Chi-Yuan Wei

Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Civil and Environmental Engineering


Gaylord V. Skogerboe


Criterion have been developed in this study for designing a stilling basin to serve as a transition from pipe flow to open channel flow. The purpose of the structure is to prevent erosion in an open channel. The unsteadiness, or smoothness, of the water surface in the model basin was used as the criterion for evaluating the effectiveness of the structure for energy dissipation.

The introduction of a short-pipe energy dissipater in the stilling basin has proven effective in dissipating energy. The stilling basin was designed for a fully submerged pipe outlet. The inflow pipe and the dissipator pipe were designed to be located on the same center line, at Y1/D1=1.5 above the stilling basin floor. The slit-width ratio, W/D1, yielding the smoothest water surface was 0.5 (W/D1=0.5). An optimum dissipator pipe diameter ratio of 2.0 was established (D2/D1=2.0), while the optimum dissipator pipe length ratio was determined to be 1.0 (L/D1=1.0).

Three diameters of inlet pipe were used to determine scale effects. Within the accuracy of the measurements used in this study, no scale effects were detected.

The expanding characteristics of a submerged jet were used in establishing the length of the stilling basin. Based on the dissipator pipe diameter ratio of 2.0 (D2/D1=2.0) the stilling basin length ratio is 3.5 (Lb/D1=3.5).

Relations among the tailwater depth (dt), the outlet flume floor elevation (Y2), the height of boils in the stilling basin (hb), the width of the stilling basin (Wb),and the amount of freeboard, fb, have been studied. The interrelationships among F1, (Y2+dt)/D1, Wb/D1, and fb/D1 have been shown graphically.