Self-organized flow and porosity in Bohemian Cretaceous Basin: Results of tracer tests and other methods
Abstract
There are several areas in Bohemian Cretaceous Basin (BCB), where self-organized flow and porosity occurs. Some porosity is karstic in origin, created by dissolution of CaCO3 cement in sandstone and sandy limestone (Miskovice in Kutná Hora surround-ings), other porosity is clearly non-karstic, initiated by piping and later enlarged by collapse of overburden and sides of conduit (quartz sandstones with kaoline matrix in Střeleč Quarry).
Concerning remaining part of porosity, it is not resolved yet which process from above mentioned was more important. From hydrogeological point of view however (flow pattern and velocity), all these phenomena are similar and can be dealt together as self-organized (SO) flow and/or porosity.
Information from 32 successful tracer experiments in BCB were collected and discussed in this study. Maximum flow velocity (calculated from time of first arrival of tracer) in conduits created by SO flow are between 2.35 km/day (up to 0,4 m/s) over direct distances up to 2 km, which is extreme velocity comparable with flow velocity in well developed karst.
In other areas of BCB the tracer tests revealed maximum flow velocity in order of tens to hundreds m/day or even more (Mělnicko, surroundings of Benátky nad Jizerou). As SO flow is able to transport very quickly contamination over large distances, the future study is needed to delineate areas with SO flow and characterize the porosity and flow in detail.