About Median Drains
The precast concrete median drain was primarily designed for the upgrade of the SANRAL highway system. Roads will affect the natural surface and subsurface drainage pattern of a watershed or individual hill slope. Road drainage design has its basic objective: the reduction and/or elimination of energy generated by flowing water. The destructive power of flowing water increases exponentially as its velocity increases. Therefore, water must not be allowed to develop sufficient volume or velocity so as to cause excessive wear along ditches, below culverts, or along exposed running surfaces, cuts or fills.
Provision for proficient median drainage is of paramount importance in road design and cannot be overemphasized. The presence of excess water or moisture within the roadway will adversely affect the engineering properties of the materials with which it was constructed. Cut or fill failures, road surface erosion, and weakened subgrades followed by a mass failure are all products of inadequate or poorly designed drainage. Our median drains are most appropriately included in alignment and gradient planning.
A road drainage system must satisfy 2 main criteria if it is to be effective throughout its design life:
- It must allow for a minimum of disturbance of the natural drainage pattern.
- It must drain surface and subsurface water away from the roadway and dissipate it in a way that prevents excessive collection of water in unstable areas and subsequent downstream erosion.
The design of the drainage structures is based on the sciences of hydrology and hydraulics; the former deals with the occurrence and form of water in the natural environment (precipitation, streamflow, soil moisture, etc)