SEWAGE DISPOSAL IN SHALLOW COASTAL WATERS

Abstract

The disposal of sewage effluent into coastal waters for dilution and final disposal requires an effective mixing of sewage with the seawater in order to achieve the necessary or demanded reduction of bacterial population. Most of the design parameters originate from work done on ocean outfalls. RAWN et al. (I960) developped curves from field data for the determination of initial dilution in a waste issuing from a horizontal port. ABRAHAM (1963) extended these curves to show that the dilution is a function of the depth of discharge port, the diameter of the discharge orifice D and the FROUDE number F. The question, to which extent this calculation method is also valid for outfalls in shallow water regions, is still open. In connection with the actual design of a diffuser in shallow coastal water the method of ABRAHAM was applied together with a new method derived by BERGEN (1980) which is based upon experiments which were carried out in the Leichtweiss- Institute at semi-technical scale. After the diffuser had been taken into operation by means of in-situ measurements the demanded dilution could be checked and herewith also the reliability of the applied design method for practical use.