The Son River is the largest of the Ganges' numerous numerous tributaries from the Southern Uplands along with the Gandak , Gumti , Ghaghara , and Sarda rivers . They all have a markedly steep gradient (Son with an average gradient of 35-55 cm per km) with quick run-off and ephemeral regimes, being roaring rivers with the rain-waters in the catchment areas but turning quickly into fordable streams. These streams, being wide and shallow, become disconnected pools of water in the remaining part of the year. The channel of the Son is very wide (about 5km at Dehri ) but the flood-plain is narrow, only 3 to 5 km wide. The river has been notorious for its changing courses in the past, as it traceable from several old beds on its east, but has been tamed squarely with the anicut at Dehri, and now more so with the Indrapuri Barrage , a few km upstream.