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Draining large flat pavements


Draining large flat pavements can be a challenge. Poorly designed drainage systems are not only ineffective at clearing surface water quickly, but can be difficult to maintain and cause slip hazards from ponding. A good design along with a hydraulically efficient drainage system can eliminate these hazards and provide a long lasting, durable solution that performs as intended.

How to achieve optimum hydraulic efficiency?

There are a wide range of surface drainage systems for various applications, but when it comes to discharging surface water efficiently, it depends on how the trench drains are configured. These systems are designed to collect surface flows through the grate into channels that transport the flows to a point where it discharges into an underground pipe system or culvert. One key factor influencing the hydraulic performance of surface drainage systems is gravity and therefore the effect of ground slope and built-in slopes within the trench drain is critical.

Slope Effect Hydraulics

How does the slope affect hydraulic performance?

As the degree of slope (fall) along the channel invert increases, the velocity of the flow within the trench drain will also increase resulting in a more hydraulically efficient trench drain. The slope can be introduced into the design of the trench drain by one or a combination of the following:

  1. For flat pavements, introduce a stepped configuration using neutral channels with varying depths creating a stepped fall configuration or introduce a slope along the base of the trench run using sloped channels with built-in falls to increase the invert depth
  2. Existing pavement with natural ground fall using neutral channels with a constant depth resulting in an invert slope identical to the ground fall
  3. Existing pavement with natural ground fall in combination with slope along the base of the trench run using sloped channels with built-in falls to further increase the invert depth

Introducing a stepped configuration has the least positive impact on a trench drain’s hydraulic performance. This is because on flat level pavements, particularly with long runs, velocities are limited by significant lengths of neutral channels with no slope (fall).

In comparison, drainage runs comprising continuous sloped channels with built-in falls allow for positive drainage with greater flow velocities for optimum hydraulic performance.

draining large flat pavementsWhat are my options for drainage in flat pavements?

Draining flat pavements in the urban environment is challenging.

The 0.5% internal slope in ACO’s modular channels help to minimise undulations in the pavement for pedestrian safety. ACO’s Polycrete® Channels provide a continuous sloped run in flat pavements.

  • 40 metres in one direction (end outlet)
  • 80 metres in two directions (central or end outlets)

With all things being equal, short runs have higher hydraulic capacities than long runs.

Sloped Channels

To learn more about Channel Hydraulics, click here

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