Question about tidal currents

I was planning a daytrip in Charleston SC and came to realize that I do not understand something about tidal currents. Here in the southeast, there are a whole lot of what we call “islands” but they are not the stereotypical offshore island. Instead, they are basically part of the mainland but separated from the mainland by a creek or small “river” on the backside. Maybe this waterway goes on for several miles (and so too therefore does the back side of the “island”). Anyway, since this waterway is open to the ocean or estuary on two sides, I am unsure what happens when the tide comes in (or goes out). When the tide comes in, is it the expectation that the tidal current flows in from both sides such that somewhere in the middle the opposing currents meet to create a rising tide but slack current? Or is it the case that one entrance/exit/mouth will always win out (i.e., if the tidal current is flowing into one entrance, it will be flowing out the other and vice versa)?

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It depends a lot on other factors such as depth and topography (shape of the bottom) of the channel, what the bottom is made of (sand, rock, coral etc) winds, how rapidly the tide is rising.

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  • get current table - eg:
    (I use for Cumberland I, Jekyll I, FL barrier I’s (use tide table) )
    Charleston well covered
  • get local knowledge
  • if don’t have any of above, figure about 1/2 way up island (on mainland side)

Situations like that can be tricky to figure out without local knowledge. I’ve seen both situations - one where the current flows one way on an incoming tide and reverses with the outgoing tide (although it can be very hard to figure out which way is “in” and which way is “out” sometimes) and also a situation where the tide comes in/goes out from both sides and there is a “continental divide” in the middle. I think the second type is less common, I see it locally in some mangrove tunnels that have open water at each end, but are fairly narrow with lots of turns which slows down the flow. In continuous channels the water tends to go one way or the other.

If you really want a good puzzle, try to figure out what the heck the tide charts mean in relation to currents in the lower Florida Keys! With the Gulf of Mexico on one side and the Straits of Florida on the other, which way is “out”??


Start with your tidal range. That determines the volume of water that gets moved several times a day due to the tides. The daily range around Ketchikan, Alaska is around 23 feet. The harbor in some small towns are pretty empty at low tide with boats sitting in the mud flats. The Bay of Fundy in NS, is around 43 feet.

The tidal rips in the San Juan Islands and north of there in BC are strong enough to bury buoys, creat whirlpools, and generate currents over 10 knots. Paddling requires a knowledge of the tides. It is like a chess game with nature since most people can only paddle about 3 knot an hour or a little more.

Get a tide table and start observing the local tides. Get out in a power boat and look around if you can. Or at least find some smart that knows the water.

Maybe this will be helpful.

I’ve paddled the ICW behind the barrier islands in the Charleston area several times.
Never thought about which end the tide is coming around but either inlet is where it is most noticeable.

Depends on the details of each, tidal range and force and same for the water flowing out from the river. FWIW the salt mix zone for the Hudson River form Manhattan can come up as far as Poughkeepsie depending on the details. Not a tidal force of concern up that high, but it speaks to how pervasive a flow of water can be.

… and Poughkeepsie is over 80miles upstream.
Again, get a current chart (if available).
Where I am on the St Johns river - Jacksonville is about 25 miles upstream (of ocean).
There is a strong ebb and flood downtown (there is a bit of a river constriction (narrows). Also, the current lags the tide by about 3 hours - eg, if low tide is at 12pm, the current continues to ebb until 3pm.

I paddle that area. Tides range roughly between 4 to 7 feet.

On Club Creek out of McClellanville there is a tidal node that when you pass it the current heads in the opposite direction. It drains the marsh going into Five Fathom Creek and also drains at the other end in the opposite direction into Muddy Bay. Where this seem to occur most often is when the marsh creeks have outlets into two or more different bodies of water that drain the marsh.

Where will you be paddling? I might know the particulars about that area.

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It wouldn’t be the case that water flows in one inlet and out the other. If the ocean level has risen higher than the sound level, it will flow in both inlets. If you have a deep/wide inlet that supports the flow of a larger volume of water, more water will flow into the sound from there. So a flooding current may flow in through the harbor inlet, and flow in to the NE, all the way to and right on past shallow Breach Inlet. In other words, current will be flowing into both inlets, but a much larger volume of water can flow in through one inlet vs the other.
I’m out at Seabrook Island. Let me know when you’re around if you’d be interested in paddling.

@Monkeyhead, you probably know much of this already, but its a good place to expand the topic of tides in general for the recreation paddler; not only to clarify tides but to explain how they can work for you or against you by exacerbating marginal conditions within minutes if just one variable changes.

Tidal flow is amazing. While high and low tides can be calculated years in advance, weather patterns can change peaks, lows, duration, timing and depths. As noted above by other members, normal extremes can be significant towards the poles. The Chesapeake Bay is unique in that the 100 mile length makes it a perfect interval so it may be high at the extremes and low in the middle.

Where fresh water outflow meets salt water, the lighter fresh water overrides the heavier salt water, which creates a churn that mixes nutrients and oxygen to enhance the diversity and viability of life that flourishes in the waterway. In such bodies of water, its easy to explore ecosystems that thrive in fresh, brackish and salt walter, all with in the same paddle day.

Tides are complicated by high and low pressure weather systems (ex: a hurricane), or high winds that blow water into or out of rivers, sounds, bays or coastlands and salt marshes. The normal tide that I record logs is typically about .2 ft when low to about 1.2 ft high, but during the spring perigean tide, it’s closer to 2.0 ft high, because the Sun and moon are closest in the nothern hemisphere). We also experience at least 4 or 5 astronomical events annually where tideal extremes can be extremely low or up to 3 or 4 ft. Extreme lows when conditions work together with a wind out or the North or Northwest can result in mud flats out to the end of the pier, or cover it when aided by winds out of the Southeast.

The extreme high conditions make it ideal to explore otherwise shallow tributaries and flats. Understanding tidal influence is fairly easy, if you have local knowledge of the tides, river outflow, ocean current streams, channels and shoal, especially where they form around deltas and islands. Regardless of tide chart reports, its easy to verify flow by sitting stationary and watching your drift, or noting navigation bouys and shellfish trap floats, to observe water flow and the direction the marker is leaning. This example shows outflow speeds of between 3 to 4 mph.

Another indicator is the tide line of debris that collects at the meeting between incoming and outgoing flow. By comparing the line to its proximity to tide datum points, you’ll get a real time readout of how it correlates to the reported tidal schedule.

Even without floating debris, you can see the influence wind has on tidal flow, where wind blowing with or against the tidal flow will change the surface texture. In the case below, the main channel had no visible indicators evident in the water texture but the water racing through this outlet funneled not only the outgoing tide, but the outflow of two combined tributary rivers, as well as several basins that bottled up the high tide that contributed to additional flow as the tide dropped. The resulting outflow had a south wind confront the south bound falling tide. That created a smooth surface with the wind blowing the same direction as the incoming tide, indicated by smooth water, but it created ripples where it meets the outflow.

Such visual indicators are useful and often obvious to the fishing Kayaker, because fish typically congregate near shoals on specific sides to take advantage of food sources that happen to float by. Other fish may may seasonally favor deep channels or warmer water in shoals as appropriate. Current and tides can accentuate wave heights as the water depths change from deep channels to shallows. These underwater features are important to note, because changes in flow or wind can double wave height locally without warning. That can create treacherous conditions for a novice, if conditions were marginal to begin with on the outgoing leg.

Especially when traveming solo, its importantbto understand wind and currents to time passage to give you an advantage of an assist to landfall in the event of a capsize. It’s also beneficial to know the actual flow direction and wind to coincide with travel direction where possible, or throw it all out and just fight it.

Where many paddlers use the opportunity to meander and enjoy the scenery, and others use falling rivers or ocean waves to ride the surging conditions, the open water waterways influenced by tidal currents provides a wide range of opportunities, where you can fight or benefit your trip. It also offers great diversity if you’re willing to paddle potentially challenging environment.

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Hey Castoff,

I made that trip 2 days ago, on Saturday. Specifically, I put in at the boat ramp on 171 just as you come onto Folly Island, and headed northeast-ish towards Morris Island (Folly “River” on the backside of the island) and walked over to the lighthouse. Then back. It was a nice paddle and a beautiful day. I’ve launched from that ramp for years when I come to Charleston (which I try to do at least once a year [I live in Atlanta]) but I always head in the opposite direction over to Kiawah. It looked like it would have been hairy to try and round the east end of Folly for a circumnavigation of Folly. Lots of surf and white camps out for some distance (although it looked like it might have been possible to paddle inside the worst of it). That wasn’t my plan to begin with but it did make me wonder if a reasonably competent and experienced paddler could comfortably do that trip under different circumstances. When I was there it was max low tide (especially low I suppose as I heard it was a “King Tide”). Perhaps the conditions for making that turn would be more favorable on a higher tide, maybe near slack current.

Cape Fear,
I’m back home in Atlanta now but try to get out to the Charleston area at least once a year and would be happy to go paddling with you. I’ll send you a DM next time I’m down that way (probably not until next year as I just got back from your area). I’ve definitely benefited from your posts over the years, often in response to questions I’ve had. You have a great deal of good info.

We spent a week at the beach many summers on Folly. Often with a dock on the Folly River. I surf my kayak there and Isle of Palms. I have also put in at the bridge ramp but car parking without a trailer is limited. Another good put in is on the Stono River at the end of Sol Legare Rd on the right close to where you cross the bridge to Folly. Lots of good paddling around the area. I have also paddled the Habor and points north of Charleston.

I haven’t circumnavigated Folly, but have done so around Dewees Island, Capers Island, Bulls Island, and Cape Island.

Do you camp or rent when you come down this way. I am about 2-3 hours from the coast depending on where I’m headed in that area. Let me know when you get back this way. I would be glad to show you some paddling spots if I’m available.

I use to always camp at James Island County Park but lately I’ve been doing hotels. Creekside Inn this time which was reasonably priced and right on a marshy tributary of the Stono. Spent a couple of days in Savannah this time and up to Charleston for 3. I’ll give you a holler! I’ve never had a problem parking at the ramp but I have generally avoided weekends. You’re right though. I definitely noted the very high ratio of trailer to car parking which seems a bit odd because I know a lot of kayakers use that ramp. I did Sol Legare once, and also the ramp at the parking lot of Bowen’s Island Restaurant. Well, obviously there are a ton of destinations and launch points in C’ton. In contrast, it seemed like the ramp options were more limited in the Savannah area.

The boundaries between tidal flows around a barrier island are quite dynamic. Inlet size and flow, weather and wind all play a role. Usually the flows will meet and mingle only at the highest tides, if at all. If you are paddling in situations where flows mingle you may not know which direction the flow is going to go until levels drop a bit. Tides flow starts out slow at the change and is fastest at mid-tide. You will have a little time to get on the side you desire while you can still paddle against the tide if you need to. is a great resource. When starting out with tidal paddling start small and cautious. Start on a small, more sheltered creek, you’ll have plenty time to get on big water when you develop some condition reading skills. Find an access, find out when it will be an hour before high tide to start. Paddle with the tide until it slacks and turns and ride it back. If it is flowing hard, make sure you are on the correct side of the creek/river to make the landing. Likely you will not have a good time paddling against the tide if you miss it.

Always check your local marine forecast, too.

Most of our paddling is south of Charleston on the ACE Basin. I highly recommend it. Lots of good access, a variety of conditions from frshwater to the sounds.


I’m very familiar with that area. We’ve been living in James Island for the past few years until a few weeks ago. I was there doing some work on the house over the weekend. Folly Beach has been my regular launch for the past 3 years. Mostly I’ve launched from Folly Beach County Park, but I’ve used the Folly boat ramp often too. From the neighborhood I could launch into Clark Sound at higher tide levels and paddle out to the lighthouse and could circumnavigate Morris Island. At lower tides the stretch of pluff mud to access the water became a bit much, so driving a few miles to Folly was more regular. But yes, circumnavigating Folly Beach or Morris Island are both quite reasonable given a day where conditions match what you’re hoping for. Definitely send me a message next time. We’re now on Seabrook Island, which is the other end of Kiawah. I recently paddled from there to Morris Island Lighthouse with Mark Ervin during his Greater Loop expedition. It’s pretty amazing what he did.


@sedges, absolutely correct. To anyone unfamiliar with the tides (Dark Blue on the rise, then reversing on the ebb), the constant river outflow (Light Blue), but the large river in the center that flows around the island is more of a standing body than a river that adds current except that the large size makes it capable of filling or emptying large quantities of tidal water. The flow is exacerbated by the shoal areas (White circled). Note that the small circle is essentially the delta for the river on the left, the Gunpowder, where the slower flow allows silt to accumulate, which restricts the depth to between 2 and 3 feet as the tide rises and falls. However, the outflow never compares to the main channel which drains the Susquehanna River Valley. So a storm in NY or PA can add an unexected outflow that can pile onto an incoming tide then increase the force of a typical outflow and disrupt tidal reversals or durations. Yesterday we were out and the slack tide persisted several hours longer than anticipated.

On one trip, I absent mindedly took the yellow course as if I intenfed to cross the Bay, influenced mostly by cross currents. However, I turned north and my speed of 4.5 mph dropped to 2.9 mph for 1 1/4 miles. Then it picked up to 5.2 mph through the cut between the island and the point of the mainland. Fortunately, that meant that I had the waves to my back which increased from 18 to 36 inches throughthe cut. In the delta where the bottom is 2 to 3 feet, waves though that section are always choppy and confused, caused by the standard outflow of the rivers. Notice how depths leading up to thebisland, south of the delta and in the main channel to the east of the island, the bottom varies from 12 feet to 26 or more, especially in the mainchannel, where speeds can reach 3 to 4 mph and cause taller waves to build. A change in the wind, which happens with approaching storm, or a reverse tide will pile on even more. The effect is like going out abd returning with the door slammed in your face.

Taking the red course puts the waves through the cut on the port or left side of the boat, but at least its less effort to cross against the current outflow. That’s where I might typically deploy a rudder on the 175 Tsunami. Not to turn, but to keep the boat tracking straight, while I can manage in the 145 Tsunami with little trouble.

Combined with my dissertations on GPS, this shows how a real-time readout on speed can be helpful to read the conditions and understand how they will influencing the trip. It shows how speed fell on the up river leg by 1.6 mph, and I only gained a .7 mph advantage on the return leg. An important thing to understand about perception is that unless you see the drop, many paddlers will overcompensate to reach the original sensation of speed. That is a mistake. Because by pushing your limit, you begin to go anerobic. Consequently, you deplete energy reserves faster. Then when you get into trouble, you bonk! I’ve been with several kayakers who bonked. There’s nothing more pathetic than watching someone paddle two strokes and stop for ten, while the tide or wind pushes them backwards for more than they paddled. One guy went out a 10 ft boat and I was in a 14 ft boat. He though he could hang with me because he was a long time paddler and I was a novice in his mind. We were on a 12 mile round trip and he lasted 8 miles. I had my GPS and saw he was tiring, so I asked if he wanted to beach at a park so I could pick him up there, because the last four miles was restricted access. You’re all alone out there, even when someone is with you.

Open water in a large body like a bay appears to be constant across the expanse, but it is not. The average kayaker may think this is crazy, obsessive compulsive or inconsequential. I wouldn’t disagree, but it’s shows how deceptive open water can be. On one trip, I paddled up the Bay into a combined tidal outflow and a falling tide. I dropped from a consistent 5.4 mph in the cross flow to the opposite side, before heading upstream and my speed dropped to 3.6 mph for 6 miles. I was wasted for the last 4 miles of that trip. Four of those 6 miles could have been very dangerous if I didn’t throw an empty whiskey bottle at an approaching thunderstorm (I made that up), but there was an approaching thunderstorm that fortunately passed a few miles south, which I could see.

Many beginning kayakers average speeds of about 1.65 to 1.96 mph (actual recorded readings, and the speed graph looks like a California earthquake). Nothing wrong with that, but a simple GPS can give a lot of valuable information, if you know how to interpret it, even if it has built in error.

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