geos3009 - mod 1 - estuaries

8/2/2019 GEOS3009 - Mod 1 - Estuaries

1/53

ESTUARY TYPES ANDPROCESSES

Module 1


2/53

What is an estuary?

Definition is difficult. Classified by physio graphical parameters ie:

geomorphology and hydrology only early definition(Cameron and Pritchard, 1963) an estuary is a semienclosed coastal body of water having a free connectionwith the open sea and within which sea water is

measurably diluted with fresh water derived from landdrainage


3/53

Four major elementsi) its a coastal feature,ii) it has provision for salt water,iii) the salt water must be measurable,iv) fresh water is derived by rivers.

Excludes tides


4/53

Dalrymple et al. (1982) a new geologically-orientateddefinition the seaward portion of a drowned river

system that receives sediment from both fluvial andmarine sources and contains facies influenced by tide,wave and fluvial processes. The estuary is consideredto extend from the inner limit of the tidal facies at its

head to the outer limit of coastal facies at its mouth.


5/53


6/53

Classification by tidal range (Hayes, 1975) Micro-tidal estuaries Meso-tidal estuaries

Macro-tidal estuaries

Evolutionary classification (Dalrymple et al., 1992) Wave dominated estuaries

Tide dominated estuaries

Morphological classification (Fairbridge, 1980) Seven types


7/53

ESTUARIES

Comprise 5% of Earths surface, but only 2% of ocean

volume; However ~60% of world population Estuaries amongst most populated areas in world For transport, industry, residence, and recreation.

Estuaries have high biological productivity


8/53

High level of food production Coastal waters supply ~90% of global fish catch. Human activities - sedimentation from cleared land,

over fishing/trawling, destruction Wetlands,eutrophication, pollution, dams, canals and dykes forflood protection

Dynamic systems associated with river mouths


9/53

Estuaries are tidal, lower part of rivers and associated

valleys Distinction difficult consider it a continuum ofdelta estuarine landforms

Processes function of catchment and receiving basin

Balance of wave, tide and river exerts controlover morphology and evolution.


10/53


11/53

Deltas Shore-line protuberances River supplied sediment accumulates faster thanredistributed

By waves, currents and tides Affected by tidal dynamics, mixing of fresh & salinewaters


12/53

Estuaries Seaward part of drowned river system receivingfluvial & marine sediment

Influenced by tide, wave, fluvial processes. Comprises fluvial-dominated upper section

- marine-influenced lower zone

- central mixed region.


13/53

Tide-dominated estuaries Macro tidal Dominated by tidal currents

On pro-graded coastal plains Funnel shaped, wide entrances Well mixed due to strong bi directional tidal currents Rapid flows re-suspend & transport sediment


14/53


15/53

Three zones- upstream river dominated,

- central mixed energy zone- seaward marine dominated Central zone area of sediment convergents river

and marine processes


16/53

Wave-influenced estuaries Enclosed or partly enclosed behind wave built sandbarrier

On wave dominated coast

Separated from open ocean by sand barrier Inlet intermittently closed Gradation to coastal lagoon may be permanently orintermittently open

Decrease in water area and depth with time due to:- input of sand from shelf- extension of fluvial deltas from rivers- vertical accretion of mud in central estuary


17/53


18/53

Sedimentation rates in central mud basins ~1mm/yr Along NSW coast - different stages of infill

Tidal range attenuated by narrow entrance


19/53

Coastal lagoonsFeatures:

i) shallow where salt and fresh water interact,

ii) water impounded by some type of sedimentarybarrier and,iii) connection with sea restricted Aligned parallel to coast, separated by barrier

Impounded by sand barrierLow salinity


20/53


21/53

Morphological definition of estuaries (Roy 1982, 1984

Three types of estuary on basin morphology & condition

of seaward entrance- Type 1: Drowned river valley estuary - Deep, openocean entrance, full tidal range

- Type 2: Bay Mouth Barrier Estuary - Narrow entrance,

attenuated tides- Type 3: Saline Coastal Lake/Lagoon Closedentrances

All have central basin


22/53


23/53

Type 1 drowned barrier estuaries

sub aqueous flood tide delta

extensive fluvial delta & channel fill sequence


24/53

Type 2 barrier estuaries Due to shallow valleys Marine-sourced sediments have considerable subaerial expression ie barriers, spits, & wash over flats

Landward portion terrestrially derived forming networkof delta distributory mouth bars, medial channel bars


25/53

Type 3 coastal lakes Relatively small barriers, beaches & wash-over fans Flood tide deltas poorly developed or absent

Fluvial deposits consist thin wedge of sandy delta &flood plain deposits mantling peaty muds of centrallake - dominant facies

Estuaries evolved from one type into another

Sometimes a continuum.


26/53

AUSTRALIAN ESTUARINE AUDIT(Oz estuaries)

Of 979 estuaries, >40% small catchments (


27/53

Value of estuaries (NLWRA, 2002). Middens of Indigenous Australians shellfish and fishbones

Sydney Harbour middens >40m high For transportation, agricultural manufactured goods Ports, shipping, industry, agriculture, tourism,residential development

Human-made capital and natural capital


28/53

Natural capital - habitat, sporning, nursery environmentsfor fish Habitats & breeding regions for birds, and marine

animals Nutrient cycling Provide natural buffer between land & ocean Salt marshes and mangroves

Sediment and nutrient filtration by trees, salt marsh &other wetland flora


29/53

Human capital - natural assets Sheltered deep water for shipping, industry & urbandevelopment

Detrimental influences on natural assets

Fisheries critically dependent on environmental statusof ecosystem

Survival of commercial activities dependent on

disturbance Commercial fishing in Australian estuaries ~$0.4 b/y Prawn fisheries, oyster farming, barramundi & mudcrab fisheries


30/53

Estuary-dependent fisheries are fish and crustaceansspend part of life cycle in Estuarine environment i.e.estuary a nursery area.

Estuaries worth ~$40 m/yr NSW oyster industry worth ~$29m 1999/2000 Productivity 1997 to 2000 declined by 350 t due to

poor estuarine condition Prawn production north NSW worth $107m 1999/2000


31/53

Production declined 8912 t in 1997/1998 to 5605 t1999/2000

Catch declined 1800 t from Qld and NT to ~600 t

recreational catch $3.6 m.Commercial crab productionin 1999/2000 - $42.3 m Qld, NSW, SA, WA and NT.

Recreational fisheries in Aust $2.9 b/y with >60% in

estuaries (i.e. $1.7 b)


32/53

Port infrastructure (NLWRA, 2002). Port Melbourne, largest port in Aust, handles $50 b/y Trade Qldss ports >$14 b/y

Marine-based tourist industry from Aust ports >$5 b/y


33/53

Australian Estuaries Audit (NLWRA, 2002)

Classified by process, type and condition.

Six sub classes relative to wave, tide and river energyto control geomorphology

Includes drowned river valleys, embayments, smallcoastal lakes, lagoons and creeks.

About 40% total estuaries strand plains & tidal creeksdue to low river discharge low relief.


34/53

Stage 1: Assessment Australian near-pristine estuaries.

Provided cost effective basis to focus management These estuaries require improved understanding ofprocesses to provide conservation & managementstrategies.


35/53

Summary of condition

50% near-pristine,

22% largely unmodified, 19% modified and 9% extensively modified.


36/53

Key pressures identified by Audit

1. Excess nutrientsFrom decaying plant & animal material, eroded soil,sewage, industrial discharge, storm water run off,fertilizers, garden waste, agricultural run off.

2. Sedimentation Fine grain sediments from catchment & near shoremarine sands important

Excess sediment associated with nutrients, toxicants,and pathogens

Catchment erosion caused by vegetation clearing &land use practices

Sediments may bypass estuary.


37/53

3. Habitat lossShallow sandy flats, sea grass beds, salt marshes,mangroves and wetlands influenced by drainage, landclearing & dredging activities.

4. Changes to flow and tidal flushingConstruction of dams, removal of fresh water increasedsedimentation, shell fish survival and impact fishreproduction.


38/53

5. Pathogens and contaminantsSources human and animal waste, sewage andstormwater, contaminants associated with industrialdischarge, agricultural run off, shipping and stormwater.

6. Introduced pestsIntroduction of exotic biota result in ecological &economic impacts. May destroy native populations;

degrade habitats, effect fishing, boating, swimming.

7. Modifications to ocean entrancesArtificial entrances impact estuarine ecology e.g. larval

recruitment & export to & from estuary.


39/53

SEDIMENT TRANSPORT PROCESSES

Estuaries are conduit by which sediment transported

from rivers to sea.


40/53

Modes of sediment transport Three transport modes - wash load, suspension &bedload within a continuum

Wash load - finest fraction, clay particles kept in

motion by turbulence Suspension by erosion of sediment of estuary bed Grain size


41/53

Grains >150mm move as bedload

Initially grains move by saltatingReversal of current velocities give periods of slackwater, suspended material settles


42/53

Mud, silt and sand (Wolanski, 2007) Cohesive sediment mean particle size 62.5m Silt is 4-62.5m Mud & sand transported in water column by differentprocesses

Sand carried mainly on bottom, mud in suspensionSuspended particulate matter (SPM) comprisessediment & biological matter


43/53

PHYSICAL, CHEMICAL, BIOLOGICAL ANDANTHROPOGENIC PROCESSES CONTROLLING

CONTAMINANT BEHAVOUR IN ESTUARIES

Physical partitioning is grain size, surface area, specificgravity, magnetic properties

Chemical partitioning refers to separation, identification& quantification chemical components Physical & chemical factors strongly interrelated.

A 1, 2


44/53

B 1, 2 G 1, 2

C

D

E

F

A.Atmospheric deposition 1. wet, 2. dryB.Fluvial inflow 1. particulate 2. dissolved phases

C.Permanent burialD.Benthic diffusionE. ResuspensionF. ResettlementG.Export 1. particulate 2. dissolved phasesH.Absorption/desorption

H


45/53

ESTUARINE PROCESSES

Inputs of metals to estuary

Stormwater: Fluvial discharges to estuary for dissolved & particulateheavy metal phases

High- and low-precipitation conditions Stormwater most important point source of heavymetal contaminants to estuaries


46/53

Atmospheric deposition:

Atmospheric metal contributions to estuary by directdeposition & indirectly via the catchment.

Leachates from reclaimed lands: Original area of estuaries reduced by reclamation ofintertidal areas using domestic/industrial waste &contaminated estuary sediments

High dissolved metal-release rates measured inlaboratory leachate column experiments usingsimulated rainwater and seawater percolating throughfield infill material

Metal measured in leachate from reclaimed lands


47/53

Benthic diffusion: Calculated from core data & from analyses of porewater

Metals tightly bound in bottom sediment by sulfides,

metal influx insignificant.


48/53

Export of metals from the estuary

Permanent burial: Sediment surface layer (hydrous layer)(top 20cm)

interacts with water column through resuspension Underlying sediment physically isolated fromoverlying water

Underlying sediment is a chemical sink


49/53

Contaminant export under low- and high-precipitationconditions for stratified estuaries:

During dry weather, small supply of stormwater mixes

with saline water close to entry points Particulates flocculate out of water column &dissolved forms adsorb to particles

Main water body well mixed at, or close to normal sea

water salinity throughout waterway Particulate-dissolved metal phases stable over periodsof weeks in main water body

Under these conditions marine export negligible


50/53


51/53

During high-precipitation, stormwater rapidly entersestuary as discrete, buoyant layer of high-turbiditywater ~1m thick & moves quickly down harbour exits

estuary Density differences between salt & overlyingfreshwater during rainfall events retard mixing &promote seaward transport


52/53

Plumes provide mechanism for contaminants("first flush") to bypass estuary -dispersed at sea

Settling rates under these conditions minor Settled matter metal concentrations low with minimalmixing along boundary layer in upper estuary


53/53

geos3009 - mod 1 - estuaries

Documents