How is the characterization of Water bodies done ? The characterization is done by classification into three major components:
1. Hydrology
2. Physico-chemistry
3. Biology.
Water quality assessment is based on appropriate monitoring of the above three components.
Hydrodynamic features
The hydrological cycle inter-connects all freshwater bodies from the atmosphere to the sea. The different stages of water ranging from rainwater to marine salt waters make the water constitute a continuum. The inland freshwaters form parts of the hydro-logical cycle and they appear in the form of rivers, lakes or ground-waters.
These principal types of water body are closely interconnected. These forms may influence each other in a direct manner, or through intermediary stages. Each of the three forms has distinctly different hydrodynamic properties.
Rivers are primarily characterised by unidirectional flow of current. This is accompanied with a relatively high, average flow velocity ranging from 0.1 to 1 metre per sec. The river flow is supposed to be highly variable in time, based on the climatic situation as well as the drainage pattern.
Thorough and continuous vertical mixing is achieved in rivers as a result of the prevailing currents as well as turbulence. Lateral mixing may happen only over longer distances downstream of major confluences of the water body.
Lakes are primarily characterised by a low, average current velocity of 0.001 to 0.01 metre per sec. To quantify mass movements of material, one can use water or element residence times, ranging from one month to several hundreds of years. Currents
within lakes are found to be multi-directional. Many lakes experience alternating periods of stratification as well as vertical mixing; the periodicity of which is regulated by climatic conditions as well as lake depth.
Ground-waters are primarily characterised by a rather steady flow pattern in terms of direction as well as velocity. These are largely governed by the porosity as well as permeability of the geological material. This results in poor mixing and, based on local hydrogeological features, the ground-water dynamics can be extremely diverse.
There are multiple transitional forms of water bodies. These water bodies demonstrate features of more than one of the three basic water body types mentioned above. These water bodies are characterised by a specific combination of hydrodynamic features. The most important transitional water bodies are listed as below:
1. Seas and oceans
2. Lakes and reservoirs
3. Swamps and marshes
4. River channels
5. Soil moisture
6. Ground Water
7. Icecaps and glaciers
8. Atmospheric Water
9. Biospheric Water
10. Fluxes
11. Evaporation from oceans
12. Evaporation from land
13. Precipitation from oceans
14. Precipitation from land
15. Run-off to oceans
16. Glacial ice
Alluvial and karstic aquifers are considered to be intermediate between rivers and ground-waters. The flow regime is rather slow for alluvial and very rapid for karstic aquifers (also referred to as underground rivers).
As a result of the range of flow regimes noted above, large variations in water residence times happen in the different types of inland water bodies. The hydrodynamic characteristics for each type of water body are primarily dependent on the size of the water body as well as on the climatic conditions prevailing in the drainage basin. The hydrological regime (discharge variability) of the rivers form the governing factor for rivers.
Lakes are normally classified by their water residence time as well as their thermal regime resulting in varying stratification patterns.
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