Estuarine

1
Estuarine Coastal Modelling Course
MODULE I ESTUARIES - AN INTRODUCTION
Michael Hartnett, Environmental Change Institute,
NUI Galway
2
ESTUARIES AN INTRODUCTION OBJECTIVE To
provide a basic introduction to estuaries,
influencing factors and importance
3
ESTUARIES - AN INTRODUCTION CONTENT- I Estuari
es II Tides III Rivers IV Mudflats V Primary
production
4
I ESTUARIES
5
I ESTUARIES What is an estuary? An estuary is
an inlet of the sea, reaching into the river
valley as far as the upper limit of tidal rise,
usually divisible into three sectors a)
a marine or lower estuary, in free connection
with the open sea b) a middle estuary,
subject to strong salt and freshwater mixing
c) an upper or fluvial estuary, characterised by
freshwater but subject to daily tidal
action Dionne (1963) Estuaries
primarily defined by- tides (saltwater)
river (freshwater)
6

• I ESTUARIES
• Irish estuaries
• Coastal water bodies

7

• I ESTUARIES
• Defining a particular estuary-
• Often not easy where does it end?
• Transition between river, estuary, coastal
  embayment and open coast often gradual
• European Environment Agency (EEA) Transitional
  Waters
• bodies of surface water in the vicinity of
  river mouths which are partly
• saline in character as a result of their
  proximity to coastal waters but which
• are substantially influenced by freshwater flows

8

• I ESTUARIES
• EPA delineation of Irish estuaries-

9
I ESTUARIES Ranges of physical dimensions-
10
I ESTUARIES Humanity and estuaries

• Estuaries/continental shelves-
• 5.2 earths surface
• 2 oceans volume
• C. 60 population live along estuaries/coasts
• Worlds population doubles in 30-50 years
• Coastal population doubles in 20 years

11
I ESTUARIES Humanity and estuaries

• Anthropogenic impacts-
• Overfishing
• Sedimentation
• Pollution (chemical, heavy metals)
• Wetlands destruction
• Eutrophication
• Eutrophication-
• Excessive nutrients (sewage/agriculture)
• Reduced oxygen (hypoxia DO lt 2mg/l anoxia DO
  0mg/l)
• Hypoxia migration of fish, crab, shrimp
• Poorly flushed waters-
• 84,000 km2 of Baltic Sea anoxic

12
I ESTUARIES Classification of estuaries

• Topographic classification-
• Coastal plain estuaries
• Fjords
• Bar-built estuaries
• Other
• Salinity/stratification classification -
• Highly stratified
• Partially mixed
• Well mixed

13
I ESTUARIES Topographic classification

• Coastal Plain
• Drowned river valleys
• River flow ltlt tidal prism
• Relatively shallow lt 30m depth
• Extensive mudflats and a deeper
  central channel
• Examples Cork Harbour, Kilalla Bay
• Majority type
• Fjords -
• Formed by glacial erosion
• Relatively long and deep gt 30m
• Shallow cill at mouth
• Example Killary Harbour

Volume of water between high low tides
14
I ESTUARIES Topographic classification

• Bar-built structures
• Similar to coastal plain estuary
• Greater sedimentation
• Characteristic bar at mouth
• Areas of deposition
• Shallow, extensive lagoons and waterways
• Examples Wexford Harbour
• Other -
• Estuary not defined above
• Formed by volcanic eruptions, landslides etc

15
I ESTUARIES
Salinity classification Highly stratified

• Salt wedge type estuary
• Light, fresh water overrides dense salt
  water

EXAMPLE
Net outflow at top and inflow at bottom Dense
salt wedge advances along bottom until river
forces can no longer be overcome Two important
points Halocline not a perfect jump Surface
salinity gt 0 ppt
Vertical salinity gradient
16
I ESTUARIES
Salinity classification Partially mixed

• Tidal action mixes salt water upwards and
  freshwater downwards.
• Net upwards flow of salt water
• Again get two-layer flow-
• Lighter surface water flows seaward
• Denser bottom water flows landward
• Salinity increases seaward
• Riverflow ltlt tidal prism

EXAMPLE
17
I ESTUARIES
Salinity classification Well mixed

• Tidal flow gtgt river flow
• Bottom friction causes complete vertical
  mixing
• Salinity-
• Same value for surface and near bed
• Salinity decreases landward

EXAMPLE
18
II TIDES
19
II TIDES
What are tides? Tides are the regular and
predictable movement of water caused by
astronomical phenomena and the topography of the
water basins (i.e. the depths and shape of the
coastline). The principle causes of tides are
the gravitational effects of the Moon and Sun on
the Earth-Moon-Sun system, and the movements of
those three bodies within the system.
Lunar affect
Effect of Sun
20
II TIDES
Tidal dynamics

• Spring-neap tides
• Earth-Moon-Sun alignment
• Spring tides
• Higher amplitude
• Faster currents
• More pollutant transport
• Neap tides
• Lower amplitude
• Lower currents
• Less transport
• Less mudlfats exposed

21
II TIDES
Tidal dynamics A tide is a repeated cycle of sea
level changes
22
II TIDES
Tidal dynamics

• Main Features
• Usually semidiurnal
• two high and two low tides per day
• Difference between the two tides
• higher and lower high water
• Tidal constituents orbital contribution
• Moon principle lunar semidiurnal constituent
  M2
• Sun principle constituent S2
• Combined for total tidal dynamics

23
II TIDES Tide Tables
24
II TIDES Tidal Constituents
25
II TIDES Tidal Variations
26
II TIDES
Tidal dynamics

• Phase amplitude
• Phase
• Time difference between tides
• Measured in degrees 3600 in a tidal cycle
• High and low water 1800 out of phase
• Amplitude
• Amplified near coasts
• Lines of constant amplitude cotidal lines
• Zero tidal motion amphidromic point
• Phase / amplitude depend on local coastal
  bathymetry and morphology
• 15 min difference in HW between Roches Point and
  Cork

27
II TIDES Tidal Currents
28
II TIDES
Sources of tidal information

• Newspapers Irish Times, Irish Independent etc
• Proudman Oceanographic Laboratories
• http//www.pol.ac.uk/ntslf/tidalp.html
• WXTIDE32 (Tide predicting software)
• http//www.wxtide32.com/
• UK Hydrographic Office
• http//easytide.ukho.gov.uk/EasyTide/EasyTide/
  index.aspx
• Marine Institute
• www.marine.ie
• Admiralty Charts/Nautical Almanac

29
III RIVERS
30
III RIVERS Significance of rivers

• Freshwater inflows-
• Salinity gradients
• Mixing
• Duration of ebb/flood currents
• Sediments
• Temperature
• Pollutant loads chemicals, nutrients, metals,
  pathogens
• Temporal variations-
• Seasons, storms
• Flow variation
• Pollutant load variation

31
III RIVERS Significance of rivers

• High density gradients-
• Pycnocline/salinity fronts
• Local pools of freshwater
• Less mixing

Table with river flow data for Irish rivers
32
III RIVERS Significance of rivers
Temporal variations
Recorded flow
Recorded nitrate nitrogen
33
III RIVERS
Sources of river information

• EPA - Micheal McCorthaigh
• http//www.epa.ie
• Office of Public Works (OPW) Tony Smyth Mark
  Adams
• http//www.opw.ie/
• ESB
• http//www.esb.ie/
• Consulting Engineers
• Local Authorities
• Universities

34
IV MUDFLATS
35
IV MUDFLATS

• What are mudflats?
• Mudflats are deposits of mud, silt and clay found
  in sheltered intertidal areas.
• They range from soft muds in the most sheltered
  inner areas of harbours and estuaries, to firm
  sands in more wave and current-exposed areas.
• This is a dynamic habitat, and its continued
  presence depends on maintaining the balance
  between the rate of deposition of sediments from
  the water column and the erosion of sediment by
  tidal and wave action.
• Many areas can alter significantly with times,
  such as Wexford Harbour, Morecombe Bay (England)

36

• IV MUDFLATS
• Significance of mudflats
• Difficult regions to model
• Shallow water depth
• Models become unstable
• Flooding and drying routines
• Conservation of mass
• Source or sinks for organics/metals/BOD
• Dynamic environments

37
IV MUDFLATS Wexford Harbour dynamic
1997 2006
38
IV MUDFLATS
Sources of information

• Admiralty charts
• Surveys
• Geological Survey Ireland (GSI)
• Local Authorities
• Private companies

39
V PRIMARY PRODUCTION
40
V PRIMARY PRODUCTION

• What is primary production?
• Production of organic material by plants
  (phytoplankton) from inorganic material and
  sunlight (photosynthesis)
• Primary' in being the first use of solar
  radiation, the main energy source for biological
  processes
• Plankton
• Organisms that have limited mobility in sea water
• Phytoplankton single celled plants
• Diatoms
• Dinoflagellates
• Zooplankton microscopic animals

41
V PRIMARY PRODUCTION

• Inorganic material
• Carbon - ubiquitous
• Nutrients - Nitrogen, Phosphorous
• Organic nutrients from sewage gt inorganic forms
• Limiting nutrient
• Quantifying phytoplankton
• Biomass concentration (mg/l)
• Indicator - chlorophyll_a (mg/l)

42

• V PRIMARY PRODUCTION
• Significance of primary production
• Estuaries/coastal waters
• High nutrient loads (agriculture, sewage etc)
• Highly productive, 90 global fish catch
• Eutrophication over supply of nutrients
• Low level benefits for fish?
• Moderate levels changes ecosystem
• Severe levels species die-off
• fisheries collapse
• oxygen depletion

May be naturally induced
43
V PRIMARY PRODUCTION

• Simple pelagic food web
• Primary production
• Sedimentation of detritus
• Remineralisation

44
ESTUARIES - AN INTRODUCTION CONTENT- I Estuari
es II Tides III Rivers IV Mudflats V Primary
production
45
Estuarine Coastal Modelling Course

• MODULE I
• ESTUARIES - AN INTRODUCTION

• Michael Hartnett, Environmental Change Institute,
  NUI Galway