Pjw. Roberts et Wh. Snyder, HYDRAULIC MODEL STUDY FOR BOSTON OUTFALL .2. ENVIRONMENTAL PERFORMANCE, Journal of hydraulic engineering, 119(9), 1993, pp. 988-1002
Hydraulic model tests were done on the Boston Harbor out fall diffuser
with the number of risers and their spacing maintained constant at th
eir final design values. It was found that eight ports per riser resul
ted in higher dilutions than 12, because with 12 ports the plumes merg
ed and collapsed to a single rising column. Extended duration tests sh
owed that the waste field was stable, that its thickness increased ver
y slowly with time, and that dilution decreased very slowly with time.
The flux-average dilution was estimated from the movement of dye stre
aks to be only 1.1-1.2 times higher than the minimum dilution, a much
smaller ratio than usually assumed. The mathematical model ULINE was f
ound to be generally conservative in predicting dilution. Better predi
ctions were obtained with a new mathematical model RSB, which well sim
ulated the observed waste-field characteristics for the final design.
The effect of varying the number of risers was not so well predicted b
y RSB, however, due to the very large effective port spacing for this
diffuser. Thus, hydraulic model tests are still needed for atypical di
ffuser designs, such as encountered here.