<Dd> d l (\ displaystyle dl) is the flow path length between the two piezometers (Length, usually in m or ft) </Dd> <P> The hydraulic gradient can be expressed in vector notation, using the del operator . This requires a hydraulic head field, which can only be practically obtained from a numerical model, such as MODFLOW for groundwater or standard step or HEC - RAS for open channels . In Cartesian coordinates, this can be expressed as: </P> <Dl> <Dd> ∇ h = (∂ h ∂ x, ∂ h ∂ y, ∂ h ∂ z) = ∂ h ∂ x i + ∂ h ∂ y j + ∂ h ∂ z k (\ displaystyle \ nabla h = \ left ((\ frac (\ partial h) (\ partial x)), (\ frac (\ partial h) (\ partial y)), (\ frac (\ partial h) (\ partial z)) \ right) = (\ frac (\ partial h) (\ partial x)) \ mathbf (i) + (\ frac (\ partial h) (\ partial y)) \ mathbf (j) + (\ frac (\ partial h) (\ partial z)) \ mathbf (k)) </Dd> </Dl> <Dd> ∇ h = (∂ h ∂ x, ∂ h ∂ y, ∂ h ∂ z) = ∂ h ∂ x i + ∂ h ∂ y j + ∂ h ∂ z k (\ displaystyle \ nabla h = \ left ((\ frac (\ partial h) (\ partial x)), (\ frac (\ partial h) (\ partial y)), (\ frac (\ partial h) (\ partial z)) \ right) = (\ frac (\ partial h) (\ partial x)) \ mathbf (i) + (\ frac (\ partial h) (\ partial y)) \ mathbf (j) + (\ frac (\ partial h) (\ partial z)) \ mathbf (k)) </Dd>

What is the meaning of head in water pumps