Tools for investigating the origin of anomalies in chloride content of groundwater in coastal lowlands
de Ruiter, J.C. (1989). Tools for investigating the origin of anomalies in chloride content of groundwater in coastal lowlands. Natuurwet. Tijdschr. 70(1-4): 278-287
In: Natuurwetenschappelijk Tijdschrift. L. Walschot/Natuur- en Geneeskundige Vennootschap: Gent. ISSN 0770-1748, more
Also appears in:
De Breuck, W.; Walschot, L. (Ed.) (1989). Proceedings of the 10th Salt-Water Intrusion Meeting Ghent (Belgium), 16-20 May 1988. Natuurwetenschappelijk Tijdschrift, 70(1-4). Natuurwetenschappelijk Tijdschrift: Gent. 408 pp., more
In this paper are described various tools which can be used to investigate the origin of anomalies in chloride content of groundwater. (1) The best tool for starting an investigation of this kind is to look for and maps or other information in order to get an idea of the succession of different landscapes in the area from e.g. the end of the Pleistocene until now. Transgression stages with salt-water influence may have alternated with regression stages with freshening influences from rivers and peat moors. A change of the relative altitude of parts of the landscape may have caused a reversal of the direction of freshening and salinizing processes. For instance, peat moors originally grew several metres above MSL in areas which are now deep polders. Also the coastal dunes became much higher and broader causing different flow systems and probably formed a safeguard against salt-water intrusion. (2) A possible second tool is the chemical groundwater classification according to STUYFZAND, with emphasis on cation exchange in order to determine the difference between salinizing and freshening processes in combination with chloride content. As no time labels are pinned on the processes, interaction with the information on landscape changes in the area is necessary to design some hypothetical successive situations. (3) To screen the hypothetical situations a third tool, the study of isotopes is chosen. With isotope measurements a differentiation of the ages and the origins of fresh water can be made (rain-water and melting-water rivers, infiltration water in peat moors etc) . (4) Hand in hand with the study of isotopes other chemical parameters can be used, depending on the hypothetical origin of the groundwater. (5) The fifth tool to be used in the remaining hypothetical situations might be two- or three-dimensional groundwater flow and transport modelling. For an example, to model a former peat moor, some parameters must be determined from other known parameters, e.g. influence depth and influence time. However, no data about the heights of the former peat moors in the western part of the Netherlands are known. By making different models the plausibility of the hypotheses might be tested, using a number of hypothetical heights as input data for the model code. The aim of these exercises is not only to explain the origin of the anomalies in chloride content but also to get a better insight in the reactions of flow systems on changes of the environment. Our environment is often changed by groundwater extraction and artificial infiltration, by changing polder levels, by dumping polluted soil on exfiltration areas transforming them into infiltration areas etc. Therefore the consequences of these actions must be known very well.
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