News & Bulletins
Consistent with the USGS planned conversion from National Geodetic Vertical Datum of 1929 (NGVD29) to the North American Vertical Datum of 1988 (NAVD88), the Hudson River – Black River Regulating District will be upgrading the datum used to record water level elevation at all of its reservoirs.
Effective February 1, 2019 the datum at surface-water and ground-water stations operated by the Hudson River – Black River Regulating District in partnership with the USGS will be converted from the National Geodetic Vertical Datum of 1929 (NGVD 29) to the North American Vertical Datum of 1988 (NAVD 88).
NGVD 29 has been the benchmark used by surveyors and engineers as the standard position from which measurements are taken. Originally called the Sea Level Datum of 1929, it was created for vertical control surveying in the United States, and is what is referred to by the inaccurate term “sea-level.” The sea itself is not level, but is subject to variations caused by currents, wind, barometric pressures, temperature, and the topography of the sea floor. Because mean sea level at one location can be quite different than mean sea level at another location, it is not an accurate benchmark for measurement. Satellite technology has also discovered ground elevations that have risen or fallen due to geological activity and the effects of gravity.
Technological advancements have created the ability for greater accuracy, resulting in the North American Vertical Datum of 1988 (NAVD 88). The NAVD 88 was completed in June of 1991, contains an additional 100,000 miles of leveling and was constrained only to the primary tidal benchmark at Father Point/Rimouski, Quebec, Canada. It is a great improvement over its predecessor in terms of mathematical techniques employed as well as being based on the Earth’s observed gravity field. NAVD 88 is compatible in principle with the Geoid, the mathematical system of describing the relation of the Earth’s gravity field to elevations.
All federal agencies are required to use NAVD 88. The US Army Corp of Engineers, the Federal Emergency Management Agency and United States Geological Survey have all adopted the new datum.
For the rivers, streams and reservoirs that are monitored by the Regulating District within the Black and Hudson River watersheds, the NAVD 88 elevation number is a shift of approximately .88 to .11 feet lower than the elevation in the NGVD 29 standard. This variation is due to geographical differences. For example, a water level for the Great Sacandaga Lake is 771.00 ft. and will be 770.12 in the NAVD 88 standard. The difference is referred to as the “shift between datums”. Only the numerical value for the elevation changes; the depth and volume remain the same.
Marcy, D. (2016, July 01). Why am I “Mean” About Sea Level? Retrieved from https://geozoneblog.wordpress.com/2012/09/24/why-am-i-mean-about-sea-level/
NEW ORLEANS DISTRICT. (n.d.). Retrieved from https://www.mvn.usace.army.mil/Missions/Engineering/Survey-Section/FAQ/
Sarasota County Water Atlas. (n.d.). Retrieved from http://www.sarasota.wateratlas.usf.edu/shared/learnmore.asp?toolsection=lm_navd88
Vertical Datum Upgrade. (n.d.). Retrieved from https://www.swfwmd.state.fl.us/resources/data-maps/vertical-datum-upgrade
Please take notice that the Board of the Hudson River-Black River Regulating District will conduct two (2) meetings for the transaction of such business as shall come before the said Board at the Warren County Municipal Center, 1340 State Route 9, Conference Room 5110, Lake George, NY 12845 on Tuesday, December 11, 2018 beginning at 10 AM. The Audit Committee Meeting will convene first, followed by the Regular Board Meeting. A video recording of the Meeting shall be accessible from the District’s website (www.hrbrrd.com) not later than two business days after the close of the meeting.
Richard J. Ferrara
BLACK RIVER AREA OFFICE
The Hudson River-Black River Regulating District, a New York State Public Benefit Corporation responsible for regulating the flow of the Hudson and Black Rivers, is seeking applications for the position of Administrative Assistant for its office located in Watertown, NY. The Administrative Assistant, under general supervision, perform a variety of technical, administrative and accounting duties, requiring the applicant to attain knowledge of Regulating District operations and office practices. Strong communication and software skills are required. Use of computer applications such as spreadsheets, web page, word processing, calendar, email and database software in performing work assignments.
Requirements include a high school diploma with six year’s experience in an office setting, or an Associate’s Degree with three year’s experience in an office. Must be knowledgeable in “Word” and “Excel” or similar word-processing, spreadsheet and database programs, and must be skilled in the use of a networked computer including e-mail. A valid New York State driver’s license is required.
As an Equal Opportunity Employer, minorities, woman, and veterans are encouraged to apply.
Qualified candidates should forward their resume and a letter of interest by November 14, 2018 to:
Hudson River-Black River Regulating District
P.O. Box 420
Northville, NY 12134
Localized rain storms and occasional heavy precipitation, as well as a few National Weather Service notices of flash flooding in the Hudson River and Black River watersheds, has had the tendency to leave the casual observer believing that both river systems have received “plenty” of water throughout the summer. Those situations have also made it difficult for the same casual observers to understand why the Great Sacandaga Lake and Stillwater Reservoir elevations have been lower than normal since early June.
In the simplest of terms, reservoir operation is centered on the quantity of water entering the reservoir (inflow) and quantity of water leaving the reservoir (release). The elevation of the reservoir varies depending upon whether the inflow to the reservoir is greater or less than the release of water from the reservoir. Release of water is controlled, inflow is not.
When the amount of water entering a reservoir is greater than the amount leaving the reservoir, the elevation of the reservoir increases. Conversely, when the amount of water entering is less than the amount exiting, the elevation decreases. In the first scenario – when the inflow exceeds the release – water is stored in the reservoir, in the second scenario it is not.
The release of water from a reservoir is typically a known and determined quantity and, generally, based on fixed demands downstream of the reservoir such as waste assimilation, environmental concerns, and industrial needs, to name a few.
Despite periodic rainfall in June, July, and August, river flow in the Hudson and Black River watershed continued to remain significantly below average. Hudson River monthly average flow measured only 47% of historic average in June and 47% and 48% in July and August, respectively.
Black River monthly average flow (without augmentation from Stillwater Reservoir) measured approximately 49%, 57%, and 71% of historic average in June, July, and August, respectively.
This lower than average natural river flow produced greater than normal demand for the release of water from the reservoirs.
The amount of water entering a reservoir, or inflow, is dependent upon the amount of precipitation that falls on the reservoir watershed and how much of that precipitation runs into the reservoir.
During the three month period June through August the Great Sacandaga Lake and Stillwater reservoir received significantly less inflow than historically enters the reservoirs.
|Percent of Average Reservoir Inflow – June, July, August 2018|
|Great Sacandaga Lake||35%||24%||65%|
The product of greater than normal demand for the release of water and significantly less inflow than historically enters the reservoirs sustained a condition similar to the second scenario detailed above and, for the three month period, resulted in inflow which was less than the release causing the elevation of the reservoirs to decrease.
State’s Reservoirs PREVENT MAJOR HUDSON RIVER FLOODING
Great Sacandaga Lake and Indian Lake Reservoir Reduce Peak Hudson River Flow by 74%
The Great Sacandaga Lake and Indian Lake Reservoir provided 1.93 billion cubic feet of water storage on January 13 preventing the Hudson River from reaching flood stage from the Town of Hadley to Fort Edward. The State’s two Hudson River regulating reservoirs stored more than 14.37 billion gallons of runoff on Saturday, reducing the peak Hudson River flow by approximately 26,100 cubic feet per second (cfs) Saturday morning.
Last week’s rainfall and runoff from melting snow caused the Hudson River to reach a peak flow of about 9,500 cfs at Hadley and 13,000 cfs at Fort Edward on Saturday morning, according to the U.S. Geological Survey. The storage capacity of the Great Sacandaga Lake and Indian Lake Reservoir prevented the Hudson River at Fort Edward from reaching flood stage.
Without the combined storage capacity of the State’s Hudson River regulating reservoirs, Hudson River flow would have peaked at more than 35,000 cfs at Corinth and 39,000 at Fort Edward. The reservoirs prevented the Hudson River from reaching a flood stage of 28.5 feet at Fort Edward, about 0.5 feet below major flood stage, on January 13. Operation of the Great Sacandaga Lake reduced the height of flood water by more than 4.5 feet, significantly reducing potential flood damage to buildings, roads and bridges in Hadley, Corinth, South Glens Falls, Glens Falls, Hudson Falls, and Fort Edward.
If Great Sacandaga Lake had not been constructed to retain a flood event like that which occurred on Saturday then flooding and inundation of roads in Northumberland, camps in Lake Luzerne, parts of Route 9N and cellars in homes in Corinth, first floors of structures along Old Bend Road in Moreau, and numerous roads and property in the Village of Fort Edward, would have occurred.
April 10, 2017
State’s Reservoirs PREVENT MAJOR HUDSON RIVER FLOODING
Great Sacandaga Lake and Indian Lake Reservoir Reduce Peak Hudson River Flow by 67%
The Great Sacandaga Lake and Indian Lake Reservoir provided 2.23 billion cubic feet of water storage on April 7 preventing the Hudson River from reaching major flood stage from the Town of Hadley to Fort Edward. The State’s two Hudson River regulating reservoirs stored more than 16.64 billion gallons of runoff on Friday, reducing the peak Hudson River flow by approximately 32,850 cubic feet per second (cfs) Friday morning.
Last week’s rainfall and runoff from melting snow caused the Hudson River to reach an average flow of about 16,400 cfs at Hadley on Friday morning, according to the U.S. Geological Survey. With the storage capacity of the Great Sacandaga Lake and Indian Lake Reservoir, the Hudson River at Fort Edward never reached flood stage.
Without the combined storage capacity of the State’s Hudson River regulating reservoirs, Hudson River flow at Corinth would have peaked at more than 49,250 cfs, and would have resulted in Hudson River flow exceeding major flood stage at Fort Edward by more than 2.3 feet on April 7. Operation of the Great Sacandaga Lake reduced the height of flood water by more than 6.2 feet, significantly reducing potential flood damage to buildings, roads and bridges in Hadley, Corinth, South Glens Falls, Glens Falls, Hudson Falls, and Fort Edward.
If Great Sacandaga Lake had not been constructed to retain a flood event like that which occurred on Friday then major flooding including roads in Northumberland, camps in Lake Luzerne, parts of Route 9N in Corinth, and numerous roads and property in the Village of Fort Edward would have been inundated.