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
|Map of Below Normal 28-Day Average Streamflow
|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.
December 1, 2016 Update
Summary (details below): The U.S. Drought Monitor continues to rate 44% of Connecticut as Extreme Drought, based on data available before this week's significant rain. It has upped the area rated Severe from 25% last week to 39% this week. The 1-3 inches of rain that fell in the past week temporarily brought streamflow up to or above average levels for this time of year. However, groundwater levels have not responded as quickly, so we expect streamflow to drop rapidly until the next rainstorm. This drought remains the worst since the historic drought of the 1960s.
The Drought Watch continues for six CT counties; Drought Advisory continues for the the eastern two counties. The state also requests all residents to reduce their water use by 15%.
The number of water-utility alerts statewide calling for conservation continues to grow (for details, see Utility Alerts below). 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: Before this week's rain, 90% of CT rivers and streams measured by the US Geological Service (USGS) were experiencing low flows (the Nov. 25 alphabetical list is below). About 19% of our streams and rivers were lower than any record for the date.
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.
Public Water Supply Information. Your water utility and town web pages are the best sources of information on water use restrictions that apply specifically to you. The Department of Public Health's (DPH) Reservoir Data web page was last updated Nov. 16. It states capacity is at 74% of normal, the percentage reported on their Monthly Reservoir Status Summary for the month of October. That percent of normal is based on 34 reports that average 61% of capacity. Most of those companies had issued water use restrictions. Their list of Public Water Systems with water use restrictions was last updated Oct 24.
Utility Alerts. Aquarion Water Company this week asked its customers to cut indoor water use by 20 percent. Last month the Department of Public Health (DPH) issued a rare Declaration of a Public Water Supply Emergency for Greenwich, Stamford, New Canaan, and Darien, which was later amended to allow Aquarion to build a 1.5 mile temporary pipeline. As part of this declaration, Aquarion maintains a weekly updated water usage report on their website that includes customer usage trends, system transfers, system capacities, days usable storage remaining, and precipitation.
New Britain Water is proposing to buy 5 million to 7 million gallons of water a day from the Metropolitan District Commision (MDC). New Britain has not had to buy water for decades. The South Central Regional Water Authority is asking customers to reduce water use by 15%. Bristol issued new mandatory water restrictions. On Nov. 16, UConn lowered its alert level to a Stage III Water Emergency. A mandatory water use ban introduced by Norwalk on Oct. 6 affects two systems with the unusual addition of how it will be enforced by police. On Oct. 25, the DPH commissioner declared a Public Water Supply Emergency for City of Danbury, also affecting Ridgefield and Bethel.
DPH will allow the City of Waterbury to reduce the amount of water it is required to discharge to the Shepaug River from the current level of 6 million gallons per day to 1.5 million gallons per day (a 75% decrease), the allowable level during winter months. In order to move to the lower level, the city must institute mandatory water conservation measures and demonstrate to DPH that it is maximizing the use of all current water sources. Click here for Waterbury's Warning page.
The 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. Citing the ongoing drought, MDC is recommending a change to its policy of selling water at a reduced price to high-volume consumers.
Earlier in the year, 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 (details 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 Dec. 1, four of the six operational real-time monitoring wells run by the USGS with multiyear records reported levels lower than ANY of that station's records for the date. This a slight improvement from the low water table reports for the last three months or so. Two stations not breaking records are lower than 75% of their daily averages for the date.
Five of the live-data wells show a sharp uptick from the recent rain, something not seen after most other storms throughout the summer and fall. The USGS Connecticut office has two new live-data wells in Clinton and Salisbury. These show data going back just to August of this year, so comparisons to previous years cannot be made. Another of their live-data wells is down for repair.
There has been an apparent pattern for the last five years in which normal groundwater levels in winter and spring have alternated with well below-average in summer and fall. Click the graph to the right for a larger version in a new tab of a modified USGS graph. What is most worrisome, however, is that the below-normal levels got worse in each of those years. Five 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. Click here to see all the USGS graphs for their real-time groundwater measurements that compare levels from the last four years to the median level for each day of the year (big page, takes a long time to load). USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that this pattern may apply to all our groundwater.
Precipitation Patterns. The National Weather Service Advanced Hydrologic Prediction Service shows how the cumulative rainfall debt varies widely across the state. As of Dec. 1, 30-day rainfall was still 1 to 3 inches below normal for most of Connecticut, but it was near normal for roughly the western quarter of the state. Because most of the rain that has improved the 30-day totals fell in strong storms over the past week, it did not benefit long-term streamflow or groundwater levels very much. Public water supplies that rely on reservoirs benefitted the most. Go to this link for detailed maps and data.
For the last nine 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 and storms. For short periods, however, the blocking pattern moved away, allowing some weather systems over Connecticut, creating temporary returns to more normal rainfall. 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 are becoming more frequent. Heavy rain does not recharge groundwater aquifers as much as an equal amount of rain over longer periods would.
Rain? National Weather Service one-week forecasts and their long-range computer models are predicting near-normal rainfall for this time of year. While that is certainly good news for our rivers and streams, it would not be enough to alleviate all drought conditions. The storms that do track our way could be enough to again temporarily cause streamflow to peak above average levels, but the low water table will cause flow to quickly fall again. The NWS Climate Prediction Center's analysis for December shows a slightly higher chance for above-normal precipitation than for normal or for below- normal. Their three-month sets of predictions through May show equal chances for above-normal or normal or for below-normal precipitation. Above- normal temperatures are a little more likely than normal temperatures. This is pretty much the same three-month forecast we have seen for the past year, but actual precipitation has been much lower than normal. Their prognostications for next summer, however, hold out hope for above-normal rainfall, a prediction not seen in several years.
As of Friday, Nov. 25 (before the more recent rains), 57 of the 63 (90%) CT rivers and streams measured by the USGS were experiencing low flows*. The 12 streams and rivers in bold red below were lower than any record for the date. 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|
|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|
|CONNECTICUT RIVER AT THOMPSONVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01184000|
|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|
|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 FAIRFIELD, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01208925|
|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|
|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|
|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 R BELOW SAUGATUCK RES NR LYONS PLAIN, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01209005|
|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|
|SHEPAUG RIVER AT PETERS DAM AT WOODVILLE, CT||http://waterdata.usgs.gov/ct/nwis/uv?site_no=01202501|
|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 Tuesday, Nov. 22, 2016, at 3 p.m. 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. The U.S. Drought Monitor continues to rate 44% of Connecticut as Extreme Drought, based on data available before this week's significant rain. It has upped the area rated Severe from 25% last week to 39% this week. The only other time since the Drought Monitor began in 2000 that any part of the state was this dry was 2002 when around 16% of the state was in the Extreme category for three weeks. This means this is the worst drought so far this century. The U.S. Drought Monitor is produced by the National Drought Mitigation Center, which is also on Facebook.
As the below graph shows, Connecticut has been labled Abnormally Dry, Moderate Drought, or worse pretty often over the last few years. This graph was made before any of the state was rated as Extreme.
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, 2015, 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
Some archived Know Your Flow pages
http://www.riversalliance.org/drought/droughtarchive.cfm?filename=droughtbefore20150925.htm http://www.riversalliance.org/drought/droughtarchive/droughtbefore20150903.htm http://www.riversalliance.org/drought/droughtarchive/droughtbefore20160316.htm