$2$ The diagram shows two catchments A and $B.$ The run$-$off from Area $A$ is collected in catch

pit $x$ and from there it flows along an underground pipe $($pipe $1)$ to catch pit $Y$ where the

run$-$off from area $B$ is also collected. The combined flow from the two areas discharges

via pipe $(2).$ The Slope of both pipes $(1$ and $2)$ is $1\mathrm{.}5\%.$

$0\mathrm{.}015$

$2\mathrm{.}1$ Use Ramser Kirpich formula and find time of concentration for both catchments:

$(4$ Marks$)$

$T_c=0\mathrm{.}0195L^{0\mathrm{.}77}{S}_a^{-0\mathrm{.}385}$

$T_c=$ Time $of$ Concentration $(min)$

$S_a=$ Average channel $(main$ stream$)$ slope $(\frac{m}{m})$

$L=$ Flow length from farthest point $of$ the catchment $to$ outlet $(m)$

$2\mathrm{.}2$ Determine the pipe size between $x$ and $Y($pipe $1).$

$2\mathrm{.}3$ Calculate the discharge into the river via $($pipe $2).$

$2\mathrm{.}4$ Determine the pipe size between $Y$ and $Z($pipe $2).$

Pipe flow chart: Appendix $1,($Colebrook$-$White graph$)$

Rainfall intensity: $I=\frac{1930}{T+45}m\frac{m}{h}($T in minutes$)$