Dam-Free Micro-Hydro: Summary

Jan Borchert, Current Hydro

Microhydrony.org is dedicated to informing about the viability of micro-hydropower as an attractive renewable energy technology for some of the 6,600+ non-powered dams located across New York State. With this blog post series and the assessment behind it, we are exploring the feasibility of generating electricity using natural elevation changes without a human-made barrier to local and migratory species: dam-free micro-hydropower.

The stream stretch considered as a potential project area for this study has three waterfalls and a historic dam. It is part of the Saw Kill, a small stream east of the Hudson River located in Dutchess County, NY, which runs through the towns of Red Hook and Milan. The Saw Kill is 14.3 miles long and empties into the Tivoli South Bay, part of the Hudson River National Estuarine Research Reserve.

The purpose of this blog series was to present the potential to develop micro-hydropower at locations with a naturally-occurring elevation drops. Dam-free micro-hydro takes advantage of natural drops in elevation, diverting water through a penstock rather than leveraging an artificial barrier like a dam. Of note, most dams have been built on top of naturally-occurring stream elevation changes, so a dam removal site merits an investigation into a dam-free hydro opportunity.

The Micro-Hydropower Feasibility Report further investigated the technical and financial viability of dam-free micro-hydropower on the Lower Saw Kill. It included an assessment of three project location candidates, which led to a technical feasibility evaluation of a dam-free micro-hydropower design and its associated costs at the Second Falls (Site 2).

The report reviewed the extent to which the proposed design could mitigate environmental or social concerns tied to other micro-hydropower proposals at the Lower Saw Kill Dam in previous works for the NYSERDA/Bard microhydro initiative. Provided permitting can proceed using Bard staff or student time, the proposed 40 kW-design is estimated to provide an 8.5-year payback on a capital expenditure of $125,000 generating up to 200,000 kWh annually. Within the Saw Kill setting, a dam-free design alleviates most of the previous concerns with a micro-hydropower system at the Lower Saw Kill Dam. It could help Bard College to meet their ambitious climate goals of carbon-neutrality by 2035.

Dam-Free Hydro in the Saw Kill Setting

The Lower Saw Kill Dam is a good candidate for hydropower with neither flooding nor dam safety concerns, a largely-shaded impoundment in the midst of a forest, and only one migratory species of concern – American eel (with an eel ladder already installed seasonally at the dam). That means many of the concerns associated with existing dams were not an issue in the non-powered design and are neither an issue with the dam-free design at Site 2 (Second Falls).

The main two issues with the non-powered dam design were associated with the project’s long penstock and the ecologically important stream stretch that would have been bypassed by it, i.e. a 620-feet long bypass reach, bypassing parts of the Saw Kill below the first barrier (waterfall), closest to the mouth of the Hudson River. The dam-free design includes a penstock of only about 110 feet and is thus significantly shorter – as is the bypass reach.

The area bypassed is also of less ecological importance than the lowest stretch of the Saw Kill. The dam-free micro-hydropower design bypasses the second waterfall instead of the mouth of the Saw Kill into the tidal Hudson River. But there are other concerns the dam-free system creates that need to be discussed.

Two concerns in particular are new compared to a potential non-powered dam design: aesthetics and recreational concerns. The location of the dam-free system is next to a well-used trail. A trail-side penstock, a turbine system at the waterfall base, and the intake structure at the top will alter the aesthetics of the trail, stream, and waterfall tableau. The level of visual impact depends on the viewer’s aesthetics, of course.

To reduce these visual impacts:

• Designers could place the penstock under the trail bed instead of above ground between the stream edge and trail edge – at least for parts of the length. This approach would make the penstock potentially longer with associated head losses. Burying it may also be more costly than anchoring it to the side of the trail.
• Installing a slightly smaller diameter penstock, perhaps a 16-inch diameter pipe, could minimize installation efforts and visual implications of the penstock.
• An elaborate, attractive powerhouse structure could house the turbine system at the foot of the falls.
• The intake structure at the top of the waterfall could be camouflaged behind natural and/or artificial rocks.

The final system design should address potential concerns about visual impacts and account for these additional costs. To what degree these measures are necessary – especially with the historic concrete pool located right next to the site – is up to the site owner and the opinion of local stakeholders. Bard students use the waterfall and the pond below the fall for swimming in the summer – despite recently installed signs forbidding swimming, fishing and hunting. Bathing could be impacted by operating the hydropower system in the summer, i.e., due to reduced flow over the waterfall, which might reduce the potential hazard and liability concerns associated with students’ injuries from slipping and falling down the waterfall. The system would not affect the pond below the fall as it is the location where the bypassed water re-enters the stream. The hydro system could make this spot less attractive – a benefit or a concern.