#### HY-8 Polynomial Coefficients

HY-8: POLYNOMIAL COEFFICIENTS Table 1. Polynomial Coefficients – Circular HY-8 Equation Inlet Configuration KE SR A BS C DIP EE F 1 Thin Edge Projecting 0.9 0.5 0.187321 0.56771 -0.156544 0.0447052 -0.00343602 8.96610E-05 2 Mitered to Conform to Slope 0.7 -0.7 0.107137 0.757789 -0.361462 0.1233932 -0.01606422 0.00076739 3 Square Edge with Headwall (Steel/Aluminum/Corrugated PE) 0.5 […]

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#### Manning’s n For Riprap-Lined Channels

HEC-15 Section 6.1 – MANNING’S ROUGHNESS Manning’s roughness is a key parameter needed for determining the relationships between depth, velocity, and slope in a channel. However, for gravel and riprap linings, roughness has been shown to be a function of a variety of factors including flow depth, D50, D84, and friction slope, Sf. A partial […]

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#### Nominal Pipe Diameters

Computed pipe diameters should be increased to a larger nominal dimension to avoid pressure flow. Standard English and metric nominal sizes used for storm drains are given in the table below. Nominal Pipe Diameters English metric inch ft mm 12 1.00 300 15 1.25 375 18 1.50 450 21 1.75 525 24 2.00 600 30 […]

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#### Shear Stress & Permissible Velocity

HEC-15 Section 3.1 & HDM Index 864.2 Shear Stress Equation The maximum shear stress is given by: τ = γ⋅Hn⋅S where: τ = shear stress in channel at maximum depth (N/m2 or psf) γ = unit weight of water Hn = depth of flow in channel (ft or m) S = channel bottom slope Table […]

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#### Side Slopes & Clear Recovery Zone

Per the Caltrans Highway Design Manual Index 309.1(2), the roadside environment can and should be made as safe as practical. A clear recovery zone is an unobstructed, relatively flat (4:1 or flatter) or gently sloping area beyond the edge of the traveled way which affords the drivers of errant vehicles the opportunity to regain control. […]

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#### Trapezoidal Channel: Manning’s n

Caltrans Highway Design Manual Commonly accepted values for Manning’s roughness coefficient are provided in Table 866.3A. The tabulated values take into account deterioration of the channel lining surface, distortion of the grade line due to unequal settlement, construction joints and normal surface irregularities. These average values should be modified to satisfy any foreseeable abnormal conditions […]

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#### HEC-15: Riprap and Gravel Lining Design

Source: HEC-15 Author: RT Kilgore and K Cotton (FHWA) CHAPTER 6: RIPRAP, COBBLE, AND GRAVEL LINING DESIGN Riprap, cobble, and gravel linings are considered permanent flexible linings. They may be described as a non-cohesive layer of stone or rock with a characteristic size, which for the purposes of this manual is the D50. The applicable […]

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#### Circular Pipe: Manning’s n

Caltrans HDM Table 851.2 Suggested values for Manning’s Roughness coefficient (n) for design purposes are given in the tabe below. Manning “n” Value for Alternative Pipe Materials(1) Type of Conduit Recommended Design Value “n” Value Range Corrugated Metal Pipe(2) (Annular and Helical)(3) 2⅔” x ½” corrugation 0.025 0.022 – 0.027 3″ x 1″ “ 0.028 […]

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#### Caltrans New Riprap Classes

Source: Caltran Highway Design Manual, Chapter 870 These supersede the previous Caltrans Riprap Sizes. Caltrans requires the use of these new RSP gradations starting August 1st, 2016 in new projects and those not yet at 30 percent PS&E stage. Caltrans Highway Design Manual Table 873.3A RSP Class by Median Particle Size(3) Nominal RSP Class by […]

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