Connecticut Streamflow and Groundwater Overview
Know Your Flow!
CT Conditions At A Glance(Click on any graphic below for more information)
Streamflow in CT Now
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High Flow Low Flow Not Ranked
US Drought Monitor Map of CT
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The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. Map courtesy of NDMC-UNL.
Recent flow at a typical CT stream
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Check your forecast here
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Graphic courtesy NOAA NWS showing CT area watches and warnings if any.
Thursday, October 20, 2016 Update
The US Drought Monitor shows 89% of Connecticut in Severe Drought, a small increase in area since last week. More about the Drought Monitor data is below.
At their Oct 14 meeting, the Interagency Drought Workgroup (IDW) recommended issuance of a Drought Watch, one step up from the Drought Advisory first issued in June. They also recommended the State issue a new press release to request 15% voluntary water conservation and reduction of outdoor water use, an increase from the September request for voluntary water savings of 10%.
The number of water-utility alerts statewide calling for conservation continues to grow (for details, see Utility Alerts below). On September 29, the U.S. Department of Agriculture declared Hartford, Litchfield, Tolland, and Windham Counties natural disaster areas. There are numerous reports of private wells low or dry.
Streamflow: As of Oct. 20, 92% of CT rivers and streams measured by the US Geological Service (USGS) were experiencing low flows (alphabetical list is below). 42% are lower than any of their records for the date. USGS also reports that Connecticut groundwater levels remain unusually low and are still falling.
Stream gages normally show pulses of above-average flow when it rains, then below-average between storms. Only a few of the recent records show Connecticut's streams rising above average at all during storms; most are barely reaching average, and a few have not even come close to average during rain. Dry conditions that cause flow to be below average more often than it is above average will affect stream life if these conditions continue for unusually prolonged periods. For a review of the localized relationship between streamflow and precipitation, see below.
Utility Alerts: UConn issued a Stage IV Water Emergency Sept. 15. On Sept. 16, Aquarion Water Company issued a ban on outdoor watering in six of its towns. On September 29, the Department of Public Health (DPH) issued a rare Declaration of a Public Water Supply Emergency for Greenwich, Stamford, New Canaan, and Darien. A mandatory water use ban introduced by Norwalk on Oct. 6 affecting two systems specifically describes how it will be enforced by police. On Oct 19 Bristol issued new mandatory water restrictions prohibiting all outside uses.
Most of the companies on DPH's September Reservoir Status Summary (issued Oct 13) had issued water restrictions. DPH's list of Public Water Systems with water use restrictions (10/14 update) names 11 groups of water systems with voluntary restrictions in addition to the four mandatory restrictions described above. Berlin has also asked for voluntary conservation. The City of Waterbury is working with state agencies on drought contingency actions to allow it to withdraw more water from its reservoirs in the Shepaug River watershed. These withdrawals are regulated by a stipulated agreement (2009) that concluded litigation in the case of Washington et al. vs. Waterbury. The agreement calls for release of 6 MGD to the Shepaug River in October. Waterbury is presently complying with that agreement.
The Metropolitan District Commission (MDC) may suspend releases from their hydroelectric facility at Goodwin Dam. This dam forms the West Branch Reservoir (sometimes called Hogback Lake) on the Farmington River West Branch in Hartland just below the Colebrook River Reservoir. Fishing was banned in some areas of the Farmington River due to low water levels.
Groundwater: The water level in streams and rivers between storms depends on the flow of water out of the ground into the stream channel. The higher the water table, the more water is available to keep streams flowing. During a drought, smaller upland streams dry up faster than the larger rivers (see the graph below). An occasional brief, powerful rainstorm does not do much to help groundwater levels rise. The rain falls faster than the ground can absorb, and thus much of it becomes stormwater runoff. In that situation, public water supply systems that depend on reservoirs are affected less than those with wells because the runoff is collected by the reservoirs.
On Oct. 20, the seven real-time monitoring wells run by the US Geological Survey (USGS) all reported levels lower than 75% of their records for the date; five of them were lower than ANY of that station's records for the date. The wells that were not at their lowest recorded water levels were only a few inches above their 2008 record lows.
This year's record-breaking low groundwater levels continue a pattern of the last four years in which normal groundwater levels in winter and spring have alternated with below-average in summer and fall. What is worrisome, however, is that the below-normal levels got worse in each of those four years. Four years is not long enough to make any statistically valid conclusions about climate, however, and those station records only go back seven to 14 years. USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that the abnormally low yearly pattern seen in the real-time data may be getting worse.
Precipitation Patterns. The National Weather Service Advanced Hydrologic Prediction Service shows how the cumulative rainfall debt varies widely across the state. Only the extreme southeast corner of CT is near normal for the last 30 days. Most of the state has received less than 50% of average for this time of year. The northwest quarter of the state is more than 75% below normal. Go to this link for detailed maps and data (choose CT from the state drop-down list to see current data).
For the last six months storm tracks brought precipitation out to sea or north of us because a persistent, high-pressure system called a blocking pattern has been diverting weather fronts or storms. For short periods, however, the blocking pattern moved away, allowing some weather systems over Connecticut, creating temporary returns to more normal summer thunderstorms and storm systems. This normal precipitation did not end the drought due to the serious long-term rain deficit, but it kept it from getting worse for a while. Streamflow between storms continued to drop to low levels, however.
This is the same bad situation that we had last year (see below), caused not only by less total rainfall than normal over a long period of time but also by the intensity of the rain we did get. As our climate changes, heavy precipitation events that do not do much to recharge groundwater aquifers are becoming more frequent.
Rain? Recent National Weather Service one-week forecasts predict up to one inch of rain, but long-range computer models show a possiblity of decent rainfall if another tropical system is able to reach us. The NWS Climate Prediction Center's analysis for November through January shows equal chances for above-normal or normal or for below-normal precipitation. Above normal temperatures are a little more likely than normal temperatures.
On Thursday, Oct. 20, there were 57 USGS stream gages in Connecticut (list below) reporting low flows* up 2 from last week. This is 92% of the 62 CT gages that report statistics. The 26 stream gages (42%) in bold red were reporting flows lower than ALL their records for the date, up one from last week. To see the status of any them right now, click on the link to the right of the station name.
|Station Name||Station Website|
|ASPETUCK RIVER AT ASPETUCK||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209105|
|BROAD BROOK AT BROAD BROOK||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184490|
|BUNNELL BROOK NEAR BURLINGTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01188000|
|BYRAM RIVER AT PEMBERWICK||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01212500|
|COGINCHAUG RIVER AT MIDDLEFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01192883|
|CONNECTICUT RIVER AT THOMPSONVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184000|
|EAST BRANCH EIGHTMILE RIVER NEAR NORTH LYME||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01194500|
|EIGHTMILE RIVER AT NORTH PLAIN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01194000|
|FARMINGTON RIVER AT TARIFFVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01189995|
|FARMINGTON RIVER AT UNIONVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01188090|
|FENTON RIVER AT MANSFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01121330|
|FIVEMILE RIVER NEAR NEW CANAAN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209761|
|HOCKANUM RIVER NEAR EAST HARTFORD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01192500|
|HOUSATONIC RIVER AT FALLS VILLAGE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01199000|
|HOUSATONIC RIVER AT GAYLORDSVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01200500|
|HOUSATONIC RIVER AT STEVENSON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01205500|
|HUBBARD RIVER NEAR WEST HARTLAND||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01187300|
|INDIAN RIVER NEAR CLINTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01195100|
|LITTLE RIVER NEAR HANOVER||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01123000|
|MILL RIVER NEAR FAIRFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208925|
|MILL RIVER NEAR HAMDEN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196620|
|MOUNT HOPE RIVER NEAR WARRENVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01121000|
|MUDDY RIVER NEAR EAST WALLINGFORD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196561|
|NATCHAUG RIVER AT MARCY RD. NEAR CHAPLIN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01120790|
|NATCHAUG RIVER AT WILLIMANTIC||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01122000|
|NAUGATUCK RIVER AT BEACON FALLS||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208500|
|NAUGATUCK RIVER AT THOMASTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01206900|
|NONEWAUG RIVER AT MINORTOWN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203600|
|NORTH BRANCH PARK RIVER AT HARTFORD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01191000|
|NORWALK RIVER AT SOUTH WILTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209700|
|PENDELTON HILL BROOK NEAR CLARKS FALLS||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01118300|
|POMPERAUG RIVER AT SOUTHBURY||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01204000|
|POOTATUCK RIVER AT BERKSHIRE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=012035055|
|POOTATUCK RIVER AT SANDY HOOK||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203510|
|QUINEBAUG RIVER AT JEWETT CITY||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01127000|
|QUINNIPIAC RIVER AT SOUTHINGTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01195490|
|QUINNIPIAC RIVER AT WALLINGFORD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196500|
|RIDGEFIELD BROOK AT SHIELDS LANE NR RIDGEFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=012095493|
|RIPPOWAM RIVER AT STAMFORD.||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209901|
|ROOSTER RIVER AT FAIRFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208873|
|SALMON CREEK AT LIME ROCK||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01199050|
|SALMON RIVER NEAR EAST HAMPTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01193500|
|SASCO BROOK NEAR SOUTHPORT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208950|
|SAUGATUCK R BELOW SAUGATUCK RES NR LYONS PLAIN||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209005|
|SAUGATUCK RIVER NEAR REDDING||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208990|
|SAUGATUCK RIVER NEAR WESTPORT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209500|
|SHEPAUG RIVER AT PETERS DAM AT WOODVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01202501|
|SHETUCKET RIVER AT TAFTVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=011230695|
|SHETUCKET RIVER NEAR WILLIMANTIC||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01122500|
|STILL RIVER AT ROBERTSVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01186500|
|STILL RIVER AT ROUTE 7 AT BROOKFIELD CENTER||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01201487|
|STONY BROOK NEAR WEST SUFFIELD||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184100|
|WEEKEEPEEMEE RIVER AT HOTCHKISSVILLE||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203805|
|WEST BRANCH FARMINGTON RIVER AT RIVERTON||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01186000|
|WILLIMANTIC RIVER AT MERROW RD. NEAR MERROW||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01119382|
|WILLIMANTIC RIVER NEAR COVENTRY||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01119500|
|YANTIC RIVER AT YANTIC||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01127500|
*We are defining low flow as below the 25th percentile for that stream, OR below 25% of the mean OR below 25% of the median flow for that stream for the date. Data source: http://waterwatch.usgs.gov/webservices/realtime?region=ct&format=xml on Thu Oct 20, 2016 at 11:00am. Click here for a list of all CT stream gages comparing their flow right now to their mean and median flows for today's date.
As the graphic to the right illustrates, where a storm moves across the state, the streams show flows that peak above their averages for this time of year but then quickly drop. The streams that maintain healthy flows between storms are those draining the parts of the state where there has been decent rainfall or those controlled by managed dams.
How quickly the flow drops after each rainstorm is unique for each stream, because it depends on how much water soaked in to increase the groundwater baseflow. In watersheds with lots of impervious roads, roofs, parking lots, patios, and compacted soil in lawns, a lot of the rain typically flows over the surface or through storm drains directly into the streams, leading to flooding problems far more often than in watersheds with mostly natural surfaces. Their streamflow then drops quickly after the storm ends, and the flow levels off far lower than in streams whose watersheds have more natural surfaces.
The U.S. Drought Monitor publishes a weekly analysis of drought conditions across the entire nation based on a variety of types of data that include streamflow. The report comes out every Thursday based on data from that Tuesday. As of Oct 20, 89% of the state was rated Severe Drought. It is significant that the rating stayed the same between two previous weeks in spite of the rain that fell in Connecticut from the "linked" weather front that drew moisture from Hurricane Matthew. Connecticut has not had this much area rated this way since 2002, making this drought the second worst in areal extent so far this century.
As this graph shows, Connecticut has been labled Abnormally Dry or worse pretty often over the last few years.
For a good analysis of last year's stream problems across the state, see this press release from Pomperaug River Watershed Coalition (PRWC). Here is a key quote:
The September and October low river flows demonstrate that rivers were not supporting the critical flows needed for a healthy river habitat. In fact, sections of the Weekeepeemee River had dry river beds and the Pomperaug River was flowing only at a rate of 15% of the critical flow requirement. DEEP officials confirmed that they would expect fish mortality to increase significantly during such conditions...
Photo from PRWC.
Meanwhile, parts of Coppermine Brook in Bristol were drawn down to rocks and dirt, as shown in the photo below taken Dec. 11
in Bristol. The sandy ditch in the foreground is the stream channel. Bristol Water Company and New Britain Water Company have eight registered diversions near
Coppermine or its tributaries with a combined registered water withdrawal of 36.6 million gallons per day
(source: CT DEEP). Company representatives
report they do not withraw anywhere near that much water. Bristol Water says they stopped pumping from their well near this photo for a day but with no apparent
effect on the stream. This is a perennial stream with a state Trout Management Area below where this picture was taken. Click on the photo for a full-screen version
in a new tab.
Coppermine Brook, Bristol CT, Friday, Dec. 11, 2015; photo by Tony Mitchell
DPH issues monthly reports on their Reservoir Data webpage that includes voluntary and mandatory water restrictions in effect in that month. In the August report, DPH reported that state reservoirs were at an average 73% of their capacity (down from 91% in June, 81% in July), ranging from 48% to 100%.
Some archived Know Your Flow pages