Phase 1 Final Mill Street Dam Concept Report.pdf

MILL STREET DAM REMOVAL AND

CHITTENANGO CREEK RESTORATION

Preliminary Conceptual Design, Phase 1 Village of Cazenovia, NY

Final Report July 2025

Prepared for Prepared by

V i l l a g e o f C a z e n o v i a

90 Albany St.

Cazenovia, NY

8375 Seneca Turnpike New Hartford, NY

This report was prepared with funding provided by the New York State Department of State under Title 11 of the Environmental Protection Fund.

Mill St. Dam Removal i Final Report Preliminary Conceptual Design, Phase 1 July 2025

TABLE OF CONTENTS

1 Background

1.1 Project Purpose and Background

1.2 Project Setting

2 Data Collection and Analysis

2.1 Survey

2.2 Dam Inspection

2.3 Evaluation of Natural and Cultural Resources

2.4 Hydrology and Hydraulics

2.4.1 Hydrologic Model Development

2.4.2 Hydraulic Model Development

3 Alternative Analysis

3.1 Limited Structural Removals

3.2 Complete Dam Removal – Preferred Alternative

3.2.1 Potential Impacts & Benefits

4 Permitting Requirements

4.1 Regulatory Review Process

4.2 Impacts on Construction Schedule

5 Construction Budget Estimate 6 Next Steps

LIST OF APPENDICES

Appendix A – H&H Memos Appendix B – Existing & Proposed Sketches Appendix C – Preliminary Sediment Contamination Due Diligence Review

LIST OF TABLES

Table 5-1: Budgetary Opinion of Probable Construction Cost for Dam Removal Table 7-2. Approximate Timelines for Dam Repair & Dam Removal Alternatives

LIST OF FIGURES

Figure 1.2-1: Approximate Locations of Dams Figure 1.2-2: Project Area Figure 2.4.2-1: Water Surface Level Variations Upstream

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LIST OF ABBREVIATIONS

cfs cubic feet per second cm centimeters CY cubic yards DEM Digital Elevation Model EL elevation FEMA Federal Emergency Management Agency FIS Flood Insurance Study ft feet ft/s feet per second GSE Gomez and Sullivan Engineers, D.P.C.

HEC-RAS Hydraulic Engineering Center River Analysis System LiDAR Light Detection and Ranging MAHW mean annual high water MGD million gallons per day NHESP Natural Heritage & Endangered Species Program NOAA National Oceanic and Atmospheric Administration NYSCC New York State Canal Corporation NYSDEC New York State Department of Environmental Conservation OHW ordinary high water OPCC opinion of probable construction cost PNF Project Notification Form RTE rare, threatened, and endangered RTK real-time kinematic sf square feet SHPO State Historic Preservation Office USACE United States Army Corps of Engineers USFWS United States Fish and Wildlife Service USGS United States Geological Survey WQC Water Quality Certification

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1 Background

1.1 Project Purpose and Background

The Village of Cazenovia proposes to remove a portion of the Mill Street Dam, herein referred to as the Lower Dam (NYS ID 093-0493). It spans the Chittenango Creek approximately one-half mile downstream from Cazenovia Lake, in the Village of Cazenovia, NY. The dam is owned and operated by the New York State Canal Corporation (NYSCC), who are cooperating in the completion of this report. The parcel of land containing the Lower Dam and areas adjacent are owned by the NYSCC, while the lands surrounding the parcel are privately owned.

The primary purpose of the project is to decommission aging infrastructure and reduce backflow into the Lake as much as feasible. The project could also provide environmental benefits, including restoring natural river processes and ecological functions (e.g., sediment and flow regimes), improving water quality, and providing upstream and downstream passage and habitat access for resident fish and aquatic species. A secondary purpose, although no less important, is to restore the portion of creek between the two dams to a more natural state. Improving the overall health and appearance of this section of the waterway by installing riparian plantings, boulder clusters, and/or rock riffles can help this area resemble the character and conditions of the existing high-functioning portions of the stream downstream of the structure.

Additional potential benefits of the dam removal project include, but are not limited to:

• Elimination of dam repair and ongoing maintenance obligations for the NYSCC

• Elimination of risk associated with downstream flooding due to a potential dam failure

• Opportunities for enhanced recreation, such as a new trail network along the restored channel, made possible due to improvements in the channel reducing erosion potential

• Restoration of natural riverine processes and ecological functions

1.2 Project Setting

Watershed

The drainage area at the Lower Dam is approximately 45 square miles, while the Cazenovia Lake drainage area is approximately 8.5 square miles.

Due to the storage capacity of Cazenovia Lake, water levels rise slower in the lake than in Chittenango Creek. When the water level between the dams is high, any significant precipitation can cause the water to flow the opposite, or upstream, direction. This causes flood flows from Chittenango Creek to enter Cazenovia Lake, potentially carrying sediment and pollutants.

Upper Dam (Cazenovia Lake Outlet Dam)

The Upper Dam is located on the channel connecting Cazenovia Lake to Chittenango Creek. It serves to help regulate the water levels in the lake by means of gates that either impede or release the flow of water from the lake to the creek. It is owned, operated, and maintained by NYSCC. Refer to Figure 1.2-1 below for the location of the structure.

The dam was constructed in 1918 to regulate the water level of Cazenovia Lake and control the outflow into Chittenango Creek.

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Lower Dam (Mill Street Dam)

The Lower Dam is located on Chittenango Creek, just less than 1000 ft downstream from the Upper Dam.

The dam consists of, from left to right looking downstream, three sluice gates with a width of 3.3 ft, 4.4 ft, and 4 ft, that open and close to maintain water levels in the upstream section of the creek. A 10.7 ft wide cement block pier connects the three-gate structure to a 93 ft spillway that spans to the right embankment. Refer to Figure 1.2-2 below.

The dam was built in 1856 to support additional water supply needs for the Erie Canal expansion. It was also designed to create backflow events to store additional water in Cazenovia Lake to support navigation in the Erie Canal. At the time it was designed and constructed, the potential environmental impacts of the backflow, such as carrying sediment into the lake, were not considered.

In the New York State dam safety inventory, the Lower Dam is assigned Hazard Class A (Low Hazard), indicating that failure unlikely to result in damage to anything more than isolated or unoccupied buildings, undeveloped lands, minor roads such as town or county roads; is unlikely to result in the interruption of important utilities, including water supply, sewage treatment, fuel, power, cable or telephone infrastructure; and/or is otherwise unlikely to pose the threat of personal injury, substantial economic loss or substantial environmental damage.

Figure 1.2-1: Approximate Locations of Dams

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Figure 1.2-2: Project Area

2 Data Collection and Analysis

2.1 Survey

Publicly available Light Detection and Ranging (LiDAR) elevation data was used to provide upland topography while bathymetric data in specific locations of the channel was field collected over the course of two days in May 2024. The latter information was obtained using real-time kinematic global positioning system (RTK-GPS) survey equipment and, where needed, an Acoustic Doppler Current Profiler (ADCP).

Bathymetry data collected included water depth, channel shape and width, and provided a slope profile along the channel. Spot elevations were recorded on the dam structure during the data collection.

2.2 Dam Inspection

In May 2024, an assessment of the physical condition of dam and appurtenant structures was completed.

A visual inspection of overall structural condition found that there is noticeable deterioration in many of the block joints and in the upstream concrete facing of the dam. The deterioration is more severe in the gate opening where sections of the concrete have failed to the point that exposed reinforcement bars are visible. Several broken welds were observed in the sluiceway structure. Multiple locations of weathered and broken laid-up stones are present throughout the length of the spillway.

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2.3 Evaluation of Natural and Cultural Resources

Natural Resources

To evaluate the potential impacts of the proposed project on wetlands and rare, threatened, and endangered (RTE) species, a preliminary review of the NYS Environmental Resource Mapper (ERM) was performed. Although no RTE species were identified in the Project area, the search indicated that regulated wetlands are present; delineation will be required. NYSDEC has recently updated their wetland regulations, and these changes will need to be incorporated into the investigation and permitting efforts.

A preliminary search of the iMapInvasives Network’s database indicates that there may be the presence of two plant species in the vicinity of the project. It is recommended that this be further investigated in the next phase of the project and could be done during the wetland delineation efforts.

The Creek is classified as a C(T) stream, indicating that it is a trout stream. This will likely result in in-water work timeframe limitations for any construction proposed in the future.

Cultural Resources

A review of the site using the State Historic Preservation Office (SHPO) online Cultural Resource Information System (CRIS) was conducted. The database indicated that the dam is listed on the historic registry. Therefore, any proposed construction efforts will require consultation with SHPO before commencing.

2.4 Hydrology and Hydraulics

Summaries of the development of the analyses are provided below. Please refer to Appendix A for more detailed information.

2.4.1 Hydrologic Model Development

A hydrologic model was developed using HEC-HMS, covering the drainage area upstream of the Lower Dam, including Cazenovia Lake. The model includes two subbasins: one for Cazenovia Lake and one for Chittenango Creek upstream of the lake outlet. The Chittenango Creek watershed does not explicitly include Erieville Reservoir operations. The goal of the hydrologic model was to predict streamflow from the lake watershed and from the upper creek watershed for recurrence interval rainfall events. The model utilized a DEM from publicly available LiDAR data and rainfall infiltration was simulated using SCS Curve Number methods. Basin runoff was simulated using the Snyder unit hydrograph technique, and baseflows were defined using the regression method with common values for uncalibrated models. Rainfall data was sourced from NOAA Atlas 14 and NRCC's Extreme Precipitation Analysis tool, with a computational interval of six minutes; the model was validated by comparing results to USGS regional regression equation results, showing peak flows within the standard error.

2.4.2 Hydraulic Model Development

A combined 1D/2D hydraulic model was developed using HEC-RAS to analyze backwater, flood risk, and impacts of modifications at the Lower Dam, using streamflow predictions from the hydrologic model. The model incorporated a previous 1D model from the NYSCC1 with minor modifications. In order to provide more detailed predictions in the area of greatest interest around the Lower Dam, a 2D model was created based on the DEM modified with field collected bathymetric data. It extends from 125 ft below the Lower

1 The model provided by the NYSCC was documented in the December 2023 memo by Bergmann regarding the Upper and Lower Cazenovia Lake Dam hazard classification review.

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Dam up to Cazenovia Lake and includes 2,900 ft of Chittenango Creek upstream of its confluence with the lake. The model simulated weir and gate flow at the Upper and Lower Dams, excluding the Chenango and Forman Street bridges. Results indicate that these bridges do not impact whether backflow into Cazenovia Lake does or does not occur.

Initial conditions for water surface elevations and flow were set, with a steady initial flow in Chittenango Creek. Adjustments to default computational settings were made to address stability issues particularly related to the transition between the 1D and 2D models. Observations from April 6, 2023 and May 1, 2023 events were used for validation. While the model simulated the occurrence of backflow for both events, backflow was only observed.

A comparison of the existing condition (i.e., assuming normal navigation season operations) and after full dam removal scenarios under a flow event with a one year recurrence interval is illustrated in Figure 2.4.2- 1 below. This figure shows that the water surface elevation difference between these scenarios decreases as the distance from the Lower Dam increases.

Figure 2.4.2-1: Water Surface Level Variations Upstream

3 Alternative Analysis

3.1 Limited Structural Removals

This alternative was investigated for two potential modifications to the Lower Dam: lowered crest and partial removal. The lowered crest alternative would involve a new spillway 2.75 ft lower than the existing one. Partial removal considered keeping only the gate and sluice structures in place.

As noted earlier, the dam inspection identified deficiencies that would need to be repaired if the partial structure were to remain. These include, but are not limited to, the areas of deteriorated concrete, weathered stone, exposed reinforcement bars, and broken welds. For safety reasons, continuing inspection and maintenance of the structure would be required.

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The remaining structure would also require ongoing operation to address fluctuating water levels to address backflow into the lake, monitoring and evaluating structural portions of the dam including maintenance, as required, and removal of debris located on the dam and in the sluiceway.

In either of these options, varying amounts of barriers will remain impeding aquatic movement and limiting the rehabilitation of the section of creek between the two dams. The lowered crest scenario considered a situation where the Lower Dam was reconstructed to have a single spillway spanning the entire length of the structure, which would require the removal of the existing gate and sluice structures.

The other partial removal option, in which the spillway is removed completely, with the gate and sluice structures remaining in place, and the gates fully open. Please refer to Appendix A for further details.

3.2 Complete Dam Removal – Preferred Alternative

This alternative would remove the entirety of the existing dam structure with the exception of the abutments. This option would open the width of the channel to the greatest extent; it would also result in the loss of most of the historic structure. However, as described in Appendix A, complete removal provides the greatest reduction in the amount of backflow to the lake, and also provides additional benefits as described below. Based on review and discussion of these results with Village officials and local stakeholders, complete dam removal is the selected alternative. Refer to Appendix B for sketches of the existing and proposed configurations. For the remainder of the report, ‘dam removal’ will be complete dam removal as defined by this alternative.

Study Limitations It is important to understand that this is a conceptual assessment of dam removal based on readily available information and a moderate amount of collected field data. If the Village opts to further pursue dam removal in Phase 2, additional in-depth analysis and field data collection will be required, including sediment depth mapping, sediment sampling and contaminant analysis, additional historic assessments, a limited amount of additional hydraulic modeling, and further assessment to narrow the budgetary range. Typically, the primary cost drivers on a dam removal project aside from the structure removal itself include the quantity and quality of accumulated sediment and proposed sediment management approach; potential impacts to existing infrastructure; and water control and channel disruption during construction. In this case another important component will be the historic nature of the structure. For the purposes of this report, we have outlined the potential impacts of dam removal on various resources, followed by our assumptions and calculations to inform the opinion of probable construction cost (OPCC) estimate.

3.2.1 Potential Impacts & Benefits

Backflow Reduction The occurrence of backflow is reliant on multiple factors. The analyses show that backflow is more likely when flows in Chittenango Creek are high, initial Cazenovia Lake levels are low, and discharge capacity at the Lower Dam is low (i.e., gates are closed). Full removal of the Lower Dam has been shown to have a significant reduction in the occurrence of backflow relative to existing conditions. Refer to Appendix A for additional information.

Water Quality & Aquatic Habitat

Backflow from Chittenango Creek into Cazenovia Lake has contributed to water quality impairments and during storms events results in more nutrients in the lake which then cause algal blooms in Cazenovia Lake.

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The removal of the Lower Dam is anticipated to improve water quality in Chittenango Creek by restoring natural stream processes such as flow and sediment regimes downstream of the upper dam. The establishment of new bordering vegetation along the riparian corridor in the lowered impoundment area could also help to filter runoff and improve water quality in Chittenango Creek. Temperature and dissolved oxygen levels are expected to improve throughout the former Chittenango Creek impoundment with the transition to a more riverine reach with decreased water depths. Additionally, it allows the creek to return to a more natural state and, with the proposed construction of rock riffles or similar features in the rehabilitated channel, to promote improved fish habitat and reduce scour and erosion of the channel and banks. These improvements will support fisheries and other aquatic species and would be an overall gain for the native plant and animal community within the currently impounded section of Chittenango Creek.

Any potential impacts to water quality and aquatic habitat as a result of downstream transport of sediments (e.g., due to aggradation of aquatic habitat and/or release of sediment-bound contaminants) would be minimized with an appropriate sediment management plan for the site to be developed in Phase 2.

Sediment Transport

Dam removal generally redistributes sediments accumulated behind a dam, restoring the river and its riverine habitats to pre-dam conditions within several years after dam removal. Following dam removal, sediment transport controls the process of channel evolution, including upstream erosion in the former impoundment (i.e., headcutting), deposition of transported sediment in downstream reaches, narrowing of the channel, and creation of new floodplain areas in the location of the current impoundment site.

These processes have important benefits for nutrient cycling and habitat availability. Previously embedded gravel and cobble substrate in the former impoundment may become re-exposed, as the fine sediments that covered them are washed downstream, restoring aquatic habitat for fish and other organisms.

One concern of the dam removal process is the short-term increase in turbidity and water quality impacts that may occur if sediment accumulation is not addressed properly. However, appropriate sediment management can significantly reduce sediment-related impacts. If the sediment is to be determined to be “clean” and allowed to naturally transport downstream, this can be beneficial to the aquatic habitat in the downstream reaches by reintroducing nutrient rich fines into a ‘starved’ channel.

Water Levels & Flooding

Dam removal would result in a reduction of water levels upstream as shown in Figure 2.4.2-1. This could have potential recreational, aesthetic, or environmental impacts. Regarding flooding, dams such as this one are operated as “run-of-river” dams, whereby inflow equals outflow on a nearly continuous basis.

Therefore, the dam does not provide significant downstream flood control, but rather artificially raises the water surface elevation upstream of the dam, increasing the frequency of backwater into Cazenovia Lake. Removal of the dam would thereby reduce the frequency of backwater with minimal increases in downstream water levels during flood events. It would also eliminate the risk of a potential dam failure;

although, as noted previously, this is a low hazard dam, so there is a low risk for loss of life or property damage due to a dam failure. Even a low hazard dam failure has the potential to damage property, infrastructure, and result in a costly cleanup effort.

Fisheries

Dam removal would result in converting the impoundment to a free-flowing creek and removing a barrier to upstream passage for potential diadromous (migratory fish) that may be present in the creek, currently

Mill St. Dam Removal 10 Final Report or in the future, as well as movement for resident fish species. However, there are other barriers throughout the system to consider.

There are three dams downstream of this dam on Chittenango Creek - Cazenovia Electric Company Dam (privately owned, just less than a mile downstream), Chillangua Mill Dam (privately owned, about 9.7 miles downstream), and Chittenango Creek Dam (NYS owned, approximately 11 miles downstream). In addition, Chittenango Creek crosses under the Old Erie Canal via an aqueduct in the Town of Sullivan downstream of the Village of Chittenango. Flow to the Old Erie Canal is provided at the Chittenango Creek Dam utilizing a weir structure. The Chittenango Creek Dam does not have fish passage facilities, and it is unknown if the other dams have fish passage facilities.

Rare, Threatened and Endangered Species

Dam removal could affect rare, threatened, or endangered (RTE) species that could potentially be present in the project area. The NYSDEC Environmental Resource Mapper (ERM) and the US Fish and Wildlife (USFWS) Information for Planning and Consultation (IPaC) database was consulted in order to identify potentially state and federally endangered species in the project area. Based on preliminary investigation, it does not appear that the project is currently within a critical habitat area, and trees should not need to be cut for dam removal, so impacts to rare, threatened, or endangered species are not anticipated.

However, as dam removal design proceeds in Phase 2, a habitat survey should be conducted prior to permitting to inform the need for any measures to avoid or minimize impacts to RTE species. Formal consultation with the NYSDEC and the USFWS would be needed to confirm the lack or presence of potential listed RTE species in the project area.

Recreation and Aesthetics

Potential impacts or benefits to recreation and aesthetics due to the dam are somewhat subjective and based on individual preferences. Some people may value the existing aesthetics of a dam and the flatwater boating opportunities provided by the slow-moving backwater created by that structure. Others may value the aesthetics of water cascading over natural rocks, as would likely develop at the site if the dam were removed, and the recreational opportunities provided by a free-flowing river.

Dam removal could increase other opportunities along the restored river channel. Removing the barrier of the dam could allow for more continuous kayaking and/or canoeing trips on the creek. The improved water quality that would result from dam removal could benefit other recreational uses as well (e.g., fishing). There is also the potential for enhancement of upland recreational and aesthetic opportunities, such as walking paths and scenic lookout areas.

Cultural Resources

Since removal of the dam would require federal permitting (i.e., the US Army Corps of Engineers (USACE) Section 404 review), this project will require review under Section 106 of the National Historic Preservation Act (NHPA) (as amended) and its implementing regulations (36 CFR 800). It will also be reviewed by the NYS SHPO in coordination with the Section 106 review. Typically, this process would involve conducting a Phase 1A archeological reconnaissance survey, identifying the area of potential effects (APE), determining whether or not there will be adverse effects to historic or archaeological resources, and consulting with SHPO to reach concurrence on the findings and recommendations. The process would likely culminate with the development of a Memorandum of Agreement (MOA) which is typically an agreement between the dam owner, lead agency and SHPO. The MOA would include mitigation requirements, such as archeological monitoring and recordation during construction, photographic documentation, interpretive signage, etc.

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Operation and Maintenance

Dam removal would eliminate ongoing operation and maintenance efforts and costs.

4 Permitting Requirements

4.1 Regulatory Review Process

Table 3.5-1 below provides a summary of regulatory submittals, reviews, and permits that are anticipated to be required for this project.

Table 4-1: List of Anticipated Required Regulatory Submittals/Reviews/Permits

The following permits were determined to be applicable for the reasons described below.

Section 106 Historical Review (SHPO) –SHPO requires publicly-funded projects to be reviewed for potential effect on historic properties. This project utilizes State funding and therefore a historic review is a requirement. Gomez and Sullivan preliminarily determined that the dam is listed on the National Register of Historic Places. This was ascertained by an online database search of the Cultural Resource Information System (CRIS). Formal consultation with SHPO has not been conducted at this stage of project development, however it is recommended that this consultation be performed during the initial stages of Phase Two.

Pre-Application Consultation (NYSDEC) – Although optional, due to the complexity of this project it is strongly encouraged that a pre-application conference be scheduled early in Phase Two. This meeting with NYSDEC allows the Village to clarify project objectives and obtain the Agency's recommendations.

Such feedback can improve the project environmentally and shorten the application procedure.

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State Environmental Quality Review (NYSDEC) – State funded grant programs are subject to requirements of the State Environmental Quality Review Act (SEQR). SEQR requires all local, regional, and state government agencies to equally examine the environmental impacts along with the social and economic considerations for a certain project during their discretionary review. It is presumed that this project will be considered an Unlisted Action and will require a determination of significance, and depending on the potential impacts, may necessitate a Short Environmental Assessment Form (SEAF). A Draft Environmental Impact Statement (DEIS) is not anticipated for this project at this time.

Joint Application Form – This covers both State (NYSDEC) and Federal (USACE) Agency permit applications, and since the project will potentially affect streams, waterways, and/or wetlands, it will be required. For NYSDEC, it is presumed that the permits that will be required include Stream Disturbance, Excavation and Fill in Navigable Waters, Dams and Impoundment Structures (see below), and 401 Water Quality Certification (including pre-filing and supplemental forms). For USACE, Section 404 Clean Water Act permit and a General Permit (either NWP 27 or 53) should be requested.

Dam Safety Permit (NYSDEC) – Supplement form D-1. B “Application for Permit for the Breach/Lowering of a Dam or Other Impoundment Structure” will be required as part of the Joint Application given the nature of the proposed project.

Stormwater Permit for Construction Activity {SPDES} (NYSDEC) – Any construction activity that will involve soil disturbance of one or more acres must obtain coverage under the State Pollutant Discharge Elimination System (SPDES) General Permit for Stormwater Discharges from Construction Activity, succinctly referred to as the Construction General Permit (CGP). Although it is not anticipated at this time that the one-acre threshold will be triggered, the final acreage must be determined once the project design is better established. At a minimum, erosion and sediment controls will be required.

Application fees are not anticipated.

4.2 Impacts on Construction Schedule

Removal Timing

Some facets of dam removal implementation may be feasible during a range of flows in nearly any season.

In general, however, instream work should occur during low flow conditions, typically between June and September, to minimize impacts on fisheries and water quality and to facilitate water control during construction. To protect fish spawning, a time-of-year restriction may be imposed by NYSDEC for all instream work as well as any adjacent work that may result in suspension of sediment in a stream.

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5 Construction Budget Estimate

OPCC

A budgetary Opinion of Construction Costs (OPCC) for the dam removal alternative is provided in Table 5-

1. The following base items were included in estimate:

Contractor mobilization/demobilization Access, erosion, and pollution controls Water control Removal of dam Channel improvements

The following alternate items were included in the OPCC only as alternate items to be addressed if required:

Stabilization of remaining abutment walls Addressing impacted utilities Dredging and disposal of contaminated sediment

The OPCC was developed using Department of Transportation (DOT) published weighted average bid prices, R. S. Means Construction Cost Data, and available final costs from comparable projects.

The total budgetary OPCC for dam removal is estimated to cost $1,239,000 (2025 dollars, rounded to the nearest $10,000). Including engineering services required to complete the project (i.e., design, permitting, bidding, and construction phase services), the total project cost is approximately $ $1,640,000. It should be noted that neither an in-depth historical assessment nor a thorough sediment investigation have been completed; thus, by necessity, it requires a wide budgetary range estimate for dam removal.

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Table 5-1: Budgetary Opinion of Probable Construction Cost for Dam Removal

ITEM COST

BASE ITEMS

1 Mobilization/Demobilization (10% of Construction Cost, rounded up) $90,000

2 Access, Erosion, & Pollution Control $125,000

3 Water Control $100,000

4 Demolition and Removal Existing Structures $300,000

5 Channel Improvements $199,000

ALTERNATE ITEMS

6 Stabilization of Existing Abutments $75,000

7 Utility Work $50,000

8 Dredging & Disposal of Contaminated Sediment $300,000

Total Construction Cost $1,239,000

PHASE 2 ENGINEERING COSTS

P2-1 Engineering Design $150,000

P2-2 Resource Delineation $20,000

P2-3 Sediment Investigation $30,000

P2-4 Cultural Resources Survey & Mitigation $50,000

P2-5 Permitting $50,000

Total Phase 2 Cost $300,000

Phase 3 Engineering Services during Bid & Construction

Total Phase 3 Costs $100,000

TOTAL OPINION OF PROBABLE CONSTRUCTION COST

$1,640,000 (rounded up to the nearest $10,000)

Cost Comparison using Dam Removal Cost Model

The budgetary OPCC for dam removal was compared to an estimate from a Dam Removal Cost Estimator online screening tool developed by the USGS and others in 20232. The tool was developed based on a database of hundreds of previous dam removal project costs throughout the country along with project information such as dam and watershed size, region, and various “complexity factors” (e.g., sediment contamination, infrastructure impacts, channel construction, etc.). The tool provides a range of estimated costs in 2020 dollars (the year all project data were normalized to), which were then escalated to 2027 dollars based on historical R.S. Means construction cost indices.

Based on the USGS Dam Removal Cost Model, it is estimated that removal of the Lower Dam will cost between approximately $650,000 and $1,900,000 (2027 dollars), depending on a number of complexity

2 Duda, J.J., Jumani, S., Wieferich, D.J., Tullos, D., McKay, S.K., Randle, T.J., Jansen, A., Bailey, S., Jenson, B.L., Johnson, R.C., Wagner, E., Richards, K., Wenger, S.J., Walther, E.J, and Bountry, J.A. (2023). Patterns, drivers, and a predictive model of dam removal cost in the United States. Frontiers in Ecology and the Environment. 11. doi:

10.3389/fevo.2023.1215471. Screening tool available from:

https://wrises.shinyapps.io/DamRemovalCostPredictiveModel/ https://wrises.shinyapps.io/DamRemovalCostPredictiveModel/

Mill St. Dam Removal 15 Final Report factors such as sediment contamination, required sediment dredging and/or stabilization, infrastructure protection, water control, etc.

6 Next Steps

The following is a summary of Phase Two: Collection of Site data to support final design (e.g., sediment investigation, wetland delineation); Preparation of Plans and Specifications for Demolition/Construction of the Selected Option, Preparation of Permit Applications and Permit Submission

Phase Three: The Removal of the Dam, Site Reclamation Work and Stream Restoration

Recommended major next steps for Phase 2 of the project are as follows:

Additional Modeling – the hydraulic model will be used to more fully evaluate the impact of the proposed project on Chittenango Creek and Cazenovia Lake. This would include: (1) modeling of dam removal together with the particular creek channel improvements designed for this site in Phase 2,

(2) evaluation of alternative programs for managing the level (water surface elevation) of Cazenovia Lake, with the goal of further reducing the magnitude and occurrence of backflow beyond that which is achieved by dam removal alone, (3) modeling of improvements to the Chittenango Creek channel that are designed to mitigate the increases in downstream creek elevations that were found to result from dam removal (Appendix A).

Resource Delineation – A formal wetland delineation would be needed to quantify the size, type, function, and value of the wetlands within and adjacent to the impoundment. A vegetation inventory should be performed to determine existing fauna and likelihood of invasive encroachment, if invasives currently exist at the site. Additionally, state and federal agencies should be consulted to identify any potential rare, threatened, or endangered species in the project vicinity.

Cultural Resources Survey – It will be important to initiate planning efforts to mitigate potential impacts to historic and/or archeological resources as early as possible in the process. As such, a Phase IA cultural resources reconnaissance investigation is recommended to initiate Section 106 consultation for the project.

Sediment Investigation and Sampling – A sediment depth investigation would be needed to determine the presence and estimated quantity of sediment in the impoundment. Depending on the volume and characteristics of the sediment that may be impacted by the removal of the dam, sediment testing may be required. However, a due diligence investigation indicates that there is a low likelihood of contamination. Please refer to Appendix C for the Preliminary Sediment Contamination Due Diligence Review. It is recommended that before any additional design or permitting is initiated, a round of sediment sampling be conducted. A sampling plan should be developed in consultation with and approved in writing by the NYSDEC prior to sample collection.

Sediment Management Plan – A critical cost-driver for the project will be the extent (if any) of sediment contamination in the impoundment and upstream/downstream reference areas, which will dictate the need for active versus passive sediment management. A sediment management plan should be developed in consultation with NYSDEC.

Outreach, Design, and Permitting – Downstream property owners and relevant municipalities should continue to be engaged in the design process. Once the sediment management approach is determined, permit-level design plans would be developed and permit applications would be completed and submitted. Support for seeing these applications through to approval would be

Mill St. Dam Removal 16 Final Report provided. Plans and specifications for dam demolition, site rehabilitation, and stream channel improvements will be completed and will serve as the basis for competitive bidding by contractors to complete this work.

Schedule

If the Village elects to proceed with the dam removal, the items discussed above would need to be addressed in addition to developing detailed calculations, drawings, and specifications. Upon completing preliminary engineering, the agency consultation and permitting will need to be completed. The permitting phase can take at least a minimum of six (6) months, although given the historic nature of the structure this will likely require additional time. Once the agencies have approved the design and the design package is finalized, and the project can go out to bid; it is assumed that contractors can be under contract within a couple of months. The hired contractor will have a more accurate schedule, but it is assumed that the construction can be completed between three (3) and five (5) months. A summary of the anticipated timeline is provided in Table 7-2 below.

Table 7-2. Approximate Timeline for Dam Removal

Task and Phase Approximate Timeline

Dam Removal

Preliminary and Final Engineering Design (Phase 2) 12 months

Permitting (Phase 2) 6+ months

Bidding/Contracting (Phase 3) 2 months

Construction (Phase 3) 3-5 months

TOTAL 2-3 years

Note, this schedule does not take into account the timeframe that may be required to secure grant funding, nor does it factor in time of year work restrictions for in-water construction to protect fisheries.

Mill St. Dam Removal A-1 Final Report

Appendix A – H&H Memos

Mill Street Dam Removal 1 Summary Memo Hydrologic and Hydraulic Modeling September 2024

M E M O

TO: Project Advisory Committee (PAC)

FROM: Jennifer Wesolowski, PE, GSE, DATE: September 2024

SUBJECT: Mill Street Dam Hydrologic and Hydraulic Modeling

The Mill Street Dam is the lower of two dams operated and maintained by the New York State Canal Corporation (NYSCC). For consistency with NYSCC terminology, this memo herein refers to the Mill Street Dam as the Lower Dam. The Cazenovia Lake Association desires to assess whether modifications to the Lower Dam may reduce the occurrence of backflow into Cazenovia Lake. This memo outlines the development of hydrologic and hydraulic models and potential modifications to the Lower Dam. The modifications to the Lower Dam were assessed with respect to their potential impact on the occurrence of Cazenovia Lake backflow events, and flood risk for the Village of Cazenovia, as well as impacts to aquatic habitat, recreational use, and erosion along Chittenango Creek. All elevations in this memo refer to the North American Vertical Datum of 1988 (NAVD88).

1. Hydrologic Model Development

A hydrologic model was developed using version 4.11 of the United States Army Corps of Engineers (USACE) Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) computer software. The hydrologic model includes the entire drainage area upstream of the Lower Dam, with a separate basin for Cazenovia Lake and its drainage area. Table 1.0-1 provides an overview of pertinent parameters for each subbasin. The drainage area for each subbasin was developed from a digital elevation model (DEM) from the United States Geological Survey (USGS) that was based on a 2015 Light Detection and Ranging (LiDAR) collection for Madison and Otsego Counties, New York. Rainfall infiltration was simulated using the Soil Conservation Service (SCS) Curve Number (CN) methods, with CN and percent impervious area developed based on the 2021 USGS National Land Cover Database (NLCD) and the 2019 United States Natural Resources Conservation Service (NRCS) Soil Survey Geographic (SSURGO) database for Madison County, New York. The Snyder unit hydrograph technique was used to simulate basin runoff using an average peaking coefficient appropriate for the Appalachian highlands and a lag time computed using the methodology from NRCS Technical Release 55: Urban Hydrology for Small Watersheds (TR-55). The recession method was utilized to define baseflows, with a discharge per area for initial discharge and ratio to peak for initiating the recession constant. The initial discharge, recession constant, and ratio are based on common values used in this area of the country for uncalibrated models.

Rainfall depth-duration-frequency information was obtained from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14, while the distribution of rainfall over a 24-hour period was obtained from Extreme Precipitation Analysis interactive webtool developed by the Northeast Regional Climate Center (NRCC). Table 1.0-2 summarizes the precipitation information utilized. The hydrologic model utilizes a computational time interval of six minutes. While the hydrologic model was not calibrated due to the unavailability of sufficient data, hydrologic model results were compared to estimates using the USGS

Mill Street Dam Removal 2 Summary Memo regional regression equations methodology. The peak flows produced by the hydrologic model for the overland subbasin were within the standard error associated with the peak discharge estimated by the regional regression equation for a drainage area just upstream of where Cazenovia Lake discharges to Chittenango Creek.

2. Hydraulic Model Development

A combined one-dimensional/two-dimensional (1D/2D) hydraulic model was developed using version 6.5 of the USACE Hydrologic Engineering Center River Analysis System (HEC-RAS) computer software. A previous 1D hydraulic model was provided by the New York State Canal Corporation (NYSCC) and was utilized, with minor modifications, from approximately 125 feet below the Lower Dam to approximately 6,700 feet downstream of Lower Dam. The geometry and Manning’s roughness for the most upstream cross section was modified to provide consistency with the 2D cells to which it is attached. Additionally, the exit loss coefficient for the culvert at the Treatment Plant Road was changed from 1 to 0.5 to address hydraulic model stability issues. The 2D portion of the hydraulic model extends from approximately 125 feet below the Lower Dam to Cazenovia Lake (approximately 1,550 feet upstream of the Upper Dam), as well as approximately 2,900 feet of Chittenango Creek upstream of its confluence with the Cazenovia Lake outlet. The LiDAR derived DEM utilized for the hydrologic model was modified to incorporate bathymetric data collected during this study and assumed a triangular channel shape for reaches in between areas of data collection. This modified DEM is used to define many of the geometric features in the 2D area. The 2D area uses 25-foot computational cell size with a handful of breaklines to delineate cell faces along natural high ground. Additionally, the 2D area simulates weir and gate flow at the Upper Dam and Lower Dam. The 2D area does not include the Chenango Street bridge as no scenarios were simulated for which the low chord is impacted and the abutments are sufficiently accounted for within the modified DEM. The 2D area does not include the Forman Street bridge as preliminary results indicated that while it may influence the peak backflow discharge it did not affect whether or not backflow occurred. The 2D area is also connected to a storage area representing Cazenovia Lake. The stage-storage rating curve used for the Cazenovia Lake was based on a fishing contour map from the New York State Department of Environmental Conservation (NYSDEC).

Initial water surface elevations within Cazenovia Lake and the 2D area (using initial condition points) were defined for each simulation as appropriate, with an initial flow within Chittenango Creek being 100 cfs (i.e., approximately equal to the expected average daily flow). Similarly, time series gate openings were used to define the operation of gates at the Upper Dam and Lower Dam. The hydraulic model uses the same normal depth downstream boundary condition as the previous NYSCC model. Simulations were evaluated with a 15 second computational time step, and the default computational settings were generally utilized. However, similar to the previous NYSCC model, the 1D Mixed Flow Regime option was turned on to address hydraulic model stability issues. Additionally, the weir flow submergence decay exponent was increased from 1 to 2 to address significant oscillations in flow when the tailwater is approximately equal to the headwater at Upper Dam and the “maximum iterations between 1D and 2D” setting was changed from zero to 20 to address significant flow and water level oscillations at the 1D/2D interface.

Observations from the April 6, 2023 and May 1, 2023 events were simulated in an attempt to validate the hydraulic model. The observed flow hydrograph from USGS Gage No. 04244000 (Chittenango Creek near Chittenango, NY) was scaled based on drainage area and used as inflows for Cazenovia Lake and the upstream extent of Chittenango Creek in the 2D area. Flows were held steady for the initial 24 hours of the simulation to ensure water levels had stabilized throughout the hydraulic model. The initial level of

Mill Street Dam Removal 3 Summary Memo

Cazenovia Lake and gate settings for the Upper Dam and Lower Dam were obtained from records provided by the NYSCC. While the hydraulic model simulated that backflow occurred for both events, backflow was only documented for the May 1, 2023 event. It is possible that backflow occurred for the April 6, 2023 event, but was just not observed, as the hydraulic model indicates that backflow conditions lasted for about four hours. It is also possible that scaling the hydrograph from the gage is not a valid assumption.

NOAA records indicate that rainfall was spread fairly evenly across the entire USGS gage drainage area during the May 1, 2023 event. However, NOAA records indicate that more intense rainfall occurred within the USGS gage drainage area downstream of the Lower Dam during the April 6, 2023 event, which suggests that scaling the hydrograph may not be appropriate for this event. In order to better validate the hydraulic model, more detailed hydrologic modeling would be required. The detailed hydrologic modeling would require sub-daily rainfall records, which may be difficult to obtain, an extension of the hydrologic model to include the entire drainage area of the USGS Gage, and modification of the hydrologic model to include routing of flows through Cazenovia Lake and along Chittenango Creek. Such hydrologic modeling was outside of the scope of this study. However, the hydraulic model is considered sufficient to address the primary objectives of this study relative to backwater, flood risk, and other impacts related to modifications at the Lower Dam.

3. Production Runs

The following sections describe the Lower Dam modification alternatives considered and the associated impacts on various resources for each alternative. The NYSCC operates the gates at these dams differently during Navigation Season (Mid-May to Mid-October) and Non-navigation Season (Mid-October to Mid- May), causing the elevation duration curves for Cazenovia Lake to differ for each season. Therefore, this study utilized up to three different initial elevations for Cazenovia Lake representing high (5% exceedance), median (50% exceedance), and low (95% exceedance) levels for each season.

3.1 Alternatives Considered

This study evaluated existing conditions along with three potential Lower Dam modifications (i.e., Lowered Crest, Partial Removal, Full Removal) as described below.

3.1.1 Existing Conditions

Both the Upper Dam and Lower Dam convey water via a spillway and three gates. During the navigation season, the gates at the Upper Dam are minimally open, while two of the gates at the Lower Dam are fully open with stop logs placed to maintain water depth in the upstream channel under low flow conditions with the third gate being fully closed. This third gate is opened fully during a large storm event. During non-navigation season the gates at the Upper Dam are opened slightly to slowly draw Cazenovia Lake to approximately six inches below the Upper Dam crest, while all gates at the Lower Dam are fully opened (without any stop logs in place).

3.1.2 Lowered Crest

This alternative considered a scenario where the Lower Dam was reconstructed to have a single spillway spanning the entire length of the structure, which would require the removal of the existing gate and sluice structures. The crest of this new spillway would be about 2.75 feet lower than the existing spillway crest. This alternative made no alterations to the Upper Dam structure or operations. This alternative is intended to provide increased discharge capacity relative to existing conditions while maintaining water depth in the upstream channel under low flow conditions.

Mill Street Dam Removal 4 Summary Memo

3.1.3 Partial Removal

This alternative considered the partial removal of the Lower Dam in which the spillway is removed completely, with the gate and sluice structures remaining in place, and the gates fully open. This alternative made no alterations to the Upper Dam structure or operations. This alternative is intended to provide increased discharge capacity relative to existing conditions while preserving some of the historical structure.

3.1.4 Full Removal

This alternative considered the full removal of the…