Channel Design Channel design based on use of Manning eq. to find normal depth Yo for a specified discharge. Using Manning eq. M = 1.49 imperial 1.00 metric A = flow area R = hydraulic radius S = bed slope

Channel Flow Assumptions zFlow is fully developed rough turbulent. zChannel is prismatic, i.e. cross-section is constant along length.  Flow is uniform, i.e. S f = S 0.  A 0, P 0, R 0 = f( Y 0, geometry). zCross-section is fixed boundary.

Simple Cross-section B T y0y0 GLGL GRGR General Trapezoidal section can be: rectangular trapezoidal triangular non-symmetrical

Complex Cross-section Y X X3X3 Y3Y3 WL Datum Cross-sections can be defined by a set of straight lines joining up to 50 coordinate pairs. These can be drawn graphically and edited numerically.

Defining the Discharge Peak value of current Inflow hydrograph if one exists. User specified discharge if no Inflow hydrograph is defined

Peak flow is from current Inflow hydrograph Design of a simple channel Display table of Depth - Grade - VelocityEnter channel depth and slope, press [Design] Plot and design details appear.

Design of a complex channel (1) Draw section and specify peak flow = 15 c.m/s

Design of a complex channel (2) Check low flow channel for reduced flow = 1.5 c.m/s

Design of a complex channel (3) Increase width of low flow channel to 3.5 m Reduce Manning n=0.025

Design of a complex channel (4) Check modified section for maximum flow of 15 cm/s

Exercise zDesign a trapezoidal channel to carry 2 c.m/s with gradient of 0.3% and n=0.04 zDesign a channel which includes a low flow channel to carry maximum flow of 12 c.m/s and low flow of 2 c.m/s. Allow freeboard of 0.3 m. Try for gradient = 0.3%, n=0.04 for main channel and n=0.02 in low flow channel