DEP UPDATE

DEP UPDATE (12/22/22)

DEP has reviewed the regional weather forecasts including wind advisory and flood watches issued by the National Weather Service. The river forecasts (NWS hydrograph) increased for Mt. Marion and Ashokan Reservoir since yesterday.

The initial storm runoff and flood watch for your communities is entirely from lower Esopus watershed runoff and snowmelt. The official forecast shows the Esopus Creek exceeding the Action Level at Mt. Marion early Friday morning. In accordance with the Interim Release Protocol (IRP), DEP will shut down the Ashokan Release Channel ahead of time (typically at 17ft Mt Marion Level). DEP is currently releasing 10 MGD to the Ashokan Release channel with a turbidity of 2.5 NTU. The range of turbidity near the intakes of Ashokan is currently 2.4 – 6.1 NTU

Ashokan Reservoir is currently at 86.2% capacity with a void of 5 feet to capture storm runoff (approximately 8 billion gallons in each basin, 16 BG total ). The NWS official forecast for the east basin shows capture of the entire storm surge from the upper Esopus Creek. The level increase is forecast for 2 feet for the reservoir leaving 3 feet of void. The upper Esopus creek is forecast to go into minor flood stage. DEP is currently using 500 MGD for water supply diversions into the Catskill Aqueduct to maintain the Reservoir below the 90% level and current CSSO. The forecasts do not show chance for Ashokan spilling in the next three days. However looking out 10 days to New Year’s Eve, the forecast does increase and show a 5% chance for Ashokan spilling.

Following the storm, predictions indicate a need to increase Ashokan releases and water supply diversions. Target flows for the release channel and aqueduct will be determined after assessing how much runoff occurs. Discharge/spill mitigation releases from the Ashokan Release Channel are likely to be needed for an extended period following the storm to pursuant to the IRP. The turbidity of the releases is not currently known. They may be more turbid given the winter conditions and inability for settling in cold water.

DEP will continue to monitor conditions and make adjustments to meet the IRP.

 

Bill Richardson

John Milgrim

Details on Ashokan Reservoir storage and releases can be found at the following sites. Note NWS-AHPS forecasts for the Esopus Creek are typically updated each day by noon.

Release Levels - DEP (nyc.gov)

National Weather Service Advanced Hydrologic Prediction Service

USGS Hydrograph and Turbidity at Mt. Marion

 

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