The hydraulic gradient i is given by _________

• A. \(i=\frac{γ_w ∂h}{∂z}\)
• B. \(i=\frac{∂h}{γ_w ∂z}\)
• C. \(i=\frac{\overline{u}∂h}{∂z}\)
• D. \(i=\frac{∂h}{∂z}\)