Question Help The existing floodway across this section of the Riley Highway is to be made redundant, and replaced with a culvert arrangement beneath the road construction to provide Q50 immunity Engineers have calculated the Q50 peak stormwater flow which arrives at the existing floodway, and have specified the following design parameters: Required cross-sectional flow area of culvert structure is 2.20m2 The culvert ‘barrels’ can be either reinforced concrete pipes (RCP’s) or reinforced concrete box culverts (RCBC’s) The minimum longitudinal grade of the culvert shall be 0.5% (1:200)