Technical Notes: Determination of Manning Roughness Coefficient for PVC Gutters

Abstract

This study is about the determination of the Manning roughness coefficient for a PVC (Polyvinyl Chloride) gutter and of its capacity due to longitudinal-slope changes. Both the roughness coefficient and gutter slope are factors that greatly affect both the velocity and depth of flow in a channel. For this purpose, an experiment is performed in the laboratory using a PVC gutter with adjustable slopes. The Manning formula, i.e. a function of: flow rate; channel roughness coefficient; flow depth (wet cross-sectional geometries); and channel longitudinal-slope, is then used. Water is supplied by a pump, and the discharge flow rate is determined by collecting the water that comes out at the end of the gutter downstream using a bucket. Then, both the volume of water in the bucket and the time it taking are measured. The flow depths are measured with a ruler (the other geometry sizes of the gutter are fixed, the length of 4m, width 12cm, height 10cm). These measurements were performed five times for each slope variation with 1cm/4m step (from 1cm/4m to 10cm/4m). The results show that the values of the Manning roughness coefficient for the PVC gutter range from 0.010 to 0.014. Due to an increase in the slope of 1cm/4m to 10cm/4m, the flow depth drops 60% to 40% for the same discharge

Keywords

• roughness coefficient
• gutters
• pvc
• manning
• slope