Optimization of the Baffle Geometry of a Circular Culvert Outlet Structure to Maximize Energy Dissipation

Authors

• Kiarash Shirmahi, University of Nebraska-LincolnFollow

First Advisor

David Admiraal

Committee Members

Tirthankar Roy, Yusong Li

Date of this Version

5-2026

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Civil Engineering

Under the supervision of Professor David Admiraal

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Kiarash Shirmahi. Used by permission

Abstract

High-velocity flow at culvert outlets can lead to significant soil erosion and damage to downstream infrastructure, particularly in agricultural regions where land protection is critical. Circular culverts, commonly used in transportation systems, are especially susceptible to this issue due to flow acceleration caused by geometric constraints and installation angles. Despite extensive research on energy dissipation in rectangular culverts, limited attention has been given to circular configurations. This study addresses this gap by evaluating the hydraulic performance of baffle systems designed to reduce outlet energy in circular culverts.

A series of laboratory experiments was conducted using a scaled physical model of a circular culvert system, including an inlet, sloped pipe, and outlet dissipation structure. In a previous project, two configurations were investigated: full-width weirs and staggered baffles. Results from the initial phase demonstrated that staggered configurations provide superior energy dissipation compared to full-width weirs, with optimal performance observed at a baffle height of 0.5 pipe diameters. Building on these findings, a second phase introduced an enhanced experimental setup with adjustable baffle positioning and expanded hydraulic conditions, enabling evaluation across a wider range of geometries, flow rates, and Froude numbers.

The results indicate that optimal baffle placement is flow-dependent. The central baffle performs most effectively at approximately 0.7 pipe diameters downstream of the outlet under low-flow conditions and shifts further downstream at higher discharges, while side baffles exhibit optimal performance at approximately 1.6–1.7 pipe diameters at higher discharges and 0.2 pipe diameters far from the central baffle under low-flow conditions. These findings highlight the importance of both geometric configuration and hydraulic conditions in maximizing energy dissipation.

One limitation identified is the non-uniform velocity distribution at the culvert outlet, which complicates accurate energy estimation. Ongoing work incorporates computational fluid dynamics modeling to better characterize flow structure and determine appropriate energy correction factors. The outcomes of this research provide practical guidance for optimizing baffle design in circular culverts and improving erosion control in transportation infrastructure.

Advisor: David Admiraal