AMCS Bulletin 18
Modeling the Groundwater Catchment
This is a reformatted edition of the authors' joint 2006 M.Sc. thesis at the Technical University of Denmark. Abstract: Urban, industrial and agricultural activities threaten the groundwater resource that feeds the Sian Ka'an Biosphere Reserve, a UNESCO World Heritage site on the Caribbean coast of the Yucatan Peninsula, Mexico. The area has a complex karstic geology with high permeability features, and the thesis investigates how the water resource dynamics of the catchment that encompasses the Reserve can best be modelled. A conduit-matrix model has been found to be appropriate for modelling groundwater flow in the catchment on a local scale, whereas an equivalent porous medium model is appropriate for regional scale modelling. High permeability zones have been identified based on visual inspection of satellite imagery and confirmed using frequency-domain geophysical measurements. These zones have been incorporated into the model scenarios and have been found to significantly impact the size of the catchment. The regional hydrological modelling has shown that a significant potential threat to the Reserve is posed by the nearby urban and agricultural areas of Felipe Carrillo Puerto and Andres Quintana Roo, from where pollutants may be able to reach the Reserve in less than 10 years. Also pollution from more distant areas may be able to reach the Reserve assuming high permeability in the identified structures. Moreover, it cannot be excluded that pollution from the area covered by the proposed development plan for Tulum can spread to the Reserve. The visual outcomes of the hydrological models is expected to be valuable inputs to decision making processes concerning the management of the groundwater resources of the Sian Ka'an catchment in the future.
Table of Contents
11 Introduction 13 Description of Model Area 37 Theoretical Background for Electromagnetic Methods 41 Saltwater/Freshwater Interface Configuration 57 Configuration of Freshwater Heads 69 Identification of Potential High Permeability Areas in the Aquifer 83 Analysis of Structures with Geophysical Methods 101 Simple Generic Conduit-Matrix Model 119 Regional-Scale Hydrological Model 137 Discussion and Perspectives 139 Conclusions 141 Directions for Future Research 143 References 149 Appendixes