Bonnie Ludka, PhD, of Scripps Institute of Oceanography (SIO), spoke to about 40 people at the Tijuana River National Estuarine Research Reserve June 15 as part of the their bi-monthly speaker series. Ludka presented the results of her research into the movement of beach sand along the coast and the impact of beach nourishment on the closure of the Tijuana River in 2016. Southern California beaches are experiencing a sand deficit. She explained that beach sand is normally created by sediment flowing from rivers and cliff erosion. Unfortunately, river sand that would normally flow into the ocean is now trapped behind dams that are present in every southern California river except the Santa Margarita river near Oceanside.