The main theory on Coastal Erosion is the “Sea Level Rise”. The most of the present coastal scientists and coastal engineers say, Sea Level Rise is the cause for coastal erosion. This theory is wrong, though it contributes a fractional amount. And when the slope of the sea bed is very low then it may bring a sea invasion. In the pic below, the slope being very low, a slight rise in sea level causes a sea invasion. But this could be easily mended with biological approach