Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Stuyfzand, Pieter Jan

doi:10.1007/s11852-016-0456-6

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Title

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Author

Stuyfzand, Pieter Jan (TU Delft Geo-engineering; KWR Water Research Institute)

Date

2016-09-08

Abstract

Observations are reported on (i) groundwater recharge rates under various types of vegetation as measured with megalysimeters in the dunes, (ii) freshwater lenses along the Dutch North Sea coast in the early 1900s, and (iii) rainwater lenses that develop on top of laterally migrating, artificially recharged riverwater. Subsequently analytical methods are presented to estimate annual natural groundwater recharge as function of rainfall and vegetation, and to calculate the size, shape and transition zone of freshwater lenses on saline groundwater and rainwater lenses on infiltrated riverwater. An empirical correction factor, based on the hydraulic resistance of an aquitard within the freshwater lens, is proposed to account for the frequently observed reduction of the Ghyben-Herzberg ratio of 40. This factor raises the groundwater table, reduces the depth of the fresh/salt interface and increases the lens formation time. The suite of methods offers a tool box for knowledge based water management of dune systems, by rapidly predicting: (i) more or less autonomous changes due to sealevel rise, climate change and vegetation development; and (ii) the potential (side) effects of interventions. Knowing what happened or will happen to the fresh water lens or a rainwater lens is important, because changes impact on important natural habitat parameters such as salinity, depth to groundwater table, decalcification rate (and thus on pH, Ca/Al, PO₄, NH₄) and nutrient availability, and on drinking water supply. The analytical models are applied to predict effects of sealevel rise, coastal progradation, vegetation changes, and increased temperature of coastal air and river water to be infiltrated.

Subject

Artificial recharge
Climate change
Coastal dunes
Evapotranspiration
Freshwater lens
Rainwater lens
Sea level rise

To reference this document use:

http://resolver.tudelft.nl/uuid:91b508ea-a075-4ff8-9baf-e292cfac6ca1

DOI

https://doi.org/10.1007/s11852-016-0456-6

ISSN

1400-0350

Source

Journal of Coastal Conservation, 21 (5), 577–593

Part of collection

Institutional Repository