Figure 2.1 Preliminary Flood Hazard Map of Bulacan
Rational Method Rational Method is used to design storm sewers. It takes into consideration the physical and hydraulic properties of catchments and their effects on storm water runoff. The equation for the determination of the peak flow from a catchment is expressed by the formula: Q = CiA where: Q = peak rate of discharge C = runoff coefficient. It varies from 0 to 1.0 depending on the surface character of the area considered. i = the ratio of rainfall to time and is measured usually in mm/hr A = area covered in hectares Manning’s Formula The Manning’s Formula or equation is used for calculating the capacities of channels and pipes running part full. The flow rate or discharge and the velocity of flow in a channel or pipe running part full are given by the equations:
Q = A xV V = 1 n x R 2 3 x S 1 2 therefore: Q = A x 1 n x R 2 3 xS 1 2 where: Q = flow rate or discharge, m 3 s V = velocity of flow, m s A = cross sectional area of the conduit, m 2 R = hydraulic radius = A P P = wetted perimeter, m S = pipe or channel slope, m m n = Manning’s friction factor = 0.012 (value of n for concrete materials)
PAGASA Rainfall Warning Signals The color-coded rainfall advisory of PAGASA indicates the amount of rainfall within one hour. Red, orange and yellow warning signals is applied to the three levels of rainfall volume intensity and its associated flooding. Figure 2.2 PAGASA Infographic: Color-Coded Rainfall Warning System 2.3 REVIEW OF RELATED STUDIES The study entitled “A Proposed Drainage System for the University of San Carlos - Talamban Campus” by Dayag (1997, October) discussed about establishing an adequate storm
sewage drainage system for the University of San Carlos - Talamban Campus that will be beneficial for future development of the said campus. The existing drainage system of the university is inadequate to convey the storm water into its point of discharge. The main streamline which is the point of discharge is also deficient to accommodate storm water from the University of San Carlos sub-catchment and should be corrected by government’s responsibility. The study proposed two separate drainage systems in the service area to accommodate more storm water. Also, the study recommends a continuous maintenance of the sewers and a proper waste disposal to minimize the problem of clogging. According to Gabrielle Rosales Iglesias (2008, August) in her article entitled “Flood Disaster Mitigation and River Rehabilitation by Marikina City, Philippines”, urban flood mitigation is a complex effort wherein both structural and non-structural mitigation play equally important roles. Marikina started a flood control project for 12 barangays that includes construction or rehabilitation of major outfalls, improvements in the network canals, drainage systems, creeks and waterways. There are improvements done to sidewalks and drainage network, as well as part of a 6-km road dike. Marikina paved 500 km of roads to reduce the amount of sand, pebbles and mud that enters the drainage system. The national government
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