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Lec20_Rivers_and_Streams

# Lec20_Rivers_and_Streams - Lecture 20 Rivers Streams Part-3...

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Lecture 20 ivers & Streams Rivers & Streams Part-3 Water-Quality Environments

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Rivers and streams are lotic (flowing) systems. lentic systems are characterized by standing water. Thalweg is the line connecting the lowest points in each cross-section in a river
umerical Simulation of a Spill Numerical Simulation of a Spill 2 CC C E ¶¶ 2 C 2 UE tx x + = 2 E t x = 2 x 2 ö (,) exp ( ) 4 2 Mx Cxt Dt Dt p =- ( ) exp 4 4 x Ut M C Et Et p æö ÷ ç - ÷ ç ÷ ç = ÷ ç ÷ ç ÷ ÷ ç èø Problem: Both equations need an initial concentration C at time t = 0 0 Usually in spills (or dye studies) we know how much we dumped into the river (mass, M) How to get C 0 ? 0 M C B Hx H x B Go through example 12.1 in your text (page 219-220)

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ongitudinal Dispersion Longitudinal Dispersion Fisher’s Relation: 22 011 UB * 0.011 E HU = * Ug H S =
cQuivey & Keefer McQuivey & Keefer 0.058 Q E SB = 0.5 U Fr =< Froude number should be less than 0.5 gH

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ateral Mixing Lateral Mixing * 0.6 ; * Lat EH U U g H S == 2 0.4 B LU = Side Discharge 2 m Lat E 0.1 m B = Center Discharge Lat E
ischarge Coefficients Discharge Coefficients Q b U aQ HQ b a = = f Bc Q = () QU A U B H f == + + = 1 bf b +

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Flow often determines the variations in water-quality. Studies require the specification of: Geometry: river width and depth ( bathymetry ) River slope and bed roughness Velocity Flow Mixing characteristics (dispersion) Equations of Continuity and Momentum describe the flow. Hydrologic methods are approaches based on empirical formulations or on the use of continuity equation alone. Hydraulic methods use both continuity and momentum equations.
Flow Model Complexity Homogeneity in cross-section affects the dimensionality of the model required to resolve changes. Rivers and streams are often assumed to be one-dimensional stems (Cross- ctional mean values of velocity are assumed to systems (Cross sectional mean values of velocity are assumed to adequately represent the velocities). t tifi ti b i t t i ll i l i Stratification may be important, especially in some slow moving rivers Non-uniform flow occurs when water velocities and depths change along the length of the river. These, in turn, can be either gradually- ried r pidly varied varied or rapidly varied .

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Lec20_Rivers_and_Streams - Lecture 20 Rivers Streams Part-3...

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