{ "lid": "NSHN3", "usgsId": "01096508", "reachId": "6746036", "name": "Merrimack River at Nashua", "description": "", "rfc": { "abbreviation": "NERFC", "name": "Northeast River Forecast Center" }, "wfo": { "abbreviation": "GYX", "name": "Gray" }, "state": { "abbreviation": "NH", "name": "New Hampshire" }, "county": "Hillsborough", "timeZone": "EST5EDT", "latitude": 42.7634, "longitude": -71.4428, "pedts": { "observed": "HGIRG", "forecast": "HGIFF" }, "status": { "observed": { "primary": 4.71, "primaryUnit": "ft", "secondary": 2.92, "secondaryUnit": "kcfs", "floodCategory": "no_flooding", "validTime": "2026-10-28T01:15:00Z" }, "forecast": { "primary": 4.6, "primaryUnit": "ft", "secondary": 2.46, "secondaryUnit": "kcfs", "floodCategory": "no_flooding", "validTime": "2026-10-28T06:00:00Z" } }, "flood": { "stageUnits": "ft", "flowUnits": "cfs", "categories": { "major": { "stage": 35, "flow": -9999 }, "moderate": { "stage": 26, "flow": -9999 }, "minor": { "stage": 18, "flow": -9999 }, "action": { "stage": 16, "flow": -9999 } }, "lro": null, "crests": { "historic": [ { "occurredTime": "1936-03-20T00:00:00Z", "stage": 41.3, "flow": 0, "preliminary": "R", "olddatum": false }, { "occurredTime": "1938-09-23T00:00:00Z", "stage": 30.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2006-05-15T16:30:00Z", "stage": 26, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2007-04-17T12:00:00Z", "stage": 23.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1987-04-07T00:00:00Z", "stage": 22.4, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1996-04-18T00:00:00Z", "stage": 19, "flow": 37900, "preliminary": "O", "olddatum": false }, { "occurredTime": "2010-04-01T06:45:00Z", "stage": 18.81, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1953-03-28T00:00:00Z", "stage": 18.4, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1940-04-14T00:00:00Z", "stage": 18.1, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1996-10-22T00:00:00Z", "stage": 18.1, "flow": 57800, "preliminary": "O", "olddatum": false }, { "occurredTime": "1952-04-04T00:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1998-06-17T18:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1951-04-04T00:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1993-04-01T00:00:00Z", "stage": 16.2, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1969-04-23T00:00:00Z", "stage": 15.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1997-04-20T00:00:00Z", "stage": 15.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1993-04-13T00:00:00Z", "stage": 15.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1948-03-23T00:00:00Z", "stage": 15.3, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2004-04-02T00:00:00Z", "stage": 14.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1968-03-28T00:00:00Z", "stage": 14.2, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2003-04-01T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2005-10-26T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1970-02-12T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1972-04-22T00:00:00Z", "stage": 13.8, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1945-03-22T00:00:00Z", "stage": 13.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1967-04-05T00:00:00Z", "stage": 13.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1988-04-29T00:00:00Z", "stage": 13.3, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2005-10-10T00:00:00Z", "stage": 13, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2006-06-09T00:00:00Z", "stage": 12.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1995-11-15T00:00:00Z", "stage": 9.399999618530273, "flow": 25257, "preliminary": "O", "olddatum": false } ], "recent": [ { "occurredTime": "2010-04-01T06:45:00Z", "stage": 18.81, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2007-04-17T12:00:00Z", "stage": 23.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2006-06-09T00:00:00Z", "stage": 12.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2006-05-15T16:30:00Z", "stage": 26, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2005-10-26T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2005-10-10T00:00:00Z", "stage": 13, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2004-04-02T00:00:00Z", "stage": 14.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "2003-04-01T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1998-06-17T18:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1997-04-20T00:00:00Z", "stage": 15.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1996-10-22T00:00:00Z", "stage": 18.1, "flow": 57800, "preliminary": "O", "olddatum": false }, { "occurredTime": "1996-04-18T00:00:00Z", "stage": 19, "flow": 37900, "preliminary": "O", "olddatum": false }, { "occurredTime": "1995-11-15T00:00:00Z", "stage": 9.399999618530273, "flow": 25257, "preliminary": "O", "olddatum": false }, { "occurredTime": "1993-04-13T00:00:00Z", "stage": 15.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1993-04-01T00:00:00Z", "stage": 16.2, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1988-04-29T00:00:00Z", "stage": 13.3, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1987-04-07T00:00:00Z", "stage": 22.4, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1972-04-22T00:00:00Z", "stage": 13.8, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1970-02-12T00:00:00Z", "stage": 14, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1969-04-23T00:00:00Z", "stage": 15.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1968-03-28T00:00:00Z", "stage": 14.2, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1967-04-05T00:00:00Z", "stage": 13.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1953-03-28T00:00:00Z", "stage": 18.4, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1952-04-04T00:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1951-04-04T00:00:00Z", "stage": 17, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1948-03-23T00:00:00Z", "stage": 15.3, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1945-03-22T00:00:00Z", "stage": 13.6, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1940-04-14T00:00:00Z", "stage": 18.1, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1938-09-23T00:00:00Z", "stage": 30.5, "flow": 0, "preliminary": "O", "olddatum": false }, { "occurredTime": "1936-03-20T00:00:00Z", "stage": 41.3, "flow": 0, "preliminary": "R", "olddatum": false } ] }, "lowWaters": { "historic": [] }, "impacts": [ { "stage": 40, "statement": "This is a disastrous...life threatening flood. This compares to the Great New England Flood of 1936. Follow the advice of local officials...and evacuate if told to do so. " }, { "stage": 35, "statement": "This is a major...life threatening flood event. The river has not reached this height since the Great New England flood of 1936. Major flooding will affect the communities of Merrimack and Litchfield through Nashua and Hudson. follow the advice of local officials...evacuate if told to do so. Stay away from the Merrimack River. " }, { "stage": 30, "statement": "This flood compares to the Hurricane of 1938 flood. This is a substantial flood event. Follow the directions of local officials...evacuate if told to do so. At this height the Merrimack River is moving very swiftly. Stay away from the river. " }, { "stage": 28, "statement": "The river has not reached this height since the Hurricane of 1938. This is a serious flood event. Follow the advice of local officials...evacuate if told to do so. At this height...the Merrimack River is moving very swiftly. Stay away from the river. " }, { "stage": 25, "statement": "The river has not reached this height since May 2006. This is a significant flood event. Follow the advice of local officials...evacuate if told to do so. " }, { "stage": 21, "statement": "Flooding will occur in low lying areas from Litchfield and Merrimack...to Hudson and Nashua." }, { "stage": 18, "statement": "Flooding will begin in the lower lying sections of Hudson and Nashua as the river continues to climb above 18 feet." } ] }, "images": { "probability": { "weekint": { "stage": "", "flow": "", "volume": "" }, "entperiod": { "stage": "", "flow": "", "volume": "" }, "shortrange": "" }, "hydrograph": { "default": "https://water.noaa.gov/resources/hydrographs/nshn3_hg.png", "floodcat": "https://water.noaa.gov/resources/hydrographs/nshn3_record.png" }, "photos": [ { "id": "456220951998960110", "type": "Feature", "geometry": { "type": "Point", "coordinates": [ 42.76173, -71.44404 ] }, "properties": { "image": "https://water.noaa.gov/resources/photos/nshn3/456220951998960110.jpeg", "caption": "Gage site" } }, { "id": "548675856826700270", "type": "Feature", "geometry": { "type": "Point", "coordinates": [ 42.76173, -71.44404 ] }, "properties": { "image": "https://water.noaa.gov/resources/photos/nshn3/548675856826700270.jpeg", "caption": "Looking at gage from downstream right bank" } } ] }, "dataAttribution": [ { "abbrev": "US Geological Survey", "text": "USGS--Water Resources of the United States", "title": "US Geological Survey", "url": "https://waterdata.usgs.gov/nwis" }, { "abbrev": "USGS", "text": "01096508", "title": "Observations courtesy of U.S. Geological Survey", "url": "https://waterdata.usgs.gov/nwis/inventory/?site_no=01096508" } ], "impactsLowWaters": [], "normalThreshold": null, "hydronotes": [], "datums": { "vertical": { "value": [ { "label": "North American Vertical Datum of 1988", "abbrev": "NAVD88", "description": "A fixed reference for elevations determined by geodetic leveling. The datum was derived from a general adjustment of the first-order terrestrial leveling nets of the United States, Canada, and Mexico. In the adjustment, only the height of the primary tidal bench mark, referenced to the International Great Lakes Datum of 1985 (IGLD 85) local mean sea level height value, at Father Point, Rimouski, Quebec, Canada was held fixed, thus providing minimum constraint. NAVD 88 and IGLD 85 are identical. However, NAVD 88 bench mark values are given in Helmert orthometric height units while IGLD 85 values are in dynamic heights. See International Great Lakes Datum of 1985, National Geodetic Vertical Datum of 1929, and geopotential difference. NAVD 88 should not be used as Mean Sea Level.", "value": 86.96 } ] }, "horizontal": { "value": [] }, "notes": { "value": [] } }, "inundation": { "enabled": false, "url": "", "zeroDatum": null, "downloads": null, "siteSpecificInfo": "", "dataAttribution": [] }, "upstreamLid": "GOFN3", "downstreamLid": "LOWM3", "inService": { "enabled": true, "message": "" }, "lowThreshold": null, "forecastReliability": "Forecasts are issued routinely year-round.", "TruncateObs": "-1", "TruncateFcst": "3", "ObservedFloodCategory": "no_flooding", "ForecastFloodCategory": "no_flooding" }