Measurement of River Discharge

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Elinor Lawson
7 years ago
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2 2 Measurement of River Discharge Q = w x d x v Cass River, NZ: Q = 1.75 m 3 s -1 Q = discharge (m 3 /s) w = width (m) d = depth (m) v = velocity (m/s)

3 3 Continuous River Flow Measurement?

4 4 Cross-Section Control Flow through section controlled by installing flume or weir Critical depth meter Unique relationship between upstream head, flow velocity and width Well-constrained, precise.. but Expensive to install & maintain Drowned Sedimentation Small rivers

5 5 Stage-Discharge Rating Relationship Construct a functional relationship between an easy to measure parameter depth (stage) and discharge at a natural section If section geometry stable a simple relationship between D and W gives cross-sectional area only unknown is velocity

6 6 In Practice Stable section Rees River, Otago, NZ: Q = 345 m 3 s -1 Uniform flow Stage monitoring Method for spot gauging Communications Access

7 7 Gauging Braided Rivers?

8 Canterbury Plains Rivers Gorge locations Single thread Bedrock controlled but tens of km upstream of river mouth Gauged section on the Waimakariri River

9 9 New Technologies for Direct Gauging adcp Acoustic Doppler Measurement of bed topography and distribution velocity

10 10 Easy Deployment in Wide Rivers from bridges from boats of all sorts

11 11 Hydraulic Geometry (at a station) Leopold and Maddock, 1953 b ~ f ~ m ~

12 Hydraulic Geometry Rees River @ Invincible NIGHT VIDEO DURATION Q increases

12 12 Hydraulic Geometry Rees Invincible NIGHT VIDEO DURATION Q increases from m 3 s -1 5 fold increase in depth Automated timelapse at 1 hour intervals

13 13 Hydraulic Geometry of Braided Reaches? NUMERICAL SIMULATION PERIOD Increases in discharge accommodated largely by increases in width Exponent b ~

14 14 An Alternative Approach to Gauging? Ashmore and Sauks 2006 Linear relationship between Q and W Transferable to other reaches locally ~ 10% error

15 15 Routine Monitoring of Width From Space? Band et al., 1996 SAR data Braided rivers Alaska But: Overpass frequency low Image resolution low Classification difficult Costly

16 16 Terrestrial Image Acquisition: Oblique Photography NIWA Cam-era Continuous recording camera systems Including Waimak pylons at Crossbank BUT: Chandler et al., 2002; Ashmore and Sauks, 2006; Sunwapta River, Canada Daylight limited Weather dependent Image Classification

17 Terrestrial Laser Scanning Scanning laser ranging systems Deliver high resolution 3d point cloud data capturing surface topography Operating ranges 0.

17 17 Terrestrial Laser Scanning Scanning laser ranging systems Deliver high resolution 3d point cloud data capturing surface topography Operating ranges (6) km 3d point precision 2-15 mm Active imaging system (operates day and night) Captures water surface elevation, exposed bar topography Intensity of reflection allows direct calibration of surface cover

18 18

Characteristics of TLS Tromie Gorge 2006 High sampling rate Rapid survey acquisition times Dense spatial sampling mm scale sampling density Severn Estuary 2007 Precise individual

19 Characteristics of TLS Tromie Gorge 2006 High sampling rate Rapid survey acquisition times Dense spatial sampling mm scale sampling density Severn Estuary 2007 Precise individual measurements total station quality (1-4 mm) Non-invasive Remote object recording Fully 3D datasets cf single perspective airborne lidar Barton Primary School 2008 Unselective Sampling Typically...

21 21 Hyperscale Models REACH-SCALE Sampling rate enables landform recording at scales from the grain up to the reach in one single, integrated dataset BAR-SCALE Morphological models constructed at the scale of the primary building blocks of the fluvial system GRAIN-SCALE

22 22 A Crude Example Scanning the Rees River 4 m above bed Mid-range Leica Scanstation Data acquired from single station over a 300 radius Hourly scans of a flood recession Intensity rendered 3d point clouds

23 23 LOW FLOW t =0, 18/12/2008

24 24 t = 24 hrs

25 25 t = 25 hrs

26 26 t = 26 hrs

27 27 t = 27 hrs Increased exposure of bed under waning flows easily quantified as is active width High frequency monitoring storm period dynamics, day or night Simultaneous measurement of exposed topography and water surface elevation Insight into pattern and timing of bed mobility, erosion and sedimentation Empirical rating development, but also analytical and numerical reconstruction

28 28 Continuous Installations Pioneered for mining industry IP65/6 enclosures Continuously powered and relayed

29 Autonomous Data Acquisition (3d Laser Mapping)

30 Realtime Monitoring Animated sequence: 1 day per image

31 31 Autonomous Monitoring and Modelling Vision - Change detection - Visibility - Nano ITX Processor - Wake on WLAN GStix - Solar Power - Directional Antenna Meteorological Off-Site Server 1. Data Products - DTM - DoD - Surface Roughness - Water Surface Model/Data Feeds Wave Refraction Model Flood Wave Propagation Glacier Melt Model Harmonic Tidal Forecast River Stage Regional Weather Reports - Temp/Humidity - Rainfall/Wind S/D - Net Radiation - Nano ITX Processor - Wake on WLAN GStix - Solar Power - Directional Antenna 900 Mhz Mesh Wifi 2.4 GHz Wifi ADSL Hydrometric - Water Level - Turbidity - Water Quality - Nano ITX Processor - Wake on WLAN GStix - Solar Power - Directional Antenna Site Monitor TLS - Reigl LMS-Z420i 2km TLS - IP67 Enclosure and PC - Wake on WLAN - External Webcam Monitor - Hybrid Solar/Wind Power - Directional 2.4 Ghz Antenna Off-Site Server 2. Quality Control / Maintenance - Data Delivery QC - Data QC - Automated Retargeting TLS - Local Data Archive & Backup - SQL Server Interface - Reprogramming - Manual Trigger Distribution / Monitoring Web Data Archive Automated Visualization Automated Distribution System Reports Alarm Notifications

32 32 Developing an Operational System Pylon mounted long range scanner km radius Calibration of wetted width, water level, exposed recessional topography Active station part of a sensor net responding to model and data feeds Onboard processing and reduced resolution data relay Empirical W-Q rating (tested on the Waimak?) Development and testing of analytical and numerical forecasting systems suitable for ungauged reaches

Index-Velocity Rating Development (Calibration) for H-ADCP Real-Time Discharge Monitoring in Open Channels

Index-Velocity Rating Development (Calibration) for H-ADCP Real-Time Discharge Monitoring in Open Channels Hening Huang Teledyne RD Instruments, Inc., 14020 Stowe Drive, Poway, CA. 92064, USA (Tel: 858-842-2600,