From snowpack to Pyramid Lake

This is not a forecast for winter 2026-27. It stays here. Live river gauges and the El Niño outlook are different clocks.

USGS built the original ARkStorm scenario as a hypothetical month-long atmospheric-river sequence, approaching but not exceeding the 1861-62 California storms. USGS Open-File Report 2010-1312. In 2013-14, DRI and partners downscaled that scenario to Tahoe, Truckee, Reno, Sparks, and Carson City as ARkStorm@Tahoe. DRI's ongoing ARkStorm@SierraFront 2.0 updates the work with a climate-model storm sequence and newer flood-risk data for the Truckee and Carson basins.

DRI's project page notes that communities on this Sierra Front are among those most affected by atmospheric-river flood damages, and that projected losses could increase four-fold by 2090 compared with 1990 levels, citing Corringham et al. 2022. That is a worst-case research frame, not a claim about this winter. DRI, ARkStorm@SierraFront 2.0. Dams, canals, and storage that would have to survive a storm like this sit in How resilient is this system?

This is not today's river reading. It stays here. The gauges above, the El Niño outlook, and the ARkStorm worst-case box are different clocks. Open items from this box also sit on the Basin Watch List, each with its own last-confirmed date.

The legal frame is settled in documents, not in this page's opinion. The Orr Ditch Decree (1944) still governs Truckee rights. Congress passed Public Law 101-618 in 1990. The Truckee River Operating Agreement was signed in 2008 and took effect in 2015. Reclamation, TROA.

Ranked choke points

1. Tahoe Dam still has an open rehab study. Reclamation's Lahontan Basin Area Office says the dam at Tahoe City dates to 1913. It has no air-entrainment protection on the outlet works, freeze-thaw damage on the downstream face, and a history of gates that stick. The documented failure mode is loss of outflow control, not a catastrophic emptying of Lake Tahoe. Reclamation, Lake Tahoe Dam. Status as of September 2026: a rehabilitation study opened in October 2023 is still listed as in progress on that page.
2. The Truckee Canal still has a residual lining gap. On January 5, 2008, a canal breach in Fernley flooded about 590 homes and caused an estimated $50 million in damages. Reclamation, Truckee Canal. Phase 1 lining, about 3.5 miles and about $35 million, was completed May 22, 2024. TCID's public-safety project describes an EIS-scale lining need of 12.7 miles, of which Reclamation lined 3.56 miles in that first phase. TCID, Truckee Canal Public Safety Project. The remaining miles are the honest leftover, not a claim that the 2008 reach is still unlined.
3. Stampede's documented overtopping risk has a federal fix, not an open threat. Reclamation's Safety of Dams FAQ says investigations showed Stampede needed an 11.5-foot raise to prevent overtopping that could fail Stampede and Boca Dam six miles downstream. Reclamation, Stampede SOD FAQ (PDF). Tahoe Quarterly reported that raise already in construction in 2017, with Boca's separate seismic work in design. Tahoe Quarterly, 2017. This page treats that deficiency as documented and remediated, not as a live cascade warning.
4. Wildfire turbidity is a known operating problem, already managed. The 2024 Gold Ranch Fire on this same corridor showed the pattern: ash and sediment hit the river later, after rain or snow on the burn scar. TMWA's published response is to lean on groundwater and other off-river sources rather than treat degraded river water. Detail lives in Fire, not here.
5. TMWA's two river plants were checked and are not a confirmed single-point failure. Chalk Bluff is published at 90 MGD. Glendale is published at about 25–37 MGD. The utility also lists 82 wells. TMWA, treatment. This page did not find a sourced claim that either plant is the basin's single point of failure.
6. ASCE grades Nevada, not this river. The 2025 report card gave the state an overall C+, with dams C- and drinking water C-. On the state page, about 30 percent of state-regulated dams in the National Inventory of Dams with a condition rating were Poor or Unsatisfactory. Those are statewide scores. They do not rank Tahoe Dam, Stampede, or TMWA's plants. ASCE, 2025 Nevada Infrastructure Report Card. ASCE, Nevada state grades.

Do we need more reservoirs?

Reclamation's 2015 Truckee Basin Study, presented again to TMWA, said that under the driest end-of-century climates there could be a need for as much as 800,000 acre-feet of new storage, "equivalent to four Stampede Reservoirs." That figure is for all Truckee users, municipal and agricultural, not TMWA alone. The same briefing said snow is falling less as snow and running off earlier, so existing reservoirs have to spill flood water before it is needed later in the year. The Nevada Independent, on the Reclamation briefing. A 2018 Berkeley Lab study of snowpack above 10 major California reservoirs, not this basin alone, projected on average a 79 percent drop in peak snowpack water volume by 2100 and a snow season 39 days shorter. Berkeley Lab, 2018. Rhoades et al., GRL 2018.

Arlan Nickel, then the basin study manager, told the Independent that new large dams are "probably not a very good alternative under future conditions." He said the existing reservoir system is already inefficient because of evaporation: of the roughly 600,000 acre-feet available for storage in Lake Tahoe each year, 400,000 acre-feet evaporates. He pointed instead toward storage insulated from evaporation, including aquifers, and toward updating flood-release rules with the Army Corps.

What is being pursued instead

TMWA has injected treated surface water into wells since 1993. That is a bank, not a new water right. TMWA recharge program. USGS and TMWA studied a larger option at Bedell Flat. USGS SIR 2021-5137. In the Independent's basin-study coverage, TMWA's John Enloe, then director of natural resources planning and management, said the agency could end up storing about 50,000 acre-feet in places like Bedell Flat as an emergency supply. That was feasibility talk. The USGS report later cited TMWA modeling that a 2 million gallon-per-day ASR target would exceed estimated aquifer capacity. This page treats Bedell as a studied site, not a built 50,000 acre-foot bank. Groundwater chapter.

The Advanced Purified Water Facility at American Flat is the other built-scale play. It is a TMWA and City of Reno project under OneWater Nevada, not a university plant. Smart Water Magazine, on April 9, 2026, called it a $200 million facility when Carollo Engineers was selected for construction management. Smart Water Magazine, April 9, 2026. Groundbreaking was August 31, 2026. University of Nevada, Reno coverage of that ceremony, and later local reporting, put the figure at $221 million. UNR is a OneWater research partner and covered the event; TMWA's communications office is the source for the construction schedule. UNR, September 1, 2026. OneWater Nevada, APWF.

Martis Creek Dam, completed in 1972, has unused built capacity. The Corps lists a 20,400 acre-foot flood pool and says the lake is maintained at minimum pool, covering 70 acres. USACE, Martis Creek Lake. Tahoe Quarterly reported that the dam once ranked among the Corps' highest-risk inventory, then, after a 2013-2016 review and with the gates held open, the Corps lowered that rating. Tahoe Quarterly, 2017. Reclamation's 2023 Truckee Water Management Options Pilot modeled flood operations both with Martis assumed in service and with it left out. Reclamation, Truckee WMOP. Status as of September 2026: the Corps page still lists minimum pool. This site found no public reactivation timeline.

Flood worst-case is ARkStorm on this river. Fire and turbidity are Fire.

This is the Floriston Fire after the fact, not a live perimeter. It stays here once the NIFC polygon is gone. The live map above is a different clock.

CAL FIRE listed ignition at 10:01 a.m. on September 16 at Interstate 80 and Floriston Way, nine miles northeast of Truckee. The first public threat list was the highway, the Truckee watershed, and nearby natural resources. A YubaNet radio log from that morning has two helicopters already working when Tankers 88 and 89 arrived with Air Attack 230 from Grass Valley. At 1:14 p.m. the incident commander asked for 10 more water tenders, four engine strike teams, and four dozer strike teams. CAL FIRE's 1:22 p.m. post ordered 20 engines, eight dozers, 10 water tenders, and 12 hand crews. A forest hand crew also mobilized that morning. This page does not name it. More than one real hotshot crew in this country shares a similar name, and only one outlet printed one.

Command left initial attack overnight. CAL FIRE says the Sacramento Regional Incident Management Team took over at 7 a.m. on September 17, in unified command with the California Highway Patrol and the Humboldt-Toiyabe and Tahoe national forests, and handed the fire back to local agencies on September 22. The resource block still on that incident page: 1,175 personnel, 62 engines, 25 water tenders, 8 helicopters, 3 dozers, and 34 crews. NIFC later held the same 622-acre footprint at 96% contained. No source says which water those tenders or aircraft actually drew from.

Full retrospective in Journal. Sources: CAL FIRE; YubaNet; NIFC WFIGS.