**4. Measures to halt sea water intrusion**

Where sea water intrusion is already a fact, there are measures to halt it. First of all, groundwater extraction should be diminished. While there are no visible signs of sea water intrusion in the Kerala Tertiary aquifers, there is a gradual development of surface water utilization for the larger towns in the coastal plain, which is a good measure to protect the coastal aquifers. On the Indian east coast, this is more difficult as the river flows are lesser there. Ballykraya and Ravi [13] describe the creation of a barrier by artificial recharge near the coast. A similar measure has been taken in the Salalah plain by well recharge of treated waste water along the coast line [14, 15]. A new approach, which could be more efficient, is when fresh water recharge into the nonsaline part of the coastal aquifer is combined with pumping of saline water near the shoreline [16].

Other aquifers on the Indian east coast has groundwater of a similar age and the same period and mechanisms of recharge may apply [9, 17]. The paleoclimatic data from India are abundant from both marine sediments as well as local pockets on current land illustrating the

**Figure 6.** Sea water levels during the last glacial period. The SW monsoon had, as per the abundant paleoclimatological

Recharge and Turnover of Groundwater in Coastal Aquifers with Emphasis on Hydrochemistry…

http://dx.doi.org/10.5772/intechopen.73301

83

The past climate change has, in several aquifers near sea, formed a sequence of Ca-HCO3 → Na-HCO3 → Na-Ca-Cl types of groundwater formed by flushing of an initially formed saline/ brackish aquifer by fresh water [24, 25]. This could be seen laterally in Kerala (**Figure 1**). The direction of the recharge flow is from SE toward NW directed by the topography of the underlying Precambrian, which is likely to be intersected by faults in the same direction. The same zonation is seen depth-wise for instance in the Mekong river delta and in the Red River delta in Vietnam [26].

A secondary effect of flushing is that the softening effect of the process creates Na-HCO<sup>3</sup>

the case on the Indian SE coast where the sedimentology is more intricate [10, 11].

of groundwater (**Figure 7**) which tends to mobilize fluoride [27–30]. Where the recharge is less of a "piston flow" process, there will be more mixed forms of groundwater types. This is often

Another effect of the last glaciation is the common occurrence of arsenic in groundwater in Holocene sediment, for instance not only in the Bengal delta [31–36] but also in other coastal plains in S and SE Asia [37–39] like in the Mekong river delta, the Red River delta, and the Irrawaddy river delta. When the sea level was lowered before Last Glacial Maximum (LGM) at around 18 kA before present, the sediments were subject to erosion and redeposition and this lowered the organic matter content [39]. Contrarily, after LGM, the sea level rose and created abundant wetlands rich in organic matter [40]. These sediments become easily anoxic with reduction of ferric oxyhydroxides and mobilization of arsenic into groundwater [41].

type

variations in the strength of the SW monsoon [18–23].

data published, a wet period before LGM followed by a dry period after the LGM.
