$120$

$3.$ An elevated tank with a fixed water level of $67$ m supplies water to the distribution network shown in Figure $1.$ The network has $5$ pipes with the following parameters: Length $=450m,$ Hazen$-$Williams $\text{'}$ C $\text{'}$ factor $=110,$ and Diameter $=305mm.$ The $2$ demand nodes in the network are at an elevation of $9$ m $.$ The demand at the $2$ demand nodes are: $Q_2=200\frac{L}{s}$ and $Q_3=50\frac{L}{s}.$ A valve along pipe $3($P$3)$ is initially closed.

a$)$ Determine the hydraulic grade line $($HGL$)$ value at nodes N $2$ and N $3.$

b$)$ The valve along pipe $3(P3)$ is opened gradually such that no transient pressures are produced. Will the pressure head at node N$3$ be higher or lower than in part a$)?$ Describe the hydraulic changes in the network that account for the change in pressure head at N$3.$ Be as specific as possible.

Page $2$ of $4$

$98-$Civ$-$A$5-$December$2016$

Figure $1.$ Network layout.