It's a long story, but here it is:
Lakeport Dam at Lakeport
Water Level and Flow Constraints:
June 1 through Columbus Day (Summer Recreation Season)
To the extent that weather conditions allow, levels are managed between 504.32 and 502.80 to
facilitate the use of the lake for recreational enjoyment. Depending upon events and forecasts
lake levels are allowed to climb to 504.80 (about 6 inches above full) for short periods of
time to allow discharges at Lakeport to be managed to alleviate or lessen downstream
flooding/flood peaks and to avoid exceeding the capacity of downstream hydropower plants.
Currently, a considerable amount of judgment is applied when making decisions regarding flow
release during these high water periods. Since the wasting of water in excess of the
hydropower capacity at Lakeport Dam (1,050 cubic feet per second (cfs)) is of concern, the
decision to do it is based upon factors such as: rate of rise (inflow), soil moisture
condition, basin vegetation status, precipitation forecast and estimated length of time to
return levels to within the normal range. When levels reach 504.50+/-, the number of
complaints regarding shoreline structure damage or usability increases. This 71-square-mile
lake has hundreds of permanent and seasonal homes with varying degrees of shoreline development
When the level rises much above the full pond level of 504.32, impacts begin to occur. There
is at least one marina that experiences problems with bridge access (low clearance) when levels
begin to climb above full.
Issues associated with the lower end of the summer recreation range relate to hull/motor
damage to boats and, like high water, to structure usability. Many abutters are accustomed to
a certain range of water levels during the recreation season. However, when the lake is at
the lower end of the range, docks and other structures may become less accessible (ex: hull
draft is larger than depth at dock). The 250 cfs minimum outflow at Lakeport Dam can
sometimes far outpace inflow during the summer recreation season and this, combined with
normal summer evaporation, will cause the lake level to typically drop 12 to 15 inches over
the course of the summer.
Columbus Day through December 31st
To the extent that weather conditions allow, the lake level is managed between elevations
503.00 and 503.50 during this period by releasing water at a rate that can be fully utilized
by the downstream hydropower plants (250 to 1,050 cfs). This is done to facilitate shoreline
property maintenance. If deemed appropriate, and based upon basin conditions and weather
forecasts, levels will be allowed to climb above this range to prevent releases at Lakeport
from exceeding 1,050 cfs. When the level begins to encroach on the full summer elevation
(504.32), releases will be increased beyond the capacity of the hydropower plants to make
lowering the lake level the first priority. DES also endeavors to reach a target level of
approximately 502.80 on December 31st, which is approximately six inches above the full
drawdown depth of two feet. The water stored in this remaining six-inch band is release
during the coldest months of January and February.
January 1st through May 31st
To the extent that weather conditions allow, water is released from Lakeport Dam to reach the
full 2-foot drawdown (502.32) in the lake by about the end of the first week of March. The
actual depth of the drawdown varies from year to year depending upon meteorological conditions;
including prevalent base flow rates and snowpack. From March through May 31st the lake level
is allowed to climb as snowmelt, soil moisture and lake ice conditions allow. Discharges at
Lakeport Dam are made based on both actual and predicted weather events. Ideally, flows will
be maintained between 500 and 1,050 cfs throughout the period. During extremely cold periods,
flows lower than 500 cfs cause frazzle ice to form along a steeply sloped reach upstream of
Franklin center, causing maintenance problems and reduced turbine efficiency at the local
hydropower stations.
Summary of Operation Under Normal Conditions:
Lake Winnipesaukee is filled to between elevation 504.10 and 504.32 by June 1st. From June 1st
to Columbus day, Lakeport Dam is operated as necessary, and in conjunction with other dams
along the reach depending upon prevailing conditions, to maintain a minimum discharge of 250
cfs and to keep the lake from rising to more than 6 inches over full (504.80). Natural
meteorological conditions, coupled with the minimum discharge, typically cause the lake to
gradually drop during the months of July through October. On or near Columbus Day, a two-week
shutdown of flows at Lakeport Dam is initiated to facilitate maintenance in the river reach
from the dam to the confluence of the Winnipesaukee and Pemigewasset rivers. After the
shutdown, discharges are returned to between 250 and 1,050 cfs, depending upon prevailing
runoff and water level conditions within the basin, to facilitate the generation of hydropower.
These increased flows are maintained until the lake level drops approximately 1.5 feet to
elevation 503.00. Once this level is reached, the releases are managed so as to provide for
a lake level at or slightly above this elevation on January 1st. Additionally, DES endeavors
to maintain a discharge between 500 to 750 cfs through the extremely cold months, as lower
flows during these periods promote the formation of frazzle ice, which complicates the
operation at some of the hydropower facilities. The objective is to achieve a maximum
drawdown elevation of 502.32 in late February or early March, and then begin refilling the
lake in mid to late March depending upon forecasts and the extent of the snowpack.
Summary of Operation Under Flood Conditions:
Releases from Lakeport Dam are kept to a maximum of 1,050 cfs (the maximum capacity of the
hydropower plant at Lakeport), if possible. If the lake continues to rise or if more rain is
forecast, releases at Lakeport Dam are generally increased in stages of 250 - 500 cfs per day,
and flows are adjusted at the other dams along the river to keep pace with these releases and
local inflow. Flows above 1,050 cfs are achieved by operating the hydro plant at maximum
capacity and incrementally opening the dams 3 large floodgates. After the peak of the flood
has passed, and after flows in the lower portion of the basin have had an opportunity to
recede, flows at Lakeport Dam are increased and adjusted to keep the lake level receding
until it returns to the approximate level for that time of year. Any changes to the discharge
at Lakeport Dam are made in consideration of the effects of those changes on the downstream
reach.
The Weirs channel, which is relatively narrow and may be as little as 5 to 6 feet deep in some
areas under full lake conditions, may act to back water up into Lake Winnipesaukee during high
runoff events. In addition, the measuring flume just upstream of the Lakeport Dam may inhibit
the ability to pass water downstream. However, the capacity of the flume exceeds other
constraints to flow downstream of Lakeport Dam. Therefore, the flume is not considered a
limiting factor in flood operations.
Drawdown
Although Lake Winnipesaukee is operated within a 2-foot wide operating band, there isn't a
traditional drawdown of this lake as experienced by many other smaller impoundments
throughout the state. Rather, the traditional 9 to 12 inch drop of the lake level experienced
through the summer is maintained through the Fall season. Then in January, flows are increased
at Lakeport Dam to gradually lower the lake to about elevation 502.32 - or 2 feet below full
lake. This level is usually reached in late February or early March.
http://www2.des.state.nh.us/rti_home...0at%20Lakeport