NEED FOR NEW STANDARDS TO PREVENT DEPOSITION IN WASTE-WATER SEWERS

Both self-cleansing-velocity and minimum-shear-stress approaches have been used to investigate the effect of the relative ow depth in a sewe r as an important factor influencing the buildup of deposits in a sewe r designed for full flow. Each of the approaches indicates favorable d eposit-free flow conditions for sewers with relative-normal flow depth s ranging between 0.5 and 1.0. For relative flow depths well below 0.5 the same sewers show a strong tendency to form deposits. Nomographs h ave been developed for circular sewers partially clogged by deposits f or easier computations of flow depths. Shear stresses in partially clo gged sewers have been computed and discussed in relation to deposit th ickness; the study here is limited to initiation criterion only.