Thursday, June 23, 2005

Mail from Dr.D.N.Seshagiri #

I would like to know whether NEERI or INDOMER have carried out any geotechnical studies on the stability of the excavated slopes of the dredged channel. These slopes will be under a head of water. What is the angle for the cut slopes provided in the design? How many benches? If so, width of the benches. Has it been checked for its stability? The cut slopes of the Panama Canal (both above water line and below) still pose stability problems. What about possible heaving of the bed of the channel? Should there be a slope failure or heaving of the bed, will they not creat surges (mini tsunami?)Kindly refer to my letter published in Deccan Chronicle (Chennai edition) dated 21.06.05 entitled "Flip Side"

D.N.Seshagiri, Retd. Director, Geological Survey of India.
23 - 06 - 2006, 9.28 am


Our Reply:

1. To our knowledge, NEERI , INDOMER or L&T Ramboll Consulting Engineers Ltd., (who have prepared the Detailed Project Report for SSCP) have not carried out the geotechnical studies on the stability of the excavated slopes of the dredged channel.

2. The studies (as far as we know from the NEERI EIA and the Executive Summary of the Technical Feasibility Report) that have been conducted so far are as follows:

a) Analysis of Hydrography data of Palk Bay - collected by NHO

b) Geological Strata along Navigational Canal in Adam's Bridge Area - Jet Probe Drilling study - NSDRC conducted this with the help of Indomer Coastal Hydraulics Pvt. Ltd., - (Please note:No study exists for Palk Stait area still)

c) ‘Hydro Dynamic Modelling and Ship Manoeuvring Studies for SSCP’ - This, probably has been done using "Cornell Mixing Zone Expert System (CORMIX)" software - by Indomer-Alkyon (This modelling as we have noted in our article, has not considered the real time events of Cyclones or Tsunamis) (NEERI EIA does not mention Indomer with respect to this study; however, it is likely that it was done by Indomer as sentences of the Hindu press report we had quoted in our paper on Indomer and the one that is in NEERI EIA are similar but with some manipulation! (Note 1)

d) Bathymetry and Shallow Seismic Survey in Identified area (for the Canal) in Adam's Bridge - 4 km X 20 km showing bathymetry less than 12 m was idenified for detailed bathymetry and Seismic Survey in Adam's Bridge area. Micro Bathymetry was also carried out in 4 Km X 4 Km - Conducted by ? Indomer Hydraulics or NIOT, Chennai (Please note:No study exists for Palk Stait area still).

3. Wih respect to the study on the Geological Strata of the identified area (for the canal) in the Palk Strait area, the following note, by none other than NEERI (in the executive summary of the TFR), is of great concern for everyone:

"The costs may face upward revision as it has been observed that in more than 50% of the dredging contract there has been very large cost overruns mainly due to poor soil investigation. Investigations carried out in this study are based on sub-bottom profile except for three borings in Adam’s Bridge and there is apprehension that hard strata will be encountered in Palk Bay/Palk Strait area. If bottom strata turn out to be rock, the dredging costs will change drastically, as blasting might be required." (Ex.Summ.NEERI TFR - p.xviii)


4. We share your concern that as the channel's slopes will be under the water head, a thorough study of them is necessary.

5. The channel will have side slopes of 1:3.




(Courtesy : Ex.Summ. NEERI TFR) (Note 2)

6. How many benches? - Nothing is reported in the published material available with us (EIA and Ex.Summ. TFR)

7. Yes. We agree. Slope Failiure or Heaving of Bed can not be ruled out till you have the consistent studies that prove otherwise.

8. Mini - sea surges (should we use the term tsunami here?) - is defintely a possiblity.

.......................................................................................................................................................

Note 1. The Hidu report says : "Tide/wind induced flow during various seasons, the wave propagation, (and) the sediment transport pattern remain similar with the same magnitude and direction after opening the channel for the region falling 500 metres away from the channel..."
At the same time, NEERI EIA tells us: " ...It can be inferred from these graphs that the effect of the sity water when discharged will be localised and restricted to about 1000 meter from the discharge point..." (NEERI EIA p-6.9)

Note 2. Executive Summary of NEERI's Technical Feasibility Report can be downloaded from the following link. Please find it at the attatchment section at the end of the article you see in the link. Click Here to access the link.


# Dear Dr.D.N.S!

We would be glad to have your letter to Deccan Chronicle titled "Flip Side" published here in this blog.

Please send it to : manisanga@gmail.com

Thank You

Yours Sincerely,

Dr.R.Ramesh

............................................................................................