insuring that discharges
occur in conformance with the
“rule
curve.”
The rule curve sets a target
lake level for each day of the year. The
targets are based on state law and on
historic operating guidelines designed
to maintain the lake at optimum levels
for navigation and recreation.
The Rogers Rock Gage is a continuous
monitoring device operated by the
United
States Geological Survey (USGS). The
Commission records and reports the level
each business day about 9:00 am. This
becomes the daily lake level used and
reported by the Commission. 316.06' is 0
datum on the RRG
The lake’s target elevation for
summertime is 3.5' on the Rogers Rock
Gage (RRG). This converts to an
elevation of 319.56' MSL (mean sea
level). A daily lake level reading
higher than the rule curve means that
water is discharged from the lake. A
lake level lower than the target level
requires that the discharge gates are
closed.
Q.
What affects the lake level?
Q. How is the summertime target level
set?
Q.
Why is the lake level too low on
occasion?
Q.
Why does the lake get too high at times?
Q.
What has caused the high lake levels
during June in recent years?
Q.
Why not adjust the rule curve to lower
the lake in anticipation of heavy late
spring rains?
Q.
What affects the lake level?
Precipitation is the source of the lake.
Snow and rain falling on the 44 +/-
square mile surface of the lake
contribute water directly. Precipitation
on the 233 +/- square mile watershed
results in surface water runoff or
groundwater flows. The amount of runoff
from the watershed is affected by
several factors. The condition of the
watershed’s soil (frozen, unfrozen, dry
to saturated) the level of intermittent
lakes, ponds and wetlands in the
watershed as well as the state of trees
and vegetation (active or dormant) all
affect the amount of runoff.
Lake George is a natural lake whose
surface elevation has been raised
slightly (perhaps 2-3 feet on average)
by a dam constructed at the outlet in
Ticonderoga along the La Chute River.
The additional elevation of lake level
created by the dam can be regulated to
some extent by the dam’s discharge
structures. By using the discharge
capacity to draw down the lake to
accommodate spring runoff and by
limiting discharges at other times,
people are able to keep the lake’s
level, for the most part, within an
annual range of about 12 to 16 inches.
However, natural forces sometimes exceed
human designs. Excessive precipitation
and runoff can cause the lake to rise
occasionally to undesirable levels. The
limited discharge capacity of the outlet
means that when the lake is too high it
is slow to return to normal. Persistent
dry weather and evaporation can cause
lower than desired lake levels, as well.
Q.
How is the summertime target level set?
The Summertime (June 1, to September 15)
target elevation for the lake of 3.5 on
the Rogers Rock Gage (RRG) or 319.56
above mean sea level is established by
Section 33 of the New York Navigation
Law. Under this law, the outlet
facilities must be operated in a way
that, with due allowances for natural
fluctuations, will maintain the lake at
3.5 (RRG). This level is considered an
optimum level for recreation and
navigation. Excess water is discharged
and this water may be routed through a
hydroelectric generation facility and
used for power generation.
Q.
Why is the lake level too low on
occasion?
Lake George is a natural lake that is
usually balanced within a very narrow
regime of 12 to16 inches annually, and
five to six inches in the summer.
Precipitation is the only source of the
lake. Runoff, snow melt and groundwater
are all aspects of precipitation. During
dry periods, especially late Summer and
Fall, evaporation from the surface of
the lake can exceed the incoming water
and the lake level falls. During such
conditions the discharge gates are
closed and the lake water may not be
used for power generation. A lake level
of 3.0 RRG, 6 inches below the target,
is enough of a change from normal to
generate a spate of inquiries to the
Commission office. Compare this to
neighboring lakes such a Sacandaga
Reservoir and Lake Champlain that may
range 8 to 9 feet.
Q.
Why does the lake get too high at times?
The capacity to release water from the
lake is small in relationship to the
volume of heavy runoff. The capacity has
been likened to draining a bathtub
through a pinhole. When water entering
the lake exceeds the maximum rate that
can be discharged, the lake rises.
Each winter the lake is drawn down in
anticipation of the spring snow melt.
Snow surveys help to estimate the amount
of water that is resident in the basin’s
snow pack and refine “winter pool”
target elevations. Under ideal
conditions the spring thaw is gradual,
re-charging groundwater and tributaries
and allowing the lake to slowly
replenish a foot or more of elevation to
the target level of 4.0 (RRG) around
April 1. However, nature can be anything
but predictable. A combination of rain
and melting snow can produce an inflow
of water that exceeds the storage
capacity created by draw down. Even when
inflow conditions return to normal, it
is possible only to lower the lake level
at a rate of about an inch per day.
Q.
What has caused the high lake levels
during June in recent years?
High water conditions may also be
experienced in late Spring such as in
2005 and 2006. In these years very heavy
rainfalls saturated the ground and
created large runoff events. With a land
drainage basin area to a lake surface
area ratio about 4:1. Two inches of rain
runoff can raise the lake 8 inches. A
lake level already near its Springtime
crest has little room to accept a series
of large storms. In 2005 and 2006 lake
levels rose to above normal levels
despite maximum discharge occurring.
Again levels of no more than 6 inches
above normal were cause for problems on
a lake normally maintained in a narrow
range.
Q.
Why not adjust the rule curve to lower
the lake in anticipation of heavy late
spring rains?
The late Spring targets, which have
served well for years, reserve a couple
of inches of elevation as a hedge.
Without this reserve, lower than desired
Summer lake levels may occur more often.
The Commission is monitoring weather
trends. Climatic changes causing
sustained increases in precipitation
would be cause to reconsider the rule
curve targets.
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