# Ocean Exchange Feasibility — Full Calculation _Last reviewed 2026-07-30. Publisher: David Sherrer._ ## Question Could the Indian River Lagoon's water-quality problems be solved by pumping more seawater in, or by cutting new inlets — that is, by increasing ocean exchange rather than reducing nutrient inputs at the source? ## Short answer No, and this document shows the math openly so any reader can check every assumption. The energy cost alone runs into the tens to hundreds of millions of dollars per year, before construction, before permitting, before operations, before maintenance, and before the ecological consequences of pushing the lagoon toward a higher-salinity regime that favors Florida red tide. The natural experiment already exists inside the lagoon. The Indian River County section already has 2-16 day residence times from Sebastian Inlet and Fort Pierce Inlet, for free, and it has not fixed the water quality problem there either. ## Physical parameters | Parameter | Value | Source | |---|---|---| | IRL surface area | 353 sq mi (225,920 acres) | [SJRWMD Fast Facts](https://www.sjrwmd.com/waterways/indian-river-lagoon/facts/); confirmed by [EPA](https://www.epa.gov/sites/default/files/2018-01/documents/58692_an_river_lagoon_an_introduction_to_a_natural_treasure_2007.pdf) and [FDEP](https://floridadep.gov/sites/default/files/Indian-River-Lagoon-AP-System-Management-Plan.pdf) | | IRL average depth (excluding ICW) | 4.0 ft | Same as above | | IRL total volume | 903,680 acre-feet (~294 billion gallons) | Calculated: area × depth | | Northern IRL residence time (50%) | ~107 days | [Phlips et al. 2020 (NOAA repository)](https://repository.library.noaa.gov/view/noaa/37330/noaa_37330_DS1.pdf); Smith 1993; FDEP 2013 | | Northern IRL full exchange | ~2 years | Same as above; also [FIT Restore Lagoon Inflow Phase 3](https://research.fit.edu/media/site-specific/wwwfitedu/indian-river-lagoon/documents/restore-lagoon-inflow-research/RLI-Phase-3-Final-Summary-Report.pdf) | | Indian River County section residence time | 2-16 days | [IRC Lagoon Management Plan (Tetra Tech)](https://indianriver.gov/Document%20Center/Services/Natural%20Resources/Lagoon/Lagoon-Management-Plan.pdf), citing Kim 2003 | ## Engineering constants | Constant | Value | Source | |---|---|---| | Energy to lift 1 acre-ft of water 1 ft at 100% efficiency | 1.02 kWh | [UC ANR Pub. 82040](https://ucanr.edu/sites/default/files/2011-03/82040.pdf) | | Realistic pump-station efficiency | 70% | Standard engineering assumption for low-head, high-volume pump stations | | Effective head (conservative low estimate) | 10 ft | Assumption; real systems typically operate at 20-40 ft. 10 ft is a floor. | | Florida commercial electricity rate | ~$0.11/kWh | [US EIA Electric Power Monthly, Table 5.6.A](https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a); cross-confirmed by [Florida DOR TIP 25B06-01](https://floridarevenue.com/taxes/tips/Documents/TIP_25B06-01.pdf) and [FPL business rate schedule](https://www.fpl.com/content/dam/fplgp/us/en/rates/pdf/bus-eff-jan-2025.pdf) | ## The calculation To sustain a given water residence time _T_ (days), the lagoon volume must be exchanged approximately once every _T_ days. So the annual volume to pump is: Annual volume = Lagoon volume × (365 / T) The energy required to pump that volume is: Energy (kWh/yr) = (Annual volume in acre-ft) × (Effective head in ft) × 1.02 kWh / pump efficiency The annual electricity cost is: Cost = Energy × $0.11/kWh ## Three scenarios ### Scenario A — Match Indian River County's free exchange (10-day residence) This is the ambitious target: make the whole IRL flush the way the IRC section already does naturally. It is what "just add ocean exchange" would actually mean, if the goal is to move the needle. - Annual volume: 32.98 million acre-ft/yr - Daily volume: 29,447 million gallons per day (MGD) - Flow rate: ~45,561 cubic feet per second (cfs) - Energy at 10 ft head, 70% eff: 480.6 million kWh/yr - **Annual electricity cost: $52.9 million/yr at 10 ft effective head** - **Annual electricity cost: $159 million/yr at 30 ft effective head** For comparison, 45,561 cfs is roughly one-third the average discharge of the Mississippi River at Vicksburg. Moving that volume of seawater into a shallow estuary is a civil engineering project of a scale never attempted in the Indian River Lagoon. ### Scenario B — Cut northern IRL residence time in half (~50 days) A moderate target: don't match IRC, just meaningfully improve current conditions. - Annual volume: 6.60 million acre-ft/yr - Daily volume: 5,889 MGD - Flow rate: 9,112 cfs - **Annual electricity cost: $10.6M/yr at 10 ft head; $32M/yr at 30 ft head** ### Scenario C — Reduce northern IRL residence time by 30% (~75 days) A minimal-intervention scenario. - Annual volume: 4.40 million acre-ft/yr - Daily volume: 3,926 MGD - Flow rate: 6,075 cfs - **Annual electricity cost: $7.0M/yr at 10 ft head; $21M/yr at 30 ft head** ## What these numbers do NOT include Everything above is only the electricity cost of running the pumps. It excludes: 1. **Capital construction cost.** Pump stations at this scale, plus the intake and outfall pipes, plus any new tidal-exchange channels through the barrier island, would run to billions of dollars. The C-44 Reservoir project in South Florida, for scale reference, cost hundreds of millions of dollars for 50,600 acre-feet of storage capacity — and that is a still-water reservoir, not a high-flow pumping system. 2. **Operations and maintenance.** Typically 3-5% of capital cost per year. 3. **Permitting and environmental review.** A project of this scale would require multi-year state and federal environmental review under NEPA, ESA, Clean Water Act, and Florida state permitting. 4. **Ecological disruption from salinity change.** Species adapted to the IRL's current brackish conditions — seagrasses, oysters, many fish species — would experience salinity shifts they are not evolved for. 5. **Increased Florida red tide risk.** Karenia brevis, the organism responsible for Florida red tide, has an optimal salinity range of 27-37 PSU and is strongly suppressed below salinity 24. Only 3% of positive K. brevis samples in Florida's 1954-2002 historical database came from waters below salinity 24. Pushing the IRL toward stable higher-salinity conditions moves it into K. brevis's preferred range. Sources: [Steidinger 2009 (Nova Southeastern archive)](https://nsuworks.nova.edu/cgi/viewcontent.cgi?article=1013&context=hcas_etd_all); [Errera et al. and multi-decadal salinity synthesis (USDA repository)](https://www.fs.usda.gov/rm/boise/AWAE/scientists/profiles/Magana/EffectsKbrevis.pdf); [Phlips et al. 2020 (NOAA repository)](https://repository.library.noaa.gov/view/noaa/37330/noaa_37330_DS1.pdf); [Bugica et al. PLoS ONE 2020 on Nueces Estuary salinity-driven HAB increases](https://pmc.ncbi.nlm.nih.gov/articles/PMC7500669/). ## The natural experiment If tidal exchange with the ocean were, on its own, a workable solution to the IRL's water quality problems, we would expect the segments of the lagoon closest to open ocean inlets to be visibly healthier. They are not. The Indian River County section of the lagoon has residence times of 2-16 days — comparable to or better than Scenario A above — courtesy of Sebastian Inlet and Fort Pierce Inlet. Water within a quarter-mile north or south of those inlets remains chronically impaired. The county's own management plan, prepared by Tetra Tech, states this directly: > Seawater exchange does not reduce [nutrient loading]. > > — [Indian River County Lagoon Management Plan](https://indianriver.gov/Document%20Center/Services/Natural%20Resources/Lagoon/Lagoon-Management-Plan.pdf) That is not the publisher of this site saying so. That is the engineering consultant, in a plan commissioned by Indian River County's own government. ## Publisher's position (stated as such) _This paragraph is labeled explicitly as the publisher's stated position, not as a neutral fact. It is here because the site's rules require positions to be disclosed rather than smuggled in._ The solution to pollution is not dilution. It is eliminating the source. The nutrient loads that drive the IRL's harmful algal blooms, seagrass die-offs, and fish kills come from wastewater, septic tanks, stormwater, and legacy muck already on the lagoon bottom. Increased ocean exchange, whether pumped or via new inlets, is symptom management applied at industrial cost, backed by the one place inside the same lagoon where the exchange is already free and it has still not worked. The publisher of this site does not consider it a serious alternative to the SOIRL program's source-reduction strategy. ## How to check this Every constant and citation above is public. The full calculation script is at `/sources/downloads/ocean-exchange-calculation.py` and can be re-run by anyone with Python. If you have a source that changes any of the assumptions — a public engineering study, a real proposed pump-station design, a peer-reviewed salinity-tolerance study for K. brevis in the northern IRL specifically — send it via the corrections route and it will be read.