Farmers can tap it using ‘skimming wells’, says study
There is hope for farmers who have farm lands in the 13 mandals of Krishna district with incursion of saline water.
According to an extensive study made by civil engineer and faculty member of Velagapudi Ramakrishna Siddhartha Engineering College Kudaravalli Seeta Ram Prasad, there is enough freshwater in the ground to raise a crop even in these mandals. Fresh water is available in the form of “floating fresh water pockets.”
According to the Groundwater Department data, 13 out of the 28 delta/coastal mandals in the district have been categorised as saline. The mandals are Gudlavalleru, Guduru, Kaikaluru, Kalidindi, Koduru, Kruthivennu, Machilipatnam, Mandavalli, Mudinepalli, Nagayalanka, Nandiwada, and Pedana. As per the estimates of the department, 93,712 hectare metres of saline water is available in these mandals.
But, according to the survey made by Mr. Ram Prasad for his doctorate on ‘Hydrochemical studies and groundwater potential of Krishna Eastern Delta’, floating freshwater pockets are available all along the coast. Because of the higher density of saline water than the fresh water, rainwater collects in pockets over the saline groundwater, thus being referred to as floating fresh water pockets.
Groundwater quality maps
Fresh water from these floating pockets could be pumped up using ‘skimming wells’.
Mr. Ram Prasad, in a span of eight years, has prepared detailed maps of groundwater quality, measuring important laboratory parameters like electrical conductivity, Chlorine-Bicarbonate ratio, Chemical Facies, Wilcox classification, and US Salinity.
Using surfer software, he has prepared contour maps. With the help of these maps, it is possible to sink skimming wells and pump out the fresh water from the pockets, Mr. Ram Prasad says.
The fitness of groundwater for irrigation depends on the electrical conductivity. It is an index of the dissolved solids concentration. Low salinity water has conductivity between 0 and 250 micromhos/cm. Low salinity water can be used for irrigation with most crops on most soils. Medium salinity water has conductivity between 250 and 750 micromhos/cm. Plants with moderate salt tolerance can be grown (grasses do well) with it. High salinity water has conductivity between 750 and 2,250 micromhos/cm. This water should not be used on any soil with restricted drainage or where excessive water is not available for continuous leaching. Special management for salinity control is necessary with this water.
Mr. Ram Prasad says the quality of water pumped up from the skimming wells should be constantly monitored because it is not unlimited. Crops could be cultivated by selecting saline-resistant varieties and mixing fresh water to saline water to reduce the conductivity.