NEARSHORE MEASUREMENT AND CORRELATION OF WAVE AND CURRENT

PROFILES

Philippe Tissot, James Rizzo, Deidre Williams

Conrad Blucher Institute Texas A&M University-Corpus Christi

ASBPA National Coastal Conference, Virginia Beach,

October 17, 2014

Outline

• Motivation

• Experimental Geometry & Deployment

• General Metocean Conditions during Initial Study

• Correlations

• Experimental Limitations

• Mobile Apps

• 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

25%

50%

75%

WEST EAST

SOUTH

NORTH

0 - 50

50 - 100

100 - 150

150 - 200

200 - 250

250 - 300

300 - 350

350 - 400

5%

10%

15%

WEST EAST

SOUTH

NORTH

0 - 2

2 - 4

4 - 6

6 - 8

8 - 10

10 - 12

12 - 14

14 - 16

16 - 18

5%

10%

15%

WEST EAST

SOUTH

NORTH

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

General Metocean Conditions (6/9-10/11, 2014)

Variable Median Range

Significant Wave Height 0.7m 0.1-1.8m

Typical Wave Period 5.5s 2.1-11.2s

Nearshore Longshore Current [m/s] 0.04m/s [-0.6m/s , 0.6m/s]

Offshore Longshore Current [m/s] 0.07m/s [-0.6m/s , 0.6m/s]

Wave & Longshore Current 0 0.5 1 1.5 20

50

100

150

200

250Bob Hall Pier Significant Wave Height Distribution

Significant Wave Height [m]

Fre

qu

en

cy

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

Wind

6/19 7/1 8/1 9/1 10/1 10/7

-10

0

10

20

Along/Accross Shore Winds During Study Period

Time 6/19-10/7 2014

Win

d S

pee

d [

m/s

]

6/19 7/1 8/1 9/1 10/1 10/7-1

-0.5

0

0.5

1

Bob Hall Pier Water Levels & Tide Predictions

Time 6/19-10/7 2014

Wa

ter

Lev

el

[m a

bo

ve

ms

l]

Measured Water Levels

Tidal Predictions

Alongshore wind median: -1.3m/s (+ Northwest) Cross-shore wind median: 5.0m/s (+ Onshore)

Alongshore and Cross-shore Wind During Study Period

6/19 7/1 8/1 9/1 10/1 10/11

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Time 6/19-10/11 2014

Lo

ng

sh

ore

Cu

rren

t [m

/s]

Offshore Longshore Current

Nearshore Longshore Current

Longshore Currents Comparison of Longshore Current with Alongshore Wind

Comparison of Nearshore and Offshore Longshore Current

6/19 7/1 8/1 9/1 10/1 10/11-1.5

-1

-0.5

0

0.5

1

1.5

Lo

ng

sh

ore

Cu

rren

t [m

/s]

Alo

ng

Sh

ore

Win

d [

(1/1

0)m

/s]

Alongshore Wind

Longshore Current (offshore looking sensor)

Longshore Current Correlations (Pearson)

Correlation of longshore currents with along shore wind: • Nearshore longshore current = 0.73 • Offshore longshore current = 0.87

Correlation of longshore currents with significant wave height: • Nearshore longshore current = 0.22 • Offshore longshore current = 0.03

Other Correlations: • Significant wave height and across shore currents

(nearshore = 0.28, offshore = 0.14) • Cross-shore wind & significant wave height = 0.26

6/19 7/1 8/1 9/1 10/1 10/11-1.5

-1

-0.5

0

0.5

1

1.5

L

on

gsh

ore

Cu

rren

t [m

/s]

Alo

ng S

ho

re W

ind

[(1

/10)

m/s

]

Alongshore Wind

Longshore Current (offshore looking sensor)

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

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]

Bob Hall Pier Nearshore Across-shore Current for Bin 5 (21.5-26.5 m)

Signal Strength

Standard Error

Across-shore Current

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

0

1

2

Bob Hall Pier Nearshore Across-shore Current for Bin 10 (46.5-51.5 m)

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 6 minutes measurements

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

Offshore Longshore Currents

10/6 5:45AM

9/27 11:00AM 9/28 6:55AM

Examples of longshore current

profiles

Offshore Longshore Current

Signal to Noise Ratio

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

Offshore Longshore Current

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 defined by currents ~ 21-65m from the offshore looking sensor

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

• App/website for general users (Beach Conditions App) http://cbi-apps.tamucc.edu/bhpwave/

Apps

• App/website for oil spill responders (prototype) • http://apps.proto.cbi.tamucc.edu/bhpwave.osr/

Apps

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

Web Access to Data

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

Web Access to Data

Discussion/ Conclusion

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

• Observations strongly correlated to nearshore wind

• Ability to detect rip currents

• Continuing observations and analyses

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

• Can nearshore sensor readings be appropriately nowcast using other observations and NOAA model outputs?

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.

Abstract Two current profilers were installed during spring 2014 on Bob Hall Pier, Corpus Christi, Texas. The sensors provide near real-time measurements of nearshore conditions including significant wave height, typical wave period, average along and cross shore currents and current profiles. The instruments are installed and maintained to National Ocean Service standards and are gathering a rare long-term data set of nearshore conditions along the Texas coast. One of the sensors provides current profiles up to 110 m offshore of the end of the pier in bins of 11 m while the other sensor monitors currents in the nearshore in narrower bins with the potential for identification of rip currents. The instruments are installed near two inlets and associated sensitive avian and aquatic habitat. In addition this monitoring station provides invaluable 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 Mustang and North Padre Island. Other applications include providing information appropriate for search and rescue situations, reporting surf conditions and alerting beach-goers to conditions favorable to the onset of rip currents.

The installation and performance of the sensors will be described. Initial measurements will be presented for various conditions such as seasonal frontal passages and strong southerly wind events which typify the climate along the south Texas coast. The current profiler is collocated with a tide gauge and atmospheric sensors. The new observations will be correlated with these measurements as well as with data from further offshore sensors collected by the National Data Buoy Center (NDBC) and the Texas Automated Buoys System (TABS). To facilitate stakeholder access to the information, two apps designed for smart phones and other mobile devices are being deployed with the targeted audiences of oil spill responders and the general public visiting the beach, respectively.

Alternate Study Location

Slide

~ 4km

Argonaut SL500 Specifications