The dam driver of our disappearing beaches

By Anna Talken

From the pristine, desolate beaches along the Lost Coast to the white sandy beaches in San Diego, California offers a diverse array of coastal beauty. Wildlife thrives in many of these ecosystems, such as around Point Conception in Santa Barbara County, a coastal biodiversity hotspot where the southern and northern ranges of many species collide. Beaches are refuges for many types of invertebrates, seabirds and marine mammals. They also provide recreational opportunities for people and support a significant portion of California’s tourism economy. Nearly 40% of the world’s population lives in the coastal zone, and in California alone, roughly 40 million people live in coastal counties.

Unfortunately, natural processes such as coastal erosion threaten oceanside environments where we often recreate and build communities. This dynamic zone on the edge of land and sea is constantly undergoing morphological changes. Coastal erosion is not a new phenomenon, as it has began long before humans inhabited the planet. Processes including storms, tsunamis, and changing sea levels have continuously altered the coastline. However, human activity has had a profound influence on the rate of coastal erosion. Estimates show that the amount land lost to coastal erosion between 1984 and 2015 is nearly double the amount of land that has accreted, illustrating the instability of this nearshore zone. While sea level is often portrayed as the primary driver for coastal erosion, other anthropogenic activities that cause the disappearance of our beaches are often overlooked.

Ironically, one reason why beaches are disappearing globally is due to a specific type of infrastructure located inland. Dams are one of the primary drivers of coastal erosion, impeding sediment flow and as a result drastically altering the sand replenishment along the coastline. Over the past 150 years, nearly 1,500 dams have been constructed in California for water supply, flood control and hydroelectric power. However, the environmental impacts associated with dams have been largely overlooked, from the destruction of habitat and blocking important fish species from reaching the ocean, such as Steelhead, to restricting the flow of sediment to the coast.

Nearly 100 billion tons of sediment are estimated to be stored behind dams worldwide. On a local level, an estimated 3 million cubic yards of sand is trapped by the Matilija dam in Ventura. As sea levels rise and natural causes that lead to coastal erosion, including storms and cyclones, are projected to worsen under future climate conditions, the future of beaches has never been more at stake.

Instead of addressing the problem upstream, efforts to shield coastal communities result in failing infrastructure on the coast. In an attempt to artificially protect a shifting coastline, people across California continue to build seawalls, revetments and groins. By 2018, nearly 150 miles of the California coastline had been armored with seawalls and other artificial infrastructure to prevent coastal erosion. Unfortunately, these efforts have unintended consequences. Beaches in front of seawalls vanish as storm surge and wave action pulls the sand out to sea and a lack of sediment replenishment from coastal bluffs starves the beaches of sand. Over time, areas with seawalls may temporarily protect the homes behind them, but at a high cost – beaches that once were thriving ecosystems and recreational areas are now entirely gone.

Restoring our beaches and protecting the California coastline is not hopeless. ‘Green infrastructure’ has been utilized to reduce coastal erosion by planting vegetation and rebuilding dunes instead of constructing seawalls. Restoration of mangroves, seagrass beds and estuarine ecosystems aid in buffering the coast and retaining sediment. Yet, the removal of dams may be an overlooked way to restore sediment to our disappearing beaches. The removal of the Elwha and Glines Canyon Dams from the Elwha River, Washington beginning in 2011 represented the largest dam removal project in history after nearly 100 years of the dams reducing sediment flow to the coast. Roughly 18Mt of sediment was resupplied to the coast after the first 5 years, resulting in shoreline accretion in an area that had been battered by coastal erosion prior to the dam removal. The Matilija Dam in Ventura is scheduled to be removed by 2025, which may help to replenish local riparian zones and beaches. Removing dams has proved to be a costly and lengthy process, but can be an important step for retaining our beaches, restoring riparian habitat and opening up river runs to economically and culturally important fish species.

Because of our innate human desire to live in coastal environments, we have attempted to control natural processes and alter the ecosystem to benefit our needs. We dredge harbors to prevent sandspits, construct groins to alter longshore drift and bring in trucks full of sand to artificially restock our disappearing beaches. We have built dams that have stopped millions of tons of sediment from replenishing the shoreline and constructed monstrous seawalls that have caused the powerful ocean to swallow up beaches. Nature managed to sustain its beaches for millions of years without artificial interference – the more we attempt to override natural processes, the more it seems to cost us. Removing dams may be an important step towards restoring the natural flow of rivers and letting nature replenish the coastline as it has always done.