Introduction
Urban drainage presents a classic set of modern environmentalchallenges: the need for
cost-effective and socially acceptable technicalimprovements in existing systems, the
need for assessment of the impact ofthose systems, and the need to search for sustainable
solutions. As in allother areas of environmental concern, these challenges cannot be
consideredto be the responsibility of one profession alone. Policy-makers,engineers,
environment specialists, together with all citizens, have a role.And these roles must be
played in partnership. Engineers must understandthe wider issues, while those who seek
to influence policy must have someunderstanding of the technical problems.
The development of infrastructure has created large areas of impermeable land where
rainfall events cause surface water runoff to enter watercourses, through conventional
drainage systems, quicker and in larger quantities than from Greenfield sites, increasing
the likelihood of flooding to receiving watercourses.
Construction of urban highways and arterial roads substantially alter the perviousness of
the areas. Large amount of permeable areas are replaced with hard surfaces. The
diminution of permeable surfaces lessens the depression storage and infiltration. The
paved surfaces speed up the conveyance of runoff. Thus, urban highways result in greater
quantities of runoff at higher rates than would occur under pre-highway conditions. Storm
water management aims at minimizing or preferably eliminating entirely.