The design of access ramps for drainage channels typically involves a deliberate orientation: sloping downwards towards the downstream direction. This strategic choice serves a crucial purpose in preventing a phenomenon known as overshooting.
Overshooting occurs when supercritical flow, characterized by high velocities and shallow depths, encounters an obstacle or abrupt change in channel geometry. In the case of access ramps aligned against the direction of channel flow, the ramp itself can act as such an obstacle, causing the water to “jump” over the ramp and potentially overtop the channel banks.
By sloping the access ramps downstream, engineers ensure that the water flow smoothly transitions over the ramp, minimizing the risk of overshooting and maintaining the integrity of the channel. This design consideration is particularly important in channels prone to supercritical flow, where the consequences of overshooting can be severe, including erosion, flooding, and structural damage.