Failure of Coastal roads in every monsoon, is due to un-scientific design/construction activities?

Densely populated coastal stretch of Kerala state approximately 600 km long, having severe erosion of roads due to high waves during the south-west monsoon every year. Government being spent millions of rupees every year before and after monsoon periods and this become a routine process. Don’t we have a long term solution to this issue? Are we dealt with this issue scientifically? Our maritime standards are not updated since 1980, research and developments in this area are significantly advanced for the last three decades particularly in Europe. We have excellent institutions across our country, unfortunately no specific curriculum and career guidance in this sector. Our coastline is more than 5000 km, unfortunately we don’t have a code of practice or at least guidelines for the design and construction of coastal structures such as revetments, coastal protection system and breakwaters particularly for rockworks.

Each location should be considered uniquely in terms of its topography, bathymetry, and presence of natural headlands, artificial groins or offshore breakwaters as the artificial nourishment prevents or reduce the potential erosion. We should also recognizes that sound understanding of ground and environmental conditions are essential at each location to establish maintenance free, long serving and low failure protection system.

Oceanographic field data acquisition is necessary to establish site conditions as well as to provide a means of calibrating the numerical wave model used to provide design wave, current and tide details. Alternatively these data can be acquired from relevant port authorities provided that the data is adequate and having a minimum period of one year, preferably ten years or more.

Numerical wave modelling shall be undertaken to determine the wave climate that impacts at the coast and the proposed edge protection system. The wave model shall be constructed based upon wind and wave data obtained from the data collection studies above. The numerical wave model results at near shore locations shall be used to design the edge protection system. Studies shows that significant wave heights for near shore determined from offshore waves taking into account shallow water effects such as refraction, diffraction and shoaling, the process would result into up to 20% uncertainty. The above investigations and studies shall comprise the following minimum information / activities for the edge protection design / construction for each location.

·      Most significant wave height (Hs) for return periods of 1,10,25,50 and 100 years including wave periods.

·      Tides and current data at each location

·      Geotechnical site investigations for bearing capacity, settlements and slip failure assessments.

·      Topographic and bathymetric survey details

·      Identify relevant nearby quarries and prepare quarrying plans including transportation arrangements from quarry sources up to stacking area near the work site. 

·      Design the protection and under layer system either Hudson or Vander Meer theories conforming to CIRIA rock manual

·      Check the geotechnical stability for slip failure including increase in pore water pressure during storm.

·      Establish a safe level of the top of road by allowing minimum overtopping discharges during monsoon.

·      Provide suitable pedestrian path and drainage facility throughout the length of road

·      Provide wave reflection walls on the sea side of the road in order to reduce the overtopping discharge.

·      Physical model testing may be required to establish that the above design data at specific locations where wave data are not reliable or other reasons like complex bathymetry and near shore wave transformation inaccuracies.

·      Finally a reliability check ie the design of the proposed protection system should be such that, during the construction and throughout its indented service life, it has an acceptable low probability of failure. A service life of 25-40 years is reasonable to consider for the design with nominal annual maintenance. The design wave should normally have a much longer return period in order to reduce the risk of failure. The analysis requires realistic collection or establishment of uncertainties related to construction materials and inaccuracies or deviations from the design and more importantly the uncertainties related to design wave height as stated above. If the probability of failure is not acceptable, the design must be further refined to achieve the required low probability.

·      Materials and construction quality control and assurance required to follow strictly the requirements of CIRIA rock manual.