Spring tides at the Falls of Lora

Playing at the Falls of Lora is very dependent on the tides, particularily the tide heights during Springs - so I have been doing a little digging to find out more about them.

Causes of Spring tides

Tides are caused by the varying gravitational effects of both the sun and the moon. If the moon didn`t exist, we would still have tides, but they would be a lot smaller.

Spring tides are caused when the sun, the earth, and the moon are all in line, and the gravitational effects of the sun and the moon combine. However there are also other factors that have an effect as well.

During the equinoxes, when the sun is "over" the equator, the gravitational effect of the sun is greater, so Spring tides tend to be higher in March and September.

Another factor is that the orbit of the moon round the earth is not circular, but is elliptical in shape. When the moon is at its nearest point to the earth, it is called the "perigee". When it is at the furthest away point from the earth, it is called the "apogee". There are 13 perigee`s and 13 apogee`s per year. The gravitational effect of the moon is greatest when it is at its perigee - and the result is a slight increase in the size of the tides.

If the time of the perigee coincides with the time of a Spring tide, then the result is a Perigee Spring tide, which is higher than a normal Spring tide.

Yet another factor is the fact that the elliptical orbit of the moon is not fixed, but varies a bit in shape, so that on different perigee`s, the moon is slightly nearer to or further from the earth compared to other perigee`s.

So the various Perigee tides are different.

Combining all these factors results in some noticeable variations in Spring tide heights throughout the year.

It is interesting to note that the highest tide in each Springs is one or two days after the new or full moon, which is a bit odd, as it is the new or full moon that causes the Spring tides.

The height of the low tide

After all that, the above only considers the height of the high tides, it doesn`t consider the height of the low tides, or the tidal range. Yet the height of the low tide and the tidal range have a considerable effect on the quality of the waves produced.

It is therefore quite important when consulting tide tables to look at the low tide height as well as the high tide height, and to calculate the tidal range.

I think that generally, play boats looking for good sport on the ebb tides need very low low tide heights.

I don`t think it just so critical for sea kayaks who are using the flood tide.

Semi-diurnal tides

There is yet another factor that has an influence on the quality of the waves at the Falls of Lora.

Most - but not all - of the world`s coastlines experience semi-diurnal tides - which means there are two high tides, and two low tides every day - and this includes the Falls of Lora.

More precisely, there are two high tides and two low tides every 24 hrs 50 mins.

The problem is that the tides produced by the two sets of tides don`t match - so a typical day will have

a higher high tide
a lower low tide
a lower high tide
a higher low tide

These four tide levels are not neccessarily in that order, the lower low tide may be before the higher high tide, or it may be after the higher high tide.

So sometimes the largest tidal range is before the higher high tide, and sometimes the largest tidal range is after the higher high tide.

Or to put it another way, sometimes the flood tide has the largest tidal range, and sometimes the ebb tide has the largest tidal range.

This is obviously going to have an influence on the quality of the waves at the Falls of Lora, both on the flood tide, and on the ebb tide.

Yet another consideration is that sometimes it is the early morning Spring high tide that has the highest tide level, and sometimes it is the late afternoon Spring high tide that has the highest tide level.

Other factors that influence the waves

There are loads of other things that can affect the tide heights and the quality of the waves - such as

storms out in the Atlantic
atmospheric highs and lows
wind - both speed and direction
rainfall - Loch Etive has quite a big catchment area - if there has been significant rainfall, loads of rivers are feeding water into Loch Etive, and the loch starts to rise. During the flood tide, when the tidal flow is incoming, this water can`t escape, it piles up, and flows out during the ebb tide. So this effects the amount of water flowing in and out during the tidal flows

So there is a big elememt of luck in there as well.

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