Comparative Evaluation Of Runoff Coefficients For Some Selected Residential Building Roofing Sheet Materials

Water is universally one of the most important natural resources necessary for survival of both plants and animals. Base on a strategy called rainwater harvesting system, a small-scale rainwater harvesting system was assembled in the Teaching and Research Farm of the Agricultural and Environmental Engineering Department, Federal University of Technology, Akure, Ondo State, Nigeria. The Campus is located in Akure South Local Government Area of the State. It lies between Longitude 5.12° and 5.20° East GMT and Latitudes 7.15° and 7.25° north of the Equator. Experiments were conducted to evaluate the performance evaluation of water quantity from three roof patterns and three different roofing sheet materials, such as plastic polycarbonate (PPC), clay tile (CT) and metallic (M). Direct collection of rainwater harvested (RWH) served as the control without runoff coefficient (RC).  Rainwater harvested (RWH) for the three roofing sheet materials from August to November, 2017 were obtained in order to determine their runoff coefficient (RC). From the results obtained, PPC roofs RC was 0.82, CT roofs RC was 0.93, while M roofs RC was 1.04, for August. Also PPC roofs RC was 0.78, CT roofs was 0.66 while M roofs RC was 0.77 for September. The RC values obtained for PPC. CT. and M roof materials for October; 0.90, 0.55 and 0.84, respectively. November RC values for PPC, CT and M roof materials were; 0.92, 074, and 0.82, respectively. All these obtained results were compared with the RC standard limit. The control RWH values obtained from this study were generally higher when compared with RWH values obtained for the three roofing sheet materials except for the month of August.