Kelani River, having the total length of 145 km and 2292 sq km of river basin is the second largest watershed and it is the most polluted river in Sri Lanka due to rapid growth of industries located in close vicinity of the river and passes through the country through most populated capital city.
The main sources of water pollution in Kelani river is the land based sources such as treated and untreated industrial effluents, agricultural runoff, domestic and municipal effluents. The gravity of water pollution is apparent when examining water quality measurements of Kelani River, which meets a major part of the demand for pipe borne drinking water supplies of Colombo. Kelani River is an important source of drinking water for the Colombo District and there is a water supply intake point at Ambatale, 14 kilometers from the river mouth. However, sewage from low-income settlements and industrial effluents (especially from tanning and metal finishing and processing industries) from a large number of industries are discharged conveniently to the Kelani River.
Furthermore, the lower reach of the river has been subject to saline water intrusion from the ocean making the water non-potable due to excessive sand mining and lowering of river beds at the lower reaches in the Kelani River, where sand mining is particularly severe with the salt wedge has extended inwards to Ambatale (about 14 km from its point of discharge) on several occasions. This is a serious concern as much of the potable water supply for Colombo is extracted from the Kelani River at Ambatale.
The discharge of wastewater into the environment from industrial activities is regulated by the Environmental Protection Licenses (EPL) schemes implemented under the provisions of the section 23 (a) of the National Environmental Act of 1980. As specified in the Act it is mandatory to obtain an EPL to discharge wastewater into the environment from an industry. Industries which discharge wastewater into the environment are required to treat their wastewaters up to the relevant standards to be qualified basically to obtain an EPL. The licenses so issued will specify the standard and criteria to be met by the respective industry discharging its effluent into the environment.
Even though the industries are covered with environmental protection licensing schemes, there is no regular monitoring mechanism to evaluate their meeting of discharge criteria and to control the pollutant loads discharged into the Kelani river.
The pollution status of the Kelani river and some of its tributaries were investigated from 2003 with respect to pH, Electrical conductivity, Turbidity, DO, BOD,COD, Chloride, nutrients and microbiological parameters. Also, some dissolved form of heavy metals such as Pb and Cr were analyzed. Principal component analysis revealed that the river water was negatively impacted by pollutants from anthropogenic sources as well as natural sources. Seawater intrusion faecal contamination and erosion of the soil into the river water are natural activities stressing the river water quality. Seven sampling sites of the main river and five sampling sites from its tributaries were selected considering the pollution impact on various activities. Sampling sites has been selected 58 km away from river mouth to landside up to Avissawella.
GPS locations with map – Kelani River
Evaluation of the water quality of Kelani River using Water Quality Index
pH ,Turbidity, Dissolved Oxygen , Biochemical Oxygen Demand, Chemical Oxygen Demand ,Nitrate , Phosphate and dissolved form of heavy metal in water such as Chromium and lead were considered to evaluate water quality index for all sampling locations in line with the proposed CEA’s inland water quality standards by using water quality data from 2010 to 2012. Since microbiological analysis were not carried out consistently for the total monitoring period. That was not considered for the evaluation of Water Quality index. Faecal coliform and the turbidity are always exceeded the standards in all sampling locations during total monitoring period.
Summary description of the water quality of Kelani River
The anthropogenic activity such as gem mining and river sand mining causes sever damage to the river bed and increases the turbidity of the river water in all sampling location . Microbiological contamination and the turbidity is major sources of water pollution in Kelani river. Turbidity (which is a measure of the light-transmitting properties of the water) is also a measure of the suspended particulate matter in the water and depends on the fineness and concentration of particles. The variation of turbidity is always associated with the incoming suspension of sediment particle flowing along with the storm water may be due to mining activities of the upstream of the river as well the continuous rain. Turbidity which implies the activity relates to sand mining , Gem mining and impact on uncontrollable urban runoff is always exceeded the standard value throughout the monitoring period in all sampling locations
Least no of parameters and the lowest frequency of deviation from the standard value are recorded in sampling sites at Hanwella and Welivita . Highest no of parameters and the frequencies of deviation from the standards are reported in sampling sites at Seethawake Ferry and Victoria bridge. . The water Quality index of these two locations is lower and the ecological condition of the water is poor.
The highest WQI score in the Kelani river was detected at the middle of the river located at Welivita (68) the lowest score was detected at the sampling site at Thulduwa ( 46) and Seethawake (51).
The quality of the river water at Thulduwa and seethawake ferry had inferior quality with compare to the lower reach of river and rapidly deteriorated during past three years rapidly. The ecological condition of two sampling sites indicates that the water quality is poor. The sampling site at Seethawake ferry gets the industrial waste water from the Seethawake industrial zone .The parameters always exceed are COD (37%),BOD (13%) Dissolved Oxygen (43%)and Heavy metals (7%)other than the turbidity.
The sampling sites in the middle of the rivers that is Pugoda Ferry, Hanwella Bridge, and kaduwela Bridge had a superior water quality compared to the its upstream ,may be due to the dilution effect receiving waters from tributaries, . The highest WQI is reported from the sampling sites at Welivita and Pugoda ferry . The ecological condition of these two locations is fair.
The WQI of the main tributaries such as Wak Oya , Pugoda Ela are in the range of 51-59 and the ecological condition is poor.
The worst ,very poor ecological condition is reported from the sampling sites at Raggahawatte which flows contaminated industrial waste water from Biyagama Industrial Zone. Most of parameters were exceeded the standard value during the total monitoring period which implies the industrial pollution. The parameters always exceed are COD (36%),BOD (7%) Dissolved Oxygen (27%)and Heavy metals (7%)other than the turbidity.
The secondly contaminated tributary is Ma Oya .It is mostly polluted due to the discharge of organic waste . ,Most of the time ,the parameters always exceed are COD (13%),BOD (60%) Dissolved Oxygen (80%)and Heavy metals (7%)other that the turbidity.
Microbiological pollutants in some locations may possibly due to the disposal of untreated or partially treated sewage (example, from household latrines and hotels, etc occurring on the banks) .Water Quality indexes evaluated annually is clearly indicated that the river water is deteriorated gradually in all sampling locations