nearshore wave and current measurements ......measurements for 4/9/2014 3:00-4:00 pm cst pwl =...

NEARSHORE WAVE AND CURRENT MEASUREMENTS IN THE COASTAL BEND

Philippe Tissot, Larry Dell, James Rizzo & Deidre

Williams

Conrad Blucher Institute Texas A&M University-Corpus Christi

American Shore and Beach Protection Association, Texas

Chapter Symposium, March 20, 2015

Outline

• Motivation

• Experimental Geometry

• Experimental Limitations

• General Metocean Conditions during Study Period

• Correlations

• Initial Nowcasts & Operational Model Predictions Comparisons

• Conclusions & Future Work

Study Location

Bob Hall Pier, North Padre Island, Corpus Christi, Texas

Current profilers: Xylem (Sontek) Argonaut SL500 (500khz, 2-D)

378 m

Nearshore (looking) sensor

Offshore (looking) sensor

Map/sattelite imagery from Google

51 m

120 m

Current Profilers Winch Boxes

Across-shore Current Profiler I-Beam

NWLON Wind Sensors

Longshore Current Profiler I-Beam

NWLON Stilling Well

Solar Panels

Instrument Installation

Experimental Geometry

54” (137 cm)

124” (314 cm)

120” (306 cm)

Water Depth: 244” (620 cm)

Offshore Looking Sensor (vertical)

Offshore Looking Sensor Current profile: 10-120 m in 11m cells

Average currents: 21-109m

+Y or North

+X or Offshore

Nearshore Looking Sensor Current profile: 1.50-51.5 m in 5m cells Average currents: 21.5-46.5m

+X or South (-X for North)

+Y or Offshore

measurements for 4/9/2014 3:00-4:00 PM CST pwl = 6.54+/0.0.2m above station datum

~ 30m

I-Beam & winch for offshore looking sensor

Sensor

I-Beam

Pier Pile

Offshore Looking Sensor Deployment Geometry

Pier Pile

NWLON Pile

Offshore Looking Sensor Experimental Geometry

Interference up to 15-20m

Picture from Sontek (http://www.sontek.com/productsdetail.php?ADP-Acoustic-Doppler-Profiler-4)

Potential interference from piling with side

lobes

Offshore Longshore Current

0 1000 2000 3000 4000-10

0

10

20

30

40

50

60

70

Time [30 min increments]

Sig

na

l to

No

ise

Ra

tio

10-21m 21-32m 32-43m 43-54m 54-65m 65-76m 76-87m 87-98m 98-109m 109-120m

0

10

20

30

40

50

60

70

Sig

nal

to N

ois

e R

ati

o

10-21m 21-32m 32-43m 43-54m 54-65m 65-76m 76-87m 87-98m 98-109m 109-120m0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

Sta

nd

ard

Err

or

[m/s

] Standard Error

Signal to Noise Ratio

Signal to Noise Ratio


10-21m 21-32m 32-43m 43-54m 54-65m 65-76m

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

|Lo

ng

sh

ore

Cu

rre

nt|

[m

/s]

0 500 1000 1500 2000 2500 3000 3500 4000-1

-0.5

0

0.5

1

Lo

ng

sh

ore

Cu

rren

t [m

/s]

21-32m

32-43m

43-54m

54-65m

Offshore longshore current are consistently measured in the range 21-65m from the offshore looking sensor

Bin 5

0 100 200 300 400 500 600

-5

-4

-3

-2

-1

0

Ele

va

tio

n, m

(N

AV

D8

8)

Distance Across Shore, m

Legend

Jul 2007

Sep 2010

Oct 2011

Sep 2012

Sep 2013

Nearshore Bathymetry

~ 1.6 m

Profile History 245-m south of Bob Hall Pier

0 200 400 600 800 1000 1200-10

-8

-6

-4

-2

0

2

4

6

Ele

va

tio

n,

m (

NA

VD

88

)

Distance Across Shore, m

Distance Across-shore, m

Distance Across-shore, m

5%

10%

15%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1414 - 1616 - 18

General Metocean Conditions (6/1/14-3/19/15)

Variable Median Range

Significant Wave Height 0.64m 0.04-1.8m

Typical Wave Period 5.9s 2.0-11.2s

Nearshore Longshore Current [m/s] 0.00m/s [-0.8m/s , 0.9m/s]

Offshore Longshore Current [m/s] -0.01m/s [-1.2m/s , 1.4m/s]

Wave & Longshore Current

• Meteorological conditions from NWLON station • Ocean conditions from project current profilers

Wind

Bob Hall Pier Significant Wave Height Distribution

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80

50

100

150

200

250

Signficant Wave Height [m]

Freq

uen

cy

Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-15

-10

-5

0

5

10

15

Win

d S

peed

[m

/s]

Alongshore and Cross-shore Wind During Study Period

Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

W

ate

r L

evel [m

ab

ove m

sl]

Bob Hall Pier Water Levels and Tidal Predictions

Tidal Predictions

Measured Water Levels

Alongshore wind median: -0.0m/s (+ Northwest) Cross-shore wind median: 3.1m/s (+ Onshore)


-1

-0.5

0

0.5

1

1.5

Long

shor

e C

urre

nt [m

/s]

'Offshore' Longshore Current

"Nearshore' Longshore Current


-1

-0.5

0

0.5

1

1.5

Lo

ng

sho

re C

urr

ent

[m/s

]

Alo

ng

sho

re W

ind

/ 10

[m

/s]

Alongshore Wind / 10

Longshore Current

Longshore Currents Comparison of Longshore Current with Alongshore Wind

(offshore looking sensor)

Comparison of Nearshore and Offshore Longshore Current

Correlations

Correlation of longshore currents with along shore wind: • Nearshore longshore current = 0.74 • Offshore longshore current = 0.85

Correlation of longshore currents with significant wave height: • Nearshore longshore current = 0.22 • Offshore longshore current = 0.04

Other Correlations: • Significant wave height and across shore currents

(nearshore = 0.23, offshore = 0.15) • Cross-shore wind & significant wave height = 0.24

Pearson pair correlations computed over matching data pairs for the period June 1, 2014 through March 19, 2015

Longshore Current Correlations (Pearson)

6/19 71/ 8/1 9/1 10/1 11/1 12/1 12/31-1

-0.5

0

0.5

1

1.5

Lo

ng

sh

ore

Cu

rren

t [m

/s]

TABS D Longshore Current

Nearhsore Longshore Currrent


• TABS Network (GERG) • Data: 6/19/14-1/2/15 • Correlation = 0.69 • Differences during large

wave events (Dolly) & frontal passages

Use relationship between significant wave height (Hm0) and water level standard deviation (σ) *:

Nearshore Wave Nowcast

*See: Park, Heitsenrether & Sweet (2014) Water Level and Wave Height Estimates at NOAA Tide Stations from Acoustic and Microwave Sensors, J. Atm. Oc. Tech 31, 2294-2308. Also Parke & Gill (1995), Shih & Rodgers (1981).

𝐻 𝑚0 = 𝛼𝜎

0 0.1 0.2 0.30

0.5

1

1.5

2

Water Level Standard Deviation [m]

Sig

nific

ant W

ave H

eig

ht [m

]

y = 6.519*x + 0.1114

data

linear fit

-1 -0.5 0 0.5 10

100

200

300

400

500

600

700

Model - Measurement [m]

# C

ases

Unbiased Stdev = 0.15m

• Historical reconstruction of significant wave height: swh = 6.52 (stdev of water levels) + 0.11

• Applied to hourly data from Bob Hall Pier 3/1/2003-3/1/2014

Nearshore Wave Nowcast

0 0.5 1 1.5 2 2.5 3 3.50

1000

2000

3000

4000

5000

Significant Wave Height

Fre

qu

en

cy

3/1/03 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 1/1/10 1/1/11 1/1/12 1/1/13 1/1/140

0.5

1

1.5

2

2.5

3

3.5

Sig

nif

ican

t W

ave H

eig

ht

[m] Reconstructed Wave Height History

Emily Rita

Ike

Longshore Current Nowcast

• Train Neural Network to nowcast Longshore current based on

– alongshore wind: RMSE = 0.100 (0.003) m/s

– + offshore longshore current: RMSE = 0.095 (0.002) m/s

– + wave: RMSE = 0.074 (0.003) m/s

– based on std(water level) instead: RMSE = 0.080 (0.002) m/s

0 1000 2000 3000 4000 5000 6000 7000-1

-0.5

0

0.5

1

1.5

Time [30 mins 6/18 - 12/31/2014]

Lo

ng

sh

ore C

urren

t [m

/s]

Measurements

ANN (1 input)

ANN(2 inputs)

-0.4 -0.2 0 0.2 0.40

200

400

600

800

1000

1200

1400

Model - Measurements [m/s]

# C

ases

Unbiased Stdev = 0.07m/s

NGOFS Comparison

Comparison with NOAA’s Northern Gulf of Mexico Operational Forecast System (NGOFS) 6/19/14 – 3/6/2015

Bob Hall Pier

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Observed Current (m/s)

Pre

dic

ted

Cu

rre

nt

(m/s

)

Longshore Current Comparison

y = 0.4*x + 0.0016

All data

Linear Correction Model

Wind Over 20 mph

y=x line

R-Squared = 0.725RMSE = 0.0515

RMSE=0.14m/s (without correction)

Nearshore Across-shore Current (bins)

6/10 7/1 8/1 9/1 9/25-1

0

1

2

Acr

oss-

sho

re C

urr

en

t [m

/s]

Bob Hall Pier Nearshore Across-shore Current for Bin 1 (1.5-6.5 m)

Cross Shore Current

Standard Error

Signal Strength

6/19 7/1 8/1 9/1 9/25-1

0

1

2

Acr

oss

-sh

ore

Cu

rren

t [m

/s]


Signal Strength

Standard Error

Across-shore Current

6/19 7/1 8/1 9/1 9/25-1

0

1

2


Time 6/19-9/25 2014

Acro

ss-s

ho

re C

urr

en

t [m

/s]

Across-shore Current

Standard Error

Signal Strength

30min sampling 6min sampling

6/10 7/1 8/1 9/1 9/25-1

0

1

2

3A

cro

ss-s

ho

re C

urr

en

t [m

/s]

Bob Hall Pier Nearshore Across-shore Current

Time 6/19-9/25 2014

46.5-51.5m

21.5-26.5m

1.5-6.5m

Goal: Assessment of conditions favorable to onset of rip currents Measurements: Across-shore current in 10 x 5m bins, 30 minutes measurements (17 min averages) till 9/2 followed by 4 minutes measurements every 6 minutes

9/3: Impact of Tropical Storm Dolly swh: 1.6m twp: 10.2s 6 m/s onshore wind

8/27: High Wind Event swh: 1.2m twp: 8s 6 m/s onshore wind

9/22: Cold Front swh: 1.2m twp: 7s 10 m/s onshore wind

3650 3700 3750 3800 3850 3900

-1

-0.5

0

0.5

1

1.5

Acro

ss-s

ho

re C

urr

en

t [m

/s]

Bob Hall Pier Nearshore Current Profile

1.5-6.5 m

6.5-11.5 m

11.5-16.5 m

16.5-21.5 m

21.5-26.5 m

26.5-31.5 m

31.5-36.5 m

36.5-41.5 m

41.5-46.5 m

46.5-51.5 m

http://lighthouse.tamucc.edu/qc/260 – stations 259 and 260

Web Access to Data

http://lighthouse.tamucc.edu/qc/260

Discussion/ Conclusion

• Two current profilers/wave sensors installed at Bob Hall Pier, Corpus Christi, Texas, recording nearshore conditions

• Observations strongly correlated to alongshore nearshore wind

• Comparison of measurements with NOAA operational models (NGOFS, NWPS)

• Accuracy of nowcast using other observations and/or NOAA model outputs? (extreme events?)

Questions/Suggestions? • Funding from the Texas General Land Office (TGLO) R&D 2014-2015 Funding

Cycle, Award No. 13-437-000-7896, is gratefully acknowledged.

• The CBI field crew and information technology team are gratefully acknowledged for efficiently and creatively resolving problems during the project.

Two Horizontal Acoustic Doppler Current Profilers (HADCP), with acoustic vertical wave and pressure sensors, were installed during the spring 2014 on Bob Hall Pier, Corpus Christi, Texas. The sensors provide near real-time measurements of nearshore conditions including current profiles in X & Y as well as significant wave height and period. The instruments are gathering a rare long-term data set of nearshore conditions along the Texas coast at this location. One of the HADCPs’ mounted at the end of the pier measures offshore to a distance of 120m depending on conditions. The other HADCP is mounted perpendicular and measures current velocities from the pier northward to 50m. This sensor is set up to detect rip currents in the nearshore of a beach frequented by swimmers and surfers. CBI will describe the installation process, the performance of the sensors, and will present on the measured parameters, data, and the correlation with atmospheric forcing. The sensors provide near real-time information to facilitate the prediction of oil movement and the deployment of protection measures in case of oil spill. The measurements will also help to better understand and model sediment transport along the coast and more specifically for the periodic renourishment and maintenance of the nearby popular beaches located along the Texas Coast such as Mustang Island State Park, Padre Bali Park, and North Padre Island. Other applications include providing information appropriate for search and rescue operations, reporting surf conditions, and alerting beach-goers to conditions favorable to the onset of rip currents.

Abstract

Alternate Study Location

Slide

~ 4km

cbi.tamucc.edu/dnr/station – stations 259 and 260

Web Access to Data

6/19 7/1 8/1 9/1 9/25-1

-0.5

0

0.5

1

Time 6/19-9/25 2014

Lo

ng

sh

ore

Cu

rren

t [m

/s]

Bob Hall Pier Nearshore Longshore Current

Nearshore Currents

6/19 7/1 8/1 9/1 9/25-1

-0.5

0

0.5

1

1.5

2

Acr

oss

-sh

ore

Cu

rre

nt [

m/s

]

Bob Hall Pier Nearshore Across-shore Current Profile

Cross Shore Currents - Waves

• Waves could influence sensor readings for the furthest bins of the nearshore looking sensor (1.2m wave illustrated below)

Argonaut SL500 Specifications

nearshore wave and current measurements ......measurements for 4/9/2014 3:00-4:00 pm cst pwl =...

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