As if the constant attack on coastlines by storms, waves, and currents were not doing damage enough, the “works of man” have greatly exacerbated coastal erosion, in both the short and the long term. And often the most damaging activities take place far from the ocean.

Our preliminary research, surprisingly, tells us that the primary cause of sediment removal from beaches is not dams but sand and gravel mining. Dams are the second major cause. Sand mining along the beaches of California and Oregon began in the late 1800s. Although it had been outlawed by 1991, substantial legal mining still goes on in coastal watersheds and even a stretch of coastal dunes near Monterey. Overall in northern California, from the Russian River to the Oregon border, some 11 million tons of sand and gravel are removed each year. That figure pales in comparison with southern California, where an annual average of 55.8 million tons is extracted, mostly around Los Angeles and San Diego, though wherever there is major construction of roads and buildings, there is usually a mine nearby.

All this extraction affects the shoreline. Even off-stream gravel mining is detrimental to beaches. Floodplain mining creates large pits next to dynamically changing river channels. If these pits are flooded during peak flows, they act as sinks for sediment. The normal transportation of sediment helps to dissipate a river system’s energy. When sand and gravel are removed from within the channel, “hungry water,” deprived of its natural sediment content, creates a disequilibrium that can cause erosion of gravel bars downstream.

The second major cause of sediment removal is damming. More than 500 dams impound rivers and streams in California, affecting 38 percent of the coastal watershed (some 16,000 square miles). The dams reduce the average annual sand and gravel flow by 2.8 million cubic meters (enough to fill 1,000 Olympic-sized swimming pools) or 25 percent of normal, according to Cope Willis and Gary Griggs in the Journal of Geology (June 2004).

There are also a few minor culprits: “debris basins,” built to trap sediments during floods; seawalls or coastal armoring, which can have major local impacts; dredged navigation channels, where material is taken offshore out of the nearby littoral system, as happens in Humboldt Bay and the Columbia River estuary; and subsidence, both natural and human-induced.

Whenever sand or gravel is removed from the ecosystem, a cost, often a substantial one, is incurred downstream. Yet in project cost estimates for commercial shipping, building dams to provide water and power, or mining for construction, the cost to the coastline of sediment loss is not included. If it is referred to at all, it is considered an unpriced externality and largely dismissed.

We have attempted to calculate the amount of sand and gravel lost to the beaches and to estimate the actual cost of those externalities, for they are only “external” to those doing the extracting. To ignore them is poor accounting as far as society as a whole is concerned. To those who live along the coast or enjoy the shore, their loss is of major consequence.

If we as a society choose to tacitly accept the underpricing of certain endeavors by ignoring the negative “downstream” consequences, we should also bear the cost of compensating those who suffer losses. Yet as public monies available for that purpose become increasingly scarce, more and more often the damage goes unrepaired. In the meantime, the costs—in this case to beach communities—mount, while those who profit from the mining or dam building incur no costs from using up the natural resource, and therefore have no incentive to avoid sediment losses to the shoreline.

The economic impact of sediment losses can be estimated in three ways: in terms of replacement cost, remediation cost (which attempts to compensate for past and future damages), and repair cost (or “fixing” the shoreline to protect against future damage).

Rather than incur these costs, a far more attractive alternative for industry would be to explore more aggressively the alternatives to mining virgin aggregate.

One option, already widely used in the United States and elsewhere, is to use recycled concrete products rather than “virgin” sand and gravel in the foundations of buildings and roads. The many benefits include improved performance—in greater strength and durability, control over gradation, and the potential to minimize cracking; and reduced environmental impacts—less disposal and dumping, fewer unsightly piles of concrete rubble blighting the landscape, and of course more virgin aggregate available for projects that really need it. Economic benefits include shorter hauling distances of material that would otherwise be considered waste, and general cost savings through the use of less virgin aggregate

Sand and gravel mining is not going to stop, and although very few dams were built in the last 20 years, there is continual pressure to build more. Neither industry is likely to offer compensation voluntarily for removing beach material. Meanwhile, the coastline of California, particularly southern California, is in constant threat from erosion. If there is to be any change in the regulations governing beach deprivation, and sand and gravel mining in particular, those who are paying the price must become much more vocal in their protests.

Orville T. Magoon, president of the Coastal Zone Foundation, has more than 35 years of experience with the U.S. Army Corps of Engineers in coastal zone management, coastal structures, and their rehabilitation.

Linda K. Lent, who runs a consulting company based in Bethesda, Maryland, has been evaluating the economics of shoreline and other water resource issues for 25 years.

This article is greatly abridged. For the full text, see the print edition of Coast & Ocean.