Evaluation and improvement of hyrological concepts used in PAWN

Abstract

In the years 1976–1983 the PAWN-study (Police Analysis for the Water-management in The Netherlands) was carried out in order to assess data for a national water management policy as reported in the Nota Waterhuishouding 1984, submitted to the Dutch parliament in the framework of the preparation of the Water Management Act. Among the mathematical models used in PAWN, DEMGEN (DEMand GENerator) represents agriculture, by far the greatest interest in terms of water demand and economic importance. By simulating the hydrological cycle in agricultural areas the model produces data on sprinkling demand, total water demand, agricultural damage and the changes in groundwater levels due to water suppletion. Furthermore the model evaluates sprinkling costs, which enables cost/benefit analyses for water supply plans. After the PAWN exercises for various reasons the need was felt for a critical evaluation of DEMGEN, specifically with regard tro future applications. This also implied an updating of DEMGEN on basis of recent scientific developments. In the period 1982–1986 investigations were carried the following fields: • - evaluation and improvement of implemented physical concepts; • - development and implementation of new concepts; • - updating of input files and facilities with respect to physical characteristics; • - updating of the areal schematization of The Netherlands and the development of relevant standard procedures for this subdivision The paper deals with the results with respect to the follwoing physical concepts in DEMGEN: • - Unsaturated flow • - Evapotranspiration • - Drainage • - Irrigation Contributions were made by Rijkswaterstaat, the Delft Hydraulics Laboratory (DHL) and the Institute for Land and Water Management Research (ICW). Most of the studies dealt with separate concepts, whereas Rijkswaterstaat also carried out an integral sensitivity analysis and a validation of DEMGEN on basis of data from two experimental catchments in The Netherlands. In all investigations the sensitivity of certain assumptions and the estimation of reliable model parameters was the major topic, rather than the assesment of the highest possible degree of accuracy in the simulation of physical processes.