Increased roughness in reinforced concrete box culverts
by Adam Samuel Hill, M.S.
Washington State University
Chair: Rollin H. Hotchkiss
The purpose of this experimental investigation was to determine the extent to which
trapezoidal-shaped corrugations placed within a barrel of a reinforced concrete box culvert
decreased water velocity within the barrel.
Flow measurements were conducted in a tilting flume in Albrook Hydraulics Laboratory
at Washington State University in Pullman, WA, using a half-scale simulation of the
corrugations expected to be used in the field. Discharges ranged from 24.1-144 L/s and slopes
ranged from 0.3-10.1 percent. Tests were also conducted in a flume in Sloan Teaching
Laboratory using a quarter-scale simulation, where discharges ranged from 13.9-97.1 L/s. The
flume slope was zero. Depths were measured using a point gage at seven different locations in
Sixty-eight tests were used to determine the Manning ‘n’ value. Manning’s ‘n’ is
inversely proportional to the submergence ratio and to the aspect ratio. Experimental errors in
the determination of Manning’s ‘n’ ranged from 4.3-10 percent. Manning’s ‘n’ values for
replication tests were within 3.2 percent of the original test.
Undular jumps did not occur in experimental testing; however, hydraulic jumps did form
in some experiments upon initially reaching the corrugations. The jumps are caused by the
change in critical slope due to the increase in roughness. Three different flow situations were
observed during upstream supercritical flow experiments.
Velocities within the corrugations decreased 44-66 percent compared to upstream
supercritical velocity. Broken-back Culvert Analysis Program (BCAP) outputs compared
reasonably well with experimental results within the corrugations if inputs were set so the
hydraulics at the break were the same as the upstream experimental data. The program suggests
a hydraulic jump will form within the corrugated outlet section of a broken-back culvert.
Velocity data were collected using an Acoustic Doppler Velocimeter (ADV) and
compared with a study by Ead et al. (2000). The velocity profile was found to fit a log law
profile using the Prandtl equation for rough turbulent flow for data points above the corrugation
crest. The shear velocity was 2.9 times higher and the Nikuradse equivalent sand roughness was
100 times higher than values found by Ead et al. (2000).
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:concrete culverts flow meters
Date of Publication: