Storm Drainage Design Project - Assignment Example

April 18, 2009 Storm Drainage Design Project Introduction Our study of storm drainage would allow us to understand the meaning of hydrograph. It would allow us to understand why hydrographs are formed. The basic factors that affects hydrographs will also be learned and why do we have to study hydrographs. A graph for the discharge of water in rivers is called a hydrograph. Normally, line graph is used to present discharge in over time and a bar graph is usually used to plot rainfall with time. There are factors that control the shapes of a hydrograph. Weyman. (1975) included in his statement that the different shapes are shown in a hydrograph and the main components are labelled accordingly. A peak rainfall and peak discharge are two different graphs. Lag time is the term for the difference between the peak rainfall from the peak discharge. There is a little chance of flooding if the value of the lag time is great. A lag time that is short will show that water had already reached the river channel at a fast rate. The rise in the discharge shown in a graph is called the rising limb, whereas the decrease in the discharge is called the falling limb. Areas of large basins normally receive more precipitation than the small ones and the they have a larger runoff. A bigger size of runoff would mean that there is longer lag time as water has a longer distance to reach the river trunk. The shape of the basin that is elongated and larger produces a lower peak flow and longer lag time than a circular basin with the same size (Gillesania, 2006). The effects of the slopes are very important. The channel flow would fall faster down a steep slope therefore it produces a steeper rising limb and a shorter lag time. Considering the soil as an important factor, infiltration is greater on thick soil even if clay would act as impermeable layer. A longer lag time happens when there are more infiltration and more shallow rising limb A fast overland flow is observed with a higher drainage density. The temperature and precipitation are considered. The production of fast overland flow and steep rising limb by short intense rainfall is because of precipitation and temperature. Tidal condition is the high spring tides that block the normal exit for the water, extending the length of time the river from the river basin takes to return to its original flow. The volume of water that reach the river from the surface run off is the overland flow, and the through flow is the volume of water reaching the river through the soil and its underlying rock la Cynon River Hydrograph Time over Discharge Cynon River hydrograph Rainfall over time The data gathered from the Cynon river study the results above were plotted. The study was performed within a period of 4 days (96hours) continuously, taking the height reading every hour. We can notice from the readings that there is a steady flow from the start of the reading up to its reading in the 44th hour, then water began to rise after the reading of the 42th hour. The rising limb takes place at this time. The time between the rise of water and the time the water reaches the peak flow is known as basin lag time. As it reached the peak on the 55th hour, water hasalready reached the peak discharge and it is now beginning to fall down. The time water height starts to fall down is called recession limb. After the4 recession limb, discharge of the water will go back to its original flow.. The storm flow is called the total of the overland flow and the through flow. The overland flow is the flow when water rises above the through flow, and the through flow is the water that rises above the base flow. Channel Design The discharge in the is Q m3. Apply the Manning's formula to design a suitable breadth b of a channel with depth d v = R2/3S1/ 2 where: v = velocity, m/s n R = hydraulic radius, m S = channel bed slope, m/m n = Manning's coefficient of roughness A = db where: a = area, m2 b = breadth, m d = depth, m Q = Av Given Data Q = 1.5 m3/s n = 0.017 S = 1 in 3000 = 0.0003 d = 0.6 m Required = 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) A = 0.6b Wetted Perimeter = 2d + b = 2(0.6) + b = 1.2+ b Hydraulic radius = = v = n Q = Av 1.5 = 0.6b 1.5(0.017) = 0.6b 0.0255 = 0.6b = b 2.4519 = b = 14.7404 = 14.7404 = 14.7404 = 14.7404(1.2 + b)2 = 0.36 b5 14.7404(1.44+ 2.4b + b2) = 0.36 b5 21.226176 + 35.37696b + 14.7404b2 = 0.36 b5 21.226176 + 35.3769b + 14.7404b2 - 0.36 b5 = 0 b = 4.0914m. = width of base b of the open channel We must compute for the depth of the river in order to make a comparison on the discharge of water in the river and in the open channel. 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 = 4.0 = 4.0(0.017) = 0.068 = = 3.9766 = (3.9766)3 = 62.8833 = 62.8833(225 + 60d + 4d2) = 225d2 14,148.7425 + 3,772.998d+ 251.5332d2 = 225d2 14,148.7425 + 3,772.998d+ 251.5332d2 - 225d2 = 0 14,148.7425 + 3,772.998d+ 26.5332d2 = 0 By using the quadratic equation, we will get the value of d d = where a = 26.5332 b = 3,772.998 c = 14,148.7425 d = d = d = d = d = d = 3.9071m 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 in order to 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(3.9071) (4) Q = 234.4426m3/s = discharge of water in the river we can now 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 discharge in the open channel is 1.5m3/s while the discharge in the river was found out to be 234.4426 m3/s.It is most likely that we can draw water from the river. A 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 = 3.11(.6) A = 1.866m2 Q = Av 1.5 = 1.866 x v v = 1.5 1.866 v =0.801m/s H = + d where H = total head v = velocity H = + 0.6 g = 9.81 = gravitational constant d = depth = + 0..6 HP = design load 3960 = constant value H = 0.0327 + 0.6 1.5m3/s = 23775.484712233gal/min 0.6327 m = 2.0757874015748feet H = 0.6327 m HP = HP = HP = 12.462841321295horsepower. The pump to be used must have a force of 12.5 to 13.0 horsepower HP since the acquired result for the design load of the pump is 12,462horsepower. 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. The river channel is to be located 3.0 meters to 12.0 meters above the river bed. The pump load design is of great importance to the physical aspect because it has to be located at a strategic point in order for the construction of the open channel be very feasible to the nearby reservoir. Since the reservoir is to be used for the end consumers of a certain location, it must be noted that the channel design must be near the river and the reservoir. Conclusion From the study done in the Cynon river, and the computations that was made in the design of the open channel that is suppose to come from the river, there must be an open mind in making designs of this sort. There are many considerations in making a specific design for a open channels, their sources and the direction of the channel to the final destination of water in the channel. References: 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. . University of Bristol, April 14, 2009, . Flooding, BBC - GCSE BITESIZE - Flooding, BBC April 12, 2009,. Gillesania, Diego Inocencio T. 2006, Engineering Formula Series, Civil Engineering, Diego Inocencio T. Gillesania, Manila, Philippines. King, Wisler, and Woodburn, 1988, Hydraulics, John Wiley and Sons, Inc. New York. 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