Instrument Selection

1. Instrument Selection Streamflow Record Computation using ADVMs and Index Velocity Methods Office of Surface Water

2. Considerations • Sidelooker ADVM vs. Uplooker ADVM vs. ADV Point measurement • 2-D vs. 3-D velocities • Frequency • Number of cells needed • Range required to measure index velocity; Ideally need to target zone of above-average velocities

3. Side-looking ADVMs TRDI SonTek Ott

4. Frequency and Range for Sidelookers

5. Uplooker ADVMs SonTek TRDI V-ADCP Argonaut SW Argonaut XR IQ/IQ Plus

6. Frequency and Range for Uplookers

7. Argonaut ADV (Point Velocity) • Measures velocity in cell 0.6 x 0.9cm cell, at a distance of 10 cm from center transducer • Down-looking or side-looking • 10 MHz acoustic frequency • Slow flows • Small, shallow streams • Wetland/swamp flow

8. ADVM Velocity Specifications

9. 2-D vs. 3-D Profiling • Do you need X, Y, and Z velocities? • Hydrodynamic studies • Do you need to measure vertically and horizontally to some degree? • Stratified flows • Measure more of the water column? • ADVMs that measure 3-D velocities: • SonTek Argonaut-XR, TRDI V-ADCP

10. Multi-cell Capability • Advantages • Extremely useful for QA: comparison of cell velocities, horizontal flow distribution, SNR changes • May be used if main sample volume is biased • Disadvantages • Smaller cells = increased uncertainty & noise • More data to log and store a Dynamic cell

11. Which ADVM Do I Use? • Depends on site characteristics • Range of stage, stream width, depth of stream • Maximum/minimum velocities • Number of cells needed to measure • Vertical/horizontal velocity distribution • Do a site reconnaissance and make measurements before choosing ADVM! (see previous lecture)

12. Sidelooker ADVM Considerations • ADVM needs to be installed at a depth that is sufficiently below water surface and above the bed • Relatively uniform horizontal flow distribution • Stable velocity profile shape for range of flows Sidelobe Sidelobe Measurement Volume

13. Uplooker Considerations • ADVM installation and communication can be more difficult • Prone to sediment covering transducers • Can be used when channel depth is not sufficient for a side-looker • Required when the vertical velocity profile is not stable or has an unusual shape

14. Overall Considerations • It is not necessary for the acoustic instrument to sample the full width or depth of the channel as long as a stable relation between index and mean velocity can be derived • Should be located in or near the region of maximum velocity Remember: You are measuring an “INDEX” of the overall channel velocity!!

15. Case Studies Instrument Selection

16. Spruce Creek near New Smyrna Beach • Tidal • Relatively shallow • Variable flow distribution • A lesson in site selection • Equipped with 2 Argonaut SLs

17. Second SL installed mid-channel on bed-mounted concrete pad. Increased depth enabled larger sampling volume. Original SL mounted to the gage platform. Small sampling volume due to depth limitations.

18. Tomoka River near Ormond Beach • Tidal • Complex hydraulics at current site location • Multiple attempts to “solve the puzzle”

19. Flood tide Ebb tide Tomoka River at Ormond Beach Gage

20. Second Sontek SL Sontek XR Original Sontek SL

21. What Would You Do? Instrument Selection

22. Example 1 • Poorly-Mixed Confluence

23. Example 1 – con’t • Move site downstream • Multi Cell ADVM • Use a lower frequency ADVM to increase measurement volume

24. Example 2 • Bi-Directional Flow

25. Example 2 – con’t • UplookerADVM or ADCP • Mount your SL at an angle? • Install near-surface and near-bed salinity and temperature probes • Any other ideas? Non-acoustic instruments?

26. Example 3

27. Example 4

28. Example 5

29. Outfall structure Lift gates 184 ft. Example 6

30. Lock and Lift Gate Structure Lock and lift gates may not always open at same time Shallow Water Need an Index site at bridge piers Example 7 • Question: • Can you index a location with horizontal flow angle variation? • If so, what equipment would you use? • Answer:Perhaps….. • ADVM with multi-cell • Should recon with temporary ADVM installation

31. Vegetation Direction of flow Example 8 • Flow area changes with time • Flow angles change • Velocity profile may change • Vegetation may interfere with acoustic signal

32. More Examples….

33. Instrument Considerations - Examples • Taylor River at Mouth near Florida Bay • Lake Tarpon Outfall Canal • Tellisford Mill Leat (England )

34. Taylor River Example • Gage installed 1996 • Backwater • Tide • Wind • Installed AVM at mouth • Main site problem– Flow patterns • Channel depth changes abruptly at mouth • Bay flow patterns and river flow patterns interact at mouth Mouth of Taylor River

35. Taylor River Example – Complex flow Characteristics Solution?

36. Taylor River Example – Solution ADVM installed 100 feet upstream • ADVM installed upstream • Not a AVM deficiency, site location problem • The quality of the velocity data would have been improved if AVM had been installed upstream

37. Example – Lake Tarpon Outfall Canal • ADVM 320 ft. upstream • ADVM 20 ft. from shore because of vegetation Outfall structure Lift gates 184 Flow ADVM

38. Lake Tarpon Outfall - 320 ft. US of dam

39. Lake Tarpon Solution • ADVM moved 2,000 ft. upstream • Based new location on reconnaissance with ADCP and one lift-gate open • Irregular flow distribution extends ~1,500 ft. upstream

40. Tellisford Mill Leat – Site Details • 8 m wide channel • 3 Mhz H-ADCP installed • Mean depth of 1.5 m. • H-ADCP depth 0.62 m above bed. • Sampling range begins at 1 meter and extends to 4 meters

41. Tellisford Mill – Channel Profile at Beam 2

42. Issue at Tellisford Mill • Profiling range was set up to avoid any boundary interference (measuring range denoted by blue hatched vertical lines)

43. Issue at Tellisford Mill • Months of good data were collected before some strong reflector moved into the path of the upstream beam (debris or vegetation growth – detected by new SNR peaks closer to the instrument and within the sample range).

44. Tellisford Mill Beam 2 velocity (and hence flows) here were biased slightly low. Beam 2 SNR increasing with time compared with Beam 1 as hitting solid object in range

45. Diagnosis of the problem 1. Apr 9 – good decay curve within sample range 3. Apr 16 – double peak developing 2. Apr 11 – small peak develops at ~3.5m 4. Apr 21 – fully developed peak 6. May 15 – obstacle (weed) removed and good decay curve returns 5. May 9 – peak enlarging

46. Tellisford Mill – The Solution • The area was manually dredged and the object was removed. The “object” was submerged aquatic vegetation (SAV) that was not visible from surface. • Re-growth has occurred since and SAV can be seen to flatten down out of the sampling area when higher velocities occur. • If permanent site, would consider reducing sampling range and developing a new index velocity rating – only in for a short period, will keep existing range and attempt to manage the weed.

47. Tellisford Mill – Lessons Learned • Carefully choose profiling range – don’t profile too close to banks/shallows as even if SNR plots okay during installation may not always be the case. • Carefully select mounting depth – balance between maximizing velocity, stage range and bed profile. • Demonstrates importance of downloading raw data for diagnostics purposes - problem would not necessarily have been picked up from telemetry. • Site knowledge very important – patterns of deposition, scour and weed growth (where visible – ADCP surveys important) – consider temporary deployments to assess site in range of conditions?

48. Any Questions?