The Dutch coast is covered with groynes or dikes by about 40%. The remaining part does mainly consist out of barred beaches. These barred beaches can also be present in between the groynes.. In the chart below

the red lines show the 'hard'beaches.

Two beachtypes will be considered to say something about the dangers of ripcurrents. The flat coast with 1 or more sandbars and a low slope and the beaches with groyns, the hard coast. The type of rip is related to the type of coast.

FIXED RIPS

As discussion picture the same picture will be used as is used in the chapter RIP recognision.

The following points are important for the presence of ripcurrents:

a. Wave height.

The biggest cause of rip-currents is the presence of waves. If waves hit shallow water they will break. This area is called the surfzone. If a wave breaks he will suck the water in front of him, fall over and rush onto the shallow area, beach or sandbar, depending on slope and wave speed. The ammount of sucked water is transported to this shallow area and causing an increase of water level, named set-up. Depending on length the wave will need to run out or dissapear in deeper water like a trogue behind a bar, the set-up will vary. The wave height is not constant also, causing a difference in set-up. The set-up will be much more than the set-up, so in most cases the level will increase. Set-up is very sensitive for wave height and less for the wave period. Also the wave direction does influence the set-up. What the effect of set-up will be will be discussed later.

b. Location (see picture above)

The location of the rip is of importance. In the picture we see the green lines and the red lines. The green lines are drawn in rips on the beach. Those rips may be active during high tide. The red lines are rips situated in the 1st bar. Normally these rips stay wet and during low tide it might be possible to walk through them. The yellow lines indicate dry sandbars or beach. No set-up will be overthere. If the bar is wet and waves are breaking on the bar the change on set-up is present. 

c. The shape of the shallowness.

The setup does only occur is there are breaking waves. As described before the slope of the shallowness is important for the wave setup generation. If a wave can run a long distance before the wave will disappear the setup will be higher also. As we can see in the picture the witdh of the bar is not constant. The effect will be a different set-up depending of the spot on the bar. The deepness of the bar in m NAP (New Amsterdam Peil) is not the constant also.

The rip is also a shallownes. However as we can see in the picture (red lines) the waves are not breaking in this rip. So the setup in the rip will be low. The setup of the bar if present will be higher. It is the difference in setup what finally will cause a ripcurrent.

If waves are breaking in the rip a setdown/setup proces will occur overthere also. A setup will weaken the rip current howver a setdown will increase the the rip current in the neck of the rip. Most of the time the head of the rip will be smaller in case of rip setdown.

 d. Tide

The existance of a rip current is depending on factors mentioned before however which rip is active is directly related to the actual water level. The astronomical tidal level is well known for almost each place on earth. However the actual waterlevel is depending on the astronomical tide and the weather influence like wind, wind direction and time. The variations caused by the weather can be tremendous.

Conclusion when is a fixed rip dangerous?

 The moment of presence of ripcurrents is depending on the following aspects:

• wave chacteristics;
• shape of shallowness;
• deepness of shallowness;
• deepness of rip;
• actual water level.

As you can see it is difficult to answer this question clearly. In general we can say that the risk is present in the 1st bar during low tide and more towards the beach during high tide.

There is no permanent spot where you can point to and say overthere it is dangerous. In a few hours the situation can change completely. This is why permanent prevention of drowning in fixed rips is difficult and time consuming.

Be careful and indoubt consult the local lifeguard, they know the situation at the best. Watch the lifeguard signal flags.

Are you the best swimmer there is? Do not forget that if you go into the water others will do the same. They might be not so perfect as you are.

Permanent rips

At a sandy flat coast with groynes there will be 2 causes for dangerous rip currents. The 2 main causes are the tidal currents and the wind direction and force.

Most of the time the permanent rips are situated at both sides of the groyne. Lets look at the main causes:

a. The tidal current

Twice per 24 hours there will be an eb tide (current to the South) and a flood tide (current to the North).

The currents are not exact synchronised with the water level but have a different patern. For the Dutch coast between Hook of Holland and Den Helder the average pattern is as follows:

At high tide the flood tide will continue about 4 hours, than the change from flood tide to ebb tide for about 1 hour, the pre-eb tide for about 3 hours, the lowtide, the after eb for about 2 hours, the change from eb tide to flood tide for about 1 hour and the pre-flood for 1,5 hour. Total cyclus is about 12,5 hours.

If the groyne is visible the tidal currents will be pushed sea-ward by the groyne. If the groyne is flushed the upper tidal current will cross the groyne and the lower deeper current will be pushed seawards also. So during the existance of tidal currents it is dangerous at the groynes. If the water level is high enough to flush the groyne it still will be dangerous because a swimmer who is pushed over the groyne will be hurt by sharp edges of stones and little shells.

b. Wind direction and force.

If the wind is not perpendicular to the coastline but for instance between a corner of 45^{0 or} less a longshore current will develop. This longshore current is not the same as the lngshore current as described by the fixed rips but a longshore current alongside the complete coast. The current is maximum in the surfzone and when this current hits a groyne a permanent rip current will occur.

d. Combination of factors

If the longshore current and the tidal current have the same direction the permanent rip current will be very dangerous. In case of presence of groynes you can conclude that every 24 hours a dangerous current will be present for about 16 hours minimum. In case the distance between the groynes is more than 200 meters also the presence of fixed rips may occur.

The swimming in the neighbourhood of groynes and other obstacles is not wise and should be avoided. 

 Flash rips 

De flash rips do exist at high waves and stormy weather. Due to irregular waves set-up variations will arise at some spots causing short rip currents in the surf zone. These currents are short, from 1 to 5 minutes and can put people in danger quickly. Most of the time these currents will be present when the local lifeguard has the red flag in top. The red flag actually means it is forbidden to swim.

 Baby rip 

Baby or mini rips are small rips on the beach bar and will be dry during low-tide. Because these rips are small and shallow it is a nice place for small kids to play. However be aware that kids can fall easily and can drown at these places because they will not be able to stand up. NEVER leave kids alone at these places. Never leave kids alone in the sea or trogues, always supervise them and keep 1 or 2 eyes on them. 

Other coasts

Other coasts we will find at Zeeland, Walcheren and the Wadden islands like Vlieland and Terschelling. Tidal currents can be very strong here and cause strong permanent rips.

On those places were the Dutch authorities did build big dykes it is not wise at all to go for a swim. Were dykes are the currents are strong and there will be no or less beaches. Avoid these places.

What to do if you get into a rip current!

The next factors are important:

1. The watertemperature (see chapter Cold Water)

2. Your condition (See chapter swimming condition)

3. Your capacity to stay calm and not panicing.

Point 3 is always valid. If you get gripped by a rip your first priority will allways be:

Stay floating!!!!

Do not spill your energy by swimming aganst the ripcurrent. Als swimming with the current and trying to escape sidely out of the current will not be easy. You have to know what tidal current is present to prevent swimming aganst the tidal current. Als it is difficult to navigate and see what progres you are making. Specially if you are not used to that kind of situations. 

Switch over to surfival by using as less energy as you can to stay afloat. Try to maintain your temparature as constant as possible. In survivalcourses in the offshore they are learned to the so called foetis posture. However to do this you should train this before in a swimming pool. Try if you are on the top of a wave to put up your arm to attrack attention. Stay calm and breath without getting water in.

If people on the beach see you they will probably call 112 or warn the lifeguard. Don't forget that rescuing you will take some time also. That is why you must be prepared to survive this time The best thing is to swim only on guarded beaches and let someone know you are out in the sea. He or she can watch you and call 112 if necesary. 

Do you see somebody drowning in a rip do the following:

- call 112 or the local lifeguard;

- do not go into the water yourself , rescue swimming is top-sport, untrained people will get into problems very soon;

- try to let the victim know you have see him;

- if more peole are present and they are good swimmers you can start a rescue action only if there are rescue materials available like surfboards;

- do not forget that many unprepared rescuers did drown while the victims did survive;

- when life guard is arriving point out where the victim is;

- follow further instructions of the lifeguard.

In de USA heeft men een indeling gemaakt die aangeeft hoe hoog het risico is. Deze categorieën worden gebruikt in de muiwaarschuwingen via het lokale weerstation. Deze website gebruikt het systeem zoals dat in de USA is opgezet.

 IN the USA they did categorise the severity of rips. These categories are used in the area rip warnings transmitted by the meteological radiotransmitters.

The categories are as follows:

 Low (green): The expectation is that wind and wave conditions will not cause any rip currents of importance. However this  will never be valid for permanent rips at the groyns. Watch the signs and warnings of local Lifeguards.

Medium (yellow): Strong and frequent ripcurrents are possible. Weak and less experienced swimmers are advised  not to go for a swim.

 High (red): Life threatening rip currents will be present. Due to circumstances rescueing will be difficult. In the Netherlands a lot of places will hoist the red flag indicating the severity also it is forbidden to swim in that case.