In former days no new water was supplied to the tanks during dry season. The stored water was used for irrigation. At the end of the dry seasons no water was left in Valakulam tank (tank no 7) and the riverbed was used for growing cucumbers and other vegetables.
Today there is a new water sources for the tanks. Sewage water is a constant stream which feeds the tanks also during dry season. Throughout the city surface rainwater gets harvested from the streets and is directed via drainage systems to the tank. Unfortunately these drainage systems are misused. Sewage water is let in and is reaching the tank without treatment. The key victim is Valankulam tank since this tank is located in the centre of the city.Drainage system (open and closed)
Sewage water from households (washing, cleaning and toilets) contains a lot of nitrogen and phosphorus, - prefect growing conditions for water hyacinth. Furthermore the weather conditions during dry season enhance growing. Temperature between 28 and 32 degrees lots of blue sky and sunshine are idle. All these factors make water hyacinth growing faster. The growth slows down during monsoon when the temperature gets a bit cooler the sky is cloudier and the nitrogen and phosphorus concentration gets diluted.
Now we are looking for treatment options of the sewage water to slow down the water hyacinth growth.