**11. Conclusion**

Construction of road network in an urban or semi – urban settlement requires a good drainage system that can convey rainfall surface runoff from impermeable surfaces created by road surface and built up areas. The efficiency of such a drain depends upon the road/invert grade, construction standard and ethics adopted, and maintenance culture.

On flat areas open concrete and pipe drains are hardly efficient in the disposal of rainfall runoff, and are unsustainable especially in a developing economy. A sustainable drainage system in such an environment is the trenchless drain with inbuilt drainage facilities comprising water absorption unit and grass cover. Field and laboratory observations have shown that the system is low cost both in construction and maintenance. It disposes accumulated surface water soon after a rainfall and reduces the incidence of erosion downstream since potential concentrated runoff is eliminated. It also introduces aesthetics values to the environment, and an antidote to mosquito breeding which consequently reduces the incidence of malaria. It is not suitable in sloping area and in districts with impermeable soil layer just below.

Built up environments or housing units could be provided with articulate arrangement of trenchless drain, absorption units and green cells within the premises to minimize the volume of water discharge onto the roadway. This concept will reduce the quantum of water concentrating to form a deluge that may ultimately result to

urban flooding, fluvial flooding and downstream erosion. The articulate arrangement of trenchless drain and comprehensive absorption units is an area of research and development interest.
