Storm Drainage Design - Essay Example

April 27,2009 Storm Drainage Design Project Introduction In the study of storm drainage design, we will be able to learn the functions of hydrographs in the design of open channels and reservoir. A hydrograph is a graph, either a bar graph or a line graph. A line graph is normally used to plot the discharge of water over the time, while a bar graph is the rise of water in the river over the function of time. There are factors that control the shapes of a hydrograph. According to Weyman, 1975 there are different shapes that are shown and the main components are labeled. The components of a hydrographs are the rising limb, the falling limb ,the peak discharge and the lag time. As we go along this course work ,we will be able to understand what hydrographs are. Cynon River Hydrograph Time with respect to river height Cynon River Hydrograph, Time with respect to rainfall The graphs above are the results of the Cynon river study data. The study took 4 days to finish nonstop. The measurements of the river height and the discharge are done every hour for 96 hours. The rainfall was plotted using the bar graph and the discharge was plotted using the line graph. In the analysis of the rainfall, you will notice that the rainfall is fluctuating. It is not as though there is a steady rise in the rainfall. The line graph shows the rise of discharge of water in the river, As the rainfall increases, the discharge also increases. The graph satisfy the components of a hydrograph. From the start of the study, you will notice that there is almost a steady flow of water in the river. That means that there is no increase in rainfall. At the start of the 44th hour, the water start to rise. This part of the graph is called the rising limb. This is the part of a hydrograph when water rises too the point of peak discharge. After it reached the peak point, the water stars to recede and this part is called the falling limb or the receding limb. This part denotes that rainfall is finally over and that the accumulated water in the river starts to stabilize again. The part of a hydrograph that is the highest point is called the peak discharge.. this is when there is the greatest amount of water in the river. The lag time is the period of time taking place between the peak rainfall and peak discharge. Computations By the application of the Manning's Formula, we will be able to get the value of breadth b of the open channel with the following data Channel design Given Data Q = 1.0 m3/s n = 0.012 S = 1/2000 = 0.0005 d = 0.5 Formula to be used V = where: v = velocity Q = Av R = Hydraulic Radius Q = A S = slope A = bd n = Manning's coefficient R = Q = discharge Computations: A = db = 0.5(b) Q = A R = 1.0 = 0.5b 1.(0.012) = 0.5b 0.012 = 0.5b = 0.5 0.5429 = 0.5 = 1.0858 = (1.0858)3 = b3 1.2801 = 1.2801 = 1.2801 (1.0 + 2b + b2) = 0.25b5 1.2801 + 2.5602b + 1.2801b2 = 0.25b5 1.2801 + 2.5602b + 1.2801b2 - 0.25b5 = 0 b = 2.2104 m. The value of depth of the river is also needed in order to solve for the value of the discharge of water in the river. The acquired value for depth will help us acquire the value fro the cross-sectional area of the river. In that way, we will be able to solve for the value of the discharge on the river. Computations; Q = Av where: A = cross-sectional area v = velocity = 4.0 m/s A = bd b = 15 m. A = 15(d) R = R = v = v = 4.0 = 4.0(0.012) = = 2.1719 = (2.1719)3 = 10.2451 = 10.2451(225 + 60d + 4d2) = 225d2 2,305.1475+ 614.7069d + 40.9804d2 = 225d2 2,305.1475+ 614.7069d + 40.9804d2 - 225d2 = 0 2,305.1475 + 614.7069d + 1 84.0196d2 = 0 By quadratic equation; solve for the value of d, d = where a = 184.0196 b = 614.706 c = 2,305.1475 d = d = d = d = d = d = 5.58 m After we achieve the result for depth d, we will now be able to solve for the value of discharge Q in the river. We need the value of the discharge in order for us to decide whether the river would be used as the water source of a nearby reservoir Solving for the discharge Q Q = Av Q = 15(5.58) (4) Q = 334.80m3/s = discharge of water in the river Now that we have the value of discharge in the river, we can compare the discharge of water in the river and of the channel. The river will be able to supply water for the open channel. The design load of the pump will depend on the discharge in the open channel, as suggested by Freemen and Young, 2000. The design load of the pump is equal to the discharge ofwater in the open channel. Computations for the design of a water pump: HP = where Q = discharge H = total head 3960 = constant H = Q = Av A = bd A = 2.2104(.5) A = 1.1052m2 Q = Av 1.0 = 1.1052 x v v = v = 0.9048 m/s H = + d where H = total head v = velocity H = + 0.5 g = 9.81 = gravitational constant d = depth = + 0.5 HP = design load 3960 = constant value H = 0.0461 + 0.5 1.0m3/s = 15850.323141489gallons/min 0.5461 m = 1.7916666666667 feet H = 0.5461 m HP = HP = HP = 7.17 horsepower Instead of using a pump with 7.0 HP force, we must use a 7.5 HP pump or an 8.0 HP pump. Since we acquired the result for the design load of the pump to be 7.17horsepower. It is safe to say that water discharge in the open channel will be allright . The pump will be able to fulfill the requirement of the design of the open channel. Thus, there will be enough water in the river to go to the reservoir nearby. In the sketch of the pump operation, the pump is to be located 3.0 meters to 12.0 meters above the river bed. The flow of water coming from the river is to pass thru the pump in order to accelerate the flow of water, thus fulfilling the design data of the open channel. The pump is required to pump water at the rate of 1.0 cubic meters per second so that the design load of water required to pass thru the open channel will not overflow nor have a less flow than the required. The design load of the pump is satisfy the flow of water in the open channel going to the nearby reservoir. Conclusion In the calculations that we have performed, we were able to establish the fact that in the design of open channels, the cross-sectional areas of channels is very important in the establishment of the of the design load of a pump to be installed for the use of accelerating the flow of water on certain conditions. Understanding the design load of a device is necessary so as not to make any errors in the proposed open channels. The design of drainage system had been used for many years now especially for water impounding. In the design of any storm drainage, the accumulation of the basic data and the familiarity with the site and the basic understanding of hydrologic and hydraulic principles and the drainage policy which are associated with the design aare of utmost importance. References Aarne,Vesilind, J. Jeffrey Pierce and Ruth F weiner, 1994. Environmental Engineering. Butterworth Heinemann. 3rd Edition. Flooding, BBC - GCSE BITESIZE - Flooding, BBC April 12, 2009,. King, Wisler, and Woodburn, 1988, Hydraulics, John Wiley and Sons, Inc. New York. Pump Equation and Formula Calculation, 2007, AJ Designs, April 10,2009, . Stott, Tim, Flood Hydrographs, Fluvial Geomorphology, Learning and Research Technology University of Bristol, April 19,2009. . Pierce, Jeffrey J. and Weiner, Ruth F. 1994, Environmental Engineering Butterworth Heinemann. 3rd Edition Waugh D. 1995. Geography: An integrated Approach, Walton-on-Thames, Nelson. Chapter 3 Drainage Basins and Rivers, 48-52. Weyman DR. 1975. Runoff Processes and Streamflow modelling, London, Oxford University Press, 54 pp. Young and Freemen, 2000. University Physics. Addison Wisley-Publishing Company,Inc. Singapore Read More