Chapter 6 · Try it yourself

Sand Budget

A beach is not a pile of sand. It is a river of sand that happens to be standing still for a moment. In Monterey Bay the sand comes in from rivers and crumbling bluffs, slides along the shore, and then drops into a canyon deeper than the Grand Canyon, right off Moss Landing. Change what goes in and out, and see whether the beach grows or shrinks.

Winter waves

Things people build

Map of a Monterey Bay beach.
Each moving dot stands for about 2,000 truckloads of sand a year.

This beach’s sand budget

Coming in

    Going out

      Change in beach width
      +5 m per 10 years

      Growing

      Simplified model with illustrative numbers for one stretch of southern Monterey Bay beach. One truckload is about 10 cubic meters of sand. We spread each year’s gain or loss over a 10 km long beach and a 15 m deep active zone (from the dunes out to where waves stop moving sand). The last beach sand mine in the United States, at Marina on this bay, stopped mining in 2020.