Selecting Flow Metering Sites And Evaluating Data

Transcription

1 Insert Slide Title Here Selecting Flow Metering Sites And Evaluating Data Patrick L. Stevens, PE Luis Mijares ADS Environmental Services

2 Strategy for Selecting & Evaluating Flow Metering Sites 1. Criteria for Site Selection 2. Understanding Metering Technology 3. Flow Meters Provide two types of information 4. Are the Data good? 5. What are data telling me about pipe hydraulics?

3 Ideal Site Hydraulics Clean manhole (silt, debris, grease, etc.) Straight & smooth flow One pipe in & one out preferred No drop connections Avoid Hydraulic Jumps

4 Physical Inspection is most common way to select or rule out bad metering site

5 A B C D

6 E F Let s take a look at Flow Metering Technology

7 No Flow Meter on the Face of the Earth Measures Flow Directly All meters measure some other physical entity and calculate flow rate. Flumes and Weirs measure only depth Open Channel Sewer Flow Meters measure Depth and Velocity. The Continuity Equation is used to Calculate Flow rate.

8 Open Channel Meters use Continuity Equation Flow Rate = Wetted Cross Sectional Area x Average Velocity 4" 3" Area of flow 2" 1" Depth

9 Typical Metering Installation Incoming Line Stable Hydraulics D & V measured in same place. Avoid Disturbances in MH Channel Far enough upstream to avoid drawdown

10 Open Channel Technologies Depth (only two) Pressure Sensor Ultrasonic Downlooker Ultrasonic Uplooker Velocity Average Doppler Peak Doppler Gated Doppler Travel Time Faraday Surface Doppler Radar Cross Correlation

11 Pressure Depth Sensor water

12 Pressure Depth Basic Operation The cable contains wires and an air tube that opens at the top of the manhole air Diaphragm with Strain Gauge water Port to Sewer Air vent tube The sensor contains a gauge to measure the pressure difference of the water and air The pressure sensor is typically mounted to the bottom of the pipe above any silt

13 Ultrasonic Depth Sensor water

14 Ultrasonic Depth Sensors Can be Uplooker or Downlooker Measures up to the Pipe Diameter Measurement Based on Time No Drift

15 Ultrasonic Down Looking Depth Sensor

16 Ultrasonic Up Looking Depth Sensor

17 Depth Sensor Technologies Offer Different Window of Precision Ultrasonic Depth Precision Pressure Depth Precision is based on a percentage of Full Scale Inches 4" 3" 2" 1" Ultrasonic Depth Pressure Depth M J J A gpm 0.2% of Full Scale (11.5') =0.28 inches

18 Velocity Technologies Cross Correlation ADS FlowShark Pulse Average Hach-Sigma 940 ISCO 2150 Continuous Wave Peak ADS FlowShark Doppler Surface Hach-MMB Flo-Dar Gated ISCO ADFM Electromagnetic Hach-MMB Flo-Tote Time of Transit Accusonic

19 Doppler Technology is Similar to Traffic Radar

20 Peak Combo Sensor During Full Pipe Pressure Depth Automatically Switches Pressure sensor previously calibrated Can be raised on block above silt level

21 This meter configuration is suitable for only those sites with a uniform slope through the manhole invert.

22 Types of Flow Monitors

23 Hydrograph Precision and Bias

24 Basin Flow and Prioritization Rain Flow (MGD) Basin Size Has Cost Leverage 02_34S Hydraulic Analysis = $4,000/meter, Physical Inspection = $2.5/LF & Rehab. = $ 7/LF $4,000 $3,500 $3,000 $2,500 $2,000 $1,500 $1,000 1 Mon Nov 2004 $500 $0 Rainfall Pipe Flow Qfinal(g) 385,000 LF 85,000 LF 31,000 LF 8,100 LF Hydraulic Analysis Physical Inspection Rehabilitation Total 8 Mon 15 Mon 22 Mon 1 Wed Date Rainfall (in)

25 In Uniform Flow Conditions this scattergraph is produced. The combination of a Manning Curve, meter data and confirmations reveal accurate meter in uniform flow.

26 Spotting Bad Velocity and Bad Depth

27 Possible Hydraulic Conditions At Flow Metering Sites A B C D E F A. Uniform Flow B. Transition to Backwater C. Within Backwater D. Supercritical Flow E. Hydraulic Jump F. Subcritical Flow

28 Dead Dog Silt Silt and Obstacles result in backwater at a meter.

29 Dead Dog The Stevens-Schutzbach method fits a Lanfear-Coll curve to the data and quantifies the Dead Dog. Dead Dog = 6.45 in.

30 What is a Dead Dog?

31 High Technology proves the existence of the Dead Dog in sewers

32 This Junction Dogs could have resulted in the recommendation to clean the line.

33 Junction Dogs or Hydraulic Dead Dogs are created by downstream turning structures, junctions or poor outlet conditions from the manhole.

34 Regardless of the cause of a Downstream Dead Dog, flow approaching the velocity sensor becomes deeper and slower (a variable cross section). Where is Velocity measured by a Doppler sensor? Cross section gets smaller and velocity is higher. Meter Hump

35 The Offset Joint Dead Dog. Higher velocity is found as water spills over the offset joint. Velocity Will be affected by this flow. Depth measured here.

36 The Log Ride Dead Dog. Higher velocity is Found in the Log Ride zone.

37 The Log Ride Dead Dog. Higher velocity is Found in the Log Ride zone. Super Critical Flow Causes Log Ride Effect

38 Hydraulic Jump Fr = 0.7 Fr = 1.0 Fr = max min MGD 8 Flow Velocity (ft/s)

39 Undular Jump or Standing Waves MGD Fr = max Fr = MGD 5 min Fr = Flow Velocity (ft/s)

40 KB_ Scatter Graph KB_04 Stevens-Schutzbach (C-SS = 5.48; d-dog = 0.77) Fr = 0.7 Fr = 1.5 Fr = 1.0 Fr = 1.5 Fr = VFINAL (ft/s) D dog of 0.8 inches suggests the cross sectional in the upper flow should be reduced by 0.8 inches DFINAL (in) Iso Q (MGD) KB_10 18 Scatter Graph KB_10 Lanfear-Coll (C-LC = 9.53) Stevens-Schutzbach (C-SS = 16.11; d-dog = 4.32) Fr = 0.7 Fr = 1.0 Fr = Log Ride effect from a steep incoming pipe. VFINAL (ft/s) This stair step pattern formed by the few days of green data is the characteristic pattern of standing waves Iso Q (MGD) The Dead Dog of 4.5 inches 4 is due to the Log Ride effect 3 from a steep incoming pipe DFINAL (in)

41 Scattergraphs can be used to define Four Types of hydraulic conditions & Dead Dogs Type 1 Super Critical Flow. No chance of Dead Dog or silt. Type 2 Hydraulic Jump passes through ring. The Zorro Z is the sign. Type 2A Standing Waves. Stair steps. Type 3 Log Ride Effect. Velocity in transition zone without a Zorro Z or standing waves. Type 4 Sub Critical Flow. Real Downstream Dead Dog. Could have silt.

42 Properly Deployed, a Flow Meter will see Upstream and Downstream (Double the information by looking at Scattergraphs) Dry Weather Flow Weekdays, Fridays and Weekends W eekdays W eekends Friday MGD Hours Upstream Downstream Depth - Velocity Flowmeter

43 Iso-Q Lines

44 In an ideal pipe, the pipe can surcharge and the Hydraulic Grade Line will be parallel to the pipe. In this situation the pipe should be carrying full capacity Hydraulic Grade Line Depth - Velocity Flowmeter

45 Surcharge By the Book

46 Bottleneck Downstream of Flowmeter HGL is Nearly Flat for Several MHs Upstream HGL Depth - Velocity Flowmeter ROOTS

47 Bottleneck & Capacity Loss Operational Capacity is 55%. Replacement or pipe bursting may be the solution here.

48 Upstream SSO SSO Upstream of Flowmeter Depth - Velocity Flowmeter ROOTS

49 Upstream SSO Operational Capacity is 50%. Replacement or pipe bursting may be the solution here. Signature of U/S SSO. (Cluster of data constant V constant D)

50 SSO and Bottleneck Downstream of Flowmeter Depth - Velocity Flowmeter ROOTS

51 Downstream SSO Operational Capacity is 50%. Replacement or pipe bursting may be the solution here. Signature of D/S SSO. (V increase at constant D) 51

52 Soft Restriction Roots create a restriction that does not follow an Iso-Q line.

53 Soft Restriction

54 Two Major Branches in Sewer. Intuitive meter locations here.

55 Two Major Branches in Sewer. Knowledge of Scattergraphs says to place one meter upstream of Double barrel siphon.

56 Scattergraph upstream of siphon reveals that it is a severe restriction and surcharged 7 feet. VFINAL (ft/s) Stevens-Schutzbach (C-SS = 2.65; d-dog = 3.40) Scatter Graph EN_04 Theoretical Capacity is ~ 2.1 mgd Operational Capacity is ~ 0.6 mgd 84 inches Inv ft DFINAL (in) Iso Q (MGD)

57 Scattergraph Poster

58 Conclusions 1. Physical inspection of sites is critical first step in site selection. 2. Select the appropriate technology 3. Review of scattergraphs after installation provides a second view of suitability of site or adverse hydraulic conditions; Hydraulic Jumps, Dead Dogs, Junction Dogs and Log Ride Dogs. 4. Place meters in locations that can offer more hydraulic knowledge to engineers and modelers.

59 Questions Patrick L. Stevens, PE Luis Mijares

60 The End