ASCE Northern Colorado Branch and CSU ASCE Joint Meeting for November 

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Please join us as we hear from Dr. Chris Thornton about a unique reservoir expansion project for Denver Water near Boulder, Colorado. Gross Reservoir near Boulder, Colorado

Physical Modeling in Support of the Gross Reservoir Expansion Project

Denver Water's Gross Reservoir Expansion (GRE) Project is located on South Boulder Creek near Boulder, Colorado. The objective of the GRE Project is to increase the storage capacity of Gross Reservoir from approximately 42,000 acre-feet to about 119,000 acre-feet. Expansion will be accomplished by raising the existing 340-foot high Gross Dam by 131 feet to an ultimate height of 471 feet, resulting in the highest stepped spillway in the United States.

 Physical modeling was performed, at a 1:24 (model: prototype) length scale to support the design, and optimization, of the Gross Dam spillway. The spillway design included physical characteristics that were atypical and generally beyond the criteria presented in industry design procedures. This included a stepped spillway chute on an arch dam with a downstream slope of 0.5 horizontal to 1 vertical (0.5H:1V) with converging chute walls. Site conditions dictate the need to hold the location of the existing spillway toe in the proposed raise and existing infrastructure requires the stilling basin contain and control the hydraulic jump.   The initial stilling basin design was based on a Reclamation Type III hydraulic jump stilling basin (USBR, 1987) incorporating super-cavitating blocks. Physical modeling showed uncharacteristic performance of the preliminary Type III basin and demonstrated the need to move the baffle blocks significantly farther upstream to effectively contain the hydraulic jump inside the basin and thus properly dissipate the energy.  Further testing also showed that the overall length of the stilling basin could be significantly reduced while maintaining required hydraulic performance. This presentation will provide a summary of the initial design development, the physical hydraulic model results, the unique hydraulic characteristics of the basin with the steep approach spillway chute, and the corresponding design modifications implemented based on the physical model results.

Presenter:  Dr. Chris Thornton

Chris Thornton, P.E., PhD.  Director, Hydraulics Laboratory.  Colorado State University.  Fort Collins, CO 80525

970-214-3902, cit@colostate.edu

Chris is the Director of the Hydraulics Laboratory at Colorado State University.  He received his PhD in Hydraulics at Colorado State and is a registered Professional Engineer in the state of Colorado.  He has over 25 years of experience in conducting hydraulic model studies and has specialized in steep slope, high energy, supercritical flow conditions and performing prototype performance tests on engineered protective techniques.  Dr. Thornton has been instrumental in the development of industry standard methods to evaluate articulating concrete block systems and was a technical author of NRCS NEH Part 628 Chapter 54.  Recent collaborations with industry have resulted in multiple physical hydraulic model studies, coupled with 3-D CFD modeling, providing critical design support and project optimization.  Physical hydraulic model construction techniques developed under Dr. Thornton’s direction have proven instrumental in facilitating model modifications and determining design implications.  Dr. Thornton teaches the Senior Design series for the graduating Civil and Environmental Engineering students and has authored and co-authored numerous papers and reports in the area of open channel hydraulics and hydraulic structures.

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Register before the end of the day, Wednesday, November 3, 2022.

Gross Reservoir Expansion