IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Author(s):
Ashvin Kamal Wickramasooriya *
and Hingulwala Arachchilage Dharmagunawardena **
* Faculty of Applied Sciences, South Eastern
University of Sri Lanka, Sammanthurai (E.P), Sri Lanka, telephone : 0094-67-2260073, e_mail :
awickramasooriya@yahoo.com
**
Keyword(s): fluoride, infiltration
AbstractFluoride is an essential element for the human body because it
promotes dental health, essential for growth of bones and also permits tooth decay. Many health problems may arise
by either deficiency or excess of Fluoride. Drinking water is the main source of Fluoride required by humans.
Therefore, Fluoride concentration in drinking water may influence on human health caused by Fluoride. Majority of
the Sri Lankan population does not have modern pipe-bone water systems especially in the rural areas. They depend
on surface water and groundwater sources such as dug and deep hand pump wells, rivers and channels for their
domestic water requirements. Therefore, study of the natural hydraulic processes and their effect on the behavior of
Fluoride in surface water and groundwater are great importance in these areas. A problem of growing concern is the
excessive concentrations of Fluoride found in many low plains of the dry zone, notably in the Anuradhapura and
Polonnaruwa districts. The Fluoride concentration in many wells of these areas exceeds 1.5 mg/l and poses a health
hazard to the consumers.in In these areas, wide prevalence of dental fluorosis specially among children of school
going age. The slow rate of groundwater movement and high evapo-transpiration in the low plains of the dry zone
tend to increase the Fluoride concentration.Within the areas of high Fluoride bearing groundwater, it is still possible
to find certain areas specially close to an irrigation tanks, with considerably low Fluoride concentrations with regards
to the safe limits of drinking water standards. Since surface water contain low Fluoride concentrations compared to
groundwater by infiltration of surface water from the irrigation tanks could be a major governing factor for this
situation.
The possible effects of hydraulic processes specially the surface water infiltration of Fluoride content
of groundwater was studied in the Polonnaruwa district, in a small village situated below the major irrigation tank;
Parakrama Samudraya. The behavioral patterns of the groundwater table and groundwater Fluoride content
revealed that the concentration of Fluoride in groundwater of the area is controlled by the infiltration of the surface
water from the tank and the irrigation channel. It was found that the Fluoride of groundwater is low in the vicinity to
the surface water bodies especially in the down-slope sides. Fluoride concentration increases in the direction of
groundwater flow and away from the surface water bodies within the area of influence of the surface water.
On
account of the widely spread surface water irrigation network in the Polonnaruwa district, it could be expected that
the low Fluoride areas close to irrigation tanks and channels are a result of infiltration and dilution of Fluoride content
by the surface water.