Connecticut Streamflow and Groundwater Overview
Know Your Flow!
CT Conditions At A Glance(Click on any graphic below for more information)
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.
Map of Below Normal 28-Day Average
Recent Flow At a Typical CT Stream
(click graph for details)
(click graph to see more well data)
Check your forecast here
(click map to go to state weather page)
Graphic courtesy NOAA showing CT area watches and warnings if any.
Mar 23, 2017 Update
Summary (details follow)
The U.S. Drought Monitor downgraded the areas of Connecticut rated Extreme rating two weeks ago, and this week lowered the severity rating of the eastern 12% of the state to Abnormally Dry. As of March 21, 42% of the state was rated Severe, 46% Moderate Drought. As a percentage of area, CT remains the most drought-afflicted state of all 50.
Streamflow varies widely across the state. It is
near normal where temperatures have allowed the deep snow from recent
melt, below normal elsewhere. The improvement in groundwater levels
has slowed, and remains low for half of the
worst drought since the
historic drought of the 1960s continues.
Interagency Drought Workgroup (IDW)
met on Mar 8, and was expected to not recommend any changes to the state's drought alert level. The Drought Watch
would then continue for six CT counties; Drought Advisory continues for the eastern two
counties. The state is still requesting all residents to reduce their water use by
10 to 15%.
Most, but not all, water utilities have ended mandatory conservation measures.
Due to the ongoing drought conditions, the Department of Energy and Environmental Protection (DEEP) issued a Public Notice that it "...suspends the minimum stream flow standards ... commonly known as the 'spring freshet' release standard, for the period of February 15, 2017 to March 15, 2017.... Questions regarding this action may be directed to Doug Hoskins, ... 860-424-4192, firstname.lastname@example.org." For more information, please see the IDW freshet discussion from Jan 20.
Due to the lack of the Spring freshet, many more streams, when compared to their records for the date (see below), are exhibiting low flows between storms. On March 9, 76% of CT rivers and streams measured by the US Geological Service (USGS) were experiencing low baseflows, compared to 19% the previous week. An alphabetical list of low-flow rivers is below. Until this week the graphs for most (not all) river and stream gages were showing a normal pattern of about equal areas above-average flow when it rains (or when there are days with rapid snowmelt), then below-average between storms and days without snowmelt. For those streams where snowmelt or mandated releases regularly created higher flow in previous years, the current flow is well below average. The 28-Day Average Streamflow map from the USGS categorizes most of Connecticut as well below normal because "normal" for that period includes high flows in previous years from spring freshet releases from dams that did not occur this year. See Streamflow Graphs and Storms below for more explanation.
Dry conditions that cause flow to be below
average more often than it is above average is affecting stream
life throughout the state. Fishermen have reported long stretches
of rivers with no catch at all. Whatever dormant life is left on
our stream bottoms will be lost if flow remains too low to prevent
the stream from freezing solid when temperatures get unusually cold. This is different from the common winter fish kills explained in fact
sheets from CT DEEP.
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 monthly web page dated Feb. 6 stated that capacity was
at 87% of normal, the percentage reported on their
Monthly Reservoir Status Summary for January. (Note that "normal" for
January is 91% of
capacity.) The 87%
of normal is based on reports from 34 large water systems that use
reservoirs. That percentage means those reservoirs averaged
80% of capacity. Most of those water utility companies had
issued water use restrictions or asked for voluntary conservation. The DPH also has a
separate list of
Public Water Systems with water use restrictions, last
updated Dec. 12, 2016.
Aquarion maintains on its website a weekly updated water usage report that includes customer usage trends, system transfers, system capacities, days usable storage remaining, and precipitation. Their graphs and charts indicate conditions are near or even above their trigger levels for water usage alerts.
Darien, and New Canaan are working with Aquarion on a water-demand study that
could be completed next month. They are examining the overuse of water that,
combined with years of below-average rain and snow, has caused a statewide
drought. The study could result in permanent water conservation guidelines. Area residents with their own wells are also expressing frustration with water conservation measures.
The water table normally reaches its highest levels from this time of year until late spring. Over the last few weeks the water in most wells has either slowed its steady rise or has leveled off. Day to day, groundwater has been moving up with rainfall and snowmelt, but then it drops again. If this year's plateau has been reached, it does not bode well for our rivers and streams if drought conditions intensify again.
On March 16, two of the six real-time monitoring wells run by the USGS with multi-year records was reporting a water table lower than any daily averages for the date for those wells. Three others, though not setting records, were lower than 75% of their averages for the date. The other well is near average but falling. These numbers have not varied much in the past month.
Until the past few weeks, all eight live-data
were showing the water table recovering steadily from the their
lowest levels in
September. Until November, more stations were breaking
low-water-level records than those that were
merely very low. Some well levels have been rising or falling
depending on the weather. Most however are showing that the depth of the
water table is still trending upward but that trend is leveling off.
The USGS Connecticut office this year added live-data access to two additional
wells, in Clinton and Salisbury. The live data displayed by these go back to
August of last year, but comparisons to their monthly measurements of
previous years can be made using the USGS's
Watch website. For example, the March 16 measurements from the Clinton
and Salisbury wells were close to or above normal for their March measurements going
On March 16, the most recent measurements at 40% of the 70 wells on the
Watch website were near or above normal; 36% were labeled below
were much below normal. However none had measurements lower
than any previous years measurement at those wells going back 16 to 20 years.
The number of wells reported below normal are a little higher than in previous
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. How much groundwater is contributed by snow depends on several factors including slope, rate of snowmelt, and whether the ground beneath the snow is frozen or saturated.
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. There are two trends of great concern. One concern is that that the below-normal levels in Summer and Fall got worse in each of those years. The other concern is that the water table has not recovered this year as it has in previous 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 levell for each day of the year (lots of data, so it 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.
Watch website is an excellent source of data for examining
historic and current trends. The map of CT (example below) is color
coded the same way the USGS Connecticut streamflow map is colored to
show how the most recent measurements compare to historical records for
each station. Graphs can be made to chart water levels for all 70 wells.
(See also climate news: Climate Change Threat to Both the Natural World and to Human Civilization)
Why is Connecticut still in Drought Watch and Advisory status? If the deep snow snow from recent storms melts rapidly, we will have the same situation the US Drought Monitor narrative summary the Northeast for February 28 described:
"...the much warmer-than-normal temperatures rapidly melted a significant amount of New England snowpack. Snow melting this fast pretty much just ran off into the rivers and streams as opposed to slowly entering the ground to recharge the ground water."
According to the National Weather Service Advanced Hydrologic Prediction Service, precipitation over the last 30 days has been about half of what we would normally get at this time of year in the eastern part of the state, around 75% of normal for the western half. At the beginning of 2017, near-average precipitation had been gradually improving long-term streamflow and groundwater levels. In January and February however, precipitation was fairly heavy but infrequent, averaging out to near-normal 30-day amounts. Periods of unusually heavy precipitation like this do not compensate for unusually dry weather even if they average out to normal because heavy rain does not all soak in to recharge groundwater. In March however, below-normal precipitation has been once again affecting groundwater and stream levels. If snow melts slowly enough that most of the water infiltrates the soil, it can help to improve long-term drought conditions, but the rapid melting early in the month did not replenish groundwater very much. Go to this link for detailed maps and data.
For most of 2016, storm tracks brought precipitation out to sea or north of us because a persistent high-pressure system called a blocking pattern was diverting weather fronts and storms. It was only when that blocking pattern moved away for short periods that some weather systems came over Connecticut, creating temporary returns to more normal rainfall. That 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 in 2015-2016 (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. Not all drought conditions went away last winter. As our climate changes, heavy precipitation events are becoming more frequent. Heavy rain does not recharge groundwater aquifers as much as the same amount of rain over longer periods would.
Rain? The National Weather Service's one-week forecasts show some rain and snow with temperatures that could allow a slow melt of the snowpack. This would be best to relieve long-term low-flow stream conditions because it would raise the water table.
long-range (16-day) computer models are predicting normal precipitation and
temperatures, good news for our rivers unless the rain comes as unusually heavy
Each month, the NWS Climate Prediction Center issues analyses of global atmospheric conditions that could influence general temperature and precipitation patterns. Their March 16 analysis for trends through May show equal chances for above-normal, for normal, and 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 was much lower than normal. The NWS Climate Center's prognostications for the Summer, however, give a 40% chance for above-normal rainfall, a 33% chance for normal, and a 27% chance for below normal precipitation. That prediction for June, July and August was the same for the previous three months.
The USGS data file we usually use for assessing low flow rivers has not been available since Mar 16. Here is our analysis from Mar 9:
Water levels and flow rates in our streams dropped unremarkably after recent storms, falling to levels similar to what we have seen for the past month. However, when comparing streamflow to previous years' records for March 9, we found that 47 of the 62 (76%) Connecticut rivers and streams measured by the USGS (listed below) were experiencing low flows*. There were 12 the previous week. To see the status of any them right now, click the station's URL below.
Did the water from 35 streams get diverted over the course of a week? Of course not. What we are seeing is the lack of the Spring freshet, the expected flush of water from melting snow and from releases from dams. In previous years, many stream gage records show a distinct rise in flow at the beginning of March, so the average flow for the date from many years of data from those stations is higher than than in February. This year however, the bulk of the little snow we got melted early from abnormally warm temperatures in February. Also, DEEP issued a Public Notice that it "...suspends the minimum stream flow standards ... commonly known as the 'spring freshet' release standard, for the period of February 15, 2017 to March 15, 2017.... " For more information, please see the IDW freshet discussion from Jan 20.
On February 24, there were 7 low-flow rivers on our list, the same number as the previous week. That was a significant improvement from February 14 when there were 23, and from February 6 when there were 34 low-flow streams. In January the number ranged from 27 to 35. During most of 2016, there usually were 50 to 60 low-flow streams; on December 23 there were 53.
As streamflow between storms continues to drop at a time of year it is usually increasing, we have to be concerned about the recovery of our streams' ecosystems from drought conditions. This is especially true when the flow is lower than any record for the date, such as the seven stream gages in bold red below that were setting records on Mar 16. There were five last week.
On March 1st, only one stream gage was reporting flow lower than any record for the date, on the Saugatuck River. The flow in the Saugatuck has been setting low-flow records since November. That was also the only record-breaker the previous week, down from two of them each of the two weeks before that. Until Mar 9, the number of record-low streams had been improving since Feb. 6 when there were seven record breakers; In January the number of record-breakers ranged from five to nine. The number of record breakers were even higher for most of 2016; for example, there were 15 on Dec. 23.
|ASPETUCK RIVER AT ASPETUCK, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209105|
|BROAD BROOK AT BROAD BROOK, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01184490|
|BUNNELL BROOK NEAR BURLINGTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01188000|
|BYRAM RIVER AT PEMBERWICK, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01212500|
|COGINCHAUG RIVER AT MIDDLEFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01192883|
|EIGHTMILE RIVER AT NORTH PLAIN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01194000|
|FARMINGTON RIVER AT TARIFFVILLE, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01189995|
|FENTON RIVER AT MANSFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01121330|
|FIVEMILE RIVER NEAR NEW CANAAN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209761|
|FRENCH RIVER AT NORTH GROSVENORDALE, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01125100|
|HOCKANUM RIVER NEAR EAST HARTFORD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01192500|
|INDIAN RIVER NEAR CLINTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01195100|
|LATIMER BROOK NR I-95N EXIT 75 NR FLANDERS, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=011277905|
|LITTLE RIVER NEAR HANOVER, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01123000|
|MILL RIVER NEAR FAIRFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208925|
|MILL RIVER NEAR HAMDEN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01196620|
|MOUNT HOPE RIVER NEAR WARRENVILLE, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01121000|
|MUDDY RIVER NEAR EAST WALLINGFORD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01196561|
|NATCHAUG RIVER AT WILLIMANTIC, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01122000|
|NAUGATUCK RIVER AT BEACON FALLS, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208500|
|NAUGATUCK RIVER AT THOMASTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01206900|
|NONEWAUG RIVER AT MINORTOWN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01203600|
|NORTH BRANCH PARK RIVER AT HARTFORD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01191000|
|NORWALK RIVER AT SOUTH WILTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209700|
|POMPERAUG RIVER AT SOUTHBURY, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01204000|
|POOTATUCK RIVER AT BERKSHIRE||https://waterdata.usgs.gov/ct/nwis/uv?site_no=012035055|
|POOTATUCK RIVER AT SANDY HOOK, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01203510|
|QUINEBAUG RIVER AT JEWETT CITY, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01127000|
|QUINEBAUG RIVER AT PUTNAM, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01125500|
|QUINEBAUG RIVER AT QUINEBAUG, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01124000|
|QUINNIPIAC RIVER AT SOUTHINGTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01195490|
|QUINNIPIAC RIVER AT WALLINGFORD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01196500|
|RIDGEFIELD BROOK AT SHIELDS LANE NR RIDGEFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=012095493|
|RIPPOWAM RIVER AT STAMFORD, CT.||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209901|
|ROOSTER RIVER AT FAIRFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208873|
|SALMON RIVER NEAR EAST HAMPTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01193500|
|SASCO BROOK NEAR SOUTHPORT, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208950|
|SAUGATUCK R BELOW SAUGATUCK RES NR LYONS PLAIN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209005|
|SAUGATUCK RIVER NEAR REDDING, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208990|
|SAUGATUCK RIVER NEAR WESTPORT, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209500|
|SHETUCKET RIVER AT TAFTVILLE, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=011230695|
|SHETUCKET RIVER NEAR WILLIMANTIC, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01122500|
|STILL RIVER AT ROUTE 7 AT BROOKFIELD CENTER, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01201487|
|STONY BROOK NEAR WEST SUFFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01184100|
|WEEKEEPEEMEE RIVER AT HOTCHKISSVILLE, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01203805|
|WILLIMANTIC RIVER NEAR COVENTRY, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01119500|
|YANTIC RIVER AT YANTIC, CT||https://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: https://waterwatch.usgs.gov/webservices/realtime?region=ct&format=xml on Thu March 9, 2017. 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 is produced by the National Drought Mitigation Center, which is also on Facebook.
Their regional narrative for the Northeast on Mar 23 explains why 42% of the state is still rated Severe, and 46% Moderate Drought: "... although [Northeast] conditions have been favorably wet over the past 90 days, lingering Moderate and Severe Drought areas (D1 and D2) have reported below-normal precipitation over the same time frame. Furthermore, these same locales are still exhibiting pronounced long-term deficits, with 12-month precipitation averaging 60 to 80 percent of normal. While streamflows have rebounded, slower-to-recover groundwater levels remained much lower than average. Despite the recent rain and snow — which alleviated the short-term (“S”) component of the drought — long-term drought (“L” on the map) remained in areas where significant long-term deficits persisted."
Since the end of January Connecticut has had the dubious distinction
of being the
most drought-afflicted state of all 50 based on percentage of area,
but Oklahoma is now a close second. Other
states still have areas of Extreme Drought, and Oklahoma has a
higher percentage of area rated Severe or above, we still have the
percentage of area rated Moderate Drought and above. By adding the
percentages of each state in each category, an index or relative drought
affliction can be calculated. The following table lists the most
afflicted states in order by this index.
What Are the Most Drought Afflicted States?
|State||% No Drought||% Abnormally Dry or Worse
||Sq Miles||% Moderate
Drought or Worse
||Sq. Miles||% Severe Drought or Worse
||Sq. Miles||% Extreme Drought||Sq. Miles||Percentage Comparative Value (sum of %)||Sq Miles Comparative Value (sum of sq miles)|
As the below graph shows, Connecticut has been labeled 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