(When printing the tide tables, if you would like the row and column background colors to be visible as they are on the screen, in your Internet Explorer, click Tools > Options > Advanced, and then tick the 'print background colors and images' box, (about halfway down the list), then click 'ok'.)

Tidal Currents and their Effect
Since the Norfolk Broads consist of a group of inland lakes and their connecting rivers, the effect of tide may seem of little consequence except around Great Yarmouth, where the passage between the northern and southern waters demands their respect. Their effect however, has an appreciable influence elsewhere on sailing yachts and even motor cruisers.

The flow rate at Yarmouth is around 4mph at mid-tide. Even as high as Potter Heigham and Horning, it is still around 1mph. This may not sound very much, but when you consider that the average Broads Authority speed limit is 5mph, (which is measured 'over ground'), your boat speed through the water would therefore be 6mph with an adverse tide, and only 4mph with a favorable tide.

Again, this may not seem worth worrying about, but speed differences as small as this can take a disproportionate amount of effort, (and noise level and fuel consumption) to achieve with the type of boats used on the broads. Without getting too technical, 'displacement' type hulls have an absolute maximum possible speed based on their waterline length, irrespective of the size of their engine. Not only that, their efficiency reduces rapidly towards that limit.

A typical 27 foot cruiser requires more than twice the power to achieve 6mph than it needs for 4mph, and with smaller boats the difference is even greater as their potential maximum speed is disproportionately less.

High & Low Tide Time Variations over the System
The 'High' and 'Low' water times vary throughout the Broads because the tide takes time to fill from the sea and then drain back through the rivers. The Northern and Southern rivers also differ in the height range between low and high water and the speed of the flood and ebb currents. This is due to the fact that all of the northern rivers, (the Bure, Thurne & Ant) connect to the sea through a very narrow constricted section of the Bure as it runs through Yarmouth. The southern rivers, (the Waveney & the Yare) however, are much wider and deeper and have less restriction. 'Fighting' the current on the Yare or Waveney can be a quite discouraging experience.

The Tide Calculator shows the actual height at key points on the system for the date and time displayed, together with the next predicted low and high tide at those points.

The calculations (as with all Broads tide predictions) are reasonably accurate as regards high and low water times, but the amount of rise and fall is greatly affected by wind and rain conditions. If you are planning to pass under a low bridge, such as Potter Heigham through to Hickling, you cannot always guarantee that 'low water' will be any lower than 'high water' !!

If there has been high rainfall or if the winds in the North Sea are of any strength and from the North or North east, they tend to push the North Sea down to the restriction of the Dover Straits and keep the sea level high at Great Yarmouth. This then has the effect of preventing the ebb tide from exiting to the sea, resulting in a no low water followed by a high tide on a high tide. Passage through Potter & Wroxham bridges, (for average height cruisers) is frequently blocked for days at a time, particularly in late summer.

Therefore, if you planning a holiday cruise in advance to pass under these bridges, you are well advised to leave your plans flexible, and consult the Bridge Pilots nearer the day. (Their use at Potter Heigham is mandatory for hired craft anyway.)

The effect of Neaps & Springs
Tide height ranges vary as a result of the gravitational pull of the moon and the sun. At regular intervals, these act either in opposition, or together and have a significant effect on High and Low water levels.

The comparative low water height indicator shows graphically the variations in low water tide height at Gorleston Bar. The 'max', 'average' and 'min' values are based over a three year period of measurement. The figure shown is the actual variance in metres above 'chart datum'. This has no significance within the Broads waterways, but does reasonably reflect the comparative heights between successive low tides.

During 'Springs', (about 3 days after Full or New Moons), the sun and moon exert the most pull on the sea, and we experience both higher and lower tides than average. During 'Neaps' (around the half moon periods), the sun and moon's gravitational pull are no longer combined, and we then experience 'higher' low tides and 'lower' high tides.

This poses an interesting quandary when negotiating low bridges. During Low Tide Springs, the water level is at it's absolute lowest, so gives the best clearance for safe passage. The subsequent High Water level however, is higher than usual, so you may need to plan for your return approx. 12 hours later to coincide with the next low. If the passage is made however during a Neap period, then you may well have enough clearance at high and low water.

Links

http://www.clock-finder.com/tideclock/ is a fascinating site with links to a huge range of clock related websites. The target page of this link is the tide clock page, with over a hundred onward links.