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New Hampshire Department of Environmental Services

Station:  Winnisquam Lake (LWINH)





This station is located adjacent to the NH Route 3/11 bridge that bisects the
upper and lower portions of the lake.  The following parameters are currently
being measured at this station:

Lake Winnisquam Stage (Lake Elevation)
Air Temperature

Water Level and Flow Constraints:
The area of most pronounced hydraulic significance is the channel that connects
the main portion of Lake Winnisquam and its control structure, the Lochmere Dam.
Because this channel is relatively narrow and extremely shallow, the level of
Winnisquam must rise to achieve increased discharge at the dam. If discharges at
the dam outpace those that this channel can provide, a local drawdown will occur
between the high point of the channel (control section) and the dam.  This
condition will be interpreted by the hydro plant at Lochmere Dam as insufficient
flow to generate power, and one or more turbines will automatically shut down.
The net effect will be that Lake Winnisquam will begin to rise at a faster rate
because of the reduced outflow at the dam.  As such, coordinated flows between
Lakeport and Lochmere dams, coupled with regular monitoring of the machinery at
the Lochmere plant, are required during high flow conditions.

Much like the potentially flow constricting sections at the Weirs channel and at
the measuring flume inhibiting flows from Lake Winnipesaukee, the natural control
section of the channel upstream of the Lochmere Dam does not appear to greatly
limit the ability to pass flood flows through Lake Winnisquam.  However, the
control section does require the lake level to rise to pass these flows, and also
requires great care and effort to operate the Lochmere Dam to maintain its full
discharge capacity during floods.

High water events of the past have raised the lake to 2 feet above its normal
operating level, while prolonged drawdowns have resulted in a lake level 2 feet
lower than normal.  Both extremes are best avoided, especially the high levels.
Since the level of Lake Winnisquam generally fluctuated within a 7-inch operating
range, the shoreline structures around the lake, which tend to be permanent and
designed to function within this range, are inundated when lake levels are high.
Low water issues are less numerous, but over the years - especially following
relatively dry summers - some shallow dug wells have been impacted.  But, much
like the case with Opechee Lake, drawdowns are short in duration and lake levels
easily return to normal when discharges are resumed at Lakeport Dam.

Due to the relative inflexibility of the turbine units at Lochmere Dam, the rise
and fall of lake levels at Lake Winnisquam must be addressed through management
of the releases from Lakeport Dam upstream.  The four hydro units at Lochmere Dam
are normally configured to pass about 250 cfs each and cannot be adjusted
automatically.  Adjustments to the capacity of each machine are possible only by
changing washers (spacers) to adjust turbine blade angle.  Such adjustments are
labor intensive and require that the machine be shut down, hoisted out of its pit
and manually reconfigured.  The sole automated feature is one that will shut the
machines down (individually) when the water level upstream falls to a point
indicating that not enough water is flowing through the upstream channel to meet
the discharge capacity of the turbines.  If a machine is turned off in this way,
the corresponding rebound of the water level upstream is usually enough to
prevent additional machines from turning off.

Summary of Operation Under Normal Conditions:
The level of Winnisquam Lake is maintained between 482.17 and 482.77 on the lake
gage, or within a 7-inch operating band, through the manipulation of the
hydroelectric energy generating units at the Lochmere Dam.  These units can pass
up to a maximum of nearly 1,200 cfs before manual operations (opening gates or
removing stoplogs) are required.  A small turbine or manual operations provides
between 35 to 45 cfs to the bypass reach on a year-round basis.  By manipulating
flows on the basis of Lakeport discharges and local inflow, the level of Lake
Winnisquam can be kept within the bounds of the operating band fairly easily.  

Summary of Operation Under Flood Conditions:
For flows above approximately 1,200 cfs, it becomes necessary to manually open
waste gates or remove stoplogs at the dam.  As flows continue to increase, an
occurrence that is usually directly related to discharges from the Lakeport Dam,
care must be taken to avoid over-operating the dam.  The channel that provides
the connection between the main lake and the dam is quite shallow in some areas,
so the possibility exists that the dam can be opened up to pass more than this
channel can provide.  This would result in an exaggerated drawdown just upstream
of the dam, which in turn, would cause one or more of the turbines to
automatically shut down.   NHDES staff monitors a staff gage at the right
abutment of the Lochmere Dam, so it is generally possible to track this
localized drawdown and compensate as necessary.  All too often, however, rapidly
changing conditions (sharply rising or falling inflows) require the need for
timely and frequent visits to the site.  As noted, discharges from Lake
Winnisquam are related to and dependent upon conditions at Lakeport Dam,
especially during flooding.

Lake Winnisquam is drawn down approximately 2 feet every other Columbus Day (even
numbered years) for a period of approximately two weeks. Except for the obvious
impacts to access and recreation during the bi-annual two-week drawdown, low water
issues are rarely encountered.

This meteorological station is operated and maintained by
the New Hampshire Department of Environmental Services (DES).
Most data relayed by satellite or other telemetry have received
little or no review. Inaccuracies in the data may be present
because of instrument malfunctions or physical changes at the
measurement site, including backwater effects due to ice formation.
Although the data presented herein is intended to be an accurate
representation of actual conditions, it is presented for
informational purposes only and the user is cautioned to use it at
his/her own risk.   

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

copyright 2008. State of New Hampshire