The importance of maintaining your drains
It’s important to note that a drain that isn’t maintained serves no purpose and will inevitably undermine safety and walkability.
Trench drains are effectively the inlet structures of the stormwater network, these pavement elements must allow surface level access for easy maintenance. Asset owners must maintain them!!!
Here are some key points to consider when selecting trench drains:
- High water velocities in a trench drain will reduce the amount of maintenance required and will result in longer times between maintenance operations. There are 3 ways to achieve this:
1. Water moves under the influence of its own weight. The deeper the water, the quicker it moves. Trench drains designed with a ‘V’ profile ensure higher water velocities. Oddly enough, the benefits of high-water
velocities are realised during minor (and more common) rainfalls events, where water depths (hence velocities) need to be maximized to produce a better self-cleaning effect. This is extremely important because it ensures drains are sediment-free in preparation for the next major storm event that produces the peak flows. ‘U’ shaped drains with flat bottoms, whilst easy to manufacture, are prone to sedimentary build up as the geometry tends to minimise water depth and therefore water velocity.
2. Trench drains comprising sloped channels is the easiest way to ensure water velocities are at their maximum. This is the most effective tool a designer has in their tool kit. Water runs downhill, so make the hill bigger!
3. Smooth inert materials like polymer concrete, enable water to flow with less friction at its optimum speed. Porous concrete channels are rough and get rougher with age as they are prone to biological and chemical attack and degradation.
- Designers can choose to specify a small inlet grate to stop litter from entering the channel or a large inlet grate for litter to drop and be arrested at the outlet of the channel.
Due consideration needs to be given to both the hydraulics of the grate inlet and channel outlet. As a factor of safety, a blockage factor should be applied when sizing up drains. - Manufacturers should ensure that grates can easily be removed and replaced and the pits at the end of run to have removable rubbish baskets. This encourages and facilitates regular maintenance.
- Pavements that are drained with trench drains are easier to maintain than pavements drained with pits. This is because for a large site, pipes that connect to stormwater pits are difficult to access and clean. Most trench drains offer continuous access from the surface along their entire length.
