CLEARWATERS: Water level management

The New York State Canal Corporation (NYSCC), a subsidiary of the New York State Thruway Authority, is the proud steward for the New York State Canal System, a great, historic 524-mi waterway. This legacy was born more than 175 years ago. The tradition of navigation along New York's canals endures uninterrupted, and the resurgence of development in the historic communities along the canal continues. The extensive canal system contains fifty-seven locks for navigation. Fixed crest or movable dams control upstream water elevations at each lock.

Oneida Lake's surface area of 80 mi² and its drainage area of 1382 mi² make it the largest water body of the Canal System. Oneida is integral to the larger 5100-mi² Oswego River Basin that extends from Rome to Macedon. The Oswego Basin includes the Finger Lakes and the Seneca, Oneida, and Oswego Rivers, all of which discharge into Lake Ontario through the Oswego River at Oswego, NY.

Oneida's importance to the Canal

Oneida Lake is a multi-use reservoir that serves as the primary navigation link in the heart of the New York State Canal System. The lake's shore also has numerous residential properties; marinas and fishing charters; and a complex ecosystem that contains a tremendous fishery, extensive wetlands, and waterfowl.

Water level management is paramount to each of these uses; however, there are instances where different uses may be in opposition with each other. A balanced approach is required to maintain the primary navigation function along with the other uses.

Figure 1. Caughdenoy Dam Control Structures

Many streams flow into Oneida Lake along its 55-mi perimeter; however, only the Oneida River on the western edge drains the lake. This discharge is regulated at the Caughdenoy Dam 5 mi downstream from the lake. The Caughdenoy Dam (Figure 1) is a movable dam that spans the Oneida River. It includes seven 52-ft wide by 12-ft high taintor gates. This dam was constructed in 1951-52 to replace the original concrete fixed-crest State Dam built in 1910. A secondary control structure spans the old Oneida Lake Steamboat Canal adjacent to the Caughdenoy dam that was part of the abandoned Erie Canal System, but it is not actively used to maintain lake levels.

Figure 2. Oneida River control structure. Click for larger image in new window.

Navigation is provided through Lock E-23 (Brewerton) located south of Caughdenoy along Anthony's Cut. Figure 2 shows the layout of these structures.

Locks are structures that allow boats to be raised or lowered from one river level to another. Figure 3 shows a typical lock. Rivers were transformed into canals when constructed dams formed pools of sufficient depth for navigation. The higher the dam, the deeper the pool of water behind the dam.

Locks were constructed adjacent to these dams to allow boats to navigate the system by either lifting or lowering the boat to the next pool level. Water flows into or out of the lock chamber in the process of raising or lowering boats by pressure of the higher level of water through the control of valves at the upper and lower end of the lock and not by pumps.

Figure 3. Typical lock operation schematic. Click for larger image in new window.

Oneida Lake level regulation efforts are aimed at providing sufficient water for navigation throughout the navigation season while minimizing flood damage. The navigation season extends from the first Monday in May through the first Sunday in November.

The system's water levels are lowered after the navigation season to provide storage for spring snowmelt and storm runoff. Under normal conditions, water levels are raised gradually before navigation season to predetermined safe levels for summer use. In the summer, levels are regulated to provide reserve capacity sufficient to contain moderate runoff.

Establishing ideal levels

The water level is controlled, to the extent possible, to specified “rule curves” or “regulation curves” that depict ideal lake levels. Rule curves are the historical compromise for water level management that have been established to balance competing interests for target water levels. The Oneida Lake rule curve is functionally a set of targeted minimum and maximum water levels that vary in linear fashion throughout the year. Figure 4 depicts these rule curves.

Figure 4. Oneida Lake rule curves

The rule curve process starts by establishing the top and bottom of the curves (highest tolerable level, lowest tolerable level) to avoid severe flooding or drought conditions. Within that range, water levels during the navigation season are given the highest priority to ensure a stable, reliable water supply for navigation purposes throughout the low-water summer months. Critical habitat concerns also drive target levels toward the high side of the range.

The minimum desired stage on April 1 is 370.3 ft BCD (Barge Canal Datum); it increases to 371.15 ft BCD by June 1. The target level decreases to 370.6 ft BCD on September 1 and 370.3 ft BCD on December 1. The maximum desired stage on April 1 is set at 371.0 ft BCD and increases to 371.2 ft BCD by June 1; it remains constant until August 15 and then decreases to 370.7 ft BCD on December 2.

NYSCC's objective is to maintain water levels between the minimum and maximum rule curves throughout the navigation season. The variation between the minimum and maximum targets is less than 0.5 ft and at times much less.

Operation of dam and locks

The gates at the Caughdenoy Dam are operated during the navigation season. They are opened or closed incrementally in an attempt to achieve targeted water levels. Each gate is fully opened at the end of each navigation season and remains fully open throughout the winter and spring-runoff times. Thus, the lake reverts to a run-of-river mode based on variations of uncontrolled precipitation and runoff. The gates are returned to operation after spring runoff but before the start of the navigation season to achieve targeted water levels.

Locks are not designed to be water control structures, and they cannot convey high discharges of water. Locks, therefore, are not used for flood control anywhere in the canal system. Were locks operated for flood control and sustained high discharges, their structural integrity would be jeopardized, and damage to the lock would have serious consequences to navigation.

From the ideal to the real

The rule curves are developed as an ideal guide for average conditions; the problem with their use for water level management is that average conditions are rarely achieved for any length of time, given the drainage basin's highly variable pattern of precipitation. Water level management, therefore, must be reactive and based on observed water levels, the rate of rising or falling, and observed and forecasted precipitation.

NYSCC uses a simple form of real-time management to operate the water control structures in the Oswego River Basin based on observed water levels and stream flow combined with actual and forecasted precipitation and snow cover.

The actual water level is predominately a function of uncontrolled precipitation, and operation of the gates at Caughdenoy can usually achieve a water level that corresponds to the rule curve. Uncontrolled precipitation and snowmelt can create situations where targeted water levels cannot be met, however. Droughts as well as floods are phenomena that disrupt management of the water level.

Flood control is necessary throughout the canal system, not only along the lake shore but also in downstream canalized portions of the system. Water level management must take into account the needs of upstream and downstream areas on a systemwide basis.

NYSCC collects the following data throughout the Oswego River Basin to assist it with lake level management:

Lake and canal levels, stream flow, and precipitation Stage gauges at Sylvan Beach, Cleveland, and the upstream end of Lock 23 in Brewerton help to determine daily lake levels. The rate of flow in the Oneida River is continuously measured through a USGS gauge at Euclid, 5.5 mi downstream of the Caughdenoy Dam. Daily precipitation is recorded at a rain gauge at Lock 22 and 23.

Biweekly snow surveys during the winter The variation of snow depth, snowpack water content, and snowpack density are tracked. Snow surveys use data from thirty-nine measurement locations in the watershed including the Tug Hill Plateau and the southern portion of the watershed, each of which has considerably different snowpack distribution.

The table below identifies the small range of operation between minimum navigation level and the flood damage level.

Oneida Lake water level summary

Summer navigation level	Min navigation level	Flood damage level	Average annual max level (1926-2001)
371.2	370.3	372.4	372.5

Lowering Oneida Lake in anticipation of a severe storm event, even if possible, is not necessarily appropriate since low water levels may then persist and adversely affect navigation and other water uses. Normal summer storms—short thunderstorms with highly variably precipitation—result in localized flooding and, therefore, are easier to manage. These storms produce considerably less runoff since the soil is not saturated as it might be during spring runoff. Further, the highly forested watershed intercepts substantial rainfall and fosters high evapotranspiration rates from the vegetation during the growing season.

When high-water levels occur on Oneida Lake, they often persist. The maximum discharge from Oneida Lake is about 9000 ft³/sec with all gates fully open at Caughdenoy, with lake levels above flood stage, and with considerable flooding downstream of Caughdenoy. Under this condition, lake levels can only be lowered at a maximum of 0.3 ft/day assuming no inflow—a poor assumption during the spring. Therefore, high water levels, when they occur, tend to remain for a long time. Fortunately, flooding is an unusual phenomenon, and Oneida Lake water levels are normally within the rule curves.

Source: New York State Canal Corporation

Management of lake levels will continue to be arduous, especially during severe uncontrolled precipitation and snowmelt. NYSCC is committed to operation of the Canal resource and will continue to monitor the system and adjust water control structures to ensure opportunities for recreational activities. The Canal Corporation's water management efforts dovetail with its improvements to the locks, docking facilities, adjacent parks, harbor developments, and the Canalway Trail System. All further Governor Pataki's vision of creating a first-class tourist destination and an engine for economic development.
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Howard M. Goebel, PE, PH is a hydrologist with the New York State Canal Corporation. Phone 518-436-3055.