CS(AR)-2/2014 : Storm water management in Otteri Nullah sub basin, Chennai corporation, Chennai, Tamilnadu

Abstract

Otteri Nullah sub basin spread over an area of 30.63 sq km is one of the 12 sub-basins of Chennai Municipal Corporation (174 sq km). The study entitled "Storm Water Management in Otteri Nullah Sub basin" envisages development of a 2-D dynamic rainfall-runoff storm water management model (XP-SWMM) to study the adequacy of existing drainage network of the subbasin draining to Buckingham Canal for different return periods. The model predicts runoff hydrographs based on the input hyetograph and the physical characteristics of the sub basin. Since the only hourly rainfall data was available at Nungambakkam IMD station near to the Otteri Nullah sub basin, five more tipping bucket rain gauges and two automatic water levels recorders were installed in the study area.

The DEM and land use/cover maps of the sub-basin were prepared from DGPS survey and satellite data. The storm water drainage network details and Otteri Nullah longitudinal profiles/cross section details at every 30 m chainage were collected and GIS database was prepared. Using thematic layers of DEM, drainage network and road network, total 88 micro watersheds were delineated in the Otteri Nullah sub basin. The drainage network was. schematized into 121 nodes and 120 links in the XP-SWMM model. Model parameters like Node/link characteristics, pervious/impervious area, soil type, average width/slope and SCS-CN were computed for each micro watershed using GIS data base. Based on measured rainfall and water level data in the study area, few events were selected for the model performance in terms of runoff computation and to calibrate and validate the model. After successful calibration, it was found that even a peak discharge of 27.57 m3/s generated from the hyetograph of 24 hour design storm of 2 years return period having maximum hourly rainfall of 48.89 mm is causing flood at many locations. The drain sections were then modified as proposed by PWD. The model simulation predicted adequacy of drainage upto design storm of 5 years. The impact of flood water diversion link from Otteri Nullah, west of Annanagar to Cooum river found that there is 38% of reduction in the peak flow against 2 - years return period storm. The hydrographs at outfall of the sub basin developed for various return period would be very useful for adopting best management practices.