Is Q=CiA Dimensionally Consistent?

Shed runoff flow rate Q has been computed under the Rational Method using the equation: Q = CiA for a very long time, but ever so often, a new user would ask if this equation is dimensionally consistent. In this equation, the units of Q is cfs (cubic feet per second, or ft3/sec). C is […]

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4. PAVEMENT DRAINAGE (Based on HEC-22, Third Edition, revised August 2013) Effective drainage of highway pavements is essential to the maintenance of highway service level and to traffic safety. Water on the pavement can interrupt traffic, reduce skid resistance, increase potential for hydroplaning, limit visibility due to splash and spray, and cause difficulty in steering […]

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Manning’s Equation

Water flows in a sloping drainage channel because of the force of gravity. Flow is resisted by the friction between the water and wetted surface of the channel. The quantity of water flowing (Q), the depth of flow (y), and the velocity of flow (V) depend upon the channel shape, roughness (n), and slope (S). […]

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Caltrans Riprap Sizes

This has been superseded by Caltrans New Riprap Classes. D50 Equivalent Spherical Diameter RSP Class D50Size1 D50Weight   inches pounds 8 Ton 71 17600 4 Ton 56 8800 2 Ton 45 4400 1 Ton 36 2200 1/2 Ton 28 1100 1/4 Ton 23 550 Light 16 200 Facing 12 75 Backing No 1 12 75 […]

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Circular Pipe Alternate Depth

Flow conditions in a closed conduit can occur as open-channel flow, gravity full flow or pressure flow. In open-channel flow the water surface is exposed to the atmosphere. Gravity full flow occurs at that condition where the conduit is flowing full, but not yet under any pressure. Pressure flow occurs when the conduit is flowing […]

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FHWA Riprap Size

Source: FP-14 Standard Specifications Author: FHWA Table 705-1 Gradation Requirements for Riprap(1) Class % of Rock Equal or Smaller by Count Range of Intermediate Dimensions,(2) Range of Rock Mass,(3) DX inches (millimeters) pounds (kilograms) 1 100 9 – 15 (230 – 380) 59 – 270 (27 – 120) 85 7 – 11 (180 – 280) […]

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HDS-5 Inlet Control Equations

INLET CONTROL EQUATIONS A.1 INTRODUCTION This appendix contains the inlet control equations used to develop the design charts of this publication (HDS-5). Section A.2 contains the equations for the unsubmerged and submerged inlet control equations. Section A.3 demonstrates how the Section A.2 equations are used to create dimensionless design curves for culvert shapes with coefficients […]

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HEC 14: Riprap Apron

10.2 RIPRAP APRON The most commonly used device for outlet protection, primarily for culverts 60 in (1500 mm) or smaller, is a riprap apron. An example schematic of an apron taken from the Central Federal Lands Division of the Federal Highway Administration is shown in Figure 10.4. Figure 10.4. Placed Riprap at Culverts (per Central […]

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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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