#### HEC-15: Vegetative Lining Design

CHAPTER 4: VEGETATIVE LINING AND BARE SOIL DESIGN Grass-lined channels have been widely used in roadway drainage systems for many years. They are easily constructed and maintained and work well in a variety of climates and soil conditions. Grass linings provide good erosion protection and can trap sediment and related contaminants in the channel section. […]

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#### HEC-15: Permissible Shear Stress

HEC-15 Section 6.2 – PERMISSIBLE SHEAR STRESS Values for permissible shear stress for riprap and gravel linings are based on research conducted at laboratory facilities and in the field. The values presented here are judged to be conservative and appropriate for design use. Permissible shear stress is given by the following equation: τp = F*.(γs […]

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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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#### 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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#### 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 Design of Roadside Channels, 3rd Ed

Author(s): Kilgore RT, Cotton GK Publisher: FHWA Year: 2005 Links: PDF Subjects: channel lining, channel stabilization, tractive force, resistance, permissible shear stress, vegetation, riprap, manufactured linings, RECP, gabions Flexible linings provide a means of stabilizing roadside channels. Flexible linings are able to conform to changes in channel shape while maintaining overall lining integrity. Long-term flexible […]

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#### Channel – Grass Lining

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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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