Garden with Insight v1.0 Help: Hydrology - Water Table Dynamics

The water table height is simulated without direct linkage to other soil water processes in the root zone to allow for offsite water effects. The model drives the water table up and down between input values of maximum and minimum depths from the surface. The driving mechanism is a function of rainfall, surface runoff, and potential evaporation, as given in the equation [Equation 90] where WTBL is the depth in m from the surface to the water table on day i, W1 is the driving function, and WTL is the appropriate limit.

The driving equations are [Equation 91] and [Equation 92] where RFS, QS, and EOS are the sums of rainfall, runoff, and potential evaporation for 30 days before day i and W2 is a scaling factor. Equation 92 causes the water table to rise faste than it falls because the denominator is larger during recession.

The maximum wtaer table depth, WTMX, is substituted into equation 90 for WTL when the water table is falling (when W2 is negative). Conversely, WTL is set to the minimum water table depth, WTMN, on the rising side [Equation 93] and [Equation 94].

Obviously, equation 90 gives highest rates when W2 is large and when WTBL ~~ WTMN the rate of rise approaches zero. The reverse is true on the falling side.

Equation 90:

WTBL(i) = WTBL(i-1) - W1 * (WTBL(i-1) - WTL)
W1 = min(0.1, abs(W2))
WTL = WTMX if W2 <= 0.0, WTL = WTMN if W2 > 0.0
Code:
same
Variables:
WTBL(i) = WaterTableDepth_m
WTBL(i-1) = waterTableDepthYesterday_m
W1 = boundedDrivingFunction
W2 = drivingFunction
WTL = limitToWaterTable
WTMX = maxWaterTableDepth_m
WTMN = minWaterTableDepth_m

Equation 91:

W2 = (RFS - QS - EOS) / EOS)
Code:
same
Variables:
W2 = WaterTableDepthDrivingFunction
RFS - QS = sumRainfallMinusRunoffPrev30Days_mm
EOS = sumPotentialEvapPrev30Days_mm