O'Shaughnessy Reservoir

At a glance

Before the lake

The stretch of the Scioto River that O'Shaughnessy Reservoir now covers was farmland and small crossroads settlements in Concord and Liberty townships, Delaware County, before the dam went in during the 1920s. Two villages anchor the pre-dam landscape. Bellepoint, at the reservoir's north end where Mill Creek meets the Scioto, was laid out in 1835 and held a post office from 1837 to 1907; it survives today as an unincorporated community whose edge the reservoir now laps against, but it was never itself flooded. A few miles south, Powell also sat directly on the river, and both villages still appear by name on a 1901-1903 U.S. Geological Survey topographic quadrangle of the area, taken two decades before the dam existed.

An 1866 atlas of Delaware County's Concord and Liberty townships, read directly against the river corridor, records the working landscape that the reservoir would later cover: two water-powered mills sat right on the channel ("G. Mill" at Cutlers Corners and "West Mill" in Liberty township), along with named farms (Fair View, Valley View, Pleasant Hill, Maple Shade, River Farm and others), a spring called Sulphur Spring, and two cemetery symbols marked directly on riverside parcels. Several extended families held large adjoining tracts along this stretch, most notably the Case family in Liberty township — S.W. Case, Dr. Case, Miles S. Case and others held adjoining parcels — along with the Cruikshank, Cutler, Cellar, Marks, Wilcox, Thomas, Standish, Lowry and Bartholomew families. A tributary called Salt Rag Lick and a stream then known as Tylers Run also drained into the Scioto in this stretch; Tylers Run survives as a named tributary on modern hydrography.

Dublin itself, on the Franklin County side just downstream, sits almost exactly where the dam was eventually built — which is why the structure carries the name it does in local usage as much as the man it was formally named for. Fishinger Bridge, shown crossing the Scioto below Dublin on the pre-dam topographic map, survives today only as the name of Fishinger Road in Columbus.

No source located names a pre-existing town that was wholly or partly drowned by the reservoir. That absence is notable: unlike lakes built by damming already-settled valleys, the O'Shaughnessy taking appears to have displaced scattered farms and a handful of buildings rather than a town center.

Building the dam

Columbus's water story on the Scioto begins upstream of O'Shaughnessy, with an older, smaller dam. The city built what became Griggs Reservoir in 1904-1905, at a cost of about $700,000 (a 1924 city annual report gives $640,000, a figure that does not match Wikipedia's $700,000, so the discrepancy is noted rather than resolved). For its first seventeen years the dam carried no proper name at all — first "Jeffrey Dam," then simply "Storage Dam" — and it was not formally renamed Griggs Dam, for city engineer Julian Griggs, until December 18, 1922, by which point the much larger dam upstream was already under construction. For twenty years, Griggs was the only reservoir supplying Columbus's drinking water.

The man the newer dam would be named for spent his whole career making that dam happen. Jerry (Jeremiah Patrick) O'Shaughnessy started with the City of Columbus in 1870, at around 17 years old, digging the foundation trenches for the city's original waterworks. He rose through every position in the water department and became superintendent in 1896, a post he held for roughly the next twenty-five years. As early as 1913 he was pushing for a second, larger dam upstream of Griggs, and at the time of his death in 1921 he was, in Mayor James Thomas's own words, "the first to urge and point out the necessity for the construction of an additional dam, on which engineers are now at work." Columbus City Council voted to name the still-unbuilt dam for O'Shaughnessy within two weeks of his death — four years before it was substantially finished and five years before its formal dedication.

Site selection took more than a year of preliminary surveys, including 22 diamond-drill borings, before settling on a spot on the Scioto about four miles north of Dublin. Mayor Thomas's 1921 annual report to city council, printed in the Columbus City Bulletin, projected that the new dam would "completely flood 800 acres of land and impound five billion gallons of water" — a planning-stage estimate that lines up reasonably with the 741 acres a 1928 engineering paper says were later cleared and grubbed across the finished pool footprint, every tree and stump over two inches in diameter cut and pulled to at least six inches below grade, done purely as an extra water-quality precaution even though the supply would also be filtered.

City records name at least some of the private owners paid for their land. A series of "emergency" purchase ordinances passed in October and November 1922, while construction was underway, authorized the city to buy parcels in Liberty and Concord townships. Harley E. Burns was paid $6,817 for 30.1 acres in Liberty Township. George F. Miller, whose 111.5-acre tract in Concord Township was later held in part by Elmer L. Zimmerman(n), was paid $4,170.50; that ordinance also fixed the reservoir's design pool elevation at 858.0 feet above mean sea level, tied to U.S. Geological Survey benchmarks at Dublin and Bellepoint — a genuine 1922 primary-source elevation figure. A separate 1922 ordinance authorized the city to negotiate with the State of Ohio to replace flooded buildings, including a laundry, at the state's Girls' Industrial School in Delaware County, meaning the taking touched an existing state institution as well as private farms. These figures come from scanned City Bulletin ordinances with imperfect optical-character recognition, so they should be read as a close but not fully verified transcription; no complete owner list covering the whole flooded footprint has been found, and neither reservoir's records mention a relocated cemetery.

Construction itself, from 1922 to 1925, was handled by the Thompson-Starrett Company of New York, which had recently worked on the General Motors Building in Detroit and the Woolworth Building in New York City. Frank L. Packard, a leading central Ohio architect, designed the twelve-arch reinforced-concrete road bridge that still runs atop the spillway. Laborers were advertised wages of 40 to 50 cents an hour for a ten-hour day, with on-site commissary lodging available for $7 a week. At least one construction worker died in an accident in November 1924, though no name or details of the incident have been found. Builders used two traveling cableways, trucks hauling material from a rail spur three miles away at Powell, log-crib coffer-dams sunk with rock fill, and 553 grout holes drilled to seal seepage under the dam; the finished structure took 79,565 cubic yards of concrete, with sand shipped in from Dresden, Ohio, 55 miles east.

The dam's spillway was sized with a very specific disaster in mind. The Great Flood of 1913 had killed as many as 100 people in Columbus and torn out more than two and a half miles of the city's west-side levee a decade earlier. O'Shaughnessy's spillway, with a discharge capacity of 110,000 cubic feet per second, was deliberately engineered at roughly 50 percent above that flood's actual peak flow. Even so, the dam was built purely for water supply, not flood control; the city's own reservoir FAQ is explicit that when the pool is full, excess water simply spills over the top rather than being held back by gates.

Columbus City Council's decision to name the dam for O'Shaughnessy came with an unusually public payoff. When the dam was formally dedicated on May 15, 1926, the ceremony was "heralded by city newspapers, covered by live radio broadcast and documented by newsreel," an extraordinary amount of publicity for a piece of water infrastructure. At completion, the dam's water supply was sized to serve a population of half a million people, roughly double the city's actual size at the time. The structure was listed on the National Register of Historic Places on July 5, 1990, as "O'Shaughnessy Dam and Bridge."

Stories

The ditchdigger who got a dam named after him before it was built

Jerry O'Shaughnessy started at the very bottom in 1870, digging trench for the new Columbus waterworks. Fifty-one years later, having worked his way up to superintendent, he was still pushing for a second, bigger Scioto dam — a project he never lived to see finished. Council's decision to name the unbuilt dam for him within two weeks of his death, rather than wait for its completion, is the detail that makes the story land. One oddity remains unresolved: the historical marker honoring him gives two different birth years in the same short text, "1856" in its header and "1853" in the body.

Reindeer, a Christmas promotion, and the accidental founding of a zoo

The Columbus Zoo and Aquarium exists because a newspaper contest got out of hand. In late 1927 the Columbus Dispatch ran a Christmas promotion that ended with the paper receiving a gift of six live Alaskan reindeer. Publisher Harry P. Wolfe, fresh off a visit to the St. Louis Zoo with Mayor James Jay Thomas, decided the animals deserved more than a backyard pen. On September 17, 1927, the city voted to build a 21-acre zoo, "Riverside Park," on the reservoir's east bank — land the dam's own 1920s planners had already set aside for parks. The water utility and the zoo have shared a fence line ever since.

A subdivision built on a lake that didn't exist yet

Most Ohio reservoirs researched in this project displaced an existing town. Shawnee Hills is the reverse: it was created by the reservoir. Almost as soon as the pool filled in the mid-1920s, speculative developers platted more than 3,600 tiny lots, each about 35 by 70 feet, directly on the new shoreline as a resort fishing getaway. Streets were graded, but water and sewer were not; early cottages ran on private wells and outhouses. The scattered additions did not formally incorporate as a village until 1942, and as late as 2001 the whole place amounted to only about 419 residents, 200 homes and 30 businesses. A public sewer agreement with Columbus did not arrive until the 2000s, roughly eighty years after the first lots sold.

The dam built to survive the flood that had already happened

The engineers who sized O'Shaughnessy's spillway in the early 1920s had personally lived through the Great Flood of 1913, which killed as many as 100 people in Columbus. They built in a deliberate margin, sizing the spillway's discharge capacity at about 50 percent above that flood's peak flow. Yet the dam remains, by design, a water-supply structure rather than a flood-control one: when it fills, water simply spills over the top the way it would over a mill dam.

The summer Columbus almost ran dry

For most of the twentieth century, Griggs and O'Shaughnessy together were simply "the reservoirs," taken for granted. That ended in 1988, when a severe drought pushed both reservoirs low enough that Columbus came close to running out of drinking water. The scare produced a plan called "Water Beyond 2000" and, a quarter-century later, the John R. Doutt Upground Reservoir, completed in 2014 near Richwood. Doutt holds more water than Griggs and O'Shaughnessy combined, yet unlike its two older, far more visible predecessors it is fenced, closed to the public, and unknown to most Columbus residents.

A same-name coincidence, three time zones away

Anyone researching this dam quickly runs into a much more famous namesake: the O'Shaughnessy Dam at Hetch Hetchy in Yosemite National Park, central to a century-long San Francisco water-rights fight. It shares nothing with the Ohio dam except a surname — California's version is named for engineer M.M. O'Shaughnessy, completed in 1923, two years before Ohio's. The two dams, named for two unrelated men, were built within two years of each other on opposite sides of the country for opposite purposes.

The lake since

O'Shaughnessy has not eliminated big Scioto floods downstream — it has just added storage above them. The river's own gage record below the dam shows a peak instantaneous flow of 74,500 cubic feet per second on March 25, 1913, the same storm system behind the Dayton flood and nine years before the dam existed at all. The highest post-dam daily mean flow on record, 42,900 cubic feet per second, came during a January 1959 thaw-on-frozen-ground event. The lowest daily mean flow ever recorded, just 0.4 cubic feet per second on November 8, 1924, falls right around when the dam would have been closing its gates to begin filling the new reservoir, and is read as an artifact of that impoundment rather than a drought, though that has not been confirmed against a construction log.

The dam was built with a power gate-house at the west end of the spillway specifically to allow a future hydroelectric plant, a feature that sat unused for 62 years. A 5-megawatt, two-turbine hydro plant finally went online in 1987 under a federal energy-independence program. It suffered dangerous explosions when debris or ice clogged its intakes and trapped compressed air against the automatic gates, a problem later fixed with new vents, before the aging generators were shut down in February 2017. Columbus City Council approved $15.3 million in bond funding in December 2020 to rebuild the plant, targeting a return to service by mid-2023; as of contractor filings from mid-2025, the turbine replacement and generator refurbishment work was still active with no completion date given, so the plant should be treated as still offline rather than restored.

A Landsat-based water-area analysis built from 1990 through 2026 finds the reservoir's summer surface typically runs between about 3.0 and 6.5 square kilometers, roughly consistent with the National Inventory of Dams' combined normal-pool figure for O'Shaughnessy and Griggs together. Because neither reservoir has a USGS pool-elevation gage, this satellite record and the discharge gage below the dam are the best available substitutes for tracking how full the reservoir runs over time.

The water

O'Shaughnessy and Griggs together supply raw water to Columbus's Dublin Road Water Plant, built in 1975 and rated to treat up to 65 million gallons a day for downtown, western and southwestern Franklin County. Griggs, completed in 1905, was Columbus's sole water source for its first two decades; O'Shaughnessy was added upstream in the 1920s specifically to expand that supply, and the two reservoirs together hold roughly 8 billion gallons at normal pool (about 6.3 billion at O'Shaughnessy, 1.2 billion at Griggs). The Scioto above the dam drains agricultural land across Delaware, Marion, Union and Logan counties, a working farmland watershed with a drainage area of roughly 980 to 988 square miles.

The city runs remote real-time water-quality sensors and an algal-research and monitoring program across its surface reservoirs, including O'Shaughnessy, and can treat with powdered activated carbon, potassium permanganate, ozone and biologically active carbon filtration if algal toxins become a risk, or shift the depth at which it draws water to avoid a bloom layer. No dated public record of a specific harmful-algal-bloom advisory at O'Shaughnessy or Griggs by name has turned up, in contrast to some other Ohio lakes with chronic bloom problems.

Unlike some Ohio reservoirs, O'Shaughnessy has no USGS stage gage tracking pool elevation directly. What exists instead is a continuous discharge record immediately below the dam (USGS gage 03221000), running from 1921 to the present, plus a water-quality station at the dam face tracking temperature, conductance, dissolved oxygen and pH since 1998. Swimming is banned by Columbus city code on all of the city's reservoirs, though boating and fishing are allowed on both Griggs and O'Shaughnessy.

Sources

• O'Shaughnessy Dam (Ohio), Wikipedia)
• Griggs Dam, Wikipedia
• Great Flood of 1913 in Columbus, Ohio, Wikipedia
• Bellepoint, Ohio, Wikipedia
• Concord Township, Delaware County, Ohio, Wikipedia
• Jerry O'Shaughnessy historical marker, hmdb.org
• California O'Shaughnessy Dam marker (unrelated, for context), hmdb.org
• Landmarks of Delaware County: O'Shaughnessy Dam, 1808delaware.com
• Curious Cbus: the early history of the Columbus Zoo, WOSU
• 1927: The Columbus Zoo and Its Place in History, Columbus Zoo blog
• Shawnee Hills Comprehensive Plan Update, Delaware County Regional Planning Commission
• Central Ohio's hidden reservoir: the John R. Doutt Reservoir, cwcolumbus.com
• O'Shaughnessy Dam hydro power history, Delaware County Historical Society
• O'Shaughnessy Dam historical perspective, Delaware County Historical Society
• SNOFLO / National Inventory of Dams record OH00751
• Columbus City Bulletin, April 9, 1921, Columbus Metropolitan Library CONTENTdm
• Columbus City Bulletin, October-November 1922 issues, Columbus Metropolitan Library CONTENTdm
• Columbus City Bulletin, Mayor's Annual Report for 1921, Columbus Metropolitan Library CONTENTdm
• Annual Report of the City of Columbus, 1924, Columbus Metropolitan Library CONTENTdm
• OAC / Huntington Library finding aid on the California O'Shaughnessy Dam (unrelated, for context)