Hydraulics Modelling and Report

The report comprises 3 parts; -HR computer-based modelling to generate a stormwater channel design; -cross checking the computer based design calculations with hydraulic theory; and -a comparison and reflection. Part 1 Design a trapezoidal stormwater channel using HEC-RAS that satisfies the design requirement as set out below. Design Information/Requirements • The channel is required to carry the 10 yr ARI design discharge equivalent to 55 m3/s, see figure 1. • The inverts of the existing creek at 5 cross-section locations are given in Table 1. • The stormwater channel should be trapezoidal in shape, see figure 1. The channel floor slope is 1(V):20 (H) while the side walls are 4(V):1 (H). Maintain the existing alignment of the creek in your design. • The channel should have the same shape and size along the full length of the creek. • Use a normal depth with a friction slope of 0.001 as the starting water level at section 2000. • A Manning ‘n’ of 0.025 is appropriate for this project. • Optimise the size of the channel by ensuring the water level is within 0.1 m of the top of the channel. 1) HEC-RAS - Provide a drawing showing the dimensions of the designed cross section 2) HEC-RAS - Provide a long section of the channel showing the invert level, water level, top of bank level. 3) HEC-RAS - Provide a table showing for each cross section the velocity, water level, freeboard, bank level Part 2 Use the Standard-step method spread-sheet available to replicate the HEC RAS results. Note that this spreadsheet is only applicable to rectangular channels. The spreadsheet formulas for Area, Wetted Perimeter, Hydraulic Radius, etc., need to be modified to handle a trapezoidal channel. Also consider how the channel slope (So) should be changed. 1) SS - Print the relevant portion of the Standard-step method Spread-sheet showing the calculation for each cross-section Part C - Comparison and Reflection - Compare for all the cross-section the flow depth calculated by HEC-RAS and by the SS spreadsheet. Explain why the results of part 1 and 2 are very similar - Identify the sources (three) of the small difference in the results obtained in part 1 and 2 Provide explanation sought in part 1 (no more than 1 paragraph); and for part 2 list differences only (no discussion required).