Submerged Discharges of Dense Effluent

An analytical and experimental study of discharge of dense fluid is conducted. Of interest is the near field dilution obtained by a multiport diffuser structure located on the bottom of the water body and consisting of vertical ports extending above the bottom and spaced equally along a line perpendicular to a steady receiving water current. Experiments are performed in a laboratory flume in which a single dense jet with varying discharge and cross flow condition are studied. Some two dimensional two layer flows obtained by multiport discharges are also studied. On the bases of the laboratory investigations, the near field is separated into four regions; the jet region; impact region; upstream region and downstream region. Empirical equations for dilution and geometry of the jet based on dimensional analysis are obtained for the jet region. A previously developed two dimensional theory for the water depth in a channel below free overfalls is applied to the impact region to provide a boundary condition for the analysis of the upstream wedge region. The observed behavior of the upstream wedge is found to correspond to frictional two-layer flow theory. Application of the results to an actual design is possible if the effluent flow rate and density, receiving water depth and current ranges are known. A design procedure is developed for choosing the port diameter, discharge velocity, port spacing and port height to meet a specified level of near field mixing

Frame:for soprano sax, bass clarinet and tape

1. In eutrophic lakes, large amounts of the cyanobacterium Microcystis may overwinter in the sediment and re-inoculate the water column in spring. 2. We monitored changes in pelagic and benthic populations of Microcystis in Lake Volkerak, The Netherlands. In addition, sedimentation rates and the rate of recruitment from the sediment were measured using traps. These data were used to model the coupling between the benthic and pelagic populations and to calculate the contribution of overwintering benthic and pelagic populations to the magnitude of the pelagic summer bloom. 3. Changes in the benthic Microcystis population showed a time lag of 314 weeks compared with the pelagic population. This time lag increased with lake depth. The largest amount of benthic Microcystis was found in the deepest parts of the lake. These observations suggest horizontal transport of sedimented Microcystis from shallow to deep parts of the lake. 4. Recruitment from and sedimentation to the sediment occurred throughout the year, with highest recruitment and sedimentation rates during summer. Model simulations indicate that the absence of benthic recruitment would reduce the summer bloom by 50%. 5. In spring, the total pelagic population was three to six times smaller than the total benthic population. Yet, model simulations predict that the absence of this small overwintering pelagic population would reduce the summer bloom by more than 64%. 6. Reduction of the overwintering pelagic populations, for instance by flushing, may be a useful management strategy to suppress or at least delay summer blooms of Microcystis. [KEYWORDS: harmful algae ; Microcystis ; model ; population dynamics ; recruitment ; sedimentation]