Assuming I have 2 layers of unsaturated soil (with a depth of 1.5 meters and 11 meters, respectively), can I estimate the water content in the second layer if I only have the volumetric water content (θ) in the first layer, hydraulic conductivity in all layers, and the groundwater recharge?

My idea is by utilizing the Buckingham-Darcy equation for the upper boundary to quantify the percolation rate. Thus, the water content in the second layer can be quantified by differencing the cumulation percolation rate and the cumulative groundwater recharge. Tthe percolation rate is defined as:

q_perc = K . dH/dz;

my question: is there any relation between volumetric water content and the hydraulic head gradient (dH/dz)? or do you have other suggestions?