Mathis Dam Spillway

The Mathis Dam Spillway project highlights Alden’s integrated hydraulic and structural engineering services in which there was close collaboration between hydraulic modeling, hydraulic design, and structural design experts.

Alden used numerical modeling and physical modeling to evaluate the discharge capacity and pressure distribution on the surface of the Mathis Dam spillway, and as a result, Alden developed a spillway shape modification that eliminated the negative pressures on the spillway. These spillway modifications were designed and detailed and approved by FERC in May 2018.

Project Summary

• Mathis Dam is an Ambursen-style dam built in 1915, using a slab-and-buttress type construction. It's Existing spillway does not follow an Ogee profile. As a result, there were concerns with negative pressures on the spillway face and the peak reservoir stage during the Probable Maximum Flood (PMF).
• Alden used numerical modeling to assess potential changes in the spillway capacity and reservoir levels resulting from spillway gate replacement. Numerical modeling showed that surface pressures were low enough to lift the spillway slabs and adversely affect spillway performance.
• Based on the results of the numerical modeling, a 1:15 physical model was constructed. The physical model was used to confirm negative pressure results and to develop modifications (ventilation step) to eliminate the negative pressures.
• Alden provided structural design, plans, and documentation for the spillway modifications. The design was submitted to FERC and approved with no comments.
• Construction for the spillway modifications is scheduled for fall 2019