Water Balance Approach
Updated 2-layer model by direct insertion of observations - Jackson et al. (1981), Ottle and Vidal-Madjar (1994)
Fixed head boundary condition on 1D Richards eq. - Bernard et al. (1981), Prevot et al. (1984), Bruckler and Witono (1989)
Updated 1D Richards equation with Kalman filter - Entekhabi et al. (1994)
Updated 2-layer basin average model with Kalman filter - Georgakakos and Baumer (1996)
Updated 3-layer TOPLATS model with: direct insertion; statistical correction; Newtonian nudging (Kalman filter); and statistical interpolation - Houser et al. (1998)