Relative Effects of EIA Alternatives on Urban Hydrology in the Greater Port-Harcourt Watershed

As several cities in developing countries are urbanising at alarming rates around the world, one key concern to planners are the options that affect the hydrologic functioning of watersheds. Globally, EIA is recognised as a key sustainable development tool for mitigating adverse impacts of planned developments. However, research has shown that planned and unplanned developments alike generate significant impacts on people and their environment. Flood is a major sustainable development issue that often result from increased paved surfaces and decreased interception losses. A number of studies have advanced the concept of alternative in environmental assessment. Likewise, hydrology research lay emphasis on the influence and location of paved surfaces on catchment runoff, however, research exploring the effects of location alternative on urban hydrology context is very rare. Greater Port-Harcourt City Development Authority was charged with the responsibility to meet the growth need in Greater Port-Harcourt by implementing the Masterplan to build the new Greater Port-Harcourt (GPH) City. The aim of this research is to examine the relative effects of the location alternative at (Bori, Ogba-Omoku and Port-Harcourt area) on the urban hydrology.  HEC-HMS hydrologic model software was used to generate data for comparing runoff in three basins. The HEC-HMS software combines models that estimate: loss (runoff volume), transformation (discharge runoff), base flow and channel routing respectively. Result showed that developments although with the same spatial extent spatial extent had different effects in different basins and subbasins. The study also found that basin size instead of location of development was the main factor in the studied watershed.