Stream Flow

Stream Flow - 1/30/2012 Water velocities within a stream...

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1/30/2012 1 Stream Flow Runoff : is the total amount of water flowing in a stream, and includes overland flow, return flow, interflow, and baseflow. Water velocities within a stream are not uniform. Frictional forces decrease the water velocities along the bottom and sides of the stream channel. In stream curves, high water velocities are found on the outside of the curve and low water velocities are found on the inside of the curve. Velocity Profile • The velocity profile of a stream follows a parabolic profile, with the fastest current at the surface in the center of the channel, and the slowest at the bottom of the channel. 0.6 0.7 0.8 0.9 1 0 0.5 1 1.5 2 2.5 3 Velocity (m/s) D e p Water flowing in a stream is subject to friction as it comes in contact with the sides and bottom of the stream. • The average flow velocity is found at a depth equal to 0.6 times the total depth. • Can also use the average of 0.2 and 0.8 times the depth to represent the average velocity profile. 0.6 0.7 0.8 0.9 1 0 0.5 1 1.5 2 2.5 3 Velocity (m/s) Discharge (Q) Discharge (Q) is equal to the average flow velocity times the cross-sectional area of the stream: Q = VA where, Q is L 3 /T, say ft 3 /s or m 3 /s, V is L/T say ft/s or m/s, and A is L 2 , say ft 2 or m 2 .
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1/30/2012 2 Measuring Stream flow • Float System: Timing the travel time of an object at the surface of the water over a measured distance. Can use anything, a ball a stick, ice, etc. Not a very accurate method. But can be used as a last resort. Since measurement is at the surface, it mostly overestimates the flow rate and a correction is needed for the average flow, • usually 0.85.
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Stream Flow - 1/30/2012 Water velocities within a stream...

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