**Abstract**

Structural integrity of flexible road pavements is guaranteed if an effective road drain is provided during construction. On sloppy terrain open concrete drain has sufficient conveyance to get rid of runoff from the road system. The ability decreases as the terrain approaches near flat condition On flat terrain water often ponds on the roadway after a rainfall and conventional road drainage system is hardly effective in discharging the runoff. To address this a trenchless drainage system becomes a suitable option. This involves an engineered open trench backfilled with granular materials. The method is effective and cheaper.

**Keywords:** drainage, road, flat terrain

## **1. Introduction**

Road is an indispensible feature of any developing or developed society. It provides a means of communication, within and in-between communities and cities. It can be a single lane road or dual carriage way which aligns or cuts across with one another. During its construction, provisions are made for an effective road drainage system that will sustain the structural integrity of the road pavement. This measure will guarantee the usability and sustainability of the road for an extended period of time. The drain, located on both or either side of the road, provides a means by which runoff from the road surface and adjacent facilities is discharged harmlessly into an engineered or natural outlet.

The effectiveness of the drainage system is a function of the drain invert slope, its size or capacity and the structural disposition of the lining [1]. For a well designed drain the steeper the slope of the invert the more efficient is the discharge up to a maximum critical slope beyond which the flow becomes supercritical and abrasive. However, as the drain invert decreases to a minimum critical slope the discharge becomes subcritical, less efficient and less self cleansing. As this slope approaches a near flat regime, the potential hydraulic head approaches zero. At this stage the drain conveyance becomes paralyzed. Consequently the drainage system will functionally collapse and becomes grossly inefficient in conveying the runoff, thereby resulting to sustained flooding of the area if rainfall persists. In the same vein, the drain may be silted up, vegetation may spring up to cover the surface of the drain, and the stagnant water becomes a breeding ground for mosquitoes and other water borne disease

vectors [2]. Apparently malaria infestations and such health related hazards grow exponentially. Some functionally collapsed open drainage systems on a flat terrain in New Owerri district, Imo state Nigeria are shown in **Figures 1**–**4** below, as an illustration.

However, the discussion in this work will principally be directed to an engineered drainage system - a trenchless drain, that can permit gradual disposal of road wash/runoff on a flat terrain, after a rainfall.

**Figure 1.** *A waterlogged open concrete drain overgrown with weeds in new Owerri Nigeria.*

*A Drainage System for Road Construction on Flat Terrain DOI: http://dx.doi.org/10.5772/intechopen.105019*

**Figure 3.** *A waterlogged open concrete drain serving as mosquito breeding ground in new Owerri Nigeria.*

**Figure 4.** *A stagnant pool of water in an open concrete drain in new Owerri Nigeria.*
