Estuarine Circulation in the Rewa River, Fiji Edward Anderson - - PowerPoint PPT Presentation

Estuarine Circulation in the Rewa River, Fiji

Edward Anderson

University of the South Pacific Aquatic Science Pacific aquascipac@gmail.com

Crew

• We had an army of student

”volunteers”

• From 2004 through 2010, we sampled

the Rewa River in September or October.

• There were about 20 to 60 each class

Boats

• Halimeda is a 7.3 m vessel powered by

two 150 hp outboard motors .

• Hali can take about 15 students.
• We took about 2 to 4 cruises per year

What are we trying to achieve?

What kind of estuary is this? What is the effect of the recent dredging?

Schedule

• We embarked at 0800n and returned at

1300 so that students could go to their next class

• Organization, travel time and unloading

time left only about 2hr to2.5hr on station.

• We completed between 10 and 15

stations

• We used CTD and droughes for each

station

Estuarine types

• Where river flow is

strong, and tidal currents weak, salt- wedge type estuaries are favored

• A partially mixed

estuary where river flow and tidal mixing are about

• equal. Most

estuaries are of this type.

• Where tidal mixing

is strong, and river flow weak, a well mixed estuary is favored.

Instruments

• CTD measures

salinity, temperature and depth

• From salinity and

temperature we get density, measured as sigma-t

The Rewa Sampling plan

• The river is about 3m

deep

• It is deepest on the
• utside of the bends
• There are deep holes

upstream at Kalabo bend, near the Rewa bridge, and where the river makes a sharp turn to enter the sea

• There are about 12

stations

• All begin at the bridge
• Some terminate in Laucala

Bay, and some in the

• cean

General results

• Density is in red.
• From upstream at

Station the there is freshwater all the way to the bottom

• There is a saltwater

and shallow depth in the middle

• Outside in Laucala

Bay, there are traces

• f freshwater at the

top, but almost uniform density below that

Results to date

• We have continuous records river at

the primary gauge at Navalou from 2009 forward,

• From 2004 through 2008. project HYCOS

(SOPEC/SPC) keeps these records

• We prefer the transects which

terminate in the sea. Only the 1 2009 and 2010 satisfy all criteria.

• We present results which meet these

criteria.

River flow has a dominante effect

• Low

flow. 77.0 5

• High

flow, 255. 13

Assembled Results 2008 and 2010 2010-10-01 R2

77.05

2010-10-08 R2

255.13

The others …

2008-10-26 R2 2008-10-03 R2 2008-09-26 R2

Assembled Results 2008 and 2010 2010-10-01 R2

77.05

2010-10-08 R2

255.13

What of the people of the Rewa Delta?

End