Storm Drainage Design - Essay Example

April 28, 2009 Storm Drainage Design Project Introduction Hydrographs are used in the analysis of rivers. The line graph and the bar graph are usedto represent the activity of water flowing in rivers. Hence water from the river can be useful if we know how to make a design that is truly fruitful to end users. Usually, in the study of storm drainage, the analysis of hydrographs are considered. A hydrograph plots the river discharge and amount of rainfall as a function of time. In the study of storm drainage, the analysis of hydrographs are important. A hydrograph plots the river discharge as a function of time. Measurements are done at a certain point in a river. Rainfall is the input used to a watershed and the stream flow is also considered as the output of the watershed. A hydrograph also represents how a watershed reacts to rainfall. King1998, in his report said that the response of a watershed to rainfall depends on several factors which affects the shape of a hydrograph. This represents the effect of rainfall on a particular basin. This is a hypothetical response of a watershed to the input of rainfall. This will allow calculations of the response to any input(rainfall). Hydrographs are often affected by factors of soil saturation and the surroundings. The vegetation type and the steepness of the surrounding lands, with the drainage density(Stott,2005). Very dry weather, nornmally creates a crust on river beds and wet winters would increase the discharge. Sand and clay produces a flashy hydrographs but there could be a difference between the two. Cynon River Hydrograph Time with respect to river height Cynon River Hydrograph Time with respect to discharge The analysis of hydrographs are of utmost important in the design open channels, rivers and reservoirs. The Cynon river hydrographs are examples of the analysis of rivers which are to be used as a water source of an open channel that would supply water to nearby reservoir. The hydrograph data was used to analyze the water activity in the river after a rainstorm. The study was done for a period of 96 hours. Measurements on the height of water was done on an hourly basis. The results of which are as follows. The water level was almost constant for the first 43 hours. At the start of the 44th hour, the water level started to rise. This stage of the rise of water is called the rising limb.It reached the peak, or the highest water level on the 58th hour. As it started to fall down, it undergoes falling limb. This is when the height of water level starts to recede. The falling limb would come after the rising limb . The peak discharge is when water reaches its highest point and there is the greatest amount of water in the river. The lag time is theperiod of time that is recorded between the peak rainfall and peak discharge. Design computation of the Channel Data provided Note: Apply the the Manning's Formula to get value for Q = 0.8 m3/s breadth b, of a channel with a given value for d. n = 0.012 S = 1/2000 = 0.0005 d = 0.3 Substitute the data in the equations below: V = where: v = velocity Q = Av R = Hydraulic Radius Q = A S = slope A = bd n = Manning's coefficient R = Q = discharge Solutions: A = db = 0.3(b) Q = A R = 0.8 = 0.3b 0.8(0.012) = 0.3b 0.0285 = 0.6b = 0.3 = 1.447 = (1.447)3 = b3 3.029 = 3.029 = 3.029 (0.36 + 1.2b + b2) = 0.09b5 1.0904 + 3.6348b + 3.029b2 = 0.09b5 1.0904 + 3.6348b + 3.029b2 - 0.09b5 = 0 b = 3.5799 m. In order to get the value of the discharge in the river, the first computations will be to solve the value of depth d: From the given data v = 4.0m3/s s = 0.0005 n = 0.012, Q = Av v = v = 4.0 = 4.0(0.012) = 0.048 = 2.17 = = 10.2183 = 10.2183(225 + 60d + 4d2) = 225d2 2299.1175 + 613.098d + 40.8732d2 = 225d2 2299.1175 + 613.098d + 40.8732d2 - 225d2 = 0 2299.1175 + 613.098d - 184.1288d2 = 0 By using the quadratic equation, we can get the value of d d = where: a = -184.12 b = 613.098 c = 2299.1175 d = d = d = d = d = d = 5.570m. After we are able to get the value of d, we can now solve for the value of Q. This is important because we will need the discharge value. We will compare the value of Q in the river to that of the value of Q in the open channel. Solving for the discharge Q Q = Av Q = 15(5.570) (4) Q = 334.20m3/s = discharge of water in the river Since we have already solved for the discharge of water in the river, we can now compare discharge of water in the river with the discharge of water in the open channel. The river will be able to supply water to the open channel. A pump will be required to lift water from the river to the open channel. The design of pump will depend on the discharge of water in the open channel, as stated by Young and Freemen, 2000. The design load of the pump must be equal to the discharge of water in the open channel. Computations for the design of a water pump: HP = where Q = discharge H = total head H = = constant value Q = Av A = bd A = 3.5799 (.3) A = 1.0739 Q = Av 0.8 = 1..0739 x v v = v = 0.7449 m/s H = + d where H = total head v = velocity H = + 0.3 g = 9.81 = gravitational constant d = depth = + 0.3 HP = design load 3960 = constant value H = 0.0282 + 0.3 0.8m3/s = 1.0767716535433/min 0.3282 m = 1.0767716535433feet H = 0.3282 m HP = HP HP = 3.1479148804559 horsepower The result of the design load of the pump is very safe. Comparing the discharge of the river which is 334.20 to the discharge of the open channel, we can conclude that the river can supply water to the open channel without drying up. The computed force design load of the pump is 3.1479148804559. Therefore we can use a pump a 3.50 HP to 4.0 HP. of The water that is pumped to the open channel will not overflow. The amount of water will be of constant volume in the open channel and as it reaches the reservoir in the nearby are Sketch of Pump Operation From the results of the computations done, and as per requirements given, the open channel and the pump is to be located between 3.0 meters to 12.0 meters. The water is to be pumped up from the river, passing thru the pump and then goes to the open channel. The discharge of water that the pump will pump out from the river will maintain a constant volume so that water passing thru the open channel will not overflow nor underflow. Conclusion The design of pumps that are to be used in any body of water will always be dependent on the design of the channel in which water will pass thru. It is very important to follow the design data in order to have an efficient work of any pump. We must always use a pump with a higher work discharge in order to avoid drying up or underflowing of water, or vise versa. The study of the water source must also be considered. It is very necessary that a hydrograph be plotted so that precautionary actions will be taken in cases of overflow and underflowing. References BBC - GCSE BITESIZE - Flooding, BBC April 12, 2009,. Freemen and Young, 2000, University Physics, Addison-Wesley publishing Company, Inc. Singapore 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. . Vesilind, P. Aarne, 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 Freedman, 2000, University Physics, Addison-Wesley Publishing Company, Inc. Singapore Read More