Question

Problem 2: Designing Culverts Under a Bridge on El Rio de las Aguas Torenciales A 100-year stom event is being considered in order to design the culverts under a bridge. Figure 3 shows the storm event that may fall on the rural watershed of area 3.2 Km that drains into El Rio de las Aguas Torenciales. It generates runoff all over the watershed. The runoff flows into the river towards the ast point A (Figure 4) in the watershed where there is a bridge crossing over the ri ver Aguas Torenciales. Then the flow goes into the culverts. The time needed for the entire watershed to become tributary to the culverts at point A is about 8 hours. 300 200 100 100 2h r(h) Time in houes Ch Figure 3: 100-Year Stom Over an 8-Hour Period: Rainfall Depth (Millimeters) Versus Time (Hours) (a) Compute the average rainfall intensity i (mm/br) for this 100-year stom. (b) The Rational Method, which relates rainfall intensity i to peak runoff Q, is given by the fomula Q-CiA that only applies when using US. customary units, However, for S.L units, a correction factor (a constant k) should be used: where k 0.28; C= Rational Method runoff coefficient ;i-average rainfall intensity in mri hr A = drainage area measured in K: and 0 peak discharge in m'ls. The Rational Method runoff coefficienis assumed to be C-0.20 for this rural area of the watershed of the river Aguas Torenciales. Compute the peak rate of runoff Q (c Since the bridge is not high enough, your task is to design five identical culvert pipes to carry the flow Q under the bridge (Figure 4). All five pipes are laid down at the same level on the river bed. The new concrete cul vert pipes are expected to be smooth (with Manning's n-0.011) and will be laid down on a steep slope S-3% in order to carry a large flow without becoming pressurized and causing backwater in the river. Design the diameter of the five identical culvert pipes (by assuming they are flowing full at first), and then pick the next diameter that is available in the market so the culverts do not become pressurized. The available culvert sizes have the following diameters: 150, 200,250, 300, 375,450, 525, 600, 675, 750, 825, 900, 975, 1050, 1200, 1350, 1500, 1650, 1800, 1950, 2100, 2250, and 2400 mm ANER ER Rive CULVERTS Figure 4: Sketch of Watershed of El Rio de las Aguas Torenciales and a Cross Section of the Five Culverts at the Bridge

Answer 1

300 Llu) 0-2 150 2. 6 200 50 6- 8 b) KCiA 15.68m3/s CS Scanned with CamScanner