Storm Drainage Design - Research Proposal Example

April 12, 2009 Storm Drainage Design Project Introduction Hydrographs are important part of the study of storm drainage. Hydrographs are graphs which represents the relation of the height and discharge of water in rivers over a certain period of time. Measurements are done in certain points in the river to determine how a watershed reacts to rainfall. The response of watershed to rainfall depends on factors which have a great effect on the shape of a hydrograph. The effects of soil saturation and the surroundings are the factors that often affect the hydrograph. The steepness of the surrounding lands with the drainage density is also a factor. Dry weather or dry season, normally creates a crust on river beds and wet winters would increase the discharge. The results of hydrograph readings would determine the design of a storm drainage Cynon River Hydrograph, Time with respect to rainfall Cynon River Hydrograph Time with respect to river height In analyzing the graphs above, we could say that the height of rise of water in the river was faster that when the water subsided. A sudden rise of water in rivers occurs after a rainstorm. This is the time when there is accumulation of water in the river. Another incidence of a sudden rise of water in rivers is when there is a down pour of rain upstream. It may not fall on the exact location of the rise in water height, it could come from the accumulation of water somewhere in the upstream of the river. In the study done in Cynon river, there was a steady flow of water on the first 42 hours. At the start of the 43rd hour, water began to rise. The rise of water in a hydrograph is called the rising limb. The water reached its peak flow at its52nd hour. The time of the peak flow is known to be the basin lag time. As the water starts to fall down, the term given to the falling down of the height of water is recession limb. After the falling down of water discharge, the water height starts to normalize. The storm flow is called the total of the overland flow, and the through flow. The overland flow, is the flow at which the water rises above the through flow and the through is termed as the water that rises above the base flow. In the computations of the design of the open channel and the river, or the water source for a reservoir. or a water impounding area, there are factors or conditions to be taken into account. First, we must set conditions for the design criteria. Next, the elevation where the pump is to be placed or would it be feasible to have the pump in that certain location. If a pump is needed, how much force will the pump require in order to draw water from a river to a location higher that the river elevation. Computations of the Channel design With the given data below, it is required that we get the value of breadth b of an open channel using the Manning's Formula. After we achieve the value for the depth, it is also stated that we solve for the value of the width of the river where in, the river is the proposed water source of a nearby reservoir Given Data Q = 1.0 m3/s n = 0.020 S = 1/3000 = 0.0003 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 Solutions to the required unknown A = db = 0.5(b) Q = A R = 1.0 = 0.5b 1.0(0.020) = 0.5b 0.0200 = 0.5b = 0.5 1.1695 = 0.5 = 2.339 = (2.339)3 = b3 12.7964 = 12.7964 = 12.7964(1.0 + 2b + b2) = 0.25b5 12.7964 + 25.5928b + 12.7964b2 = 0.25b5 12.7964 + 25.5928b + 12.7964b2 - 0.25b5 = 0 b = 4.2708m. In order to achieve the for the value of the discharge in the river, the first computations will be to solve for the value of depth d: 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(0.020) = 0.056 = = 4.6783 = (4.67833 = 102.3915 = 102.3915(225 + 60d + 4d2) = 225d2 23,038.0875+ 6,143.49d + 409.5660d2 = 225d2 23,038.0875+ 6,143.49d + 409.5660d2 - 225d2 = 0 23,038.0875 + 6,143.49d + 1 84.566d2 = 0 By quadratic equation; solve for the value of d, d = where a = 184.566 b = 6,143.49 c = 23,038.0875 d = d = d = d = d = d = 4.3074 m After we got the result for depth d, we can now solve for the value of discharge Q in the river. WE need to solve for the value of the discharge because we have to make know whether the discharge of water in the river would be sufficient to supply water to the open channel Solving for the discharge Q Q = Av Q = 15(4.3074) (4) Q = 258.444m3/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 Young and Freemen, 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 = 4.2708 (.5) A = 2.1354 m2 Q = Av 1.0 = 2.1354 x v v = v = 0.4682 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 = 0.0111 + 0.5 1.0m3/s = 15850.323141489gallons/min 0.5111 m = 1.6768372703412 feet H = 0.5111 m HP = HP = HP = 6.7117203511617 horsepower The pump to be used must have a force of 7.0 HP since the acquired result for the design load of the pump is 6.7117 horsepower. It is safe to say that water discharge in the open channel will be just fine. 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. Sketch of Pump Operation As we can see ,in the sketch, the pump is to be located at a point somewhere between 3.o meters and 12.0 meters in elevation. With the help of the pump, water is drawn from the river to the open channel. At the water passes thru the pump, the pump regulates the volume of water for the required discharge that will fill in the design of the open channel to avoid overflowing. Conclusion On our study of storm drainage design, it is very important to make a study for any given problem pertaining to the design criteria of storm drainage. It is very necessary that we know how we could compute for the discharge of any given problem. We need to know the factors that would affect the design that we want. As we went along the study of drainage and open channels, we come to realize that even the rainfall and the effects of it in rivers are important aspects of our coursework. References Freemen and Young, 2000. University Physics. Addison Wisley-Publishing Company,Inc. Singapore 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. Read More