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Where does Kite Beach's sand go? A summary

An independent study of the coast from Encuentro to Cabarete Bay, using free satellite images and open-source wave and sand models. Summary of report version 0.10, 8 October 2026, with a local's report of a sandy bottom added on 9 October. The full report, with all the figures and methods, and the interactive model are online.

Version 0.11: a new satellite test shows north swells leave a mark. After a typical north swell the south-east half of Kite Beach is about 2 m wider within a few days, and western Cabarete Bay about 1.7 m wider; the summer stretch tends to narrow. Sand moves south-east in north swells, from the summer stretch into Kite Beach and on past the point.

Version 0.10: we found an error in how our scripts read XBeach's currents (they were turned twice, which scrambled their directions). Read correctly, XBeach and the current model now agree that the water near the Kite point flows into Cabarete Bay, and broadly agree along the whole coast; the Kite Beach channel is a weaker rip than we published on ordinary winter days and in north-east swells, and strongest in big north swells; and XBeach now confirms the main exit at Kite Beach's north-west end.

Local knowledge (9 October 2026): a local tells us the whole bottom of Cabarete Bay and from Kite Beach to Encuentro is sandy, out past the reefs too, with plenty of sand to be seen in the murky water. Our picture of where sand lies had come only from a satellite map of reef shapes, so we now go by the local observation. It changes some of the reasoning below (Encuentro, the Kite point, why the model sand budgets failed), but there are no new model results.

Version 0.9: the findings of an independent quality review have been worked through, the code fixed and the analyses rerun; this summary is rewritten from the new results (see the note at the top of the full report). One test was withdrawn: a short 2D XBeach run of a whole year, which had seemed to reproduce Kite Beach's seasons, turned out to be a start-up effect of that model. That was one failed test. The wave models still show the seasonal switch in the waves' push at Kite Beach (question 2).

The places named in this summary. The white dots mark the distance along the shore, measured from the Encuentro end (0 km). The back-reef is the shallow water between the reef and the beach. We don't call it a lagoon, because locally "the lagoon" means the real lagoon behind Cabarete town.

What we wanted to know

Kite Beach is noticeably wider in late winter than in late summer. We set out to answer six questions: 1. Where does Kite Beach's sand come from, and where does it go? 2. What conditions make the beach grow or shrink? 3. Are there sandbars, and does the sand move along the beach or on and off it? 4. Does surf beat build the beach or erode it? (Surf beat is the slow surge of water up and down the beach every minute or two. When a set of bigger waves breaks on the reef, it pushes extra water in towards the beach, and that water drains back out in the lull before the next set.) 5. Does Kite Beach sand ever travel south-east, towards Cabarete? 6. Does the sand just swing back and forth with the seasons, or is it slowly moving one way?

How we worked it out

We used two kinds of evidence and checked them against each other.

Satellite images, what actually happened. The European Sentinel-2 satellites photograph the coast every few days. We picked out the clear images from 2017 to 2026: 343 images of about 7 km of coast from Encuentro to the Kite point, and 325 images of 10.1 km from Encuentro to the east end of Cabarete Bay. On each we traced a waterline every 25 m along the coast and corrected it for the tide, using the measured water level from the Puerto Plata tide gauge. The traced line sits in the wet sand, about 10–17 m landward of the water's edge, but it sits there consistently, so its changes show how the beach width changes. This gives ten years of beach width for every stretch of coast. The timing of the seasons is firm; the sizes of the swings are uncertain by several metres.

Computer models, why it happened. - SWAN, a standard wave model, shows how the offshore swell changes as it crosses the reef and reaches the beach. We ran it 4,320 times: for three stretches of coast, every combination of swell height, period (the time between one wave and the next; long-period swell comes from distant storms), direction and tide, on two versions of the reef depths. - Two more detailed models, SWASH and XBeach, show what individual waves, surf beat and currents do to the sand at the beach.

How waves move sand

Waves move sand in two directions, and on a real beach both usually happen at the same time.

Along the beach (sideways). Waves rarely arrive exactly head-on. When they arrive at an angle, each wave pushes sand a little way along the beach, and over days and weeks this moves a lot of sand. Beach engineers call it along-shore drift. It goes in the direction the waves are travelling along the shore, and it can reverse when the swell direction changes with the seasons.

On and off the beach (straight in and out). Waves also move sand straight up and down the beach: - Off the beach. Big, steep or stormy waves tend to pull sand off the upper beach and carry it out into the water. It often settles as a sandbar a little way offshore, or here in the back-reef. The beach gets narrower and flatter. - Back onto the beach. Smaller, gentler waves, especially long-period swell, tend to push that sand back up onto the beach over the following days and weeks. The beach rebuilds.

Usually a combination. On most days both happen together, and sand moves diagonally: out and sideways in a storm, back in and sideways in calm weather. What matters for a beach over a season is the balance of all of it. Sand moving along the shore can take a beach's sand to a neighbouring beach. Sand moving on and off mostly stays nearby and comes back.

One more idea: capacity is not the same as actual movement. A model can say how much sand the waves could move: their "push". How much sand they actually move also depends on things we have not measured: how coarse the sand is, how much of it the waves stir up, and, in general, whether there is loose sand to move. (Here sand does not seem to be short: locals report a sandy bottom almost everywhere. But the actual amounts still can't be read off the capacity.) Everything the models say below about sand moving along the shore is this capacity, not a measurement.

What we found at Kite Beach: - The seasonal change is most likely the sideways kind. The waves push sand into Kite Beach from both ends in winter, and out of its north-west end in summer (questions 1 and 2). The models show this switch, but they cannot yet give the right size of Kite Beach's swing. - The on-and-off kind happens in every big swell. Sand is taken off the upper beach and left just offshore, then brought back. At most beaches it is a swap rather than a loss (question 3). - The whole coast is also a little wider in winter than in summer. Sand moving along the shore can't do that, so it probably comes from the on-and-off exchange, or from beyond the study area.

The findings at a glance

Top: where the waves push sand along the shore in winter (blue) and summer (red); the star is where the year-average push meets, inside Kite Beach. This is the waves' capacity, not measured movement. Bottom left: Kite Beach and the summer stretch swing in opposite seasons. Bottom right: ten years of change (coloured, with error bars) and the change after big swells compared with random dates (grey).

Answers to the six questions

1. Where does Kite Beach's sand come from, and where does it go?

As far as the waves go, Kite Beach is a sand trap. Inside the reef, the waves push sand along the shore towards the south-east part of Kite Beach from both directions, so that is where sand would collect. But the satellites do not show Kite Beach gaining sand over the ten years, so this is a pattern of the waves' push, not a measured gain.

The push into Kite Beach comes mainly from the south-east, from the Cabarete Bay side. - The waves push sand north-west along the whole of Cabarete Bay, towards the Kite point, in every month's average. The push is strongest in the west of the bay. - The Kite point itself is rock and supplies no sand. The sand is carried past the point, through the shallow water in front of it. - Just around the point, on the Cabarete side, there is a small beach that trades sand with Kite Beach through the seasons (see question 5).

From the north-west end, it changes with the seasons: - From about September to April, the push from the "between" stretch, just north-west of Kite Beach, also runs into Kite Beach. - In summer, the north-west end of Kite Beach changes behaviour. The trade-wind waves push its sand away to the north-west, along the between stretch towards the summer stretch, which is widest in August–September while Kite Beach narrows.

What about Encuentro? - Over most of the coast west of Kite Beach, the waves push sand towards Encuentro in every month's average. Yet Encuentro is not filling up. It changes only a little with the seasons (about 4.5 m, widest in November and narrowest in July, and even that is uncertain), and over the ten years it shows no clear trend. - Two explanations fit. Little loose sand may reach it, partly because Kite Beach holds sand that would otherwise travel on, like a beach just downstream of a groyne. Or a steady flow may pass through, with sand leaving Encuentro, towards Sosúa or offshore, as fast as it arrives, which would leave its width unchanged. The satellites can't tell these apart. But since locals report plenty of sand on the bottom all the way to Encuentro and out past the reefs, a flow passing through now looks the more likely. Little sand arriving may still matter close to the beach, if Kite Beach holds the sand moving along the beach face.

2. What makes the beach grow or shrink?

Kite Beach widens from October to February and narrows from March to September. It is widest in February and narrowest in September.

The likely reason is the change at its north-west end, and the wave models show it. The trade winds blow from about the east in every month's average, a little stronger in summer. What changes with the seasons is the swell: - From about September to April, north-east swells arrive, and the waves push sand into Kite Beach from both ends. - From about June to August, the swell is mostly short trade-wind waves from the east. The push at Kite Beach's north-west end reverses, and drains that end north-west, towards the between and summer stretches.

So the waves' push does reverse with the seasons, in step with the beach (as capacity, not measured movement).

The wind helps a little. Hot, dry, windy summer afternoons also blow dry sand directly: along the beach towards Encuentro, and partly inland into the vegetation, gardens and roads behind the beach. This peaks in June–August, the same months Kite Beach narrows, so it may add a little to the summer loss. It is much smaller than what the waves could move. But sand blown inland usually doesn't come back, so it is a slow permanent loss, probably a few cubic metres per metre of beach a year. That is small next to the seasonal swing, but it adds up over decades. (Full report, Section 7.6.)

How big is it? - Kite Beach is about 18 m wider in February than in September. Depending on how the waterline is traced, the swing comes out at 14–19 m. - The summer stretch, 1–2 km to the west, does the opposite by a similar amount: narrowest in April, widest in August.

What the models get right, and what is missing: - The seasonal switch: yes, as above. - The summer stretch's width: reproduced. A simple statistical model predicts it well from the waves' push along and onto the shore over the previous three months. It was fitted on 2017–2023 and tested on 2024–2026, years it never saw, and it beats both a typical year and a smooth seasonal cycle with a trend. - The size of Kite Beach's swing: missing. The along-shore sand model's ups and downs at Kite Beach roughly follow the satellites on the test years (correlation 0.62, where 1 would be perfect), but its swing is only about 0.5 m, against about 17 m observed. The statistical model does not predict Kite Beach's year-to-year ups and downs either. - One test was withdrawn. A short 2D XBeach run of a whole year, which earlier versions said reproduced Kite Beach's seasons, turned out not to be valid: every wave condition built the beach, a start-up effect of that model. That was one failed test, not proof that the models can't show the seasons.

3. Sandbars; along the beach, or on and off it?

Sandbars can't be seen in these images. Each pixel is 10 m, too coarse to show them. A few minutes of drone video averaged into one image, or a kayak with an echo sounder, would show them.

Sand moves both ways, for different reasons: - Along the beach: the drift described above. This most likely makes the seasons, and it is where the waves' capacity is largest. - On and off the beach: each big swell takes sand from the dry upper beach and leaves it just below the water's edge. Calmer waves then bring it back up. This happens on every beach we modelled, although at the sheltered middle of Kite Beach the change is tiny and may even be a slight gain. At most of them it is a swap, not a loss; at Encuentro beach in very big swells, some sand is carried out past the reef.

4. Does surf beat build or erode the beach?

What surf beat is. Waves arrive in sets. When a set breaks on the reef, it pushes extra water into the back-reef, and the water drains out again in the lull. The result is a slow rise and fall of the water level every minute or two. Behind the reef this is usually the main water movement at the beach: about 2.5–3 times bigger than the small waves that get through at the middle of Kite Beach, and 2–4.5 times at the summer stretch. At the west end of Kite Beach, where more of the waves get through, it is only a little bigger on small days.

In swell events, surf beat helps cut the upper beach, most of all in long-period swell. Mostly the sand is moved just offshore, where calmer waves can bring it back.

The middle of Kite Beach is well sheltered, and the effect there is small, possibly even a slight gain. The satellites fit this, but they cannot settle it. After the 76 biggest swells of 2017–2026, no beach changed by more than it does over ordinary weeks, once chance is allowed for. A change of 1–2 m at Kite Beach could still be missed. At most, the more exposed summer stretch was about 2.6 m narrower in the ten days after a long-period swell, and even that could be chance. Sorted by direction instead, north swells do leave a mark: the south-east half of Kite Beach is about 2 m wider within a few days of a north swell, and western Cabarete Bay about 1.7 m wider. With about six north swells a winter, that could be much of Kite Beach's winter widening (a rough estimate).

5. Does Kite Beach sand travel south-east, towards Cabarete?

According to the waves' push along the beach, very little. But the water near the point flows the other way, so some sand may.

What the waves do. On the Cabarete side of the point, the waves push sand north-west, towards Kite Beach, on practically every day. At the south-east end of Kite Beach the push turns south-east, towards the point, on most days of true north swell. Those are uncommon: about one day in 30, mostly from November to April. (North and north-north-east swells together are about one day in eight, but the north-north-east days rarely reverse the push.) The satellites back this up: after north swells the south-east half of Kite Beach is wider, and so is western Cabarete Bay, so in north swells some sand passes the point into the bay.

What the water does. Both current models now agree: the water near the shore, just south-east of the point, flows towards Cabarete Bay, at about 0.15–0.23 m/s, in winter and summer. (Earlier versions said XBeach had it flowing towards Kite Beach; that came from an error in how we read XBeach's output, now fixed.) The waves agree too: the models and the satellite images show them crossing the reef at the point from north of straight-on, which pushes the water towards the bay. No one has measured the current there yet.

So the water's direction is fairly clear, but the sand's is not. The small waves that reach the beach push sand along the beach face towards Kite Beach, while the current a little further out runs towards Cabarete Bay. Locals report a sandy bottom in front of the point, so the current has sand to carry, and some Kite Beach sand leaving south-east past the point, and sand from the small beach carrying on into Cabarete Bay, is more likely than we first thought. Which of the two moves more sand depends on how coarse the sand is and how much of it the waves stir up, and neither has been measured. This is what the models allow, not measured movement, and we can't yet say how much, or which way wins.

The small beach on the Cabarete side of the point works like a seasonal storage area: - It is widest in August and narrowest in April, the opposite of Kite Beach. - The satellites show the two trading sand. The small beach's seasonal change in sand area is close to Kite Beach's (11,600 against 13,700 m²), in the opposite season, and its ups and downs run opposite to Kite Beach's. - How the sand moves between them is not known. The waves' push runs towards Kite Beach in every month, and the current near the point towards Cabarete Bay, both with little change through the year, so neither explains why the small beach fills in summer and empties in winter. - Over the ten years, this small beach has been getting narrower, by about 2 m a year. Where that sand went is not known: Kite Beach and western Cabarete Bay show no clear trend.

6. Back and forth, or slowly moving one way?

The sand on the beaches mostly goes back and forth. Kite Beach swings about 18 m every year, but over the ten years it shows no trend that can be told apart from zero.

But the satellites can't see sand that is just passing through. They measure how much sand is on each beach, not which grains. If sand arrived from the east and left to the west, or out to sea, at the same rate, the beaches would look unchanged. The waves push sand north-west on most days, and locals report plenty of sand on the bottom, so some sand probably does pass through. We tried two ways of measuring that with the models, and neither matched what the beaches actually did: in one (XBeach) the beach's settling-in at the start of each run swamped the result; the other (the current model) leaves out what the waves do at the beach itself; and the sand formula and the grain size are not yet pinned down. (We had also blamed a thin, patchy cover of sand over rock; local observation says otherwise, so that reason is dropped. The model runs gave the back-reef too little sand, and a rerun with sand everywhere except the reef crest is planned.) So how much sand leaves towards Sosúa or into deep water is still an open question.

Underneath the seasonal swings, only a few stretches show a clear slow change: - Getting narrower: the small beach on the Cabarete side of the point, by about 2 m a year. - Getting wider: the "between" stretch, just west of Kite Beach, by about 0.7 m a year. - Perhaps getting narrower: the summer stretch, by about 0.8 m a year, but this is only just beyond the uncertainty. - No clear trend: Kite Beach, Encuentro and western Cabarete Bay.

So the satellites do not show Kite Beach steadily collecting sand. Ten years is also short for trends like these.

Where sediment goes out to sea: after big winter swells, the water outside the reef is cloudier than on quieter winter days all along the coast, including off Encuentro. It is cloudiest off Cabarete Bay, and the cloudy water spreads 1–2 km offshore of Kite Beach and the bay. There is no extra cloudiness off the Kite Beach exits. That fits plenty of sand on the bottom being stirred up, as locals see in the murky water. But big winter swells often come with rain, and the runoff from the land has not been separated.

The water behind the reef

When waves break on the reef, they push water over it into the back-reef (the shallow water between the reef and the beach). That water has to get back out to sea. A computer model of the currents over the whole reef, from Encuentro to Cabarete Bay, shows where it goes:

• The water splits along Kite Beach, like rain off a ridge. On typical winter days and in big north-east swells the split is about 350 m before the Kite point, so the south-east part of Kite Beach drains towards Cabarete Bay. On summer and trade-wind days it moves to the point, and the whole Kite Beach back-reef drains north-west.
• North-west of the split, the water runs north-west. It goes out to sea mainly through the lower, broken reef at the north-west end of Kite Beach and along the between stretch. XBeach, which follows each set of waves, confirms this as the main exit at Kite Beach.
• The Kite Beach channel is a surging rip, strongest in big north swells. Its position comes from local photos and from the gap in the breaking waves in ten years of satellite pictures. XBeach has the water going out through it at about 1.0 m/s on average in a big north swell, with surges up to about 1.9 m/s. On a typical winter day it is about 0.35 m/s (surges to about 0.6 m/s), and in a big north-east swell about 0.5 m/s (surges to about 1.1 m/s). Earlier versions overstated it on ordinary winter days and in north-east swells. The channel's depth hasn't been measured, so these speeds are estimates.
• South-east of the split, the water drains into Cabarete Bay, past the Kite point (XBeach agrees), and the bay has no reef across its middle. The bay's opening is where the most water leaves the back-reef on the whole coast.
• In a big north swell, a strong current runs south-east along the outside of the reef, because the waves arrive at an angle.
• Encuentro has no main exit in most conditions. Its reef is close to the beach, and the water leaks out through many small gaps.

The interactive model at kewlmermaid.com/kite-beach-sand shows these currents for each type of day, and lets you drop floats to see where the water takes them.

For surfers

Encuentro and Coco Pipe: - The reef is narrow and close to the beach, so the swell reaches the break almost at full size, plus a little extra as it slows on the reef: 1 m offshore becomes about 1.4 m at the break. - They work best in north swell, and the waves break hollow.

Kite Beach and Cabarete Main Reef (the break about 800 m off western Cabarete Bay): - These break further out, on a wider reef. They grow less on big days, levelling off at about 2.7–2.9 m. - They favour north-north-east to north-east swell. Cabarete Main Reef gives the softest waves of the five spots; in a typical swell all five plunge.

Tide and period: - Longer-period swell means bigger surf at every spot. - At Encuentro and Coco Pipe the tide barely changes the size. At Kite Beach and Cabarete Main Reef high tide gives about 6–17% more height than low tide. Everywhere, more waves break, and break harder, at low tide. - Inside the back-reef at Kite Beach the tide matters much more: a tide 0.4 m higher lets about 40% more wave height through to the shore.

Seasons: - December to March: the biggest days. - September and October: the most long-period swell and the most early mornings with light or offshore wind, so potentially the best-quality surf. - June to August: mostly short, messy trade-wind swell.

For the surf forecast: a lookup table for all five spots is ready. It turns an offshore forecast into a height at each spot in a fraction of a second, including the measured tide, and it tells the spots apart, which a single offshore forecast cannot. It also warns when a forecast hour is outside what the table covers, such as swell over 4 m or north-west swell. None of these heights has yet been checked against surf reports.

Rips: the Kite Beach channel carries a surging outflow through the reef, strongest in big north swells (surges up to about 2 m/s in the model), and the lower reef at Kite Beach's north-west end is the main way out through the reef at Kite Beach.

How sure are we?

The biggest uncertainty is that nothing has yet been measured in the water. - The depths: the drone surveys read deeper than the satellite-based Coral Atlas, by about 1.3 m on average and 2.5–3.5 m on the shallow reef. Local knowledge supports the Atlas there, so the models now use the Atlas on the reef. If the back-reef were really as deep as the drones suggest, the waves at the Kite Beach shore would be about 2.5 times bigger and their push along the shore about 4 times stronger, but the direction and seasons of the push would hold. This "deep" case now looks unlikely. - The sand: locals report that the bottom is sandy almost everywhere, with plenty of sand, but how coarse it is and how deep the waves stir it are assumed. They decide how much of the waves' capacity turns into real movement. Whether the reef flats just inside the breaking line are sand or rock is not yet known. - What would settle it: a few measured depths in the channel and the back-reef at a known tide, sand samples, and repeat beach surveys (below).

What next

The models have gone about as far as they can with the data we have. The open questions now need a few simple measurements. Steps 1–6 are in order of value; step 7, the drifter test, is the quickest and cheapest.

1. Measure the depth through the Kite Beach channel and the lower reef at the north-west end of Kite Beach, from a kayak or SUP on a calm morning at low tide. It settles how strong the rip is and how the outflow divides.
2. Take sand samples. A cupful of the top 2–3 cm at each site: from the dry beach, the middle and the water's edge at Kite Beach, the small beach by the point, Cabarete Bay, the summer stretch and Encuentro, plus one or two from the back-reef. Their grain size replaces the value every sand calculation assumes. Their make-up (white reef sand against dark river grains) shows where the sand comes from and goes. The full method is in the report, Section 12.2.
3. Keep a simple surf log (date, time, spot, estimated set face height), to check the surf-forecast heights.
4. Take straight-down drone photos at low tide in calm, clear water, to map the channels and to see whether the reef flats just inside the breaking line are sand or rock.
5. Survey the beaches and the back-reef twice a year (for example February and August). It is the only way to measure how much sand actually moves, and so how much passes through towards Sosúa or out to sea.
6. Get a local wind record, for the afternoon sea breeze that the global records miss.
7. Release drifters, floats that move with the water, behind the middle of Kite Beach and just south-east of the Kite point on a typical winter day. This is the quickest and cheapest test of which way the back-reef water goes and how fast (report, Section 12.4). It shows where the water goes, not the sand; for the sand, the samples in step 2 are needed too.

The surf-forecast tables were rebuilt on the corrected depths on 2 October 2026.

The interactive model, this summary and the full report are at kewlmermaid.com/kite-beach-sand. The code and data are in a private GitHub repository.