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Approaches to Establish Minimum Flows to Bays and Estuaries. Paul Montagna Marine Science Institute University of Texas at Austin Port Aransas, Texas. Presentation Outline. Case studies Lessons learned A Generic Methodology emerging?. Case Studies. Nueces Estuary, Texas, USA
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Approaches to Establish Minimum Flows to Bays and Estuaries Paul Montagna Marine Science Institute University of Texas at Austin Port Aransas, Texas
Presentation Outline • Case studies • Lessons learned • A Generic Methodology emerging?
Case Studies • Nueces Estuary, Texas, USA • San Francisco Bay, California, USA • Caloosahatchie Estuary, Florida, USA • Mtata Estuary, South Africa • National Program, Australia
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.
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.
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
Florida, USA-Water Management Districts • Northwest Florida WMD • St. Johns River WMD • South Florida WMD * • Suwannee River WMD • Southwest Florida WMD
Caloosahatchie, FL USA-Issues • Modifications (channels, canals, dams), diversions and withdrawals led to: • Decreased sediment transport, biodiversity, and habitat. • Increased eutrophication and hypoxia.
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
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.
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.
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.
Mtata Estuary, South Africa-Issues • Storage capacity is 50% of mean runoff and only 8% reaches the sea.
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.
Mtata Estuary, South Africa-7 Step Approach • Delineate geographical boundaries. • Ecoregional typing. • Assess present state and reference condition. • Determine present ecological status and importance using ecological health and importance indices. • Determine ecological management class • Set the quantity of the reserve and resource quality objectives. • Design resource monitoring program.
Mtata Estuary, South Africa-Approach • Mtata had high scores because it was an Ecological Reserve so it has a high inflow requirement.
Australian National Program -Issues • Laws requiring environmental flows to maintain health and biodiversity. • Primarily state laws. • Attempt to provide a consistent national approach.
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.
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.
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.
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).
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.
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.
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? • Don’t worry, you can start collecting now
Generic Methodology-Approach Accomplishments • Related inflow with fisheries. • Defined desired salinity regimes. • Related salinity regimes with valued ecosystem components (VEC’s). • Identified minimum flow or elevation levels related to something you want to conserve.
Generic Methodology-Adaptive Management • Monitor appropriate ecosystem indicators. • Reassess at appropriate intervals. (5 years?). • Adjust management actions.
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?
