Guwahati is a fast growing city in East India with a chronical flooding problem during the monsoon period. The drainage system of Guwahati was modeled in the Storm Water Management Model (SWMM) to get a better insight in the current capability.
The Guwahati basin modeled in SWMM
Flooding is an oft-occurring problem in urban areas. This also applies to Guwahati, a fast growing city in east India. A study was conducted to examine how the current water system deals with extreme precipitation events. A digital elevation model was used to delineate watersheds, giving a total catchment area of 36000 ha. Land uses were classified with satellite images to estimate the Manning roughness coefficient and imperviousness for the sub-catchments, classifying 90\% of the basin as forest or urban. Junction nodes were placed at the start and intersections of rivers and drains. Storage nodes were used to model two lakes. Extreme precipitation for a return period of two years were found to be 48 mm for a duration of 1 hour and 66 mm for a duration of 2 days. It is debatable whether the return period of 2 year is correct, because no areal correction was made. The Storm Water Management Model (SWMM) was used to model discharge and infiltration. Sub-catchment runoff highest in the urban city center and lowest for forested mountainous areas, originating in the high imperviousness and a low Manning roughness coefficient for urban and vice versa for forested areas. This caused a quicker and flashier runoff behavior for the city center and a gradually changing behavior for the mountainous areas. Flooding occurred in the city center at places with a low elevation. A sensitivity analysis conducted on the width parameter of the sub-catchments showed that sub-catchment infiltration and runoff are sensitive for changes in this parameter, especially sub-catchments width a low imperviousness and a large area. This study shows that the current water system is not capable to deal with extreme precipitation events with a return period of 2 years.