(net ÷ gross, +1 = all north-west)
Waves that reach a beach at an angle push sand along it. Here almost all the energy comes as swell from the south-south-west, south of the direction the beach faces, so each wave nudges sand toward the north-west. Summed over every hour of wave data since 2015, the drift is north-west on the open beaches on both sides of the cove, and at the point itself. That changes where to look for the break's sand.
North-west in every year, every season, every month.
Potential alongshore transport, computed hour by hour and summed. Each check changes one assumption; none flips the direction.
| Check | South-east of the cove | The point | North-west of the cove |
|---|---|---|---|
| All hours, 2015–2026 | +0.90 | +1.00 | +0.90 |
| Beach angle rotated −10° / +10° | +0.80 / +0.95 | +0.99 / +1.00 | +0.79 / +0.95 |
| Different transport formula (energy flux) | +0.90 | +1.00 | +0.89 |
| Weakest single year (2016) | +0.74 | +0.99 | +0.73 |
| December–March only | +0.36 | +0.99 | +0.35 |
| Swell and wind sea split apart, 2022–2026 | north-west every month | north-west every month | — |
Sand drifts north-west along this coast, so the point is fed from the south-east, the Troncones side.
Swell arrives from a median 194°, with the middle 80% of hours between 181° and 214°. The open beaches face 237° and the point faces 275°, so the swell always strikes from the south of the beach's facing direction and pushes sand north-west. Wind-driven waves here are small and carry almost none of it. December to March is the weakest season, when more waves come from the west, but even then the net is north-west.
The break's sand comes from up the coast.
If the drift is north-west, the sand that feeds the point arrives from the south-east, and anything that reduces that supply matters to the wave. The walls and decks in the cove, and the newer wall about 1.4 km north-west, all sit down-drift of the break. That makes them an unlikely way to cut off the break's own supply; their possible effects are local, and they are being tested separately.
Several possible influences on the supply have been reported but not yet measured:
- New construction in Troncones, up-drift of the break. The satellite record here ends about 3 km south-east of the break, so most of Troncones is not yet covered.
- Sand trucked in by some establishments. Placed sand can hide erosion from satellites, can differ in grain size from the local sand, and removes sand from wherever it was taken.
- The creek and lagoon outlets, which deliver sediment in floods. A pre-registered test of where the September 2026 flood plumes travel runs on the next clear satellite images.
- Dams and sand extraction upriver, still being researched.
None of these has been tested. They are where the next measurements should look.
This is potential drift, not measured drift. It is what the waves could move if sand were available everywhere. Around a rocky point, less may actually move.
The wave data come from a model grid point about 5 km offshore. The model does not see how waves bend around the point, or local currents in the cove. Bending reduces the angle but only flips the direction if waves arrive almost head-on, which they do not here.
Confirmation has to come from the beach: which side of a structure gains sand and which loses it, sediment sampling, and the path of flood plumes. Until then the direction is model-based, with moderate confidence.
Data: hourly ERA5 ocean-wave hindcast (Open-Meteo), June 2015 – September 2026, grid point 17.835° N, 101.78° W; partitioned swell, wind sea and secondary swell (Open-Meteo marine), January 2022 – September 2026, grid point 17.875° N, 101.79° W. Local beach orientation from this site's 151 shoreline transects.
Method: the deep-water form of the CERC transport formula (Ashton & Murray 2006), Q ∝ H2.4 · T0.2 · cos1.2θ · sin θ, where θ is the angle between the wave direction and the beach normal; hours with waves travelling away from the beach are excluded. Sensitivity checks: beach normal ±5° and ±10°, an energy-flux × sin 2θ formula, and each year and season separately. Net ÷ gross reported, where +1 means all transport goes north-west.
ERA5 wave heights after 1 February 2024 read about 9% low against two other wave models; that changes how much sand could move, not the direction. The along-shore component in the site's storm-event data is signed the same way: positive pushes sand toward the south-east.
Analysis run: 27 September 2026.
Cite as: "Where the sand goes: longshore drift at La Saladita", La Saladita Field Guide, lasaladita.com/findings/sand-drift/, 2026-09-27.