When the water table is above the bottom slab, uplift can exceed the structure's weight. Add a check: Uplift force < Total weight + Soil friction.
Assume a span (B) and rise (D). Compute area and velocity. In cell C10, compute: box culvert design excel sheet
= (1/B5) * (B*D) * ((B*D)/(2*(B+D)))^(2/3) * (Slope)^0.5 When the water table is above the bottom
Use a Data Table (What-If Analysis) to vary B and D until computed Q ≥ required Q. user error is common.
Even with a perfect sheet, user error is common.