First, know which number you are reading
Pool elevation describes the lake’s water-surface height against a stated datum. River stage is height at a particular gauge. Flow, in cubic feet per second (cfs), describes a rate. Inflow, dam outflow, a downstream gauge peak, an hourly value and a daily mean are different measurements. A river crest at Commerce is not the same number as a pool reading at Pensacola.
High and low: two well-documented historic pool marks
The USGS water-year 2005 report lists the reservoir maximum as 755.27 feet on May 25, 1957 and the minimum after first filling of the power pool as 713.41 feet on September 28, 1954. These are the report’s gauge-height values, in the historical lake-gauge/Pensacola scale. Its gauge zero is 1.10 feet above NGVD 1929; the figures must not be silently relabeled as NGVD 1929 elevations. [1]
The minimum is specifically after the power pool first filled—not the shallow water during initial filling. The report states that the power pool first filled April 19, 1941. Its record scope ends in 2005, so this page does not present it as a freshly audited all-time record through 2026. [1]
Historic releases: impressive, but not interchangeable
| Date | Figure | What it actually measures |
|---|---|---|
| May 20, 1943 | 300,000 cfs | USGS maximum peak flow at station 07190500, 3.6 miles downstream of Pensacola. Computed from reservoir overflow, not a modern hourly gate log. The same day’s highest daily mean is 287,000 cfs. [1] |
| December 2015 | 295,400 cfs | Event peak inflow, supplied by USACE in NWS’s monthly report. Not a release. [2] |
| December 29, 2015 | 236,165 cfs | Highest observed hourly total dam discharge in GRDA’s August 14, 2015–December 31, 2022 dataset. NWS’s event summary rounds the release to 236,000 cfs. [3][2] |
| May 23, 2019 | About 190,000 cfs | Maximum Pensacola release in the USACE event data quoted by NWS for April 29–June 11, 2019. Approximation retained. [4] |
| May 25, 2019 | 189,441 cfs | Maximum inflow in that 2019 event dataset; different date and quantity from the release maximum. [4] |
Why does a 1943 downstream peak exceed a later report’s “record release”? The sources use different sites, calculation methods, time steps and record windows. We preserve those distinctions rather than manufacture one all-time dam-release leaderboard.
A flood chronology with Miami in view
- 1943: the May flood produced the historic downstream flow peak listed above. [1]
- 1951: a prolonged sequence of rain culminated in the major July Neosho flood. GRDA’s commissioned historical study documents its severe effects around Miami and the broader watershed. We do not substitute an unsourced lake elevation for a river-flood account. [5]
- 1986: intense late-September/early-October rainfall brought another major Miami flood. The GRDA-commissioned study documents it as a separate event, decades after Pensacola’s construction. [5]
- 2007: NWS records about 2,500 residents evacuated and 574 Miami structures inundated. The Neosho near Commerce crested at 29.25 feet on July 5—a river-gauge stage, not a Grand Lake elevation. [6]
- 2015: December flooding drove the event inflow and release figures above. A high inflow is not proof the dam released the same amount at the same moment. [2]
- 2017: late-April rain nearly filled Grand and Hudson flood pools, requiring emergency releases. NWS reports Pensacola and Hudson releases were not significantly reduced until June 10. We have not verified a single exact peak outflow for this event. [7]
- 2019: repeated floods kept the Commerce forecast point above flood stage for a combined 28 days and about nine hours during May 1–June 6. The NWS/USACE event summary gives Grand Lake’s peak pool as 755.01 feet on May 26. [4]
Read the dated Miami flooding and FERC dispute summary →
Drawdowns: seasonal targets are not drought records
GRDA’s 2016 annual report records a FERC variance suspending the fall three-foot drawdown—the third suspension in five years. The former lowering supported millet seeding on shoreline mud flats; GRDA said it also affected recreational boating and safety. This was a policy/operating decision, not the lake’s lowest historical level. [8]
A later snapshot appears in GRDA’s December 2022 license exhibit, which records the rule curve following a 2017 amendment: rise from 742 to 744 feet PD during May; target 744 in June–July; lower to 743 in early August; target 743 through mid-September; lower to 742 by the end of September; target 742 October–April. Those are historical targets, subject to the stated operating exceptions—not a promise or forecast for any particular day. [9]
We have not verified a complete chronology of maintenance-related drawdowns or a date-specific repair drawdown. Ordinary low water should not be attributed to dam repairs without a dated operating record.
For today’s conditions, use today’s data
The USACE Pensacola data page links current elevation, inflow and outflow measurements. Historical figures here are not boating-safety guidance or a live lake report. [10]