Complexities in coastal sediment transport studies by numerical modelling

Abstract

Marine environmental studies related to erosion, accretion, pollution transport, dredge disposal, location of seawater intake, effluent disposal, etc., involve sediment transport studies. Numerical models use set of well linked mathematical equations arrived based on scientific principles as all natural phenomena are governed by certain rules which can be explained by scientific principles. Efficiency of numerical modeling greatly depends on quality of input parameters. When input parameters vary unpredictably with respect to time and space, many times fitting them well in numerical equations is a great task. Numerical modeling of coastal sediment transport uses input parameters such as data on suspended sediments, short duration time series data on tide, current, wave and wind, bathymetry and nature of seabed, etc. Tide is predictable to reliable extent as tide governing events and forces are cyclic in systematic natural processes. This is not same in cases of winds, waves, currents, river discharge and suspended sediment load in terms of magnitude and direction as they cannot be predicted accurately based on short term observations over space and time though their trend for a region can be obtained. If the coastal region includes rivers, obtaining reliable time series discharge data is very difficult due to irregular rainfall intensity and agricultural usage of river water in the region. Due to these conditions, numerical modeling in coastal sediment transport studies could not be validated well many times. In this manuscript, data on suspended sediment load at surface, mid-depth and bottom of a coastal location, off Dahej, west coast of India, observed every hour for 48 hours continuously have been presented and through which authors have tried to convey the complexities involved in accurate prediction of coastal sediment transport studies by numerical methods due to some unpredictable variations in the input parameters pertaining to the challenging coastal environments