Preferential Flow and Migration Zones in Geological Environment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 40

Meanwhile, the presence of permeability anomalies in the structure of the
geological environment is one of the main features controlled by structural-
geodynamic heterogeneity and regularities of regional development as well as by
the related exogenic processes.
Theoretical and experimental studies of physical regularities and mecha-
nisms of preferential flow and transport in soils and rocks have been implemented
for quite a long time. The concept of preferential flow of solutes in heterogeneous
soils has been described first by Lawes et al . [1882]. Later on, Deecke [1906] pub-
lished results of his observations of the dunes of the Darr peninsula in Germany
concerning the formation of finger-like infiltration pathways in aeolian sands
during heavy rainfall. Similar observations were made by Gripp [1961] in Germany
and Gees and Lyall [1969] in Canada. Raats [1973] and Phillip [1975] explained
these phenomena with unstable wetting front theories.
A series of studies during the last few decades were devoted to various types
of preferential flow phenomena differentiated by their physical mechanisms.
They include macropore flow in soils [ Bouma , 1981; Beven and Germann , 1982;
Singh and Kanwar , 1991], gravity-driven unstable flow [ Hill , 1952], heterogeneity-
driven flow [ Kung , 1990], and oscillatory flow [ Prazak et al ., 1992]. All the above-
mentioned cases of preferential flow have relatively small scales ranging from 10 -2
to 10 m [ Nieber , 2001].
Helling and Gish [1991] used representations described earlier by Landon
[1984] and proposed a general classification of the pore space and pore
functions, including dimensions from 10 −4 to 10 4 mm. Greenland [1977] showed
that pores with dimensions of less than 10 −1 m mainly have the function of
joint capacity.
As a larger-scale process, depression-focused recharge should be mentioned
with characteristic dimensions from 10 to 10 3 m. This type of flow is well known
to hydrogeologists and has been studied experimentally and theoretically [ Lissey ,
1971; Nieber et al ., 1993; Gurdak et al ., 2008; Gerke et al ., 2010]. An extending
consideration of the groundwater focused and diffused recharge in various geo-
logical and landscape conditions applicable in the United States, including the
karst groundwater recharge, is presented in the NRC report [2004].
Natural observations and experimental studies of the downward infiltration
and migration of Chernobyl-born radionuclides in the depressions at natural test
sites located in the Kyiv region and CEZ have been performed in Ukraine by
Radioenvironmental Center, NASU, in the postaccident period [ Shestopalov
and Bublias , 2000, Shestopalov et al ., 2002].
It is worth noting that research into preferential infiltration and migration
pathways was initiated in most cases by agricultural practice, for example, during
research on groundwater contamination with pesticides and nitrates [ Shuford
et al ., 1977; Parlange et al ., 1988]. For this reason, most authors mainly described
soils down to a depth of 0.3-1m, and the preferential flow phenomenon was
associated with heterogeneity of the soil pore space (macropore flow) and a