6.2 Tilted causeways

FIGURE 6.2

Tilted causeways

Source: MetaMeta (www.roadsforwater.com).

Reinforced Causeways (Drifts) at Ephemeral Stream Crossings Where roads cross the dry bed of ephemeral streams, reinforced causeways or drifts may be used. In addition to their function as traffic conduits, they help stabilize the unstable gravelly streambeds in mountain environments. drifts may also help retain water in the sand and gravel of the riverbed. Chapter 9 describes the application of such nonvented drifts in semiarid areas. In mountain areas, the drift may be reinforced beyond normal specifications to enable it to withstand the pressure of torrential flows and the impact of rolling boulders. The drift should not be equipped with culverts. along with the body of the drift itself, the drift consists of the approach road, the upstream protection of the stream, and the downstream apron. Because of the heavy natural armoring of mountain streams, they may not need downstream aprons.

Dissipation Blocks Use of dissipation blocks is recommended where a minor stream descends onto the road (figure 6.3). The block may be created by stacking up stones and rocks that become available when a mountain road is opened. If placed where the streams and torrents hit the road, these stockpiled stone blocks will dissipate the force of the water flows. This measure comes at no extra cost because the stone blocks are stockpiled for use in future repairs yet are often placed off-stream. The blocks are best placed 30–40 centimeters away from the side slope. flat stones may be placed between the torrent coming from the hill slope and the dissipation block to break the velocity impact of the descending water. The stockpiled stones will further baffle the force of the mountain stream. a small depressed section may be created in the road body, like a mini-causeway, to guide the streamwater across the road. a barrier to protect vehicle occupants from collision with the block would be required.