Analyse van het afvoerverloop van gebieden met hoofdzakelijk grondwaterafvoer

A model was developed for the precipitation-discharge relation in permeable areas, where surface runoff played only a minor part or none at all in the total discharge volume. The model primarily consisted of a small number (1-4) of negative exponential functions including, if necessary, one for surface runoff, the others for different types of groundwater flow.
The parameters in the model were of 3 types: the constants in the exponents, called reaction factors, expressed in time -1: the time-variant reduction factors to be applied to function outputs (the inputs for each function being the full effective precipitation); and usually a subtractive quantity. The hydrograph for an area was calculated by summing per calculation interval the reduced outputs of all functions discerned in the discharge pattern of that area, minus the subtractive.

Values for parameters as well as the number of functions integrally depended on the shape of the hydrograph measured over 2-3 complete years without previously considering physical conditions within the area, thus avoiding the introduction of other unnecessary complications. The best possible result could only be a statistical conformity between calculation and observation as, for hydrographs over long periods, errors in precipitation measurement prevented precise fitting.

The reaction factors could be interpreted physically as belonging to hydrologically homogeneous subareas. The reduction factors represented the proportional areas of them. The subtractive represented deep-seepage loss from the entire area.