Preferential Flow and Migration Zones in Geological Environment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 53

0 200 400 m

1 2 3 4 5

Figure 3.11 Scheme of depression occurrence at typical site of a sandur plain in the CEZ
with indication of absolute elevation, depression depth, watershed dividing lines, and
surface runoff directions: (1) depressions with depth to 0.5 m; (2) depressions with depth
to 1.0 m; (3) depressions with depth to 1.5 m; (4) watershed dividing lines; (5) surface
water flow directions.

3.4. indicators of PfMZ activity in depressions

Detailed experimental studies were carried out mainly of closed-type depression
morphosculptures for the reason that in the plain areas their contribution to the
vertical migration component is much higher than that of the poorly defined linear
forms. The role of linear open forms in the vertical mass transport increases signifi-
cantly in the dissected relief with absence or poor development of closed depressions.
Results of field studies and experiments implemented in the study area of
CEZ and the Kyiv region showed that mesoscale and microscale PFMZs repre-
sented by closed depressions exert a significant influence on the intensity of the
vertical infiltration and transport of radionuclides and other contaminants from
the surface into groundwater.
The depressions serve as the bases of local erosion and runoff and form local
watersheds of surface waters that converge on their central lowest parts (Figure 3.11).
It was found that in the CEZ depression systems may capture up to 60-80% of
surface runoff of plain water-divide areas [ Shestopalov , 2001]. This surface runoff
mainly forms during periods of spring snow melting and intensive rainfalls.