Newsletter and Technical Publications
Freshwater Management Series No. 5
Guidelines for the Integrated Management of
- Phytotechnology and Ecohydrology -
Underground water is formed by the infiltration
of precipitation into deeper strata within the bedrock (Figure 1.13). The depth
of infiltration, as well as the origin of the aeration and saturation zones, is
an effect of the geological substratum; specifically, the arrangement of the
strata and their physical characteristics. These are divided into three groups
according to their hydrogeological properties: of permeability between 1-0.01D;
e.g., sands, grits and gravels.
- aquifers - having an index
- aquicludes - having index of permeability between 0.01-0.0001D;
e.g., argillaceous sands and arenaceous clays,
- aquifuges - having an index of permeability of less than 0.0001D;
Water penetrates into
the pores and crevices of the rocks, filling capillaries between granules,
clefts, and even karstic caverns. In this way, precipitation may infiltrate to
aquifuge or confining strata (direct alimentation). In aquifers, or those areas
wherein the ground water is stored, layers of porosities can be distinguished,
with those layers being most porous storing the greatest volumes of ground
water. These layers tend to be most sensitive to changes in physicochemical
conditions (e.g., air temperature).
Indirect alimentation is related to the
presence of hydrological windows that result from sedimentation or erosion
processes. The amount of underground water resources and their sensitivity to
anthropogenic stress are dependent upon the type of source water. For example:
with a free water table occur at different depths, but most commonly near the surface.
They are seriously endangered by human activities such as overexploitation,
contamination, and heating. Contaminants generally spread very slowly due to
the laminar movement of water in the capillaries. They are easily renewable and
usually regenerate after rainfalls and spring snow melt.
- Confined ground water is less susceptible to
anthropopression, because they are isolated from the surface within aquifuge
rocks. This group is classified as artesian and subartesian waters. They are
also renewable, but the process is slow, and they are often over-exploited.
- Karstic aquifers are
extremely susceptible to degradation because pollutants (even suspended solids)
can easily and quickly spread over large distances due to the turbulent flow of
water within crevices. The rates of water contamination are influenced by
humidity and the water balance in the aeration zone, as well as the pressure
distribution and water balance in the saturation zone. It also is modified by
permeability and the processes of dispersion and dilution occurring in each
stratum, and also by contact with surface waters.
||infiltration and saturation excess overland flow
||Saturation areas, overland flow and subsurface storm flow
||Saturation, impervuous areas overland flow, subsurface flow
|Fig. 1.13. Examples of different
types of underground waters in areas with differing geological structure|
The hierarchy of factors causing vulnerability of ground water resources is as
follows: surface morphology, the distribution of strata, petrographic and
lithological characteristics of sediments, hydrodynamic conditions,
infiltration quantity and quality, and biological conditions in zone of
penetration and infiltration. However, the dynamics of underground waters
depend mostly on the hydrological regime of the overlying surface waters, which
may drain to (at high water levels) or be supplied from (at low water levels)
them by means of infiltration processes (Figure 1.14).
Surface waters form only
0.014% of the total water resources. However, they are extremely important for
wildlife and for the development of human civilisation. There are three types
of surface waters: rivers, lakes and marshes. Both surface waters and
underground outflows are parts of the same dynamic system. This should be taken
into consideration when new artificial reservoirs are planned and constructed,
especially along the middle and lower water course. It is also worth
emphasising that water resources are renewable, but, when the rate of
exploitation and degradation is high, they may become scarce. Therefore, the
basis for sustainable use of freshwater resources should be the preservation of
the hydrological balance between water uptake and use, and its supply and retention.
||are collectors of run-off and underground waters;
||play crucial role in hydrological cycle, because they supply seas
oceans with 45 thousand km3 of water;
||water exchange between river and other ecosystems is very intense
most rivers it takes only 2 weeks (Kaleśnik, 1975);
||thay drains underground waters, so water table of underground waters
always related to water level of the river.
|It is especially true for underground waters in alluvial
sediments (basic material covering river valley), where due to shifts
between its draining and supplying function river to great extend influences
quality of alluvial underground
||accumulate about 0,26% of the Earth freshwater resources.
||are systems saturated with water, which constitute up
to 80% of ground volume, because they are result of restricted out-flow
of both surface and groundwater, and precipitation much higher than
||it means that they store about 11,5 mln km3 of water.
|both lakes and marshes
||are responsible for water retention in catchment and
like rivers they influence quality and quantity of underground water
through infiltration and drainage.