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
(click map to go to the data page)
High Flow Low Flow Not Ranked
US Drought Monitor Map of CT
(click map for details)
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)
Check your forecast here
(click map to go to state weather page)
Graphic courtesy NOAA NWS showing CT area watches and warnings if any.
Thursday, September 22, 2016 update: Many voluntary and a few significant mandatory water conservation alerts in effect. Interagency Drought Workgroup keeps Drought Advisory in effect and requests 10% voluntary water conservation (see A Dry Summer below). The U.S. Drought Monitor puts 69% of CT in the Severe Drought category (details below). 79% of CT rivers and streams (list is below) measured by the USGS have low flow and and their groundwater measurements show that Connecticut groundwater levels remain unusually low and are still falling.
Streamflow: Click here for a display of USGS Connecticut stream gages with graphs of their flow for the past 30 days compared to their daily average flows. An alphabetical list of low-flow rivers is below. Streamflow continues to fall to seriously low levels between rain storms because long-term rainfall has been a lot less than what we normally get, and where it does rain, not all of it soaks into the ground. These topics are discussed in more detail below.
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. 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 too long. For a review of the localized relationship between streamflow and precipitation, see below.
A dry Summer. In June, the CT Department of Public Health (DPH) issued the first Drought Advisory since 2010. Their Reservoir Data webpage reported in the August monthly report that 15 of 34 water companies had asked for voluntary water restrictions, 1 company had issued mandatory restrictions, and 1 was in Water Supply Alert status. State reservoirs at that time were at an average 73% of their capacity (down from 91% in June, 81% in July), ranging from 48% to 100%. For DPH's list of Public Water Systems with water use restrictions click here. On Sep 14, the Office of Policy and Management stated that the Connecticut Interagency Drought Workgroup (IDW) is keeping the Drought Advisory in Effect and requests 10% voluntary water conservation. For the press release and minutes from the IDW, click here. UCONN issued a Stage IV Water Emergency Sep 15. On Sep 16, Aquarion Water Company issued a ban on the use of outdoor watering devices in Stamford, Greenwich, Darien, New Canaan, Mystic and Stonington. There are numerous reports of private wells low or dry.
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.
Six real-time monitoring wells run by the US Geological Survey (USGS) all report levels lower than 75% of their records for the date; three of them are lower than ANY of that station's records for the date. Another one is down for repair but it was also showing rapidly falling levels earlier. This continues a possible pattern of the last four years in which normal water 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. 30-day and 60-day rain deficits are rising as more days go by without significant rain. Even in the few places with some rain recently, streamflow drops quickly because not all the rain soaked into the ground to supply the rivers between storms. The National Weather Service Advanced Hydrologic Prediction Service at this link (choose CT from the state drop-down list to see current data) shows how the cumulative rainfall debt varies widely across the state. These heavy precipitation events that do not do much to recharge groundwater aquifers are becoming more frequent.
The dire situation last year (see below) was 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.
Rain? For most of the last six months, storm tracks brought most precipitation out to sea. For a short time near the end of August, however, some weather systems tracked over Connecticut, creating a return 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. Recent one-week forcasts show a little chance for rain. A long-range computer model shows the persistent high pressure that has been keeping us dry moving away and allowing a weather front to reach us around the end of the month. It also shows a major hurricane coming up the east coast the second weekend of October, but it often predicts storms for us at the end of it's 16 day run that never materialize.
The NWS Climate Prediction Center's analysis of the rest of September shows slightly elevated chance for above-normal precipitation, but their three-month prognostications give equal chances for normal or above-average or below-average precipitation.
On Thursday, September 22 (2:00pm) there were 57 USGS stream gages in Connecticut (list below) reporting low flows*. This is 92% of the 62 CT gages that report statistics, almost the same as a week ago. The 14 stream gages in bold red were reporting flows lower than their records for the date. Last Thursday there were 18. To see the status of any them right now, click on the link to the right of the station name.
|Station Name||Station Website Link|
|ASPETUCK RIVER AT ASPETUCK, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209105|
|BROAD BROOK AT BROAD BROOK, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184490|
|BUNNELL BROOK NEAR BURLINGTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01188000|
|BYRAM RIVER AT PEMBERWICK, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01212500|
|COGINCHAUG RIVER AT MIDDLEFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01192883|
|EAST BRANCH EIGHTMILE RIVER NEAR NORTH LYME, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01194500|
|EIGHTMILE RIVER AT NORTH PLAIN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01194000|
|FARMINGTON RIVER AT TARIFFVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01189995|
|FARMINGTON RIVER AT UNIONVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01188090|
|FENTON RIVER AT MANSFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01121330|
|FIVEMILE RIVER NEAR NEW CANAAN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209761|
|FRENCH RIVER AT NORTH GROSVENORDALE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01125100|
|HOCKANUM RIVER NEAR EAST HARTFORD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01192500|
|HOUSATONIC RIVER AT FALLS VILLAGE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01199000|
|HOUSATONIC RIVER AT GAYLORDSVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01200500|
|HOUSATONIC RIVER AT STEVENSON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01205500|
|HUBBARD RIVER NEAR WEST HARTLAND, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01187300|
|INDIAN RIVER NEAR CLINTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01195100|
|LITTLE RIVER AT HARRISVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01125490|
|LITTLE RIVER NEAR HANOVER, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01123000|
|MILL RIVER NEAR HAMDEN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196620|
|MOUNT HOPE RIVER NEAR WARRENVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01121000|
|MUDDY RIVER NEAR EAST WALLINGFORD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196561|
|NATCHAUG RIVER AT MARCY RD. NEAR CHAPLIN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01120790|
|NATCHAUG RIVER AT WILLIMANTIC, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01122000|
|NAUGATUCK RIVER AT BEACON FALLS, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208500|
|NAUGATUCK RIVER AT THOMASTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01206900|
|NONEWAUG RIVER AT MINORTOWN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203600|
|NORTH BRANCH PARK RIVER AT HARTFORD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01191000|
|NORWALK RIVER AT SOUTH WILTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209700|
|PENDELTON HILL BROOK NEAR CLARKS FALLS, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01118300|
|POMPERAUG RIVER AT SOUTHBURY, CT||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, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203510|
|QUINEBAUG RIVER AT JEWETT CITY, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01127000|
|QUINEBAUG RIVER AT PUTNAM, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01125500|
|QUINEBAUG RIVER AT QUINEBAUG, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01124000|
|QUINEBAUG RIVER AT WEST THOMPSON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01124151|
|QUINNIPIAC RIVER AT SOUTHINGTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01195490|
|QUINNIPIAC RIVER AT WALLINGFORD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01196500|
|RIDGEFIELD BROOK AT SHIELDS LANE NR RIDGEFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=012095493|
|RIPPOWAM RIVER AT STAMFORD, CT.||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209901|
|ROOSTER RIVER AT FAIRFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208873|
|SALMON CREEK AT LIME ROCK, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01199050|
|SALMON RIVER NEAR EAST HAMPTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01193500|
|SASCO BROOK NEAR SOUTHPORT, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208950|
|SAUGATUCK RIVER NEAR REDDING, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208990|
|SAUGATUCK RIVER NEAR WESTPORT, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209500|
|SHETUCKET RIVER AT TAFTVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=011230695|
|SHETUCKET RIVER NEAR WILLIMANTIC, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01122500|
|STILL RIVER AT ROBERTSVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01186500|
|STILL RIVER AT ROUTE 7 AT BROOKFIELD CENTER, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01201487|
|STONY BROOK NEAR WEST SUFFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184100|
|WEEKEEPEEMEE RIVER AT HOTCHKISSVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01203805|
|WEST BRANCH FARMINGTON RIVER AT RIVERTON, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01186000|
|WILLIMANTIC RIVER AT MERROW RD. NEAR MERROW, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01119382|
|WILLIMANTIC RIVER NEAR COVENTRY, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01119500|
|YANTIC RIVER AT YANTIC, CT||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 Tue Sep 20, 2016 at noon. 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.
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 Sep 13, 69% of the state was ranked Severe Drought. The last time this much or more of CT was last ranked this way was two weeks in 2012, but before that, CT has not had this much area ranked this way since 2002.
As this graph shows, Connecticut has been labled Abnormally Dry or worse pretty often over the last few years.
Whenever there is a powerful storm, watch for flooding! Flash flooding can easily take people by surprise. Remember, if water is across the road, Turn Around, Don't Drown! See below for general flooding information. The amount of rainfall that has come during extreme precipitation events has risen faster in the northeastern United States than in any other region of the nation.
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
When floodwaters fill the part of the stream channel that is called a floodplain, the water may find that someone has built a building or two in the channel. The water then saturates and fills any leach fields, often flushing untreated sewage out into the flow.
The floodwaters also find these really nice holes in the ground called wells to flow down into. All kinds of interesting things can be delivered to the bottom of the well, such as the aforementioned sewage, and soil, bugs, leaves, pesticides such as weed killer and insect poison, even the dog droppings from the backyard.
Very important: Any well that was flooded should be pumped and flushed out thoroughly and the system sanitized or "shocked."
The Connecticut Department of Health website has a good guide called:
There are places in Connecticut where the storm drains and the sewage pipes are combined into one system. With high rainfall, many of these combined pipes are designed to overflow into rivers and streams so the wastewater treatment plants are not overwhelmed. You really do not want to be downstream when raw untreated human sewage is entering the water. The DEEP has a map of Combined Sewer Overflows that shows the six urban areas where these can occur. Zoom in to any of them to see exactly where the combined flow may enter streams and rivers. Not every rain event is enough to cause these overflows, but it's a good idea to avoid contact with the water downstream from them after significant rain.
Unless you are an expert paddler, do not attempt to canoe or kayak on floodwaters; there are usually one or two fatalities per year. Our Connecticut Water Trails website and the webpages of the many paddler groups in the state all have good safety procedures. Here is a good article.
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 National Oceanic and Admospheric Administration (NOAA) uses a rolling 30-year average of modern rainfall data to calculate its "normals." A discussion of the 1981 to 2010 precipitation calculations can be found at http://prism.oregonstate.edu/normals. To see Connecticut's average annual precipitation, go to http://prism.oregonstate.edu/gallery/view.php?state=CT_RI.
Recently there has been much discussion of what constitutes a "100-year-storm" or a "50-year storm." These traditional terms can be misleading unless you keep in mind they are an old-fashioned way of describing probablities. A "100-year" rainfall event means that in any year there is a 1% chance of that rate of rainfall.
Here is a map showing that in Connecticut we have a 1% chance of getting 7 to a little over 8 inches of rain in a 24-hour period, depending on where you are in the state. (Image source: http://precip.eas.cornell.edu/)
Comparing this to Table 7.2 (copy below) of the CT Stormwater Manual, we note that the design criteria for managing runoff possibly should be updated if we are building our landscape to control the flow from a 100-year-storm.
Photos by Joan Smith GOSA taken 9/20/2015 at The Merritt Family Forest in Groton. The stone slab bridge lies over Eccleston Brook, which had only a few puddles despite last week's downpour. The muddy bottom is also part of EB, further downstream. The photo with the two upright stone slabs is Cowslip Brook, a tributary to EB, and the wooden bridge traverses another small tributary to EB, flowing from a vernal pool. Used with permission.
State of CT - Drought (Search)
Water Conservation tips
Water Conservation is not just for droughts; it is important because:
It saves money and energy
It insures the reliability of your water supply
It protects our natural resources
What Can I Do?
Set a voluntary water use reduction goal of 10% (whether served by public water systems or private wells)
Cut back on unnecessary water use, such as watering lawns or washing cars
Cooperate with your local water utility and follow their plans
Model Water Use Restriction Ordinance (PDF, 28KB)
Connecticut's Draft Drought Management Plan is being updated by the CT Water Planning Council Advisory Group Drought Plan Work Group.
News article: Researchers reveal cost-effective path to drought resiliency (July 21, 2016) "Published in San Francisco Estuary & Watershed, the study reveals the costs and benefits of using groundwater recharge and storage across the state. This process, known as "managed aquifer recharge," or MAR, can incorporate co-benefits such as flood control, improved water quality and wetland habitat protection. The study found the median cost of MAR projects is $410 per acre-foot (the amount of water required to cover an acre of level land at a depth of 1 foot) per year. By comparison, the median cost of surface water projects is five times more expensive -- $2,100 per acre-foot."
Some archived Know Your Flow pages
CT Drought in the News:
Fishing Banned in Some Areas of the Farmington River,
Closed Beaches on Bantam Lake,
Eversource: Our Rigorous Tree Trimming Program Will Reduce
Impact of Drought-Stressed Trees on Electric System,