TABLE OF CONTENTS There are various auxiliary hydraulic structures such as junctions, manholes, weirs, siphons, pumps, valves, gates, transition structures, outlet controls, and drop shafts in a sewer network. Information relevant to design of most of these apparatuses are well described in standard fluid mechanics textbooks and references, particularly in the German text by Hager (1994) and Federal Highway Administration (FHWA, 1996). In this section, the most important auxiliary component in modeling the sewer junctions are discussed. For sewers of common size and length, the headloss for the flow through a sewer is usually two to five times the velocity head. Thus, the head loss through a junction is comparable to the sewer pipe loss, and is not a minor loss.
A sewer junction usually has three or four sewer pipes joined to it. Under normal flow conditions, one downstream pipe receives the outflow from the junction and other pipes flow into the junction. However, junctions with only two or more than four joining pipes are not uncommon. The most upstream junctions of a sewer network are usually one-way junctions having only one sewer connected to a junction. The horizontal cross section of the junction can be circular or square or may be another shape. The diameter or horizontal dimension of a junction normally is not smaller than the largest diameter of the joining sewers. To allow the workers room to operate, usually junctions are not smaller than 3 ft (1 m) in diameter. For...
