Storm Drainage Design Project Analysis - Essay Example

10, April 2009 Storm Drainage Design Project Introduction In our study of storm drainage, the study of hydrographs and their analyses are to be takeninto account. A hydrograph is a graph that concerns about the activities of bodies of water of more specifically, rivers and channels. The analysis of hydrographs are done after a study had been made on a river. Hydrographs are records for the study of storm drainage. It is a graph of the flow in a stream over a period of time. Peaks in a hydrographs are usually the results of precipitation events while troughs represent It is graph of the flow in a stream over a period of time The peaks in the hydrograph are results of precipitation events while troughs represent dry seasons. A line graph is usually used for the discharge over time. Rainfall is plotted with the use of a bar graph. There are several factors that control the shape of a hydrograph. The different shapes are shown and the main components are labelled according to Weyman, 1975. Hydrographs have differences between the peak rainfall from its peak discharge. The difference is the lag time. If the lag time is great, there is a less chance of flooding. A short lag time will indicate that water had already reached the river channel at a fast rate. The rise in discharge shown in the is called the rising limb, and the decrease in the discharge is called the falling limb. The larger size means that there is longer lag time as water has a longer distance to reach the river trunk. The shape of the basin is normally elongated and produces a lower peak flow and longer lag time than a circular basin with the same size (Gillesania,2006). Cynon River hygrograph Time respect to discharge Cynon River hydrograph Rainfall with respect to time The line graph illustrates the change in height of water in the river over time, while the bar graphs illustrates discharge of water in the river with respect to time. The study was taken for 96 hours or 4 days. It was done continuously, taking the height reading every hour for 96 hours. All the readings vary from each other. In its analysis, there was almost a steady flow of water from the start up to 42 hours. After 42 hours, the water in the river began to rise. The rising of the water is called the process of rising limb. The time between the rise of water and the time the water reaches its peak is known to be the basin lag time. It reached the peak flow at the 57th hour in the study. This means that water had reached its peak discharge and is now starting to fall down. From the peak point, when the water height starts to fall down the process is called recession limb. After the recession limb, the water discharge will normalize. Channel Design Given data are: Apply the Manning formula to design a suitable breadth b, with Q = 1.1 m2s the given data of discharge of the channel d = 0.6 m n = 0.015 where: v = velocity, m/s S = 0.0005 R = hydraulic radius v = R2/3S1/ 2 S = slope n n = Manning's coefficient of roughness A = db A = cross-sectional area b = breadth Q = Av d = depth wetted perimeter = 2d + b v = R2/3S1/ 2 n Requirement = width of base b of the open channel Discharge Q of the river into the open channel Design of water pump to discharge water from the river to the open channel Computations: A = db = (0.6)b Wetted Perimeter = 2d + b = 2(0.4) + b = 0.8 + b = 0.8 + b. Q = Av 1.1 = 0.6b 1.1(0.015) = 0.6b 0.0165 = 0.6b = b 1.2406 = b = b3 1.9093 = b3 1.9093 = b3 1.9093 = b3 1.9093(1.44 + 2.4b + b2) = 0.36b5 2.7494 + 4.5423b + 1.9093b2 = 0.36b5 2.7494 + 4.5423b + 1.9093b2 - 0.36b5 = 0 b = 2.3065 m. Computation of discharge of water in the river Q = Av where Q = discharge in m3/s A = cross-sectional area V = velocity v = R = hydraulic radius S = slope n = coefficient of roughness A = bd b = base, width d = depth Solving for the discharge in the river A = bd A = (15)(d) A = 15d Solve for Q, v = 4.0 m/s Q = Av Q = (15d)(4.0) Solve for d 4.0 = 4.0( 0.015) = 0.6 = = 2.7149 = = 20.0106 = 20.0106 = 20.0161(225 + 60d + 4d2 = 225d2 ,502.385 + 1200.636d + 80.0424d2 = 225d2 4,502.385 + 1,200.636d + 80.0424d2- 225d2 = 0 4,502.385 + 1,200.636 - 144.9576d2 = 0 Solving for the value of d by quadratic equation d = d = d = d = d = d = 11.0817m. Solving for the discharge of water in the river Q = Av A = bd A = 15(11.0817) A = 166.20 m2 Q = 166.20 (4.0) Q = 664.80 m3/s In comparing the discharge of water in the river which is 664.80m3/s and the discharge of water in the open channel which is 1.1m3/s. It is safe to say that water can be taken from the river to the open channel to supply to a nearby reservoir which in turn would supply water to a community. A design for a pump to take water from the river will depend on the capacity of the open channel. The pump will regulate the amount of water to be supplied in the open channel so that the water that will pass thru the channel will not overflow. A suitable type of pump to be used to provide large discharge of water from the river to the channel will be determined by the following computations. Solving for discharge in the channel Q = Av A = bd A = 2.3065 x 0.6 A = 1.3839 m2 Q = Av 1.1 = 1.3839 x v v = v = 0.7940 m/s HP = where Q = discharge H = total head H = + d v = velocity g = gravity constant = 9.81 H = + 0.6 H = H = + 0.6 H = 0.0321 + 0.6 H = 0.6321 HP = where Q = 1.1 m3/s = 17435.355455638 gal.min H = 0.6321 = 2.0738188976378 ft Hp = HP = HP = 9.130749906 horsepower Therefore a 9.50 - 10.00 horsepower pump is safe to use in the design. Sketch of pump operation The location of the pump and channel bed is between 3.0 meters and 12.0 meters above the river bed. The arrows indicate the direction of water from the river passing thru the pump and to the open channel. The use of the pump is to direct water to the channel with the specified discharge in the channel. In the design of the channel, it is required to have a 1.1 m3/s. To satisfy the discharge of water in the channel, we computed for the required depth of water that will pass thru the channel. We also computed for the width of the river with a given condition of velocity and depth. Together with the computed river discharge, we came up with a discharge that will perfectly suit the design of the channel. Comparing the discharge in the river with the discharge of water in the channel, we can conclude that the design for the channel is safe, and there will be no overflowing of water nor an underflow will occur. Conclusion Surface storm run-off as overland-flow has not been observed in this drainage area. Nontheless, characteristic flood hydrographs are produced by heavy rains. A simple hydrograph is produced by an intense summer storm. The nature of physical development of the areas to be served by a storm drainage system, the storm water management plans for the area and the ultimate pattern of drainage are the key factors to be remembered. There should be an understanding of the nature of the outfall since it usually has a significant influence on the storm drainage system. Furthermore, there should be an understanding of the nature of the outfall since it usually has a significant influence on the storm drainage system.In environmentally sensitive areas, there could be water quality requirements to be taken into considerations. References Dr. Tim Stott, Flood Hydrographs, Fluvial Geomorphology, Learning and Research Technology University of Bristol, April 14, 2009, . Flooding, BBC - GCSE BITESIZE - Flooding, BBC April 12, 2009,. Pump Equation and Formula Calculation, 2007, AJ Designs, April 10,2009, . Gillesania, Diego Inocencio T. 2006, Engineering Formula Series, Civil Engineering, Diego Inocencio T. Gillesania, Manila, Philippines. Hoyt, W. C. and others, U.S. Geological Surveys. W - S pages 772, 1936. King, Wisler, and Woodburn, 1988, Hydraulics John Wiley and Sons, Inc. New York. Weyman DR. 1975. Runoff processes and streamflow modelling, London, Oxford University Press, 54 pp. Young and Freedman, 2000, University Physics, Addison-Wesley Publishing Company, Inc. Singapore Read More