Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Civil and Environmental Engineering


Dean F. Peterson


An experiment was designed to eliminate the free surface from simulated naturally roughened open channel beds from which results were compared to data with a free surface from another study. All other pertinent variables were held constant. From this comparison, a relationship was established for the additional energy loss due to the presence of a free surface in the flow over these channel beds.
P = 0.23 - 0.28 D/D25
where P is the proportion that the channel conductance coefficient (C/g1/2) is reduced due to presence of a free surface, D is the flow depth, K25 is a measurement of roughness height and D/K25 is the relative roughness and was varied from 1 to 7.

The channel conductance coefficient was found to be non-dependent upon Reynolds number.

A parameter describing bed element spacing was identified as the ratio of vertical projected area of all bed elements to the total bed area, and was found to be constant for a particular channel bed. Roughness spacing had only a minor effect on the channel conductance parameter.

The channel conductance coefficient was related to the relative roughness by a power function and the following prediction equation was established relating the channel conductance coefficient to the relative roughness and spacing parameter:
C/g1/2 = 3.0 (D/K16)0.317 exp(0.007/θ)
where D/K16 is the relative roughness and θ is the spacing parameter.