Definition of hydraulic radius: 

 R = A 



Where R = hydraulic radius 



A = flow cross-sectional area 

 P = wetted perimeter 



Approximate value of hydraulic radius for circular culverts: 



Approximate value of hydraulic radius for arch culverts: 



0.2 X Span 



Span 



Figure H-1 . Methods of estimating hydraulic radius of culverts. 



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