Water budget · Lake Lanier

Up or down? Down 0.41 ft over the last 7 days (USGS lake level).

Where the water came from and where it went, at today’s rates. Dam releases and withdrawals have no complete public feed, so they land in the leftover line, which is inferred from the other lines.

River inflowmeasured
+649 af/day≈ +0.23 in/day on the lake
USGS gauges, at current rates
Evaporationmodeled
−187 af/day≈ −0.07 in/day on the lake
Estimate from long-term averages over ~33,736 acres, estimated from USGS storage
Everything leaving that we can’t meter (releases, withdrawals)inferred
−2,438 af/day≈ −0.87 in/day on the lake
What’s left once the other rows and the storage change are counted

=Storage changeinferred
−1,976 af/day≈ −0.70 in/day on the lake
The lake's level change over the last 7 days (−0.41 ft, USGS), as a daily average, × ~33,736 acres, estimated from USGS storage

The lines above add up to the storage change: what the lake gained or lost. Inflow is current; storage is the average over the last 7 days, so the leftover also absorbs any change in pace over that time.

That leftover is about 1,229 cfs leaving the lake, mostly dam releases and withdrawals, plus whatever the upstream gauges missed.

Where it’s going

Chattahoochee below Buford Dammeasured
USGS gauge at the dam
1,186 af/day≈ 598 cfs
Evaporationmodeled
estimate from long-term averages
187 af/day≈ 94 cfs
Withdrawals and other unmetered waterinferred
the leftover from the budget above
1,252 af/day≈ 631 cfs

Chattahoochee below Buford Dam (USGS gauge at the dam) is measured downstream of the dam and stands in for releases. The withdrawals line is the budget’s leftover: city intakes, ungauged runoff and estimation error. The lines can overlap, so treat the split as approximate.

River flow toward the lake now

Swipe sideways to follow the river to the lake →

SteadyReceding · high water draining downOn the rise · climbing right nowInbound wave · big rise upstreamFlooding · NWS, by river heightNo current readingRising or falling is judged from each gauge’s last 48 hours, scaled to its river. Dot speed follows the flow. NWS flood status comes from river height and outranks direction.

Streamflow at the 2 USGS gauges, plus the current flow out through the dam (USGS). Labels are gauge readings in cfs. Line width isn’t to scale. The storage line above shows whether Lanier is up or down.

How this is computed

Inflow converts current streamflow at the gauged tributaries (USGS) to acre-feet per day (1 cfs ≈ 1.9835 af/day). Evaporation uses long-term monthly averages for the region over today’s lake surface. That surface area is TWDB’s daily survey where published, otherwise estimated from storage. With no storage reading, evaporation isn’t estimated. Inches on the lake divides each volume by that same surface area, so an inch takes less water when the lake is low and narrow than when it’s full and wide. Storage change is the lake’s level change (USGS) times that surface area, averaged per day over the last day for a once-a-day feed, otherwise over the last seven days. The leftover is what it takes to make the lines add up. It lumps together dam releases, withdrawals, and ungauged runoff, which can’t be split without data the operator doesn’t publish.

All inputs are provisional. This page is an estimate, not an official accounting.