30th January 2011, 10:08 AM
(This post was last modified: 30th January 2011, 10:20 AM by Stephen Jack.)
If you find this post slightly disjointed that is because it had to be edited according to the unofficial AUP.
Piercebridge TT episode 3 series 17.
http://www.channel4.com/programmes/time-.../episode-3
In this program Dr Robinson, describes part of the stone structure 200m down stream from Piercebridge as, “Massive great stones one on top of the other and this is a big bridge abutment”. Dr Robinson also goes on to say the “the river has shifted” as the explanation for the present day river being 100 meters from the abutment and 10 feet lower down, “rivers are dynamic”
To put this “big bridge abutment” into perspective, it's the same size as the Cong Burn abutment at Chester-le-Street “a stream of only 10 feet wide and 6 inches deep” Selkirk 'On the trail of the legions'
Neil Holbrook 'Roman bridges in Britain' describes the abutment as “a relatively small structure (8.05m long by 3.1m wide) and lay 100m to the south of the present channel of the Tees.”
There are six slots cut into the abutment, they are not shown in the program. Being just 2 feet above the stone paving, the range of uses for the slots is very limited, a complete waste of time for formwork when you are hardly off the ground, and it is double the number of slots require for formwork if the intention was to build a stone bridge. The only real use would be to support timber members in compression for a timber bridge, something which can be easily demonstrated by placing a shaped piece of timber in one of the slots.
In this “the river has shifted” explanation there are a few laws of physics which must have taken a vacation. Roman piles on the line of Dere Street are cut flush with the current river bed (Selkirk) There is no impact on the 3000 plus items found in a small area 200m upstream. Piles have been found in the current river bed on the line with the stone structure (NAG). 500 meters down stream there are pile holes with roman coins in the bottom (Selkirk) The bridge starts at a height of 2 feet, and the south side abutment is the size you would find on a small stream. So where is the river modelling, and scientific analysis, to prove that the river moved? All the evidence which does exist says the river bed level has changed very little in 2000 years.
Piercebridge, Neil Holbrook 'Roman bridges in Britain'“Even allowing for the northward shift of the river it would appear that a length of the flood plain must have originally been bridged.” Absolutely, but this can only give half the picture as a large part of the structure is missing.
If we look at Willowford bridge on Hadrian's Wall, Colin O'Connor in 'Roman Bridges' quoted a sign at the site “The river has changed its course since Roman times, leaving the eastern abutments of a series of bridges, built and rebuilt over many years, high and dry.” Aerial photographs of Willowford bridge show the high and dry part of the bridge is actually on the edge of a flood plain, exactly where it would have to be in order to allow continuous use during periods of flooding. The Willowford bridge abutments are still there after being rebuilt several times, why were the abutments rebuilt? what was the height of the flood plain?
On a standard Roman bridge, flow area is reduced by 25%. As this bridge carried Hadrians wall extra loading may have reduce flow area by 33.3% or more, barriers to people would also restrict flow. This in its self changes the flood height. Secondly the major flaw in Roman bridges, the large size of the piers, increases water velocity which subsequently undermines the foundations (O'Connor) The rebuilding at Willowford bridge was certainly the result of this process.
So was it the river that moved or the bridge that was removed?
Selkirk argued that the structure at Piercebridge was a spillway for a dam, structurally there are only three players in the game, bridging of the flood plain, a spillway or a combination of the two. Selkirk's reasoning is very good but there are a couple of problems. For starters the bridge timber work starts too low for a dam spillway, a weir is more feasible.
Secondly Selkirk argued that a bridge already existed on Dere street and you would not build one off this line. But if it was a bridge, why build it 200m down stream from Dere Street, this is unusual. Typically you would upgrade the existing structure or build a new one along side, but I think there is a sound geological reason for moving the bridge. The south bank has slipped in the past along a considerable length, The name of this area is Clife, today there is no cliff, just a slope. Although I would like to agree 100% with Selkirk’s conclusions, bank stability appears to be a very strong contender in the Roman engineers reasoning. . Future more this would mesh in with the high number of finds at the site of the original Dere Street bridge. A bridge accessible from one side, a bridge to no where, an example of Roman change of use, from bridge to shrine. Also the confined area in which the 3000 plus finds are located would suggest that there was a pool just after the bridge, it could have been caused by a dam, but erosion caused by bridges creates pools naturally.
Personally I think TT work falls way below the mark interms of what can be done in such a program. What could they have done?
Example GIS data.
They have an under worked surveyor on site with GPS. He could have surveyed the river and flood plain, made the data available on TT website and let it be analysed by 'others'.
Input from 'others'
O'Connor Roman bridges data
Environment agency data.
Local flood data
Free river modelling and analysis software HEC-RAS
Out of this you would have greater internet presence, follow up material for programs, modelled solutions for the downstream river structure at Piercebridge.
As well, important sources are not cited.
“Recently Mr R Selkirk has recovered a remarkable array of Roman coins and small
objects from around the piles and it has been suggested that they were votive offerings cast into the waters (Casey 1989).”
http://ads.ahds.ac.uk/catalogue/adsdata/...411001.pdf
Northern Echo 2005
“Rolfe and Bob were both members of a sub-aqua club and, their imaginations fired, when they heard Mr Selkirk wanted two divers to look for evidence to support his theory, they jumped at the chance.”
http://www.thenorthernecho.co.uk/archive...the_river/
Piercebridge TT episode 3 series 17.
http://www.channel4.com/programmes/time-.../episode-3
In this program Dr Robinson, describes part of the stone structure 200m down stream from Piercebridge as, “Massive great stones one on top of the other and this is a big bridge abutment”. Dr Robinson also goes on to say the “the river has shifted” as the explanation for the present day river being 100 meters from the abutment and 10 feet lower down, “rivers are dynamic”
To put this “big bridge abutment” into perspective, it's the same size as the Cong Burn abutment at Chester-le-Street “a stream of only 10 feet wide and 6 inches deep” Selkirk 'On the trail of the legions'
Neil Holbrook 'Roman bridges in Britain' describes the abutment as “a relatively small structure (8.05m long by 3.1m wide) and lay 100m to the south of the present channel of the Tees.”
There are six slots cut into the abutment, they are not shown in the program. Being just 2 feet above the stone paving, the range of uses for the slots is very limited, a complete waste of time for formwork when you are hardly off the ground, and it is double the number of slots require for formwork if the intention was to build a stone bridge. The only real use would be to support timber members in compression for a timber bridge, something which can be easily demonstrated by placing a shaped piece of timber in one of the slots.
In this “the river has shifted” explanation there are a few laws of physics which must have taken a vacation. Roman piles on the line of Dere Street are cut flush with the current river bed (Selkirk) There is no impact on the 3000 plus items found in a small area 200m upstream. Piles have been found in the current river bed on the line with the stone structure (NAG). 500 meters down stream there are pile holes with roman coins in the bottom (Selkirk) The bridge starts at a height of 2 feet, and the south side abutment is the size you would find on a small stream. So where is the river modelling, and scientific analysis, to prove that the river moved? All the evidence which does exist says the river bed level has changed very little in 2000 years.
Piercebridge, Neil Holbrook 'Roman bridges in Britain'“Even allowing for the northward shift of the river it would appear that a length of the flood plain must have originally been bridged.” Absolutely, but this can only give half the picture as a large part of the structure is missing.
If we look at Willowford bridge on Hadrian's Wall, Colin O'Connor in 'Roman Bridges' quoted a sign at the site “The river has changed its course since Roman times, leaving the eastern abutments of a series of bridges, built and rebuilt over many years, high and dry.” Aerial photographs of Willowford bridge show the high and dry part of the bridge is actually on the edge of a flood plain, exactly where it would have to be in order to allow continuous use during periods of flooding. The Willowford bridge abutments are still there after being rebuilt several times, why were the abutments rebuilt? what was the height of the flood plain?
On a standard Roman bridge, flow area is reduced by 25%. As this bridge carried Hadrians wall extra loading may have reduce flow area by 33.3% or more, barriers to people would also restrict flow. This in its self changes the flood height. Secondly the major flaw in Roman bridges, the large size of the piers, increases water velocity which subsequently undermines the foundations (O'Connor) The rebuilding at Willowford bridge was certainly the result of this process.
So was it the river that moved or the bridge that was removed?
Selkirk argued that the structure at Piercebridge was a spillway for a dam, structurally there are only three players in the game, bridging of the flood plain, a spillway or a combination of the two. Selkirk's reasoning is very good but there are a couple of problems. For starters the bridge timber work starts too low for a dam spillway, a weir is more feasible.
Secondly Selkirk argued that a bridge already existed on Dere street and you would not build one off this line. But if it was a bridge, why build it 200m down stream from Dere Street, this is unusual. Typically you would upgrade the existing structure or build a new one along side, but I think there is a sound geological reason for moving the bridge. The south bank has slipped in the past along a considerable length, The name of this area is Clife, today there is no cliff, just a slope. Although I would like to agree 100% with Selkirk’s conclusions, bank stability appears to be a very strong contender in the Roman engineers reasoning. . Future more this would mesh in with the high number of finds at the site of the original Dere Street bridge. A bridge accessible from one side, a bridge to no where, an example of Roman change of use, from bridge to shrine. Also the confined area in which the 3000 plus finds are located would suggest that there was a pool just after the bridge, it could have been caused by a dam, but erosion caused by bridges creates pools naturally.
Personally I think TT work falls way below the mark interms of what can be done in such a program. What could they have done?
Example GIS data.
They have an under worked surveyor on site with GPS. He could have surveyed the river and flood plain, made the data available on TT website and let it be analysed by 'others'.
Input from 'others'
O'Connor Roman bridges data
Environment agency data.
Local flood data
Free river modelling and analysis software HEC-RAS
Out of this you would have greater internet presence, follow up material for programs, modelled solutions for the downstream river structure at Piercebridge.
As well, important sources are not cited.
“Recently Mr R Selkirk has recovered a remarkable array of Roman coins and small
objects from around the piles and it has been suggested that they were votive offerings cast into the waters (Casey 1989).”
http://ads.ahds.ac.uk/catalogue/adsdata/...411001.pdf
Northern Echo 2005
“Rolfe and Bob were both members of a sub-aqua club and, their imaginations fired, when they heard Mr Selkirk wanted two divers to look for evidence to support his theory, they jumped at the chance.”
http://www.thenorthernecho.co.uk/archive...the_river/
