Run-Of-River Dam Construction: A Team Approach to Navigating Changing Waters

ABSTRACT ONLY - Plans are in place, contractor is mobilized, and everyone is excited to start a new multi-million-dollar rehabilitation of a 100-year-old dam on a scenic river in the Adirondacks. What began as an intake trash rack replacement turned into a custom designed dam upgrade with over 1,000 cubic yards of new concrete, a new 40' high trash sluice tower, two new low-level gates, a new trash sluice and rackraker, and much, much more. We conducted preliminary investigations including a sediment survey with bathymetry, sediment samples, record drawing review and site survey to be as prepared as possible. What possibly could change?
We will present our experience leading a recently completed dam rehabilitation project in upstate NY and the factors that influenced design changes during construction. Some of those surprise discoveries included a failure of a bulkhead before construction began, inaccurate record information, inaccurate sediment survey, unforeseen conditions of the structure, unusually heavy flows within the river, public outreach challenges and environmental considerations for the project.
Major contributors to our team's success meeting these challenges included multi-consultant cooperation, on site contractor flexibility, and innovative water control measures within a tight drawdown window. For example, the original water control plan was to use the two low-level outlet gates to continuously convey the seasonal 200 - 400 cfs of natural river flow. While the design worked in theory, the dam was able to pass less water than needed due to required changes in geometry. The team had to adjust by holding back water at an upstream facility and releasing from a downstream facility, leaving this facility 'dry'• for construction work. In addition, the team had to navigate changing financial and schedule projections, while simultaneously gaining the owner's support.
The presentation will explore the intersection of engineering design updates, river hydraulics, and construction schedule as well as financial implications to field decisions made under pressure. We will present lessons learned on how to adapt mid-construction in the field and in the engineering office to keep the project on track and within a budget with the ultimate goal of providing a safe, maintainable dam for your client.