Workers in Del Mar are finalizing an elaborate drainage system along the cliffs to prevent erosion that threatens a vital rail corridor. Like many coastal areas in California, the cliffs in Del Mar have been eroding at an average rate of six inches per year, with urban runoff and rain contributing to the problem. During wet and stormy periods, as much as six feet of the cliffs can crumble onto the beach below, posing a risk to the rail tracks that carry thousands of passengers and freight daily. The drainage system is designed to capture and redirect water from urban runoff and rain, which are the primary causes of erosion from the top down.