How the tide works on the River Arun
One tide comes in from the sea at Littlehampton and travels 14 miles up the river to Pulborough. Here's what really happens along the way: why the river backs up before the current turns, why it drains for twice as long as it fills, and what a wet week changes.
The river, from the sea to the tidal limit
Picture the Arun cut open along its length, with the sea on the left and the river climbing gently inland to the right. Watch one tide travel up it, then try a wet week or a small neap tide and see what changes.
- Current running upstream (flood)
- Current running to the sea (ebb)
- Slack water
- Water level rising / falling
- Highest and lowest levels over a tide
The rise and fall shrinks upstream
At the sea the gap between high and low water is wide. By Pulborough it is much smaller, and at Pallingham it fades out altogether. That is the tidal limit.
Low water is held up by the river
The river bed climbs as you go inland, and the river can't drain below its own level. So upstream, low water sits high and the river never empties the way the estuary does.
Height and current are different things
Rising water does not mean an incoming current. Watch the triangles (level) and the arrows (current) in the steps below: for a while they disagree.
One tide, step by step
Times are from high water at Littlehampton. Follow Pulborough on the right of each picture.
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1 Low water at the coast The whole river drains to the sea At low water at Littlehampton every point on the river is running out. Up at Pulborough the level is still falling: its own low water is hours away yet. -
2 About 2½ hours before high water at the coast The flood pushes in from the sea The sea is rising fast, and the lower river at Ford and Arundel has already turned to run upstream. Further up, the river does not know yet: Amberley is still running out, and Pulborough is still falling. -
3 About 1 hour after high water at the coast Pulborough backs up The coast is already past high water, but the tide is still travelling inland. At Pulborough the level has started to rise, yet the water is still flowing towards the sea. The tide is holding the river back faster than it can drain, so it piles up. This is the backing-up stage. -
4 About 3 hours after high water at the coast The current turns upstream, briefly An hour or so before Pulborough's high water, the level is rising quickly enough to overcome the river and the current runs upstream. It is short and gentle up here. Meanwhile the sea and the lower river are well into the ebb. -
5 About 7 hours after high water at the coast The long, slow ebb Pulborough reached high water about 4 hours after the coast and now drains for around 8 hours, twice as long as it took to fill. The sea at Littlehampton has already turned and is coming back in, while the upper river is still emptying.
Why the river backs up before it flows upstream
The Arun is always trying to run downhill to the sea. When the tide comes in, its first job is to stop that. Before any water can run upstream, the tide has to hold back the river coming down. While that is happening the water has nowhere to go, so it piles up: the level rises even though the surface is still drifting seawards.
The current only turns once the river above you is filling faster than the river itself supplies water. Down at Arundel almost the whole tidal river lies upstream, so that happens quickly and the flood runs hard. At Pulborough there is only a short stretch left before the tidal limit. The turn comes late, up to about 3 hours after low water, and the upstream flow is short and gentle.
That is why a tide table for the coast, or even a height curve for Pulborough, can't tell you which way the water is moving. You need to know how the river behaves.
What heavy rain changes
The tide is only half the story. The other half is how much water the river is bringing down from the Weald, joined by the Western Rother just above Pulborough.
- Low water sits higher. The river can't drain down as far, so the bottom of the tide is lifted.
- The rise and fall at Pulborough shrinks. The tide still lifts the river, but by much less.
- The ebb runs harder. The whole river is moving more water seawards, fastest in the lower reaches.
- No upstream push at Pulborough. In spate the current keeps running downstream through the whole tide.
Compare with step 4 above: same moment in the tide, very different river.
How much rain does it take?
Going by the Environment Agency's river gauges, in a dry summer the Arun and the Rother together bring down only about 2 cubic metres of water a second. After a wet week in winter that is more like 10 to 20, and in a flood 50 or more. Downstream at Houghton Bridge, last winter's readings show the tide's rise and fall roughly halved once the two rivers topped about 20. In the animation above, a spring tide stops turning the current at Pulborough at around 15 cubic metres a second. That is a rough guide, not a measurement: try the river flow slider.
Reading the river for real?
Paddle it with people who watch it every day
Knowing when the Arun turns, and when it won't, is the difference between an easy paddle and a hard slog. We hire kayaks, canoes and paddleboards and run guided trips on the river, planned around the tide.
Hire & trips at Fluid Adventures →
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Today's tide times
Put it into practice with the live times for your stretch of the river:
Pulborough tide times Amberley tide times Arundel tide times All River Arun tide times →
Questions about how the Arun's tide works
Why does the River Arun rise before the current turns?
Water level and current are not the same thing. When the tide comes in it first has to stop the river flowing out. So the level starts to rise, as the water backs up, while the surface is still running towards the sea. The current only turns upstream once the river above you is filling faster than the river itself can supply. At Pulborough that can take up to about 3 hours after low water.
Does the tide flow upstream at Pulborough?
Yes, but only briefly, and gently. In normal conditions the current turns upstream for a short spell in the hour or two before high water. After heavy rain it often does not turn at all: the level still rises with the tide, but the water keeps running downstream throughout.
Why does the Arun take longer to empty than to fill?
The tide travels faster through deep water than shallow, so as it moves up the narrowing, shallowing river the crest catches up with the trough and the rise gets steeper and quicker. The river's own flow also adds to the ebb and works against the flood. At Pulborough the result is roughly a 4-hour flood and an 8-hour ebb.
Why is the current so much stronger at Arundel than at Pulborough?
The current at any point has to carry all the water needed to fill (or drain) the river above it. Below Arundel that is most of the tidal river, so the water moves hard. Up at Pulborough there is only a short stretch left before the tidal limit, so there is far less water to move and the current is gentle.
Does rain change the tide times on the Arun?
High water still arrives at roughly its usual time, but a lot of rain changes the rest of the picture. Low water sits higher, the rise and fall at Pulborough gets smaller, the ebb runs harder, and the upstream current near Pulborough can disappear altogether. The Western Rother, which joins the Arun just above Pulborough, adds to that extra flow.
How far up the River Arun does the tide go?
The tide normally reaches as far as Pallingham, a few miles above Pulborough. Above there the Arun is no longer tidal. Pulborough itself is about 14 miles from the sea, close to that limit.