TABLE OF CONTENTS Various auxiliary hydraulic structures, such as junctions, manholes, weirs, siphons, pumps, valves, gates, transition structures, outlet controls, and drop shafts can be found in sewer networks. Information relevant to design of most of these apparatuses are described in standard fluid mechanics textbooks and references, particularly in Hager (1999) and FHWA (1996). In this section, the most important auxiliary component in sewer flow modeling, namely, the sewer junctions, is discussed. For common sizes and lengths of sewers, the head loss for the flow through a sewer is usually two to five times the velocity head, while the junction loss is in the order of approaching velocity head. Thus, the head loss through a junction is comparable to the sewer pipe loss, not a minor loss.
A sewer junction usually has three or four sewer pipes joined to it. Under usual flow condition, 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 in a sewer network are usually one-way junctions, having only one sewer connected to the junction. The horizontal cross-section of the junction can be circular, square, or another shape. The diameter or horizontal dimension of a junction normally is not smaller than the largest diameter of the joining sewers. In order to allow the workman room for operation, usually junctions are not smaller than 3...
