Standard Step Method using HEC-RAS-120 please attend HEC-RAS demo on Mon, Nov 13

Question

Standard Step Method using HEC-RAS-120 please attend HEC-RAS demo on Mon, Nov 13. A 10-m wide, rectangular, concrete-lined channel (n·0.013) has a bottom slope of 0.01 . There is a constant-level lake at the upstream with a lake water surface 6 m above the channel bottom. Assume the channel bottom elevation of the entrance (upstream lake) is 20 m. The channel length is 2000 m. If the flow depth at the channel entrance is critical, perform the following. Step 1) Compute ye at the entrance and compute the flow rate. Step 2) Build a HEC-RAS input file for one reach and cross-section (upstream and downstream). Boundary condition is the known water surface for upstream and normal depth for downstream Step 3) Compute flow depth within two cross sections? How is your water surface profile? Export (or capture) the water surface profile. Step 4) Interpolate between two cross sections at every 20 meters and compute the flow depth ) for up to 2000 meters downstream. Export (or capture) the water surface profile. Discuss the difference in results between Step 3) and Step 4) Step 5) Based on the result in Step 4) Find the distance from upstream at which y = 2.4 meter. Use . View Profile Summary Table" (or) and define your table to add "hydraulic depth" and "accumulated main channel length Copy and paste the screen shots that show critical depth, normal depth, and water surface profile from upstream to downstream. Four screen shots are required. Cross Section for Steps 3) and 4) and Profile for Steps 3) and 4) Example] 1. Cross-section indicating y and y How to: View Cross Section File Copy Plot to Clipboard Ctrl + V chausy.20 Pian Pian 01 1102201 2. Water Surface Profile plot (View Profiles File Copy Plot to Clipboard Ctrl+ V)

Explanation / Answer

1)

a)From Manning's equation, flow rate is Q=1/n*R^2/3*S^1/2*A

Q=(1/0.013)*((10*6)/(22))^(2/3)*(0.01)^(1/2)*(10*6)=900.65 cumecs

flow rate is Q=900.65 cumecs.

b) Critical depth yc=((q^2)/g)^(1/3)

q=flow rate / width =900.65/10 =90.065 cumecs/m , g=9.81sq m/sec

yc=9.36m

2)

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