Naturversuche zum Austausch zwischen Oberflächen- und Grundwasser
[Field Research on the Infiltration of Surface Water into Groundwater]
Huppmann, Ottmar; Kohm, Jörgen
published: Jan 1, 1980
Selbstdichtungsprozesse an Gewässersohlen vermindern mit der Zeit die Versickerung von Oberflächenwasser in den Grundwasserleiter. Für eine aktuelle und prognostische Grundwasserbewirtschaftung ist es deshalb notwendig, die Auswirkungen fortschreitender Selbstdichtungserscheinungen an Gewässersohlen zu quantifizieren. Im vorliegenden Beitrag wird ein Meßprogramm vorgestellt, das es erlaubt, die Auswirkungen der Selbstdichtung kleiner Gewässer in situ zu erfassen. Der Einflußbereich wird hierbei durch ein Nahfeld (unmittelbarer vom Gewässer beeinflußter Bereich) und ein Fernfeld definiert. Erste Ergebnisse werden dargestellt.
Substances contained in surface waters are producing a clogging of waters-beds by percolation into the aquifer. Clogging causes an increasing of the hydraulic resistivity of porous media near the waters-beds and subsequently flow from the waters into the aquifer will be reduced. With different measuring methods the degree of an existing clogging and the development of clogging in time and space will be seized directly by: a) research of permeability of the waters-beds; b) determination of the distribution of the hydraulic potential below the waters-beds; c) measuring the amount of infiltration water. Applicability of these methods is limited. ad a) Determination of permeability in laboratory is faulty among other things because of disturbance by getting the soil sample. To avoid this an appliance was developed basing on known procedures to measure in situ. The received results will be compared with laboratory determination to get the error caused by sampling. By taking a greater number of samples the variance of the permeabilities is considered. ad b) A potential field will be formed in the subsurface due to soil permeability and difference of piezometric head between surface water and groundwater. Thus information is given on position and extension of the clogged part of the subsurface. The infiltration rate can be calculated by additionally using permeability. The Variation in time of the potential field is registrated currently by an automatic platform. For recording the pressure head piezoresistive transducers are applied which seize as well saturated as unsaturated flow. In the case of unsaturated flow the water content is determined by gamma-ray logging. ad c) Besides these indirect methods (essentialy parameters for modelling the groundwater flow) the infiltration rate is determined by measuring differences of river flow. Therefore plate weirs are installed. Infiltrometers (c. g. seepage meter by H. BOUWER) and lysimeters in the bottom of the waters give additional informations on the Variation of percolation in time. The mentioned methods are completed by measurements in the adjacent aquifer. The data evaluation is done by numerical groundwater models. The described research should result in simple calculation methods for determining the infiltration rates. Especially the effect of reliability and number of available data on the accuracy of the results will be emphasized.