Approaches to Establish Minimum Flows to Bays and Estuaries

1
Approaches to Establish Minimum Flows to Bays and
Estuaries

• Paul Montagna
• Marine Science Institute
• University of Texas at Austin
• Port Aransas, Texas

2
Presentation Outline

• Case studies
• Lessons learned
• A Generic Methodology emerging?

3
Case Studies

• Nueces Estuary, Texas, USA
• San Francisco Bay, California, USA
• Caloosahatchie Estuary, Florida, USA
• Mtata Estuary, South Africa
• National Program, Australia

4
Nueces Estuary, Texas USA-Issues

• Second dam built 1982.
• 151,000 acre-ft/y required.
• No releases due to drought and impoundment.
• Salinity increased 3 fold.

5
Nueces Estuary, Texas USA-Approaches

• Flow related to harvest with models to choose
  minimal flow rate to sustain fishery (i.e., the
  State methodology).
• Minimum flow rules changed 3 times since 1990
  (Adaptive Management).
• Currently seeking mitigation strategies to gain
  relief credit.

6
Nueces Estuary, Texas USA-Restoration Efforts

• Nueces River bank lowered to increase flooding of
  Rincon Bayou and marsh.
• Salinities reduced from 150 ppt to 25 ppt,
  productivity and diversity increased.
• City received inflow credit for marsh restoration
  (Adaptive Management).

Channel
7
Florida, USA-Water Management Districts

• Northwest Florida WMD
• St. Johns River WMD
• South Florida WMD
• Suwannee River WMD
• Southwest Florida WMD

8
Caloosahatchie, FL USA-Issues

• Modifications (channels, canals, dams),
  diversions and withdrawals led to
• Decreased sediment transport, biodiversity, and
  habitat.
• Increased eutrophication and hypoxia.

9
Caloosahatchie, FL USA-Approach

• Water Management agency determined a minimum flow
  to protect habitat would protect valued
  resources.
• Recommended a minimum flow level to protect
  salinity sensitive seagrass species.

Shell Point
10
San Francisco Bay, CA USA-Issues

• Decreased Sacramento-San Joaquin River system
  inflow led to decreased abundances of many biotic
  components, particularly five threatened or
  endangered fish species.

11
San Francisco Bay, CA USA-Approach

• Workshop convened in 1991
• Identified resource salinity ranges
• Relates inflow with salinity
• Rule adopted in 1994 to ensure sufficient inflow
  to locate the 2 psu isohaline downstream to
  enhance estuarine resources.

12
Mtata Estuary, South Africa-Issues

• 1998 National Water Act requires a reserve to
  satisfy basic human needs and to protect aquatic
  ecosystems.
• Basic human needs reserve right of every person
  to 25 litres of water of adequate quality per
  day.
• The ecological reserve To protect rivers,
  wetlands, estuaries and groundwater.

13
Mtata Estuary, South Africa-Issues

• Storage capacity is 50 of mean runoff and only
  8 reaches the sea.

14
Mtata Estuary, South Africa-Approach

• Developed a 7-step process relying on value
  assessments (i.e., expert opinion) to set a
  minimum flow.
• Geography, state, health, Reserve category,
  hydrology, monitoring.

15
Mtata Estuary, South Africa-7 Step Approach

1. Delineate geographical boundaries.
2. Ecoregional typing.
3. Assess present state and reference condition.
4. Determine present ecological status and
   importance using ecological health and importance
   indices.
5. Determine ecological management class
6. Set the quantity of the reserve and resource
   quality objectives.
7. Design resource monitoring program.

16
Mtata Estuary, South Africa-Approach

• Mtata had high scores because it was an
  Ecological Reserve so it has a high inflow
  requirement.

17
Australian National Program -Issues

• Laws requiring environmental flows to maintain
  health and biodiversity.
• Primarily state laws.
• Attempt to provide a consistent national approach.

18
Australian National Program -Approach

• Basis
• Check list of major ecological processes affected
  by flow to estuaries.
• Adaptive management to assess risk associated
  with reduced flows.
• Two step methodology
• Preliminary Evaluation Phase.
• Detailed Investigative Phase.

19
Australian National Program -Approach

• Preliminary Evaluation Phase
• Define environmental flow issue.
• Assess estuary value.
• Assess flow changes.
• Assess estuary vulnerability.
• Detailed Investigative Phase
• Model project impact on transport, mixing,
  quality, and geomorphology.
• Define environmental flow scenarios.
• Use models to assess impacts of scenarios.
• Assess biota risk.
• License and development approval.
• Adaptive Management.

20
Lessons Learned

• Have to consider environmental needs prior to
  construction of water projects
• Preventing problems much cheaper than fixing
  problems.
• Different approaches used everywhere
• Range from highly technical to highly value
  laden.
• Valuing ecological services are the limiting
  factor, not technology.
• Restoration or minimum flow levels will never
  approach natural conditions.

21
Emerging Generic Methodology?

• Have legal authority.
• Have management goals based on ecological
  services (i.e., ecosystem management).
• Monitor effects and reassess ecosystem health
  (i.e., adaptive management).

22
Generic Methodology-How To Start

• Identify your estuarine typology and
  geomorphology, climate regime, and other physical
  characteristics.
• Identify your charismatic or economically
  important resources at risk.
• Identify legal or management frameworks.

23
Generic Methodology-Starting Accomplishment

• Created the framework for justifying
  environmental flows.
• Created the approach for determining
  environmental fresh water needs.
• Identified the means to implementing a minimum
  flow plan.

24
Generic Methodology-Approach

• Collect data
• Long-term flow rates
• Size of rivers, streams, estuaries, bays
• Climate (rainfall and temperature) in watershed
• Long-term state of biological resources
• Data not there?
• Dont worry, you can start collecting now

25
Generic Methodology-Approach Accomplishments

• Related inflow with fisheries.
• Defined desired salinity regimes.
• Related salinity regimes with valued ecosystem
  components (VECs).
• Identified minimum flow or elevation levels
  related to something you want to conserve.

26
Generic Methodology-Adaptive Management

• Monitor appropriate ecosystem indicators.
• Reassess at appropriate intervals. (5 years?).
• Adjust management actions.

27
Emerging Conceptualization

• Use the risk assessment paradigm to set
  environmental flows.
• The Pressure-State-Response (PSR) conceptual
  model is
• Result of consensus building
• Long history
• Successful in regulation of environmental health
  (i.e., water quality)
• Can it be used for regulating water quantity?

28
Application of PSR Model
PRESSURE STATE RESPONSE
-Stressors Character-ization -Ecological Services Effects -Agency Actions Management
29
Application of PSR Model
PRESSURE STATE RESPONSE
-Stressors Character-ization -Ecological Services Effects -Agency Actions Management
Human Health Mercury Neurotoxicity Reduce consumption
30
Application of PSR Model
PRESSURE STATE RESPONSE
-Stressors Character-ization -Ecological Services Effects -Agency Actions Management
Human Health Mercury Neurotoxicity Reduce consumption
Ecological Health High salinity Productivity or species loss Set minimum flow levels