Hydrological Measurements

Transcription

1 Hydrological Measurements Wim Luemburg. Ultra-sonic stream flow measurement Integrating rising bubble technique Discharge dilution gauging Moving boat Discharge structures Theory of errors Heat as a tracer

2 Ultra-sonic streamflow measurement L ( c vcos ) T AB Faster with current : AB

3 Ultra-sonic streamflow measurement Slower against current: L ( c vcos ) T BA BA

4 Ultra-sonic streamflow measurement Solve and eliminate c: v L 1 1 cos T AB T BA

5 Integrating rising bubble technique D vw T v L w D v r q vwd vrl Q v A r

6 Integrating rising bubble technique L

7 L

8 Bubble gauging Digital picture corrected for distortions Q=Avr

9 Discharge & Streamflow measurements - Dilution gauging Principle: -) Adding of known amount of tracer to the stream Method 1: Constant rate injection Method : Sudden injection -) Measurement of concentration downstream L 0,95 0,4 C g B a

10 Discharge & Streamflow measurements - Dilution gauging, constant rate injection Mass-balance of the concentrations when Q<<Q: Q 0 1 Q Q 0 1

11 Discharge & Streamflow measurements - Dilution gauging, constant rate injection Q 0 1

12 Discharge & Streamflow measurements - Dilution gauging, miing requirements L 0,95 0,4 C g B a Q 0 1

13 Discharge & Streamflow measurements - Dilution gauging, sudden injection

14 Concentration (g/l) Discharge & Streamflow measurements - Dilution gauging, sudden injection M () t 1 M Q t) 1 0 ( dt V-notch "Rudi" 0,7 0,6 0,5 0,4 0,3 0, 0, Time (s) Discharge: 5.09 l/s

15 Moving boat discharge measurements: Discharge measurement whilst crossing a river in a boat Measurement of: 1) position in the stream (two methods) ) stream depth (echo depth sounder) 3) velocity (e.g. current meter)

16 Moving boat discharge measurements Method 1 - Positioning by measuring angle between boat and cross section (at time interval Δt) v b v r v w

17 Moving boat discharge measurements Method 1 - Positioning by measuring angle between boat and cross section (at time interval Δt) calculation steps: v b v r cos L vb t v w v r A L d sin Q A k * v Q k * Q AB l n v w

18 Moving boat discharge measurements Method - Positioning relative to beacons on the shore (at time interval Δt) L b b 1 a b1 b 1 v b L t v w v r v b

19 DISCHARGE STRUCTURES c u H d g.. c Q b d u H d c 3 3/ 3/ 3 H g b Q Principles free (critical) flow

20 Categories discharge structures Thin/sharp crested weirs Broad crested weirs Flumes Compound measuring structures Non-standard weirs.

21 Eamples sharp crested weirs:

22 Broad crested weir Flume

23 Compound structures Under construction: Mupfure, Zimbabwe Sebakwe river, Zimbabwe

24 Discharge measurement over a spillway 3/ Q Cbh C for circular weirs = C for parabolic weirs =.03( h / R) 1.86h

25 Drowned condition sharp weirs Q Q h Q0 1 h1 n = discharge when submerged Q = 0 discharge under free-flow conditions at the same upstream head h 1 h = tail water level, relative to the verte of the notch h n 1 = elevation of the upstream water surface relative to the verte of the notch = eponent of the basic flow equation, for eample 1.5 for rectangular weirs and.5 for V-notches

26 Theory of errors: Nature of errors Random errors Systematic errors Spurious errors

27 Theory of (random) errors: Why 1) Indication of accuracy ) Find most critical parameter Measure of error: (standard deviation) Propagation of errors from mathematical relations General: y y q y q q y q q

28 y q y q q Theory of (random) errors: Independent relations: b a q ) ( * q a e.g. for: y a a y q 1 ), ( 1 * * y q a a y y q a a a a 1 1 * * or Independent relation dependent relation

29 c b y a y q * * ), ( y c b c b q y a c y b a Theory of (random) errors: e.g. for: definition relative errors: q q r q r y y r y q y r b r c r

30 Eample errors: Discharge over a crested weir: 3/ Q C. g. b. h 3 1/ 3/ r C =3% b=8.50m (width) h=0.30m (level above weir) Give a realistic value for the relative error in Q

31 Eample errors: 3/ Q C. g. b. h 3 1/ 3/ 3 r r r ( ) * r Q C b h r C =3% b=8.50m (width) h=0.30m (level above weir) r 3 ( *100) ( ) *( *100) Q r (3) (0.11) (4.5) Q

32 Eample errors: One way to reduce errors: repetition n n n n y n n * y n n n n n n y 1n

33 Heat as a tracer Distributed temperature sensing Delft University of Technology Challenge the future

34 Heat as a tracer Why heat Distribute Temperature Sensing Eamples (qualitative) Eamples (quantitative) Propagation of errors Heat as a tracer 4

35 Why heat Not conservative BUT easy to measure at high resolution (with DTS) Heat as a tracer 3 4

36 Distribute Temperature Sensing Fiber optic cable Laser pulse (~ ns) Reflections Time of flight v = c/n = ( )/1.5 = 10 8 m/s Heat as a tracer 4 4

37 Distribute Temperature Sensing Heat as a tracer 5 4

38 Distribute Temperature Sensing up to 30 km long resolution: accuracy: 1m 3min 0.1 C Heat as a tracer 6 4

39 Eamples (qualitative) Determination of seepage in a polder Heat as a tracer 7 4

40 Eamples (qualitative) Determination of seepage in a polder Source unknown Heat as a tracer 8 4

41 Eamples (qualitative) Wrong connections to a rain water sewerage 4 april 008 Source unknown Source unknown Source unknown Heat as a tracer 9 4

42 Eamples (quantitative) Maisbich Heat as a tracer 10 4

43 Eamples (quantitative) Maisbich Lateral in/outflow Long wave Short wave Latent Heat Sensible Heat Advection Advection Water Conduction Streambed: T constant Deeper soil: T=11 C Heat as a tracer 11 4

44 Eamples (quantitative) Maisbich Heat as a tracer 1 4

45 Eamples (quantitative) Mass balance Q Q Q d u L T Q T Q T Q d d u u L L Heat as a tracer 13 4

46 Eamples (quantitative) Q T L d T Q T T u 1 1 d L u AND Q T L d T Q T T 1 u d L u Heat as a tracer 14 4

47 Propagation of errors q r q Q T T T T L Q T T b c a y q q r b r c r q y d u d u 1 1 d u u 1 q q q y y Heat as a tracer 15 4

48 Propagation of errors r QL 100% T T T T d u1 u T T d1 u1 u T d Tu Tu Td Tu Tu Heat as a tracer 16 4