Shorelines can grow (accretion) or recede (erosion) due to waves, currents and the interaction with man-made or natural obstacles.  When working in the coastal environment it is critical to understand the sediment budget - where the sand comes from and where it's going.  When in balance, the beach is in equilibrium.  When out of balance, the shoreline can move, sometimes rapidly and sometimes resulting in damage to upland infrastructure. 

Sediment movement on a beach is characterized, typically, by analysis of the site's sediment budget.  OCC determines what enters, stays, moves landwards or leaves the site to formulate that budget to estimate shoreline change and designs that might address it.