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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) Precipitation 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. Drawdown: 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. |
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