NIO'S COMMENTS ON SEA INTRUSION
The recorded data on sea level rise (SLR) at Karachi and adjoining Indus deltaic area is based on the data collected over the past 100 years. The estimated rise is 1.2 mm/year and it is expected to double during the next 50 to 100 years, resulting in 20-50 cm rise in sea level (UN ESCAP, 1996). The adverse effect of sea level rise on the Pakistan coast is expected to be pronounced in the Indus delta because the delta is generally flat and low-lying.
There are no direct measurements on subsidence rates in the Indus delta, however, experience in other deltas indicate that subsidence rates at the delta must have increased due to lack of sediment flux. Indus delta could have a relative sea level rise of up to 8 to 10mm/yr as per the projected rate of global component of sea-level rise of up to 6mm/yr in the next century. If the present trends continue the Indus delta will ultimately establish a transgressive beach dominated by aeolian dunes, due to lack of sediment inputs and the high energy waves (Haq, 1999).
NIO is of the view that the Indus delta is experiencing sediment compaction like other major deltas of the world mainly due to sediment starvation and ground water extraction. However, no observed data is available to provide concrete validation of the compound impact of sea level rise and ground subsidence. The ground subsidence has already resulted in the sea water intrusion upstream to 80 km in the coastal areas of Thatta, Hyderabad and Badin districts. The primary impacts include the erosion of beaches, flooding and inundation of wetlands and lowlands, salinization of ground and surface waters, extended intrusion of sea water, and impact on mangrove ecosystem and coastal agriculture.
Long duration study is required to identify the vulnerability index of creek system, for which oceanographic observations are planned. The exact extent of the land loss has yet to be determined. The Ministry of Science & Technology has established a Seawater Intrusion (SWI) and Land subsidence (LS) Cell at NIO. The Cell is comprised of the scientists and officers of NIO, SUPARCO, Hydrography Department, Pakistan Navy, and the Ministry of Defence.
The acquisition of oceanographic, Remote sensing and coastline/bathymetric observations along the coast and adjacent areas are critical in devising control measures, and suggesting management plans.
Iincreased threats of cyclonic activity in the Arabian Sea is likely to make the two coastal provinces more vulnerable in terms of loss of life and property not only in the coastal areas but this may also extend inlands. Particularly under threat is Karachi, the largest city of the country and the hub of its industry (TFCC, 2010). In view of the scenario, and the National Institute of Oceanography (NIO) and SUPARCO have jointly prepared a PSDP proposal which was submitted as a PC-1 " Monitoring The Sea Level Rise, Sea Water Intrusion And Land Subsidence In Indus Deltaic Creek System With Special Reference To Sindh Coastal Cities Flooding" to the Ministry of Science and Technology, Government of Pakistan. The main objectives are to undertake long term qualitative and quantitative data collection using in-situ observatories and Remote Sensing Technology with a focus to address this issue. Only after undertaking a detailed study, it would be possible for the Seawater Intrusion Cell to identify vulnerable spots along the Pakistan coastline and also to estimate/predict the extend of potential threat due to climate change and other natural threats.