Table $2\mathrm{.}3$: Values of Manning's Roughness Coefficient $(n)$ for Open Drains and Pipes

$($Chow$,1959$; DID, $2000$ and French, $1985)$

$i=\frac{T^x}{(d+{)}^{}}$

where,

$i=$ Average rainfall intensity $(m\frac{m}{h}r)$;

$T=$ Average recurrence interval month and $2T100$ year$)$;

$d=$ Storm duration $($hours$),0\mathrm{.}0833d72$; and

$,,$ and $=$ Fitting constants dependent on the raingauge location $($Table $2.$B$1$ in Appendix $2.$B$).$ Table $2\mathrm{.}5$: Recommended Runoff Coefficients for Various Landuses

$($DID$,1980$; Chow et al$.,1988$; QUDM, $2007$ and Darwin Harbour, $2009)$

Note: The runoff coefficients in this table are given as a guide for designers. The near$-$field

runoff coefficient for any single or mixed landuse should be determined based on

the imperviousness of the area.Figure $2$ shows the area of the drainage basin upstream of a proposed highway culvert

near Pejabat Daerah Kampar, which is found to be $20$ hectares. In terms of soils and

surface cover, the natural drainage area is reasonably homogeneous with grass cover

with average surface slope of $0\mathrm{.}2\%,$ covering $70\%$ of the total basin area. There appear

to be two distinct flow paths converging into $0\mathrm{.}2m$ width rectangular concrete drain

at fully build up industrial zone at the lower area. Using Rational method, find the

peak discharge for $10$ years ARI at the outlet of the drainage basin adjacent to the

highway. Assume water depth for the drain to be $0\mathrm{.}1m.$

Figure $2$: Drainage Area in Perak