June 2022 G-01483.84-017-R-Rev0 Because the 43 Table 19: Results of high level culvert sizing. Culvert Ref Design inflow (m3/s) Head at culvert inlet (m) Culvert size Number of Culverts required 1 0.062 825mm 825mm 1 2 0.425 825mm 825mm 1 3 Design by others – to be integrated 4 1.821 825mm 825mm 3 5 1.306 825mm 825mm 2 6 1.386 825mm 825mm 2 7 0.058 825mm 825mm 1 8 0.496 825mm 825mm 1 9 Design by others 7.5.4 Channel Lining and Geometry The channel design objectives were: ▪ Temporary design to accommodate the 1 in 10 year event. ▪ Allow for 300 mm freeboard (potential for some channels to be less, assess detail design). ▪ Divert clean water around the WRS and discharge flows back into existing tributary below the WRS. ▪ Consider largest estimated flows during life of the WRS for design, being period Q1 for the clean water diversions, Q17 for surface runoff (i.e., largest disturbance footprint). ▪ Consider lining and channel capacity requirements for steep and shallow gradient channels. ▪ Consider overflow above the 1 in 10 event. Manning’s equation was used to calculate flow depth in trapezoidal channel for all design cases. Table 20 summaries the estimated channel dimensions (trapezoidal), flow and peak velocities for diversion channels and surface runoff drainage with the recommended lining requirements. Channel designs are based on averaged segment lengths for snapshots during development Q1 (Stage 1) and Q17 (Final Stage). Clean water channels that are very steep for a short length, if practical, it has been assumed the channel can be graded out to create a reduced average grade along that length of channel. Results of the geotechnical assessment indicate that the WRS site is underlain by surficial soils to depths of up to 4.5 m consisting of firm to hard sandy/gravelly clays. The thickness of the surficial soils increases towards the east down the gully with less than 1 m of soil material overlying weathered rock in the west of the footprint. Surface drains to direct clean water flows around the WRS should be cut into the in-situ highly weathered volcanic rock materials. No evidence of erodible behavior has been observed on site of the native vegetated soils. However, lining of the drains with turf reinforcement mat (TRM) or armour stone, in steeper gradient sections, will be necessary to protect the underlying soils (see sketch of typical Appendix E). Armour stone should be won from the non-acid generating tunnel spoil comprising strong rock, with variable size gravel/cobble/boulder particles. The maximum permittable velocity for Waikato soil types is provided in WRC
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