Groins, sand retention, and the future of Southern California’s beaches

Abstract

Beaches form a significant component of the economy, history, and culture of southern California. Yet both the construction of dams and debris basins in coastal watersheds and the armoring of eroding coastal cliffs and bluffs have reduced sand supply. Ultimately, most of this beach sand is permanently lost to the submarine canyons that intercept littoral drift moving along this intensively used shoreline. Each decade the volume of lost sand is enough to build a beach 100 feet wide, 10 feet deep and 20 miles long, or a continuous beach extending from Newport Bay to San Clemente. Sea-level rise will negatively impact the beaches of southern California further, specifically those with back beach barriers such as seawalls, revetments, homes, businesses, highways, or railroads. Over 75% of the beaches in southern California are retained by structures, whether natural or artificial, and groin fields built decades ago have been important for local beach growth and stabilization efforts. While groins have been generally discouraged in recent decades in California, and there are important engineering and environmental considerations involved prior to any groin construction, the potential benefits are quite large for the intensively used beaches and growing population of southern California, particularly in light of predicted sea-level rise and public beach loss. All things considered, in many areas groins or groin fields may well meet the objectives of the California Coastal Act, which governs coastal land-use decisions. There are a number of shoreline areas in southern California where sand is in short supply, beaches are narrow, beach usage is high, and where sand retention structures could be used to widen or stabilize local beaches before sand is funneled offshore by submarine canyons intercepting littoral drift. Stabilizing and widening the beaches would add valuable recreational area, support beach ecology, provide a buffer for back beach infrastructure or development, and slow the impacts of a rising sea level.

A Model Integrating Satellite‐Derived Shoreline Observations for Predicting Fine‐Scale Shoreline Response to Waves and Sea‐Level Rise Across Large Coastal Regions

“…In California, in particular, the sources and magnitudes of sediment input remain critical gaps in littoral sediment budgets and in the long‐term survival of beaches (particularly those in natural settings) in response to SLR (Warrick et al., 2023). In highly urban settings/environments (which are generally without significant fluvial‐sediment input), we believe that the survival of beaches in urban environments will increasingly rely on beach nourishment and/or sand retention (Griggs et al., 2020). Yet, better satellite observations (with increasingly higher image quality and quantity) and better satellite‐data‐assimilated modeling predictions (such as those developed in the current paper) will be critical to design and monitor the effectiveness of engineering interventions and nature‐based solutions.…”

Coastal Restoration Challenges and Strategies for Small Island Developing States in the Face of Sea Level Rise and Climate Change

“…Typically made of concrete, rock, or other durable materials, these structures are designed to safeguard vulnerable coastlines. However, it is important to note that they can contribute to accelerated erosion on adjacent beaches [195]. To mitigate such negative impacts, these structures could be combined with complementary measures, such as artificial reefs, coral reef restoration, restored living coastlines, or other green strategies aimed at reducing wave energy and runup impacts.…”

Coastal Adaptation to Climate Change and Sea-Level Rise

“…The ecological consequences of beach replenishment can also be significant [82]. In order to be effective, beach nourishment needs to be combined with sediment management techniques; ideally sand retention efforts [83,84], whether groins or some other mechanism to hold the sand in place so that it survives for a longer period of time and avoids frequent and costly sand feeding cycles. This requires understanding and characterizing the historic causes of erosion, either episodic or chronic, the long-term littoral drift rates and directions, and the natural processes [63,85].…”

“…In the USA, some coastal states have essentially banned any new hard structures altogether, while others have made it more and more difficult to obtain a permit unless the primary structure (a house for example) is under imminent threat. The era of routine armoring of any eroding stretch of coastline in the United States is ending, as the negative impacts of protective structures have been increasingly documented, recognized and understood and the inevitability of future sea-level rise has become more obvious [40,84]. While armor can provide short-or intermediate-term protection for private property and public infrastructure, with a changing climate and a rising sea, there are no future guarantees that today's armor will survive far into the future.…”