10 are provided in Table 2. Where the gradient of the clean water diversion gradients exceeding 2% or the design velocity exceeds 1m3/s channel lining or additional erosion protection will likely be required. Figure 3: Cross-section of a clean water diversion bund. Table 2: Clean water diversion calculations and sizing details. Clean water diversion Clean water detail reference Catchment area 5% AEP rainfall depth (mm) Peak Flow (m3/s) Base Width (m) Slope (minimum) Minimum Design Flow Depth (mm) Including Minimum 300mm Freeboard CWD-1 <5ha 263mm 1.819 0.5 2% 300 600 CWD-2 5-10ha 263mm 3.638 0.5 2% 400 700 CWD-3 10-15ha 263mm 5.457 0.5 2% 450 750 CWD-4 15-20ha 263mm 7.276 0.5 2% 500 800 Clean water diversion capacity sized using a Manning’s (n) figure of 0.035 for grass. The permanent uphill clean water diversion design details are provided by Engineering Geology Limited. 3.2. Dirty Water Diversions Dirty water diversions will direct sediment laden runoff to the sediment control measures. The dirty water diversions have been sized to provide diversion capacity up to the 5% Annual Exceedance Probability (AEP) storm event, plus a freeboard of 300mm. Dirty water diversions with slopes greater than 2% will likely require stabilisation to prevent significant erosion. Drop out pits (approx. 1m x 1m) should also be constructed within the dirty water diversion to allow heavier sediment particles to drop out before they enter the sediment retention device. Calculations are provided in Table 3.
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