Innovative Geophysics for Hydrologic Parameter Aquisition

The proposed project is part of an international cooperation submitted in the D-A-CH program entitled "Geometry, genesis and dynamic of the Yucatan karstic system". The project involves three teams: the University of Neuchâtel which will coordinate the project, the Geological Survey of Austria which has extensive experience in geophysical exploration in the region, and the Centro del Agua in Mexico which has a strong finite element modelling expertise. The aim of the project is to better understand the formation and behaviour of large and complex karstic systems. This implies the development of new measurement and field methods, as well as new modelling techniques allowing a detailed analysis of field observations and hypothesis testing. The field site for the project will be the Yucatan peninsula in Mexico, since it is one of the largest karstic systems in the world and because a large amount of data is already available even if, as outlined in the proposal, some key information are still missing. The research involves two main scientific questions: How has such a massive karstic system formed? How is it functioning today? These questions are not yet answered satisfactorily. The formation of the system is thought to be mainly the result of calcite dissolution enhanced by mixing of salt and fresh-water, but some authors argue that vertical heat transport in the peninsula enhances the mixing and this thermo-haline convection could be the main driving force for the formation of the vertical structures named cenote. Other authors disagree and reject the idea that heat is an important factor in the process. In terms of the current functioning of the aquifer, its detailed dynamic is not yet well understood and modelled because it involves complex interactions between freshwater, seawater, and tidal effects under a very small head gradient. All the current models of the system could not account for all those processes and they provide therefore only a general description of the overall behaviour. To go a step further, in this project it is proposed to focus on the two main aspects. It is firstly aimed at understanding the evolution of the permeability and the genesis of the karst system of the Yucatan peninsula over geological time scales. It includes in particular the understanding of the long term effect of the interaction between fresh water and salt water on the dissolution as well as the role of the thermal regime. It is then aimed at understanding the properties of the regional-scale preferential flow paths. More precisely it involves understanding the geometry of the current conduit systems and how it influences the regional flow and solute transport. The geometry is a result of the speleogenesis processes and therefore the two questions are intimately related. Trying to answer those two questions necessitates on the one hand the development of new groundwater flow and transport models and the acquisition of additional data to reduce the current lack of hydrological monitoring data on the other hand. This requires the development of new measurement techniques adapted to the special measurement environment of a karst groundwater regime for monitoring groundwater fluxes as well as electrical conductivities for high resolution halocline and mixing zone observation, quick capturing of conduit geometry under water and the setup of an extensive long term monitoring network for pressures and temperatures complemented by a multi-parameter probe. The task of the Geological Survey of Austria is the development and testing of those methods in Austria as well as coordination of the field work covering preparation, deployment of the monitoring setups and surveys. Further, the newly acquired data will be processed and integrated with the existing geophysical data base already developed in course of several field campaigns in the region conducted by the Geological Survey of Austria.

No additional funding sources recorded.