Storm Drainage Design Project Essay Example | Topics and Well Written Essays - 1500 words - 5

Storm Drainage Design Project - Essay Example The height of rainfall and the river discharge in terms of the river level were shown on the vertical axis using two different scales. Height of rainfall is plotted in terms of millimetres, while river level (river height) is plotted in terms of 1 x 10-1 meter. For example, the river height observed at 00:00:00 of October 12 is 0.283 meters, but in plotting the hydrograph, 0.283 was multiplied 10 and plotted as 2.83, instead. This scheme was utilised for aesthetic purposes in the desired hydrograph. Data were, however, analyzed using the original value and unit of the river level per hour of observation. As illustrated in Figure 4, river started to rise in the river at 11:00:00 hours on October 13 when rainfall reached its first peak at 1.20 mm. Interestingly, the second rain peak (also at 1.20 mm.) occurred after 10 hours at 21:00:00 of the same day (October 13). It may be observed from the hydrograph that as the second peak of the rainfall approached, river flow also reached a mini-peak. From hereon, the rising limb of the river flow was very clearly defined. From the first peak of rainfall, the basin lag time was calculated to be 22 hours. This means that it took 22 hours after the first peak of rainfall for the river flow to reach its peak. From the second peak of rainfall, the basin lag time was 12 hours. The average discharge for the rising limb (Q1) of the river flow is calculated as follows: The duration for the peak flow to return back to base flow is 46 hours. Several factors which affect the characteristics of storm or rainfall hydrographs have been described from existing literature. Each of these factors were analysed with respect to the River Cynon hydrograph. The catchment area of 160 sq. km. (Environment Agency – Wales, 2005) is considerably large, which should explain the long lag time of 22 hours before the river flow reached its peak. A large catchment area also tends to receive more precipitation, and subsequently