18 Sep DREDGING SAND IN AKULAM KAYAL
DREDGING SAND IN AKULAM KAYAL
As part of the Malayalam news bulletin, an interesting report with visuals of piled up sand was on the screen of my TV in the Kairali channel this morning at 7:00 am. I saw the blue and striped kurta wearing image of Thomas Issac also somewhere along. The voilce over said about 1 laks tons of sand now recovered as part of the program of cleaning the Kayal. This sand dredging or recovery of construction sand was part of the project launched by the Travancore cements or someone like them. There is also a plan in Thiruvallom too to go for dredging.
1. Only point I want to bring to public notice is that the sand pile in Akkulam and that might come up in Thiruvallam are part of ancient beach deposits. In fact the google earth image I am attaching will add science to my sentences. Once up on a time our seashore in Trivandrum was like to the east of Attukal Temple, Thampanoor, Pettah, Anayara and toward north further, i.e., far inaland of the modern shoreline. The Veli Hills (ridge) formed the northern boundary of the embayment, while the southern boundary of this “bay” was along the Thiruvallom Hills, whose northern edge of the latter is skirted by the Kaimanam Thiruvallom road. The drainage course were also active in that deeper time.
2. As time went by like around 4000 -4500 years ago, the sea reached the present position by a relative fall in the sealevel converting the entire bay like area into land. The Akkulam kayal is the channel for the drainage from the hinterland of Trivandrum (most of the present city) and the monsoon discharge maintained the channel that is cut through the ancient fill of sea or beach sand.
3. When the co-op bank building, east of “Padmatheerthom”, foundation was tested, before construction of the structure, some kind of drilling was employed to get samples of the substrate and it so happened a piece darkgray clay sample, recovered from the boreholes, landed on my office desk, for verification of the sediment type. But what also attracted my attention was the presence of foraminiferal tests – fossils of a marine micro-organism. To me it was the sure hint for the existence of western sea behind the Eastfort Bust Station. A s geologist, I will extend that sea to all the land at the elevation of Eastfort bus stand.
4. When the TTP wanted an extra source/supply of water the CGWB (Central Ground Water Board) was requested for help, who advised sinking of two large diameter wells in their campus at Veli. The exploratory work revealed presence of a thin limestone layer in the TTP compound to the western side of the Kochuveli Train station. This is a “smoking pistol” in so far as the presence of the western sea inside the modern land area in coastal Trivandrum. In fact, between the headlands formed by the Veli Hills of VSSC to the north and the Thiruvallom Hills in the south, there existed a large bay like extension of the modern sea, which gradually got filled in with sea and beach sediments. However, the drainages along the Akkulam kayal and the Karamana ar continued to exist and were maintained by the monsoon discharge from the land area in the east. This patch of todays land and some water courses, is in fact a reservoir of 1000s of millions of beach sand, which geoscientists will designate as ancient beach alluviam.
5. Say 4000-4500 yr ago B(efore)P(resent), the Akulam kayal basin and Karamana ar mouth were somewhere far landward of the modern shoreline, which gradually migrated toward the modern shoreline, through and over a substrate of beach sand brought in by the waves and currents of the western sea. Therefore we can dredge and get sand from the shallow waters, and if dredged somewhat deeper we will also come across the limestone reported by the CGWB from the TTP compound. As one went deep into landward the limestone has changed or “morphed” in to marine fossil bearing dark-gray shale (shale is a fine clay rich rock) that appeared in the subsurface underneath the co-op bank building at the East fort.
6. So what is the point of this note. Firstly it is no surprise to have hit the mother lode of sand. The geohistory has it that way. Secondly it is not construction grade coarser sand instead it is medium to fine beach sand and in fact ancient beach sand. Further, the volume of shell and shell fragments in the sand may be deleterious for the proposed end use.
7. I am unsure whether or not any mandatory clearance of any sort is required for changing the bottom-scape or bottom topography of the Akkulam kayal, which has a shoreline richly endowed with several important mangrove plant species. Once the kayal bed is deepened by dredging and removal of sediment, the shore sediment at equilibrium with the original kayal floor will get disturbed and the only means of reestablishing a new equilibrium will be by subaqueous slumping which will affect the modern shoreline and everything practically living attached to the shore sediment. The mangroves are no exception to this law of nature.
8. I am not sure if any scientific outfit of the government ever gave clearance for this sort of dredging sand from the kayal or river bed. The scientific approval is important in issues like this, unlike the so called administrative approvals where the scientific input is limited to the science of paper making and the software.