Oswego River Basin Study - Executive Summary

Purpose of the Study Scope Background Operating Procedures Climate Assessment Land Use Conclusions Recommendations

1.0 Purpose of the Study

The New York State Thruway Authority (NYSTA) contracted with Baker Engineering NY, Inc., to conduct an independent operational audit of the watershed management policies, procedures, and implementation practices of the New York State Canal Corporation (NYSCC), a subsidiary of the NYSTA, within the Oswego River Basin. Emphasis was placed on the assessment of the three Finger Lakes (Seneca, Cayuga, and Oneida) that the NYSCC controls, the lake outlets, and the canals.

2.0 Scope

The effectiveness of NYSCC operating procedures was determined through various means, including:

• Examining agency records and conducting interviews with representatives from agencies that manage the lakes and canals within the system;
• Reviewing documents prepared by other organizations and groups involved in water management activities;
• Interviewing other related representatives from agencies such as the New York State Department of Environmental Conservation (NYSDEC), the U.S. Army Corps of Engineers (USACE), and the New York State Department of Health;
• Attending two public meetings held to discuss basin water levels and canal operations with local residents, the business community, local municipal agencies, and State and Federal officials; and,
• Site visits to the basin.

3.0 Background

The NYSCC is responsible for the operation of locks and other water control structures, as well as the maintenance of canals within the Oswego River Basin, including Seneca Lake, Cayuga Lake, and Oneida Lake. On August 3, 1992, State legislation dictated the transfer of Canal System control from the New York State Department of Transportation to the NYSTA and created the NYSCC to manage these functions.

The NYSCC operates four canals, three of which impact the Oswego River Basin: Erie; Oswego; and Cayuga-Seneca. Five of the 22 locks within the basin are considered major water control points because of their effect on the water levels in the upstream channel and lakes. Fixed crest and/or movable dams control the upstream water levels at each of these locks.

The water levels of the basin and rivers influence the levels maintained in the canals. Operating water levels for the basin are also determined based on the various water uses, including:

• water supply
• water quality
• navigation
• hydropower
• recreation
• flood mitigation
• critical habitat
• irrigation

The water demand and the amount of water available varies for each lake and through each season. Competing demands often create conflicting water level targets; therefore, managers must prioritize water use objectives and balance the remaining needs of lake users. For example, flood mitigation interests may demand lower levels and greater water storage reserve capacity while water supply interests simultaneously demand higher water levels to provide assurances of stable water supplies during periods of below normal precipitation.

4.0 Operating Procedures

The interrelationship of the lakes and canals within the New York State Canal System mandates that canal operators follow a series of regular procedures for monitoring water levels and take prescribed actions to deal with natural meteorological phenomena and competing demands for water. Data on current conditions are gathered from various sources, such as lake operators, U.S. Geological Survey gage stations, weather services, and other water level observers. Water level management is based on the following four steps:

• determination of the present conditions;
• evaluation of the present conditions;
• implementation of appropriate actions; and,
• communication regarding changes and monitoring of effects.

Each of these steps is repeated daily, including weekends and holidays; however, frequency may increase depending on flow conditions. Hourly monitoring is performed during high water events.

5.0 Climate Assessment

A climate assessment evaluated recent meteorological conditions within the Oswego River Basin. Weather conditions during years of flooding such as 1993 were of particular interest. Climatic factors, such as rainfall, snowmelt, or intense winds, have a significant influence on the operation of the Canal System. The climate assessment examined the:

• annual precipitation (rain and snow) record for the previous 97 years;
• daily precipitation patterns during 1996 at six weather stations in the basin;
• annual maximum lake levels for Cayuga, Seneca, and Oneida Lakes;
• the April 1993 event; and,
• impact of wind and waves on flood conditions.

Highlights of the climate assessment are discussed below.

Precipitation
An analysis of the annual precipitation for the period 1900-1996 at the Ithaca weather station revealed that 1996 had the highest precipitation on record. Furthermore, 1992, 1993 and 1994 were among the 25 wettest years on record. High precipitation during these years corresponded with flooding in the Oswego River Basin.

The Ithaca weather station at Cornell University has the longest period of record for regional weather stations and was, therefore, selected as the source of data for an analysis of the annual precipitation pattern for the 97 year period, 1900-1996. The analysis demonstrated that precipitation patterns are cyclical. Periods with high annual precipitation are followed by periods with relatively low annual precipitation.

Daily precipitation patterns in 1996 at six weather stations within the basin were examined and compared to the runoff volume at corresponding downstream gage stations. The station records at Ithaca, Aurora Research Farm, Canandaigua, Geneva Research Farm, Penn Yan and Syracuse revealed that precipitation peaks in the first part of the year generally corresponded to high runoff or a developing snowpack.

Historical Water Levels
An investigation of highest annual water surface elevations over two time periods for Seneca, Cayuga, and Oneida Lakes was undertaken as part of the Climate Assessment. Table 1 summarizes the data examined and shows a comparison between the average annual maximum water surface elevations for each time period.

The data indicate that the period of 1990-1996 has experienced maximum water levels consistent with the maximum water levels experienced at other times during the history of record. A long term trend of higher levels is not evidenced by the data. The average annual maximum elevation of 447.5 feet Barge Canal Datum (BCD) for Seneca Lake between 1990-1996 falls within the range of annual highs, which is 446.2 feet to 450.1 feet for the longer period of 1929-1996. Likewise, the average annual maximum elevation for Cayuga Lake between 1990 and 1996 is 385 feet BCD, which is within the long-term range of maximum lake levels, 383 feet to 387.4 feet. Although the long term range for Oneida Lake represents only a 46 year record (1951-1996), the 1990-1996 average of 372.7 feet is within the range of annual maximums of 371.1 feet to 374.5 feet BCD.

Table 1. Average Annual Maximum Elevations

Runoff
Several factors influence the amount of runoff (overland flow) which reaches a watercourse as a result of a precipitation event:

• precipitation intensity and form (e.g., inches/hour)
• event duration (e.g., hours)
• extent of rain or snowfall within the basin (e.g., square miles)
• sequence of precipitation events and existing soil conditions
• land cover
• seasons

The casual observer might expect a noticeable increase in stream level as the result of an intense storm in the upper reaches of a watershed; however, the duration and extent of the precipitation event within the basin must also be considered when predicting the volume of runoff. Obviously, a longer storm of equal intensity will produce more precipitation than a short storm. Conversely, a steady drizzle over a long period of time can result in a volume of runoff comparable to the short, intense event. It must also be noted that precipitation intensity is not typically uniform over an area such as a watershed. Therefore, a short intense storm over a small area in the upper reaches of a watershed may have very little influence on stream levels, whereas a continuous steady rain over the entire region can have disastrous effects.

All precipitation which falls to the ground does not reach a stream as runoff. Some of the moisture is absorbed by the soil, some is transpired or intercepted by trees and plants, and some evaporates into the atmosphere. Since existing soil moisture affects the ability of the soil to absorb additional precipitation, a series of precipitation events may decrease the amount of precipitation which can be absorbed by the ground, and the excess runs off into streams. Land cover and seasonal variations in runoff are related because land covered by heavy vegetation during the growing season quickly uses available moisture, leaving less runoff. Land cover variety (agriculture, forest, urban) and distribution within a watershed can alter runoff volume because each land cover type displays differing capabilities for draining runoff. Similarly, seasonal temperature variations affect the amount of moisture which is evaporated, as well as the rate of snowmelt.

The Oswego River Basin is particularly vulnerable to flooding in the early spring when a combination of factors which may increase runoff occur simultaneously. Before the spring growing season begins, vegetation in the basin is scarce. Trees without leaves require less moisture for transpiration, the ground lacks grasses and plants to intercept precipitation and slow runoff, and barren agricultural fields may facilitate rapid runoff. A rainfall event coupled with rising temperatures and subsequent snowmelt increases the likelihood of flooding due to the sudden increase in runoff volume which reaches streams, rivers, and lakes.

1993 Event
The 1993 spring weather pattern was typical of the meteorological conditions that can cause extensive flooding in the Finger Lakes region. The impacts of this weather pattern on Cayuga Lake were investigated as part of this audit. During March and in anticipation of spring thaw, both Cayuga and Seneca Lakes were drawn down below historic seasonal levels. On March 26, temperatures began to rise above freezing and the existing snowpack which developed as a result of the March 13 blizzard melted quickly. Heavy rainfall in April increased the rate of snow melt. Flooding occurred due to the combination of snowmelt and rainfall and the lack of surplus storage in the lake to contain the additional volume of water.

The April 1993 storm event had a much greater volume of water and a longer duration than other major events in recent years. The volume of water associated with the 1993 storm is approximately three times greater than the volume associated with Tropical Storm Agnes in 1972. Flooding in 1993 was more severe than in other years due to the larger volume of water.

6.0 Land Use

Changes in land use within a watershed can have an impact on the frequency and severity of downstream flooding over time. The amount of precipitation which finally reaches a stream is influenced by the amount of moisture that is absorbed by the ground, the amount intercepted by trees or plants, the amount transpired by trees or plants, and the amount evaporated into the atmosphere. A reduction in vegetation and/or increase in impervious surfaces (e.g., highways, parking lots, roofs) which do not allow water to be absorbed by the land can increase the volume of runoff and shorten the time necessary for the runoff to reach the stream. Land development and agricultural practices which do not account for, and manage the increase in runoff that land use changes may produce, can negatively impact flood levels downstream.

Land use patterns within three areas of Cayuga County were examined to determine the nature and impact of regional land use changes over the period 1950 to 1978. Results from the study indicate that the Union Springs area experienced a 30-percent increase in runoff volume, possibly due to a decrease in brushland and simultaneous increase in high density residential and urban or commercial centers. Land use changes and changes in runoff were insignificant for the Moravia and Auburn areas. Additional land use data such as detailed information on local agricultural practices and detailed soil type data are necessary to adequately model the changes in runoff volumes. The results of the land use study are, therefore, considered inconclusive.

7.0 Conclusions

The operational audit of the New York State Canal System revealed the following conclusions:

• Substantial changes to the existing operational system and procedures are not indicated by the audit
• Systemic errors in the current operations of the system are not evidenced by the audit
• Improvements to the operating system can be made to enhance operations and are provided in the Recommendations Section
• Public awareness of the potential for flooding and actions to prevent or lessen flood damages need to be coordinated with the appropriate agencies, such as the NYSDEC; 
• A regional approach to watershed management within the entire Oswego River Basin (not just the Canal System) is needed to address:
  • floodplain building ordinances
  • construction of detention ponds
  • creation of wetlands
  • improved water and sewer systems
  • public education

8.0 Recommendations

Based on the research and analyses conducted for the operating audit, recommendations were made regarding operations of the system, public education and awareness, planning and physical improvements to the Canal System. These recommendations are conceptual; the impacts, associated benefits and costs, and potential implementation problems have not been examined. Each recommendation is briefly described.

Operations

1. Establish a real time automated monitoring system comprised of a network of precipitation gages to measure rainfall and snowfall, coupled with a network of water level sensors at key stream and reservoir locations to verify basin response in terms of water level or stream flow. This system would not change the operation of the canal system but would reduce the time and effort involved in gathering data.
2. Automate the data analyses of flows and anomalies (such as wind-driven changes) to assist in determining appropriate actions for Canal System operators.

Education

3. Increase public education and awareness of the potential for flooding. Distribute brochures and pamphlets explaining potential flood risks, methods for minimizing flood damages, as well as actions to take during and after a flood. Information on lake levels could be disseminated via a homepage on the Internet.

Planning

4. Work with local communities to enhance public knowledge of building regulations that require structures to be elevated to at least the level of the 1-percent annual chance (100-year) flood in accordance with the requirements of the National Flood Insurance Program.
5. Participate in the development of a regional watershed management plan to address floodplain building ordinances, construction of detention ponds, creation of wetlands, improved water and sewer systems, and public education. The planning process would involve representatives from all counties, communities and controlling agencies.
6. Establish a common datum and conversion factors between datums for use in the Oswego Basin. Currently, the USACE and the NYSCC have different conversion factors to convert elevations from BCD to the National Geodetic Vertical Datum of 1929 for several of the lakes. Establishment of a common datum and factors would help eliminate public confusion regarding lake level elevations.
7. Develop flood inundation maps which show areas flooded as stage increases. This information would allow the public to identify which areas could be flooded and the extent of the flooding. Also in times of high water, the lake levels should be reported as stage, not as lake elevations.
8. Review the permits for the use of land in all subdivisions owned by the NYSCC along the canal system and examine the possibility of returning the use of this land exclusively to flood storage.

Physical Improvements

9. Construct detention facilities within the Clyde River basin to attenuate the peak flows. Flows from the Clyde River basin reach the canal quickly and during periods of high flows, may prevent flows from Cayuga and Seneca Lakes from being discharged. Detention facilities on the Clyde River would allow flows from Cayuga and Seneca Lakes to be discharged before the downstream elevation is increased by the Clyde River.
10. Construct wetlands and/or detention basins in the upper portions of the watershed. The intercepted runoff could be held back from the lakes until lake levels are lowered. Wetlands and basins could also capture sediment that is associated with runoff from farmlands. This action could aid in improving water quality and become part of an overall storm water management plan.

A copy of the entire study is available for review at each of the following locations: