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Connecticut Streamflow Overview and Drought Conditions

Connecticut Streamflow and Groundwater Overview

Know Your Flow!
We update this webpage with the latest information weekly.

CT Conditions At A Glance

(Click on any graphic below for more information)
Streamflow in CT Now
(click map to go to the data page)

 [color code for]  color code for  color code for color code for  color code for  color code for  color code for               [color code for]         
   High Flow     Low Flow        Not Ranked
CT Current Streamflow. 
    Click to go to source page.
US Drought Monitor Map of CT
(click map for details)
Current US Drought Conditions. Click to open source page.
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
(click graph for details)

Link to Burlington Brook flow data
Check your forecast here
(click map to go to state weather page)
Link to NWS graphic page
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.

Click here for the USGS Connecticut stream gage web page with graphs of flow from every gage for the past 30 days compared to their daily average flows.

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.

Driest Streams and Rivers in Connecticut
(with USGS gaging stations)

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.

Streamflow Graphs and Storms

Link to Aug 13, 2014 CT heavy rainfall effect on streamflow graphics courtesy USGS and NOAA.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.


Dire situation last year...

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...

Click to enlarge
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.
Coppermine Brook, Bristol CT, Friday, Dec. 11, 2015; photo by Tony Mitchell


This graph plots the rate of flow on September 4, 2015 as a percentage of the median for each stream gage. For example, a dot at the 40% line means that stream that day was flowing at 40% of what could be considered normal for that date. The few rivers and streams flowing at or above 100% of their median rate are mostly those with flows managed by dam releases.

Click here for a search of news articles about the drought

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




Rivers Alliance of Connecticut
PO Box 1797, 7 West Street 3rd Floor, Litchfield, CT 06759-1797
rivers@riversalliance.org, www.riversalliance.org