Problem $8\mathrm{.}3$

Use the channel sketched in Figure P$8\mathrm{.}3$ and the following properties:

$($a$)$ specific weight of stone $=165l\frac{b}{f}{t}^3(26k\frac{N}{m^3})$;

$($b$)$ local depth at toe of outer bank $=25ft(7\mathrm{.}6m)$;

$($c$)$ local depth at $20$ percent upslope from toe $=20ft(6\mathrm{.}1m)$;

$($d$)$ channel side slope $=1V$:$2H$;

$($e$)$ downstream channel slope $=2f\frac{t}{m}$ile$(38c\frac{m}{k}m)$;

$($f$)$ minimum centerline bend radius $=1,700ft(520m)$;

$($g$)$ average flow velocity $=7\mathrm{.}2f\frac{t}{s}(2\mathrm{.}2\frac{m}{s})$; and

$($h$)$ surface channel width $=500ft(150m).$ Determine the size, thickness, and gradation of the riprap blanket required for the stabilization of the outer bank of this channel. If the riprap is placed over uniform $0\mathrm{.}5-mm$ sand, design the gravel filter required to prevent leaching.

Figure P$8\mathrm{.}3.$ Flow in a curved channel with riprap in shaded areas