$120$

A local distribution main is being designed in a cul$-$de$-$sac section of a subdivision $($Figure $1).$ The distribution main has a Hazen$-$Williams $\text{'}C\text{'}$ factor of $150,$ an internal diameter of $152mm$ and a length of $100m.$ The hydraulic grade line $($HGL$)$ in the trunk main is fixed at $70m$ and the centerline pipe elevation at the hydrant is $5m.$

a$)$ Check if the distribution main can provide a pressure head of $60m{H}_{2}O$ for an average day demand of $0\mathrm{.}1\frac{L}{s}.($Assume that demand occurs at the downstream point of the distribution main.$)$

b$)$ Check if the distribution main can provide a pressure head of $20m{H}_{2}O$ for a maximum hour demand of $0\mathrm{.}2\frac{L}{s}$ at the downstream point. $($Assume that demand occurs at the downstream point of the distribution main.$)$

c$)$ Check if the distribution main can provide a pressure head of $14m{H}_{2}O$ for a maximum day demand of $0\mathrm{.}18\frac{L}{s}$ plus a fire flow of $32\frac{L}{s}.($Assume that demand and fire flow both occur at the downstream point of the distribution main.$)$

d$)$ Based on your answers in a$),$ b$),$ and c$),$ does water demand or fire flow govern local distribution main sizing? Page $2$ of $5$

$98-$Civ$-$A$5-$ May $2011$

Figure $2.$ Layout of water pipe network.

Table $1.$ Pipe centerline elevations and demands at network nodes.

Gate valves in pipes $P2,P5,P7,$ and $P8$ of the network in Figure $2$ have been

closed. Gate valves along all other pipes are fully open and cause no local

losses. Calculate the flow in pipes P$6$ and P$9$ and the pressure head at node

N$2.$