Jan Borchert, Current Hydro

Now that we’ve covered the basics of dam-free micro-hydropower, it’s time to assess the potential sites the Lower Saw Kill has to offer. As mentioned in an earlier post, there are three waterfalls that could be potential dam-free micro-hydropower projects.

The three potential sites are:

  1. The lower falls, between the mouth of the Saw Kill and the Lower Saw Kill Dam
  2. The second falls, above the Lower Saw Kill Dam and next to the Mushroom Farm/Swimming Pool
  3. The upper falls, just downstream of the “Annandale Triangle” (of Annandale Rd. and River Rd.)

Due to their proximity to one another the drainage area can be assumed to be identical and thus offer the same amount of flow and identical flow patterns, with a median flow of 24.7 cubic feet per second (CFS) and more than double that (50.9 cfs) in 25% of the time.

iStream Flow, cfsiStream Flow, cfs
Flow Duration Estimates at the Lower Saw Kill

None of the sites has existing infrastructure like intakes, penstocks, or potential powerhouses. So much for the similarities; let’s look at the differences.

Site 1: Lower Falls

Site 1 Location

Site 1 is located about 195 feet from the mouth of the Saw Kill. The waterfall stretches over 170 feet and offers a total elevation change of about 38 ft. Minor rapids at either end of the falls are not included to minimize bypass reach.

Lower Falls Upstream View
Lower Falls Upstream View
Lower Falls Drone Image
Lower Falls Drone Image

The site offers two natural intake locations where the stream splits on top of the waterfall as well as a possible bypass channel on the southern side of the stream. The possible bypass channel could also be the location of the penstock if used or serve as a tailrace.

Site 1 Access

The site is rather difficult to access: the southern side of the waterfall can only be accessed over a hilly and forested trail, the northern side only over a steep slope down from Bay Road Access from the south is preferable for this mostly-manual installation as the installation team could transport materials close to the old powerhouse, and from there, carry to the site – over a distance of about 150 feet.

Site 1 Concerns

The waterfall of Site 1 connects the tidal and the non-tidal parts of the Saw Kill. This means that a potential dam-free micro-hydropower system needs to account for the densely populated and diverse populations of the downstream habitat: minimizing the bypass reach, tailrace screening, and other thoughtful ecological protection devices and methods.

Another concern with Site 1 is that its waterfall is visible from local hiking trails, specifically the Montgomery Place trails. While some people are fascinated by technology and proud of installations that help society fight climate change, others prioritize the untouched beauty of a waterfall. The design would need to be a compromise between functionality and aesthetics.

Site 2: Second Falls

Site 2 Location: Site 2 is located about 465 feet upstream of the Lower Saw Kill Dam. The waterfall stretches over 185 feet and offers a total elevation change of about 26 feet. The site includes an additional rapid on top of the waterfall which provides a potential site for an inlet. This site historically hosted an inlet structure that fed the swimming pool located north of the waterfall about three quarters up the waterfall.

Second Falls Upstream View
Second Falls Upstream View
Second Falls Drone Image
Second Falls Drone Image

Site 2 Access: Site 2 can be accessed from the north side of the Saw Kill via a maintenance road close to the waterfall. Access from the south is not an option.

Site 2 Concerns: None, though there could be objections regarding the visibility and aesthetics of the project.

Site 3: Upper Falls

Site 3 Location: The Upper Falls are located over 1,800 feet upstream from the Second Falls and about 720 feet downstream from the River Road Bridge into Annandale. The falls are hidden right behind Bard College’s Shafer House (visible in the picture below) and not easily accessible via public trails.

Upper Falls Upstream View
Upper Falls Upstream View
Upper Falls Drone Image
Upper Falls Drone Image

Site 3 Access: The site can be best accessed via Cedar Hill Rd. from Annandale Road, starting at the parking lot in front of Shafer House, proceeding to the area between the waterfall and the flood retention wall by foot. Small machinery for light construction could access the site with minimal clearing. The falls drop about 14 feet over less than 8 meters.

Site 3 Concerns: While from a technical point of view, Site 3 is an ideal side, the major issue with Site 3 is that Bard College does not own the northern part of the stream right below the waterfall. The property not owned by Bard College has a house sitting close to the waterfall, and any type of installation might be visible from there. A potential installation might need an easement with the adjacent property owner as any type of equipment likely would be installed on the side of the stream. The feasibility of this easement has not been assessed as part of this report.

Site Comparison and Conclusion

Based on the above assessment, all three sites offer the technical parameters necessary to install a dam-free micro-hydropower system. As none of the sites offer an upstream lake that could allow for a fully submerged intake structure, systems would likely have to divert a part of the stream at the top, or catch water close to the top of the waterfall for an intake structure. Beyond these commonalities, the ranking of the site looks as follows:

  • The least favorable site is Site 1 at the lower falls, mainly due to its environmental importance, but also difficulties in access and placement of the actual facility.
  • Site 3 is more accessible and doesn’t have the same environmental relevance as Site 1. However, some kind of arrangement needs to be made with the neighbor to make any kind of development possible; without all the property rights a development decision cannot be made at this point in time.
  • That leaves Site 2 as the best choice for a more detailed feasibility study: better site access and fewer environmental concerns than Site 1, and all related rights belong to Bard College alone.

It is recommended to further assess Site 3 for dam-free micro-hydropower development and to start a conversation with the neighboring property owner about the potential for hydropower generation.

Next we will discuss the Lower Saw Kill Feasibility of Dam-Free Micro-Hydro.


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