1867 Canal Excavation Profile and 1870 Canal Survey (Broad River).



The evidence speaks for itself. The 1870 survey followed by an overlay showing this survey on today's map. Also shown in the overlay is a measurement line showing the distance to the bridge from the head of the canal in the 1867 profile. The last image is the 1867 Excavation profile with landmarks (like the Broad River Bridge) noted with their distance from the canal head.

Click here for a large full scan of the entire canal survey.

Below is the overlay of the 1870 survey onto today’s map. I lined up the overlay images with the canal locks of 1870 at the same position of today’s locks (from 1890). This is not an assumption. The 1870 survey shows Smith’s Branch to be exactly 400 feet above the 1870 lock. Today, the newer lock is exactly 400 feet below Smith’s branch.  Also, the 1867 survey shows the exact same distance from the lock to the bridge as the 1870 survey and the 1867 survey shows a creek about ½ a mile below the bridge. That creek still exists today and it lines up exactly with the 1867 position thus proving that the locks of 1867 and 1870 are in the same position as today’s locks. A third supporting fact is that the overlay of the 1870 survey and 2008 aerial photo shows that the new canal embankment would cut-off a portion of the old Bull Sluice canal. Today, when you hike down the canal embankment wood trail from the diversion dam, a little way down from the steps on the left, you can see the obvious continuation of the now dry Bull Sluice canal. I took a GPS reading from this spot and it lines up exactly with where the 1890’s embankment cuts off the old canal on the overlay.

Below is an overlay of the entire canal. Notice how the Columbia-Greenville rail (on the east side of the Broad River, lines up exactly. Same with the Charlotte-Augusta rail on the east side of the Congaree River. All the streets in Columbia also line up.

Click here for a much larger scale overlay of the entire canal.

Here is another very important thing to note about the abutment location on the west side of the river: I took GPS readings from the top of this abutment and then plotted this location on an aerial photo using Google Earth. My handheld GPS is very accurate with Longitude/Latitude (within 5 feet) but not so good with elevation. That’s where a combination of Google Earth and the Richland County GIS system is useful. I matched the Google Earth aerial position with the corresponding position on the GIS system and then took advantage of the elevation data in the GIS system. The result is that this abutment is at an elevation of 166’ or 28’ above the normal level of the river. This is 2’ above the height of the abutment at 154 Castle Road but also 28’ above the normal level of the river at 154 Castle Road (because of the natural fall that occurs when heading south). From research, I found that during the bridge building of the 1790’s through the 1800’s, that it was standard to build a bridge 5 feet above the greatest recorded flood level. This was accepted to be 24 feet (worst flood + 5’) above the normal level of the river. Below is an image of the 1825 Design and Requirements document for what would be the first bridge built in the area of today’s Broad River Bridge. Again, this specifies a bridge height of 24’ above the normal level of the water. So why are these abutments 4’ above this specification. You have to consider the fact that a canal did not exist across from these sites until the late 1830s when Bull Sluice Canal was extended down to the Columbia Canal.  Initially, this canal was only for navigation and it did not carry a significant amount of water compared to the river. In 1890, however, the canal’s width was increased but a factor of 10 and the depth was more than doubled. Today, under normal river conditions, the canal carries twice as much water as the river. The affect this has on the river height can be seen by viewing the hourly historic data maintained at multiple sites along the river. This data includes the water’s height as well as the amount of water flow. Since we really want quantity of water, the best we can do is look at the river data when a large amount of water is flowing and then find a time when half as much of this amount is flowing. Interestingly, the numbers are the same for several locations on the Broad River as well as a location on the upper Congaree. Twice as much water translates into an increase in water height of 4 feet! This new location for the Confederate bridge and Compty’s 1796 bridge, exactly meet the 1825 height specification.

Below are the GPS plot of the abutment remains and the 1825 Design/Requirements document.

Below is the 1867 Canal Excavation Survey. Notice the Broad River Bridge landmark noted at 37 chains.