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Barge Canal / Mohawk River Flooding at Schenectady Examined:
Knolls Ice-jams An Obvious Site, But The Cause?

Go back to: Critical Commentary | ahead to: Decades Without Follow-Through

This information is from pp. 7-9 of Barge Canal / Mohawk River Flooding at Schenectady Examined: A Report to the People of Schenectady by James E. Duggan (Schenectady, 2007), and is reproduced here with permission of the author.

The reality of snow-melts and annual ice break-up raises important questions about the ice-jams usually formed downriver "at the Knolls", so readily observable from above along Riverview Road and below near the Rexford Bridge. Distinguishing between symptoms and cause is very important and deserves serious investigation in credible detail.

Do the geological conditions downriver from Rexford form an actual cause, or could pile-ups of ice at that site accumulate or result from something else?

Are or were reasonably concurrent conditions observed at the dam to correlate with the visibly piled ice floes closer to Rexford?

Attention usually focuses on the narrowness and major bend in the river as causing the tight wedging of the floating ice floes and a subsequent rise of the canal-river toward flood-levels. Should that perception or generally casual speculation satisfy us? No — Schenectady often experiences totally free-flow flooding and numerous near-floods — when no ice is present.

Nine-plus decades after the 1914 record-event (and the 1916 event), floods at Schenectady continue. In less than a year, three recent events (two floods and a near-flood) have passed with the "usual" alerts, mobilizations, etc, but with no apparent interest, concern or effort underway to understand or define what might be a truly underlying cause, much-less to counteract it.

Late-June 2006 — a lengthy "train" of very heavy rains fell upriver and flowed here, backwater from the dam filled low-lying basements and then it retreated slowly — were flash-boards (to 213 feet) upright on the dam during that anticipated rain-event?

Mid-March 2007 — a typical late-winter snow-melt resulted in the typical ice break-up and repeated brief jams (but apparently not at the Amtrak railroad bridge at Schenectady), finally lodging in the Rexford-Knolls narrows (William van Hoesen, Schenectady County Emergency Management, during personal conversation, reported his understanding that the moving ice jammed at the intact ice sheet extending upriver from the dam).

17 April 2007 — concurrent with a flood stage of approximately 223' at Schenectady from ice-less rain/snow-melt, a very substantial observed depth of overflow existed at the dam (minus flash-boards), although the flow evidently had dropped then 10" below the recent (for this event) high-water level.

Any pointing to ice-jams observed "at the Knolls" is invalid to identify that a probable cause. occurs there. The ice-less June and mid-April events show that forceful flows easily can overcome the narrowness and bend below the Rexford Bridge, making those local situations relatively minor factors. The active momentum of flow there acts to prevent most ice-floes from jamming by themselves — something else influences strongly.

Observations reported in the past can help to promote a more-accurate understanding and point out the "something else".

In the "Chronology" report, the final listing (3/15/1977) notes a free-flow — "…6' …of water going over the crest of the dam" — after the ice-jams had passed. Minus any flash boards then, the Vischers Ferry Dam normally impounds the river to the stage of 211'. The reported over-flow would mean a stage (there) at that "moment" of perhaps 217'. Why such a deep overflow along a crest nearly 2,000 feet long… plus simultaneous jam-free flooding at least seven miles upriver at Schenectady?

The ice-based major flood that began April 1916 can illustrate the central importance of the two questions opening this section. For that event, the "Chronology" report provided three cites from the Schenectady Union-Star, but omitted two important other points available within the included full news account. The sequence of all five points appears below, with the added two underlined (all italics added).

This five-cite composite of a perhaps fuller-than-usual scope of observations identifies or strongly suggests a strategically important dam-to-Knolls relationship during winter. Moreover, did a thick sheet-ice directly against the Vischers Ferry Dam prevent any substantial amount of water from spilling over it early in the event? How does that ice "usually" go out?

The final cite of the above-five signals an early "probably", thus specifically incorporating this power-dam as a very formative element, if not THE formative element, in the ice-jams at the Knolls and virtually all the resulting flood-levels at Schenectady. The current-less pool here stimulates sheet-ice (with internal strength able to transmit the forces to the banks) to extend far upriver from the dam, becoming "a jam-initiating point" (a term used by US Army Corps of Engineers), structurally resistant to the push of ice-floes accumulating against it.

This early-20th century perspective of dam-stimulated sheet-ice, linked with Mr. van Hoesen's stated observation in March 2007, makes "the Knolls" section of the canal/river the site of ice-jams and it deflates any logic that the geological squeezing and turning of the river there is the perennial main cause of flooding. The Schenectady Union-Star, mindful of the so-recent 1913 and 1914 floods, saw the observation of "sheet ice… from the dam" (4/3/1916) as so compelling a connection that, within two days (4/5/1916), its report characterized the possible "…menace of Visher Dam …" (included in the preceding " …Post-Dam Commentary") (2).

Officials met at an interim time (1960) on the matter of reducing damage along the Niskayuna-Schenectady Pool. Two newspaper reports indicate (a) perhaps why no responsive actions have occurred at the dam, whether as significant physical change or improved procedure, (b) that the dam has a role toward flooding at Schenectady, and (c) the notion of opening something at the dam to reduce a possible flood-stage.

"none … wished to take responsibility for dynamiting ice jams near Vischers Ferry (Dam) because of possible hazards to other downstream communities." (Schenectady Gazette, 3/2/1960)

"Nagle (former City Engineer in Schenectady) noted that the ice barrier which stretches across the Mohawk between the Knolls to the Vischers Ferry power dam is a major hazard." (Schenectady Gazette, 3/16/60)

"The state recently ordered the flood gates opened at the Vischer Ferry dam to reduce the possibility of flooding." (Schenectady Gazette, 3/16/60)

WHAT "FLOOD GATES", and — if they truly existed — why unused over the last four decades?

Footnotes

(2) the text appears in full as part of Appendix B.

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http://www.schenectadyhistory.org/mohawkriver/duggan/5.html updated July 30, 2009

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