The Tygerberg MTB Trail System covers some 80kms over the hills of Durbanville. Of the total distance, a high proportion, some 35kms, is singletrack. Much of the rest comprises existing jeep and farm tracks, packed hard and made durable by dozens of years of use by tractors.
It didn't take us long to realise that building singletrack is actually about managing erosion-by water and bicycle, and that the combination of the two can lead to early deterioration of a trail, lessening it's appeal and leaving an ugly unrideable mess.
With Winter rains in the Cape, we plan our building and maintenance for the Autumn and Winter months, as being predominantly clay, the ground is softer and more workable, and the water flows are more predictable. Water attacks from all directions;- out of the sky, running across the surfaces, seeping out of the ground, rising from springs or running in streams-none of which is apparent in the summer.
We subscribe to the IMBA methods of trailbuilding;- with correct sloping, run-offs and properly constructed bends, the natural flow should not be disturbed, water should not build up enough speed to start eroding the surface. Where water gathers then falls with speed and has no outlet, mud and erosion will soon follow.
Last winter, the first for the new trail at the Meerendal Wine Estate, we had to close the lower part of the lovely, but testing, climb known as Stairway to Heaven as soon as the first rains arrived. The bends on the incline and the trail between turned into a bog, and the punters weren't happy walking up the side of the track. We experimented with throwing stone in to the surface (didn't hold and too rough) and even a piece of conveyor belt (even more slippy). Rather than continue to return unhappy customers their day permit fees, we budgeted for a major engineering work for the next season;- putting down concrete grass blocks, 30cm square, 100mm thick with holes in to let the water pass over and through, but that would stabilise the trail surface.
We first used this method in Elastoplast Alley, a short but steep section of trail running down a thickly forested kloof on our trail at Hillcrest Wine Estate that suffered greatly from the braking effect of tyres tearing the surface up on the steep decline, as riders approached too fast and braked too hard. It was an immediate success, the erosion effect has been completely removed and that section will be solid for many years to come.
Using a team of skilled bricklayers, this is what we did at Meerendal, covering some 600m of the worst affected areas.
Step 1. Mark the trail edge with a line, then dig out trail to a depth of 100mm
Step 2. Lay blocks
Step 3. Level blocks with a line and spirit level, allowing for natural slope, and set camber on the bends.
Step 4. Backfill blocks ie cover with the dug out soil, making sure to pack the edges to stop movement.
Step 5. Leave for a few weeks for soil to wash down and settle, then return to backfill again. Blocks will remain largely hidden, but don't leave too much soil on top or it will turn to mud when it next rains. Final result will be a 365 day a year rideable surface.
A few months later, the trail has survived winter intact, and not one customer asked for his money back!