Présentations Colloques

Oral Presentation
Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Stasko Stanislaw
Groundwater in hard rock aquifer and resources evaluation base on field observation in Sudetes (SW Poland)
Results on groundwater resources evaluation in crystalline massif in Sudetes Mts. (SW Poland) composed mainly of gneisses and schist has been presented. The field observation in local catchment consist of network of springs, rivers and well in crystalline massif rocks. In group of springs under observation, four indicates average discharge over 1 l s and relatively low variability (in range 3-16) and other showed lower outflow as 0.07-0.9 l s. Groundwater runoff evaluated with base flow method in rivers, showed value in upper part of catchment ( 3.5-6.5l s km2), when in lower part,value ( 6.5 -7.5 l s km2) due to direct drainage to river valley. Groundwater in such region is low mineralized, low value of pH and high radon concentration (up to 220 Bq l). Horizontal intake are the best way to provide groundwater resources.**As a result a three-layer model of hydraulic properties water-bearing zones in hard rock have been developed based on geological observation and groundwater occurrence. Scheme is associated with spring discharge measurements, water temperature records and water level fluctuation. Model includes the top layer of a weathering zone, mostly composed by clay or sandy clay with thickness from 2m, up to 20 m + the second one is formed of dense fracture network in massif rocks and is extended up to 50 meter below land surface. The third one is formed by deep fracture system, reaching the depth of 300-500 m. The top zone is characterised by high water storage (capacity) and relatively low permeability. The second zone shows low storage ability but high transmissivity. The lowest storage and hydraulic parameters are typical of the deep fractured zone, which is the bridge between fresh and mineral water and is reported up to a depth of 500-700 m. Best condition for groundwater occurrence of the first water-bearing level show two upper zones i.e. alterites covers and fracture zone of the rock massif. ** **