The record flood of 10.87 lakh cusecs, received at and discharged from Prakasam Barrage recently, is being considered a good development by hydro-geologists of Krishna district.
Within just 19 days, the surplus over the crest of Prakasam Barrage is zero again. The floodwater that kept rising from September 30 reached a peak on October 6 and gradually reduced to zero.
The barrage authorities are releasing all the 17,000 cusecs being received from upstream to Krishna Eastern and Western Delta canals.
The geologists are sure that the freshwater-saltwater interface that moved inland in 2004 would have been pushed seaward. In a matter of weeks, they would be able to tell to what extent the line of interface has been pushed back towards the sea.
According to the present data, the groundwater in Nagayalanka, Koduru, Movva, Nandivada, Mandavalli, Kaikaluru, Gudivada, Mudinepalli, Kalidindi, Gudlavaleru, Bantumilli and Kruthivenu mandals has become saline due to poor flows in the Krishna and the canals for an extended period of over four years.
Freshwater in shallow aquifer zones is vulnerable to contamination from saltwater in lower aquifer zones. A poor flow in the river and canals coupled with heavy usage of groundwater accentuates the vertical hydraulic gradients of the saltwater front, causing rapid incursion of salinity into the groundwater.
The salinity in Krishna delta varies with depth and location. The rise in the salt concentration in wells in some areas is not uniform for a similar decline in the water table.
For example, groundwater in Gudur, Pedana and Machilipatnam mandals ranged between brackish and saline water. Avanigadda, Mopidevi, Pedaparupudi, Unguturu, Challapalli and Ghantasala mandals up to Pamarru were located on the freshwater-saltwater interface line.
The quality of groundwater in Penamaluru, Kankipadu, Vuyyuru, Thotlavalluru and Pamadimukkala mandals is considered to be of good quality.
The adverse impact of the poor flow into the river and canals, according to a survey, is a decline in rice production in tail-end mandals to the tune of 25 per cent to 50 per cent. In monitory terms, this would be close to Rs. 500 crores per annum in Krishna delta.
This does not include the indirect benefits and social costs that would be significant.
The powerful hydraulics of the floods usually results in the recharging of the groundwater through the shallow alluvial aquifers and also the paleo-channel aquifers, hydro-geologists say.