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53:071 Hydraulics & Hydrology Project #2 Flow Measurement with a Weir

53:071 Hydraulics & Hydrology Project #2 Flow Measurement with a Weir. Li-Chuan Chen, Marian Muste, Gokhan Kirkil, and Allen Bradley. Problem Statement. The Iowa DNR plans to return farmland to a native tallgrass prairie landscape as an experiment. Problem Statement.

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53:071 Hydraulics & Hydrology Project #2 Flow Measurement with a Weir

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  1. 53:071 Hydraulics & HydrologyProject #2Flow Measurement with a Weir Li-Chuan Chen, Marian Muste, Gokhan Kirkil, and Allen Bradley

  2. Problem Statement • The Iowa DNR plans to return farmland to a native tallgrass prairie landscape as an experiment.

  3. Problem Statement • A small ephemeral stream drains the site. The Iowa DNR wishes to find out how the runoff from the site changes over time.

  4. Objective • Design a weir flow control structure to continuously measure discharge at the site.

  5. Principle

  6. Principle Slope Intercept

  7. Apparatus — Weirs WEIR EXPERIMENT

  8. Procedures • Insert the weir of the desired shape. • Record the reference point of the weir. • Set the appropriate discharge in the flume and record the water level difference on the differential manometer. • Record the water surface elevation upstream of the weir. • Repeat Step 3 and 4 for four more discharges. • Repeat Step 1 to 5 for one more weir shapes.

  9. Discharge Triangular 90 h (ft) Q (cfs) Ref. Point (ft) W.S. Elev. (ft) Weir Head (ft) Data Sheet

  10. Analysis • Determine the discharge Q in the flume (using the side-contraction meter) and the head H on the weirs. • Using several measured Q-H pairs, plot log Q versus log H. • From the best-fit line to the experimental points, determine the kexp (the intercept) and nexp(the slope). • Compare kexp and nexp with values indicated in the literature.

  11. Sample Result

  12. Site Information Measure flows up to the highwater mark

  13. Engineering Analysis • Recommend a weir geometry and provide the head-discharge relationship. • Provide profile and cross-section specs for the weir site (AutoCAD sketch). • Estimate uncertainty of the discharge measurement (in ± cfs) for two cases • Estimate of the extent of ponding behind the weir for the design flood conditions (water surface profile) • Provide the client (the Iowa DNR Restoration Project Manager) with a concise report that answers the project objectives.

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