Heritage and environmental aspects were a major consideration in the design and construction, which includes special stone masonry and landscaping elements. According to AECOM construction's news release The Ashton-Montagu region and Cogmanskloof Pass in particular, experiences substantial flood damage on a number of occasions, most notably due to serious flooding in 2003.
Nature designed it to flood
The topography of Montagu is such that it is located in a basin where three rivers form a confluence. All these rivers and their combined flow are then forced into the narrow confines of Cogmanskloof and after that through Ashton to join the Breede River. A similar geographical layout at Laingsburg caused the devastating floods of 1981 where more than 100 people drowned. Montagu's history records a long list of flood events, where major damage to infrastructure and property has occured, including the hot springs resort which has twice been the victim of floods in recent times.
A major challenge was replacing the existing river bridge in Ashton, which had to be upgraded due to anticipated increasing traffic volumes, and the structure's tendency to be overtopped during large flood events. This relates to the very skew river crossing, and the fact that the existing multi-span arch shaped bridge deck and pier configuration was hydraulically inefficient, and needed to be improved to accommodate design flood events on this strategic route.
What this means in simple English is that any vertical supporting columns tend to collect debris (like floating trees), which then aggravate the flooding situation and possible failure of the bridge itself. Several options were considered to boost the hydraulic capacity of the bridge. However, a key consideration was to allow unrestricted flow in the main watercourse opening, and also to enhance the available free-board of the bridge crossing. Therefore, the most viable solution was a single-span configuration.
This would span the full 110 m width of the river, eliminating the possibility of debris build-up. A tied arch bridge type is particularly well-suited for span lengths within this range, and was selected after comparison of several alternative options. The final design adopted was a single-span concrete tied arch bridge, with a deck suspended by stay cables, and accommodating four traffic lanes and two walkways.
To allow traffic to flow freely during the construction phase, the new bridge is being constructed adjacent to the existing bridge. After the completion of the new bridge, it will be utilised as a temporary bypass, while the existing bridge is demolished and the new abutments are being built. Following this, the new tied arch bridge will be launched transversely into its final position, over the space of a weekend.
The main contractor on this R650m project has experienced financial difficulties and gone into business rescue. All work on the project has come to a halt for the past few months, whilst alternative contractors are being sourced to complete it. This is expected to cause a delay of approximately one year.
MPSA are following this story closely and it is our plan to be there on that weekend and hopefully we will be allowed to video the actual repositioning of this huge structure. It promises to be an engineering feat of note.
Readers Choice - Tom Cowell's mountain pass story (Part 2)
One day my family were playing in a remote area in the river (Groot Stroom) that runs through Meirings Poort. An elderly ‘farmer looking’ gentleman approached and after sharing our tea asked if would like to take a short hike up the mountain side to show us something special. At first skeptical, we left the car at the roadside (one could do that in those days) and followed him for about 45min through the thick steep bush. We came across a large overhang cave with what seemed a thin man made stone viaduct with flowing water along the wall.
He explained in broken English/Afrikaans that he had discovered this place as a boy some 65 years ago yet had never shown it to anyone before. We felt privileged. Before he showed us what was special about the find and with a tear in his eye, he asked us to promise to keep the site secret. Then demonstrating he told us to take handfuls of water and throw it against the cave wall. Almost immediately a 5m X 2m detailed Khoi-San rock painting began to appear. Our first ever! We were left speechless and have yet never divulged the location.
About 20 or so years ago we were picnicking on the Swartberg Pass and 'skepping' water from the stream that feeds the town of Prince Albert when a lanky chap in a beat up bakkie stopped by and asked if the water was 'vars en skoon'. We assured him it was the best water in the world. He tasted and took down a couple of water containers to fill. We got chatting about the pass, and we offered him some biltong. He said thanks but no thanks ….. biltong is not good for the heart (haart). Well, and then with that unmistakable accent he introduced himself as Chris ( Professor Chris Barnard) !
[Next week the final chapter of Tom's story will be published. Ed]
Tankwa Tour fully booked
We unfortunately had to turn some people away as this tour became fully booked within days of its release. This experiment of inviting mountain pass fans to join us on filming trips is proving to be popular and we have expanded the concept into the Jhb area as well with Mike Leicester taking his guests to drive the mysterious Eureka City Pass next weekend. We only do about 4 of these trips per year, so if you're interested in the next one on offer, please book early.
Pass of the Week:
We head off to Grahamstown, one time capital of the so-called frontier, where a young Scottish immigrant named Andrew Geddes Bain found work constructing military roads. After building the Van Rynevelds Pass (now under the waters of the local dam) and Oudeberg Pass north of Graaff Reinet where young Bain first worked as a saddler, he was appointed by the Cape military authorities to move to Grahamstown and construct the Queen's Road between Grahamstown and Fort Beaufort, to facilitate the easier movement of troops and military equipment between the two strategic points.
It was 15 km north of Grahamstown that the road had to be constructed through a kloof, where Bain found unusual rock formations which were dated to be 250 million years old. These rocks he then documented and named them the Ecca formation. The pass through the kloof subsequently also adopted the same name.
Whilst the pass itself is fairly easy by modern standards, the real story is about the self taught engineer, writer, artist and geologist Andrew Bain and his profound influence on the early history of the Cape and more importantly the role he played in documenting South African geology. His oldest son Thomas learned from his father and surpassed his father's achievements by a considerable margin to become South Africa's most famous road engineer.
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Upgraded videos added this week:
Thought for the day: "A good sailor didn't become good by staying in the harbour" ~ Anonymous.