Nghiên cứu giải pháp bảo vệ bờ biển Nam Ô Đà Nẵng

Typhoon Modelling Use of historical typhoon tracks 1986 to 2016 30 Years  40 Selected Typhoons to generate the storm surge and wave height near site... Typhoon Wave Modelling Simulat

Nam O Resort Development,

Da Nang, Vietnam

Coastal Protection Study

Ander Chow

05 September 2017

Study Site

Site

Tidal Level

MHHW +0.3m ND MLHW +0.1m ND MHLW +0.0 m ND MLLW -0.4 m ND

Wind Rose at Danang Airport

Tidal Levels at Son Tra

Typhoon Modelling

 Use of historical typhoon tracks

1986 to 2016 (30 Years)

 40 Selected Typhoons to generate the storm surge and wave height near site

Typhoon Wave Modelling

Simulation of Wave Heights and Storm Surge during passage of Typhoon XangSane 2016

Typhoon Xangsane 2016

Typhoon Xangsane (200615)

0 1 2 3 4 5 6 7 8

Typhoon Wave Heights at M1 and Pt 9

Year Typhoon ID Typhoon

Name

Max Hs M1 (m)

Max Hs Pt9 (m)

Max Hs Pt9 (m)

Extreme Wave Heights near Site (Pt 9)

Return Period (Year)

Wave Height

Hs (m)

Wave Period

US National Oceanic Atmospheric Administration

Site

Wave Rose

Wave Climate near Site

NOAA M1

Max Hs = 5.4 m Mean Hs = 0.7 m Net wave energy direction 65°Az

Max Hs = 7.1m Mean Hs = 1.2m Net wave energy direction 67°Az

When waves approach shoreline, its direction tends to align with the

seabed bathymetry contour

54º

118º 93º 81º 63º

Design Water Level = 2.19mND

Section Beach Slope

1 2

1 2

N

Pt 9

Net wave energy direction 55°Az

Longshore Sediment Transport

54º

53º

Mean Hs=0.4m Max Hs=3.3m Dominate Direction=54º

Mean Hs=0.4m Max Hs=3.3m Dominate Direction=55º

Section 1: Beach slope = 0.014 D50 of sand = 0.6mm

Annual sediment transport rate:

Section 2: Beach slope = 0.025 D50 of sand = 0.6mm

Annual sediment transport rate:

Net Sediment Transport Direction Net Sediment Transport Direction

1 2

Wave Run-up

Sea Water Level (SWL) = +2.19 mND

(100-y flood level)

Beach Profile 1

100 year flood level

100 year flood level+SLR

Swash Zone

Mean Sea Level

Setback (50m)

+2.52mND

+2.19mND

+0.0mND Wave runup level contour

+3.0mND

+0.0mND Wave runup level contour

+3.0mND

Sandy Beach System

Sediment transport Direction

17

Undermining of a seawall built on a high energy

coastline (CCD 1997)

Summary

 Wave heights near the site can reach 4 m (at 9 m depth contour)

during typhoon events

 The beach normal almost aligns with the net wave energy

direction; this implies significant cross-shore sediment transport during typhoon events; however, the long-term net longshore

sediment transport move the sands toward NW

 Look at the historical satellite images, no significant beach erosion

is found The beaches at site seem to be at an equilibrium state

This equilibrium could be affected when the beach system is

Consequence of Beach Intrusion

Approximate Contour Line of +3.0mND

Recommendation: All structures be located at the

landside of wave run-up contour

Possible encroachment on wave run-up zone

Wave Run-up Level

Offshore Breakwater

Engineering Implications on Club-house Design

1 Discrete piled foundation for clubhouse

2 Design clubhouse slab for wave uplift pressure

3 Avoid wall structure at the edge of clubhouse that

would reflect wave and undermine beach

4 Provide offshore wave attenuation structure such as offshore breakwater/submerged reef structure

Breakwater Dimension (for Southern Beach)

Parameters Unit Value (appro.)

Slope of armour structure (v:h) 1: 3

Parameters Unit Value (appro.)

Significant Wave Height m 4.84

Distance from shoreline m 380

*The relocation of structure may be considered when more information is available (e.g sounding survey).

Note: Design dimensions of offshore breakwater to be confirmed in detailed design

Offshore breakwaters

Near River Mouth

 The NW corner is very dynamic, sediments are moving around

in the river mouth area; and sediments at beaches tend to move tower NW The system seems to be stable when sediment supply from Cu De River is not disturbed

 However the sediment supply from Cu De River will decrease in future due to urban development The maintenance dredging

activity in the northern port development may reduce the volume

of sediments underlying in Da Nang Bay

 Suggest to build a breakwater with lookout to retain/anchor the

NW corner of the site development

Western Edge

Possible Lookout

+3m fill

END