The first Severn Bridge was opened in September 1966 by the Queen, to replace the ferry service crossing from Aust to Beachley. At this point the River Severn is almost exactly 1 mile wide at high water

This bridge used to carry the M4 over to Wales,
before the second bridge was built.
The first Severn Bridge is in fact two bridges. The main section spans the Severn Estuary, whilst the second smaller section spans the River Wye.
The second Severn Bridge was opened on 5 June 1996 by His Royal Highness, The Prince of Wales.

The Second Severn Crossing is 5,128m long
Distance from Source: 354 km (220 miles)
Height above Sea Level: 0m
Width of river: 3.77km (2.36 miles)
The river is much wider here than at the first river crossing. When building the bridge, the engineers had to consider the massive 14.5m tidal range, the notorious currents and the large ships that would want to pass under the bridge.
The middle section of the bridge has a clearance of 37m

Each bridge pillar weighs 2,000 tonnes and is 53m long
There are more pillars on this bridge than the first one. Can you think of reasons why his might be?
 
Estuary
The wide mouth of a river.
Silt
A mixture of sand and mud that is carried along than then dropped by the river.
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